1-s2.0-S0169409X04000687-main

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httpslidepdfcomreaderfull1-s20-s0169409x04000687-main 121

Sustained release veterinary parenteral products

Natalie J Medlicott a Niki A Waldron b Todd P Foster b

a School of Pharmacy University of Otago PO Box 913 Dunedin New Zealand b

Worldwide Pharmaceutical Sciences Pfizer Kalamazoo MI 49001 USA

Received 24 May 2003 accepted 18 February 2004

Abstract

Controlled release parenteral dosage forms have application in veterinary medicine Systems that minimize the need for

repeated injections while achieving therapeutic effects for extended periods offer benefits that make commercial development of

these products desirable While some products have already found commercial success others will result from application of

new controlled release technologies This review highlights the formulation and technology challenges in developing some of

these controlled release technologies into products Further examples of application of controlled release technologies in the

veterinary field are discussed

D 2004 Published by Elsevier BV

Keywords Parenteral drug delivery Injection Sustained release dosage forms In situ forming gels Implants Microspheres

Contents

1 Introduction 1346

2 Controlled release dosage form market 1 346

3 Formulation development challenges 1 346

31 Injection site 1347

311 The subcutaneous site 1348

312 Intramuscular site 1349

313 Drug absorption from intramuscular and subcutaneous injection sites 1349

314 Tissue reactions at intramuscular and subcutaneous site 1352

32 Technology challenges 13544 Parenteral controlled release dosage forms 1 355

41 Liquid formulations 1355

411 Aqueous-based systems (suspensions gels oil in water emulsions liposome dispersions and microemulsions) 1355

412 Oily systems (oily solutions suspensions and wo emulsions) 1357

42 In situ forming solid formulations 1 358

43 Solid formulations 1358

0169-409X$ - see front matter D 2004 Published by Elsevier BVdoi101016jaddr200402005

Corresponding author Tel +64-3-479-7275 fax +64-3-479-7034

E-mail address nataliemedlicottstonebowotagoacnz (NJ Medlicott)

wwwelseviercomlocateaddr

Advanced Drug Delivery Reviews 56 (2004) 1345ndash1365

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5 Recent advances 1360

6 Concluding remarks 1360

References 1361

1 Introduction

Sustained release dosage forms (SRDF) are impor-

tant products in veterinary medicine [1ndash4] For certain

prophalytic and treatment uses one-time or infrequent

administration has become the standard procedure

For example monthly administration is available in

most heartworm preventatives such as HeartguardR

SentinelR and Interceptor R To compete in this mar-

ket new products will need to have similar or better

administration schemes In addition the companionanimal market will continue to increase and the busy

lives of pet owners preclude frequent administration

The SRDF possess advantages over conventional

dosage forms such as improved patient compliance

thus creating more effective products Other potential

advantages include reduced side effects to the animal

and added convenience to the animal owner Stress is

often reduced for both the animal and owner by the

infrequent dosing associated with SRDF administra-

tion The SRDF also have advantages for the phar-

maceutical industry through increased sales andextended patent protection

While oral drug delivery continues to be the pri-

mary route of administration the parenteral route does

offer advantages when oral administration is difficult

The advantages can be quite varied such as overcom-

ing the physical challenge of orally dosing cats to the

logistical difficulties with controlling estrus in herds of

domesticated livestock Also interspecies variability

caused by differences in oral absorption especially

between ruminant and non-ruminant animals may be

minimized with parenteral administration [5] Con-

trolled release parenteral dosage forms (CR-PDF) may

be difficult to develop because of the need to under-

stand injection site absorption tissue drug residues

tissue irritation injectability and retention extended

efficacy testing product stability formulation manu-

facturing analytical methods and packaging

This article will provide an overview of the

veterinary medicine CR-PDF market highlight chal-

lenges in bringing these products to the market

discuss the types of dosage forms available for development and explain some of the recently

marketed CR-PDF used in veterinary medicine

2 Controlled release dosage form market

Of the total $7 billion market in 1998 for veter-

inary pharmaceuticals around $1 billion may be

attributed to controlled release dosage forms [3]

Parenteral sustained release products account for an

estimated 40 ($04 billion) Top parenteral con-trolled release products include PosilacR MicotilR

Nuflor R and Revalor R (Table 1) The main treat-

ment areas are respiratory diseases feed efficiency

improvementgrowth and milk enhancement

3 Formulation development challenges

CR-PDFs are typically administered into muscle

(intramuscular injections) or subcutaneous sites [2]

Table 1

Top animal health parenteral controlled release pharmaceuticals in 1999

Product Drug Dosage form Indication Species 1999 sales

($ million)

PosilacR Zinc bovine growth hormone Oil suspension Milk enhancer Dairy cattle 225

MicotilR Tilmicosin Solution (propylene glycolwater) Parasiticide Cattle 85

Nuflor R Florfenicol Solution (n-methyl-2-pyrrolidone

propylene glycol polyethylene glycol)

Antibiotic Cattle 64

Revalor R

CompudoseR

SynovexR

Trenbolone estradiol

progesterone testosterone

Solid implants Growth Cattle 90

NJ Medlicott et al Advanced Drug Delivery Reviews 56 (2004) 1345ndash13651346

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with the preferred site of injection dependent on the

animal and condition treated For example in meat

production the subcutaneous site may be the pre-

ferred site of administration to minimize commerciallosses due to injection site reactions and drug

residuals in the muscle Indeed one of the most

difficult problems with parenteral depot formulations

for food-producing animals is the need to deliver

sufficient drug to elicit a physiological effect but

minimize the amount of tissue residues so no

withdrawal time is assigned It is often difficult to

achieve a balance between onset of reaching the

efficacy threshold while remaining below the residue

limit and drug release duration (Fig 1) For exam-

ple administration of two long-acting oxytetratcy-

cline in cattle showed drug concentrations greater

than the maximum residue limit at 30 days post-

treatment thus withholding periods of greater than

the usual 21 days were indicated [6] Additionally

for dairy animals withholding periods that allow for

reduction of drug concentrations in milk are pre-

scribed Lactating goats administered oxytetracycline

intramuscularly as the chlorhydrate or dehydrate

showed detectable milk concentrations until 2 and

3 days post-treatment respectively [7] In the ideal

profile efficacy is achieved rapidly and maintained

for the required period of time with drug concen-

trations below the tissue residue limit (Fig 1) If the

duration of effective treatment is increased by ad-

ministered high doses withholding periods need to

be assigned for the time during which tissue con-centrations exceed the residue limit Creative meth-

ods can be sought to solve these problems such as

injecting the formulations into the animalrsquos ear to

reduce drug residues in muscle of meat-producing

animals (Fig 2) [8] The intramuscular route may

however be appropriate in companion animals when

the benefit of achieving controlled drug release out-

weighs the risk of slow release of the drug into the

muscle tissue tissue residues and some local tissue

damage

31 Injection site

Various challenges are classified under the general

heading of lsquolsquoinjection sitersquorsquo Already mentioned are

the problems of injection site residues and tissue

irritation but others exist such as drug absorption

and injectabilityretention of the system at the injec-

tion site It is recognized that the dose to be admin-

istered will have implications on the formulation

injected A drug with high potency can be given in

smaller amounts than a drug with low potency The

size limit for solid implants appears to be a thickness

Fig 1 The balance between prolonged efficacy and tissue residuesmdasha classic problem in developing sustained release dosage forms for food-

producing animals Efficacy and tissue residuemdashtime profiles are shown for an ideal controlled released delivery systems compared with

conventional delivery systems

NJ Medlicott et al Advanced Drug Delivery Reviews 56 (2004) 1345ndash1365 1347

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of micrometers to millimeters and length of mm to

several centimeters [29] Alternatively systems can

be administered as microparticulate systems or solu-

tions that undergo a physical change at the injection

site to form an implant in situ The limits for the

amount of material that can be administered byinjection are less well defined but will still be subject

to injectability issues relating to the ease of flow of the

formulation through appropriate sized needles and

acceptance of the injected material by the host tissues

Consideration of the normal structure and physiology

of subcutaneous and intramuscular sites will give

information that may be useful in defining the limits

of formulation morphology An excellent review of

the anatomy and physiology of muscle and the sub-

cutaneous tissues relevant to parenteral administration

in humans is given by Washington et al [10] Impor-

tant features relate to the cellular and connective tissue

arrangements in these sites and the relative abundance

of blood and lymphatic supplies are applicable toother animal species as discussed below

311 The subcutaneous site

Subcutaneous injections are made under the skin

(Fig 3) By lifting the skin as shown in Fig 3A and

inserting the needle through the folded skin the aim

is to deliver the injection into the space between the

dermis and the underlying subcutaneous fat layer In

many animal species subcutaneous injections are

made into the area around the back of the neck

where skin is loose and the subcutaneous site is more

easily targeted Examination of the skin structure

shows the characteristic layers of epidermis dermis

and adipose tissue (Fig 3B) Of interest in subcuta-

neous injections are the composition of the reticular

layer of the dermis and adipose layers as injection

may result in deposition in these sites The dermis is

divided into two regions the thin superficial papillary

layer (20 depth) and the deeper reticular layer (80

depth) Connective tissue of the dermis consists of

cellular components (fibroblasts macrophages lym-

phocytes mast cells neutrophils and eosinophils)

surrounded in a matrix of high molecular weight materials (collagen elastin glycoproteins proteogly-

cans and polysaccharides) water salts and other

diffusable substances In the papillary layer there is

a loosely woven mat of fibres that is rich in blood

capillary loops The reticular layer is denser with

bundles of collagen fibres that are thicker than those

in the papillary layer are and interlace to form a

strong yet deformable three-dimensional network

Underlying the dermis is the layer of subcutaneous

adipose tissue comprising predominantly fat cells

with few blood and lymphatic vessels [1112] Inthe dermis layer an extensive capillary network (the

reticular plexus) exists in the papillary layer and

around the glands hair follicles and nerve supply

of the dermis Other areas of the deeper layers of the

dermis have relatively few capillaries as this area has

low metabolic demands due to the low density of

cells in the area The lymphatic system of the skin

comprises a numerous supply of lymph capillaries in

the reticular layer which drain into plexuses in this

layer then into deeper lymphatics [11]

Fig 2 Injections made onto the subcutaneous tissue at the base of

the ear is a technique patented to minimize tissue residual in meat

producing animals [8]


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312 Intramuscular site

Intramuscular injections are made deeper into the

skeletal muscle underlying the subcutaneous layer

(Fig 3B) In all animal species the basic unit of this

tissue is the muscle fibre These are long cylinderical

structures that contain numerous nuclei encased in a

plasma membrane or the sarcolemma The muscle

fibres are organized into bundles or fasciculi of

varying sizes Complete muscles contain many fas-

ciculi and are attached to the skeleton via tendonsConnective tissue surrounds the muscle fibres and is

classified by location within the muscle Connective

tissue that surrounds individual muscle fibres is

called the endomysium that surrounding the fascic-

uli is the periomysium and the epimysium surrounds

the whole muscle [11] Two separate blood circula-

tions flow through the muscle tissues These are the

nutritive supply that flows through an extensive

capillary network in the endomysium while the

non-nutritive pathway flows in mainly in larger

vessels through the perio- and epimysium with only

a few capillaries The lymphatic system starts in

capillaries within the perio- and epimysium that

drain into regional lymph nodes The lymphatic

vessels do not appear to enter the endomysium [11]

313 Drug absorption from intramuscular and

subcutaneous injection sites

The absorptive processes that occur on injection

or implantation of systems into muscle or subcuta-neous sites are summarized in Fig 4 Differences in

drug absorption rates at different injection sites can

be attributed to factors such as the tissue composi-

tion relative dispersal forces due to muscular con-

tractions at intramuscular sites [13] and abundance

and flow rate of blood and lymphatic supplies On

injection into either muscle or subcutaneous sites the

material forms a depot The size shape and nature of

the depot formed is determined by a balance between

variables such as the formulation composition the

Fig 3 (A) Subcutaneous injection (httpwwwiacucarizonaedutrainingdogsinjecthtml 2002) (B) Relative injection depths in subcutaneous

and intramuscular injections


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total volume injected rheological properties of the

system [14] relative dispersal rates of the formula-

tion components (especially the injection vehicle)

and forces due to tissue movement and muscular

contraction To illustrate this the shapes of subcuta-

neous depots formed on injection of systems with

different aqueous solubilities and vehicle viscositiesare shown in Fig 5

A useful classification of injected delivery systems

has been given by Washington et al [10] They

classified intramuscular injections according to

whether the rate limiting step in drug absorption

was release of the drug from the delivery system or

perfusion of the muscle by the blood Muscle perfu-

sion has a greater effect on the drug absorption rate

when injected drug is immediately available in the

intercellular fluid following injection In advanced

CR-PDFs the aim is to move control of the absorp-tion to the delivery system thereby reducing the

potential for inter-injection and inter-animal variabil-

ity caused by differences in injection site perfusion If

drug release is the rate limiting step in drug absorp-

tion the rate of drug absorption from the injection

site tissue (k a ) should exceed the rate of drug release

from the delivery system or depot (k r ) (Fig 6) When

drug is present at the injection site as a solid Ballard

and Nelson [15] reported its absorption rate is pre-

dominantly dissolution kinetic rate controlled Equa-

tions to relate the absorption rate (d Adt ) to solid

dissolution rate have been derived for acidic (Eq (1))

and basic (Eq (2)) compounds These equations

describe the importance of the surface area of solid

drug (S ) water solubility ( s) of the undissociated acid

(Eq (1)) or base (Eq (2)) molecular weight of the

drug ( M ) dissociation constants ( K a and K b) and thehydrogen or hydroxide ion concentration in the

diffusion layer covering the implanted solid ([H+]dor [OH]d respectively) c is a constant

d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN

For drugs administered by injection into the muscle

and subcutaneous sites Zuidema et al [1617] have

reviewed release characteristics and absorption rates

In their reviews they describe effects of injection

depth drug lipophilicity shape of the depot formed

at the injection site affinity of the drug for the vehicle

absorption rate of the vehicle and injection volume

Once drug is injected into either site it must be

released from the vehicle or delivery system and

diffuse to blood or lymphatic capillaries for absorp-

Fig 4 Possible pathways for absorption of drugs from CR-PDFs at intramuscular or subcutaneous sites


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Fig 6 Systemic absorption of drugs from extravascular injections showing rates of release from the delivery system or depot (k r ) and absorption

into tissue capillaries (k a )

Fig 5 Shapes of subcutaneous depots formed 48 h after subcutaneous administration of (A) an aqueous solution of a water soluble dye (B) an

aqueous suspension of a water-insoluble dye (C) a solution of an oil-soluble dye in Miglyol oil 812 and (D) a solution of an oil-soluble dye in

high viscosity oily vehicle (Miglycol oil 812 containing 75 aluminium monosterate)


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tion In muscles we have already noted earlier (Sec-

tion 312) that the area is well perfused by the nutritive

blood capillary network and although regional differ-

ences in absorption rates are exhibited at different intramuscular sites depending on perfusion rates and

muscular activity absorption rates are usually rapid

Morris et al [18] reported a model describing the

dependence of drug absorption on muscle perfusion

rate in sheep They showed that when equivalent doses

of lignocaine were injected into the proximal forelimb

or the proximal hindlimb significantly higher plasma

concentrations were achieved following injection into

the hindlimbs (approximately 2 mgl) compared with

the forelimb site (08 mgl) To measure local muscle

blood flow rates technetium was also injected and the

mean technetium washout half-time (TWH) used as a

measure of the blood flow This TWH was dependant

on the injection volume and following a 01 ml

injection the mean TWH was 182F 14 min from

the forelimb site compared with 11F 04 min from the

hindlimb with washout times increasing with increas-

ing injection volume The higher peak plasma concen-

tration of lignocaine following injection into the

hindlimb muscle was attributed to its faster absorption

rate due to the greater muscle blood perfusion at this

site [18] In the subcutaneous site the abundance of

blood capillaries is somewhat low er than in themuscles and depending on the depth of the injection

and the amount of subcutaneous fat present drug

absorption rates can be slower and more variable than

from intramuscular injections [19] The delayed ab-

sorption from the subcutaneous site appears to be

greater for drugs with high octanolwater partition

coefficients [1920] so probably reflects delayed re-

lease from fatty depots Partitioning effects could

potentially be modified by altering the lipophilicity

of the injection vehicle For example Al-Hindawi et

al [21] reported a positive correlation between the partition coefficient of testosterone propionate be-

tween the vehicle and water and the drug residence

time in muscle (Fig 7) In taking this approach it must

be remembered that the vehicle may be optimized to

increase drug solubility and partitioning Following

injection dilution or absorption of the solubilizing

components of the vehicle may result in drug

precipitation and slow absorption from the injection

site This can also be observed when pH adjusted

solutions are neutralised at the injection site [22]

Conversely if the solubilizing component diffuses

slowly from the injection site drug precipitation

may not occur and the desired improvement in

absorption may be achieved [23]

314 Tissue reactions at intramuscular and subcu-

taneous siteOther important aspects to consider are the effects

at the injection site caused by interaction of the drug

and delivery system materials with the tissues The

tissue reaction may limit the volume of material that

can be injected or affect the drug absorption rate

Work in recent years has focused on the development

and use of biomaterials in humans and animals for

controlled release applications Duncan [24] defines

biomaterials as lsquolsquoany non-viable materials which be-

come a part of the body either temporarily or perma-

nently to restore augment or replace the naturalfunctions of the living tissues or organs in the bodyrsquorsquo

As such they are used in prosthesis diagnostic and

therapeutic applications [25] In a review of the

biocompatibility issues of implantable drug delivery

systems Park and Park [25] give a working definition

of biocompatibility as lsquolsquoperformance of the biomate-

rial if biocompatible should not be affected by the

host and the host should not be negatively affected by

the implanted biomaterialrsquorsquo Despite an implanted

system being biocompatible many authors report

Fig 7 Relationship between testosterone partition coefficient between injection vehicle (ethyl oleate octanol isopropyl myriste

and light liquid paraffin) and water and the residence time at an

intramuscular injection site Data from Al-Hindawi et al [21] with

permission


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the formation of a fibrous capsule surrounding the

system and as described by Anderson et al [2627]

this tissue response is not inert and is expected to

modulate the in vivo release of implanted systemOn injection or implantation of a drug delivery

system the host responds to the tissue injury with the

sequence of well defined events shown below that

constitute the healing process [28]

1 An acute inflammatory reaction

2 Chronic inflammation

3 Granulation tissue

4 Foreign body reaction

5 Fibrosis

The intensity and duration of the inflammatory

reaction are a measure of the biocompatibility of the

system Acute inflammation lasts minutes to days and

is characterized by exudation of plasma proteins and

migration of leukocytes mainly neutrophils Chronic

inflammation is characterized by macrophages mono-

cytes lymphocytes and proliferation of blood vessels

and connective tissue surrounding the material Res-

olution of chronic inflammation occurs via a foreign

body reaction and the development of granulation

tissue (macrophages fibroblasts and capillaries) indi-

cates the normal healing response and tissue recoveryat treated site The foreign body reaction consists of

macrophages andor foreign body giant cells which

may persist at the tissueimplant interface for the

lifetime of the im plant Fibrosis may surround the

implanted material [28] These processes will have an

impact on the in vivo drug release from controlled

release systems as they represent diffusional barriers

for releasing drug Additionally the infiltration of

macrophages will be important in uptake and process-

ing of particulate systems Anderson et al [27]

describe the composition of the fibrous capsule that forms around subcutaneously implanted norethines-

teronecholesterol rods and discuss the contribution of

the immune system to the in vivo release mechanism

Three identifiable layers were reported to form around

the implanted material [27] Firstly a loose cellular

layer immediately surrounding the implant then a

dense fibrous connective tissue envelope that con-

tains blood and lymph vessels Finally an outer fatty

connective tissue layer surrounds this Large numbers

of macrophages and lipid laden foam cells were

observed in the loose connective tissue layer sur-

rounding the implants indicating a significant role

of the immune system in the bioerosion of these

cholesterol implants The steps in the absorption process were suggested to be an initial release of

loosely held norethisterone by dissolution This is

followed by a period in which macrophages coat the

implant and the fibrovascular coating formed In the

first phase of release very little control of the absorp-

tion process occurs However in the second phase the

drug absorption is proposed to be regulated by the

transport of lipidnorethisterone laden macrophages

and foam cells to the lymphatic vessels in the fibrous

capsule Diffusion of norethisterone still occurs but

now the diffusional barrier is expected to be greater

due to formation of the dense connective tissue layer

and the rate is slower than occurs initially [27]

Daugherty et al [29] have also described the

fibrous capsule that forms around implanted polylac-

tic-co-glycolic acid microspheres The tissue response

was dependant on the polymer type with the more

hydrophilic unblocked PLGA allowing greater cellu-

lar infiltration and fibrosis formation between individ-

ual microparticles compared with a more hydrophobic

unblocked polymer which contained hydrophobic end

groups With the hydrophobic microspheres an ag-

gregated depot appeared to form with cellular infil-trate and fibrosis noted at the margin of the depot

This difference could be an important determinant of

the in vivo release characteristics as the effective

surface area available for release following injection

with more hydrophobic polymeric microspheres

would be restricted to the depot margin whereas the

more hydrophilic microspheres would be defined by

the individual particle size

In vaccine delivery the immune response generat-

ed at the site of injection again plays an important role

in determining the response generated For antigen-containing microparticulate systems if the particle

size of injected particles is less than 10 Am macro-

phages that migrate to the site in the initial acute

inflammatory reaction can engulf the injected particles

and transport them to regional lymph nodes that drain

the subcutaneous site [30] This gives an enhancement

of antibody response which is reported to correlate

well with the phacogytosis by macrophages and

translocation of antigen-containing microparticles to

regional lymph nodes Besides the size the number of


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particles smaller than 10 Am can also be important

[31] Additionally Kidane et al [32] has shown that

the extent of phagocytosis depends on the surface

properties such as hydrophobicity which was illustrat-ed with alginate microspheres Similarly f or li poso-

mal particulates Oussoren and Storm [33] have

reported the importance of macrophage engulfment

and transport to regional lymph nodes for absorption

following subcutaneous administration

In some cases the initial acute inflammatory

response does not resolve and an undesirable injec-

tion site reaction ensues The drug itself or compo-

nents of the delivery system may cause these

reactions In the literature a number of methods have

been published for assessing injection sites on admin-

istration of controlled release injectable systems

These methods range from gross anatomical and

histological evaluation of the injection site [3435]

to in vitro t echniques for assessing the cellular toxic-

ity [36ndash39] of systems or components of systems In

the development of CR-PDFs these tests can be used

as screening tests to predict irritation potential and

possible mechanisms of tissue injury (Table 2) An

example of the use of one of these models in the

assessment of a CR-PDF is given by Kranz et al [40]

who used the isolated rat skeletal muscle model to

describe the irritation potential of in situ forming drug

delivery systems The basis of this model is that on

injection into the isolated muscle an irritant formula-tion will cause muscle cellular damage and release the

intracellular enzyme creatine kinase (CK) The cu-

mulative CK released into the tissue bath is measured

and systems are rated quantitatively by comparison of

the cumulative CK release over a defined exposure

time (120 min) in comparison to a positive control

(phenyt oin injection) and a negative control (saline)

[3941] The solvents studied were N -methyl-2-pyrro-

lidone (NMP) dimethylsulphoxide (DMSO) and 2-

pyrrolidone Injection of polylactic acid solutions

(40 wv polymer in solvent) in each of these

solvents gave a myotoxicity rating equivalent to the

solvent alone The rank order of myotoxicity was

NMPgtDMSOgt2-pyrrolidone By examining the CK

loss with different formulation combinations these

authors were able to evaluate an in situ forming

microparticulate system for the controlled release of

bupivicaine hydrochloride and buserelin acetate [40]

The reduced myotoxicity potential as measured in

vitro showed good correlation with myotoxicity

measured in vivo which indicates good predictive

ability of this model

32 Technology challenges

Each formulation and the manufacturing method to

produce it bring forward unique challenges Studying

the physicochemical and pharmacokinetic drug prop-

erties is extremely important as it is often these

properties that sustain drug release not specifically

the formulation Formulations must be chemically

physically and microbiologically stable Challenges

with product manufacturing can be as varied as

keeping water out of oil-based injectables to agglom-eration of multiparticulate products clogging screens

to changes in critical product characteristics upon

scale-up Two good reviews on the challenges in

researching and developing drug delivery formula-

tions for veterinary medicine are available [4243]

Besides giving specific examples for CR-PDF sys-

tems they highlight similarities and differences be-

tween human and animal drug delivery

For many microparticulate systems the ability to

scale up a process to industrial sized batches is not

Table 2

In vitro toxicity tests for assessment of the irritation potential of

injectable formulations

Test Principle References

Red blood cell

haemolysis

Haemolysis of red blood

cells and release of

haemaglobin on

exposure to irritant

compounds

[36112ndash115]

In vitro cell cultures

(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell

morphological changes

reduction in cell viability

(MTT assay) and

indicators of membrane

damage (leakage of

intracellular creatine

kinase from muscle cells

or lactate dehydrogenase

for other cells)

[3738116]

Isolated rat skeletal

muscle model

Muscle cell damage is

characterized by loss of

intracellular enzymes on

injection of system

[39ndash41117ndash

120]


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straightforward and has presented many challenges

for pharmaceutical research and development person-

nel Scale-up of microencapsulation processes has

been addressed in the human medicine field [44ndash 47] but the additional expenses associated with asep-

tic processing of these microencapsulated products

may only find application in high revenue veterinary

applications such as the thoroughbred industry or

companion animal markets Additional product costs

may not be as easily justified in the agricultural

setting Since injectable systems must be sterile

delivery systems that allow sterilization by standard

techniques (filtration heat or gamma irradiation) offer

significant advantages for commercialization For sol-

id systems eg implants or microparticulates sterili-

zation can be achieved by gamma irradiation

However exposure to gamma irradiation has been

shown to affect the release characteristics of CR-PDFs

prepared from biodegradable polymers and the bio-

logical activity of incorporated protein antigens and

therapeutics The effects of gamma irradiation appear

to be dose-dependent with for example naproxen and

diclofenac sodium release rates from poly(lactic acid

glycolic acid) microspheres increasing following ster-

ilization at radiation doses of 5 15 and 25 kGy [48]

Gamma-irradiation acceleration of the polymer deg-

radation has also been reported to continue duringstorage [49] thus potentially affecting product shelf-

life To establish stability on storage efficacy testing

may need to be repeated in the stability studies For

CR-PDFs efficacy testing may involve studies with

long study periods Examples of products that will

require long duration efficacy studies include testing

of hormonal growth implants that work for more than

100 days 6-month treatment of fleas in cats or dogs

and vaccines designed to give herd or flock protection

from disease for up to a year For all of these

applications the clinical trials needed to establishefficacy are of long duration and are expensive It

would be of great advantage to have predictive

models for critical components of these formulations

so that in vitro screening can deliver maximum

information and only dosage forms that have a high

chance of achieving the desired in vivo performance

are entered into clinical trials Few studies in this area

are available and we must continue to expand our

knowledge in understanding of underlying tissue

responses to implanted and injected materials so their

effects on the in vivo behavior and performance of

new CR-PDFs can be optimized Many of the tech-

nology challenges described in this section are illus-

trated with specific examples in the following section

4 Parenteral controlled release dosage forms

Application of controlled release parenteral tech-

nology within veterinary medicine remains attractive

as reductions in dosing frequency will ultimately

reduce labor intensive collection of animals for dosing

while maximizing the therapeutic outcome from the

agent administered With this goal in mind the

development challenges of different controlled release

parenterals are reviewed in this section Formulations

are classified by their physical form into liquids in

situ forming solids and solids for this purpose

41 Liquid formulations

Controlled release depot formulations have been

commercially successful A reduced rate of absorption

for water-soluble drugs can be achieved using oil

depots Traditional liquid formulations can take the

form of suspensions emulsions (water-in-oil or water-

in-oil-in-water) or microemulsions Although theseformulations represent the simplest technology for

the manufacture of controlled release injectable for-

mulations product stability can be a major limiting

factor of especially oily suspensions and emulsions In

spite of this one of the highest selling animal prod-

ucts PosilacR is an oil suspension of bovine somato-

tropin administered once every 14 days to increase

milk production in dairy cows (Table 1)

411 Aqueous-based systems (suspensions gels oil

in water emulsions liposome dispersions and microemulsions)

Injectable suspensions of insulin have been well

accepted in the treatment of diabetes to provide long

duration control of blood glucose in humans and

animals Prolonged release systems are based on

slowly dissolving amorphous or crystalline suspen-

sions of zinc and protamine insulins Products have

resulted with different durations of action so that good

glycemic control can be achieved through choice of

insulin type and dosing regimens [50] Bertoy et al


8202019 1-s20-S0169409X04000687-main


[51] reported once-a-day treatment with Ultralente

insulin (crystalline Zn-insulin suspension) could ef-

fectively treat the majority of cats with diabetes

mellitus However Lente insulin (a mixture of sus- pended amorphous and crystalline Zn-insulin) given

twice daily may be required if glycemic control

cannot be established with the Ultralente formulation

Graham et al [52] demonstrated the use of purified

porcine insulin zinc suspension (IZS-P) for the control

of naturally occurring diabetes in dogs IZS-P was

well absorbed and plasma insulin concentrations were

observed 14ndash 24 h thus allowing for single daily

injections for many dogs

A comparison of an aqueous nanosuspension and

oil suspension by Foster et al [5354] for administra-

tion of growth-hormone releasing factor (GHRF)

showed that an aqueous nanosuspension formulation

produced less injection site irritation than an oil

suspension The nanosuspension particles were rod-

shaped with particle dimensions of 500 100ndash200

nm shown by scanning electron microscopy and were

administered as a viscous paste containing 18

GHRF in sterile water for injection Following a dose

of 200 mg in steers serum somatotrophin levels were

elevated for at least 35 days for the aqueous formu-

lation Oleaginous suspension formulations gave

durations of 14 daysAddition of viscosity inducing agents to injectable

solutions has been used to prolong absorption times

by reducing drug diffusion in the depot formed at the

injection site The effect on enhancing vehicle viscos-

ity on retention of a large molecular weight compound

at the injection site was described by MacLean et al

[55] They reported a half-life of 66 h for iodinated

bovine serum albumin (BSA) at the injection site

following injecting 03 ml of a 50 mgml BSA

solution in phosphate-buffered saline The half-life

increased up to 14 h on formulation with increasingconcentrations of Carbopol 940 to 18 mgml The

increase in retention of BSA at the injection was

dependent on the Carbopol concentration but concen-

tration could not be increased further as at 20 mgml

Carbopol the material became too viscous to inject

Phospholipid gels are another system with enhanced

viscosity described by Tardi et al [56] These gels

were prepared at a concentration of 300 mgg egg

phosphatidylcholine and erode slowly on contact with

an aqueous environment Drug release in vitro showed

slow release of vesicular entrapment drug and the

drug between vesicular structures A major potential

advantage of this system compared with conventional

liposomal preparations lies in the stability of thehydrated structures on storage and the retention of

drug within the vesicular structures by having both

entrapped and free drug in the formulation The

entrapment of a marker compound calcein was

reported as 265 in the 300 mgg gel with the

remaining calcein located between vesicular struc-

tures Only minimal retardation of release was ob-

served for the 300 mgg gel with 50 released in the

first 30 min and 100 released in about 10 h

Retardation of release occurred when the phosphati-

dylcholine concentration was increased to 450 and

500 mgg These pastes were semi-solid in consisten-

cy and released the marker over about 35 and 65 h

respectively Increasing the phospholipid concentra-

tion changed the mechanism of release from predom-

inantly erosion controlled at 300 ndash400 mgg to

increasingly diffusion controlled at 450 and 500 mg

g The retention of large multilamellar vesicular

structures following subcutaneous injection has been

reported so there is potent ial for sustaining release

with these vehicles [5758] These previous examples

of enhancing sustained release with viscosity modi-

fiers have delivered large molecules A smaller mol-ecule metoclopramide has been sustained in vitro

using the poly(ortho esters) [59] Sun et al [60]

achieved 6 days of oxytetracycline concentrations in

sheep with a single inection of a PLGA gel formula-

tion High viscosity CR-PDFs may also be useful

when injected directly to diseased sites as they poten-

tially provide a depot of drug at the site of action

while maintaining low systemic drug concentrations

The clinical efficacy of various chemotherapeutic

agents delivered directly to skin tumor sites of veter-

inary patients was demonstrated by Orenberg et al[61] They administered chemotherapeutic agents

such as fluorouracil cisplatin methotrexate vinblas-

tine bleomycin carmustine and triamcinolone in a

protein gel matrix to provided site-specific sustained

release This method of administration minimized the

typical toxic side effects of the drugs and resulted in a

50 reduction in tumor volume in 81 of the lesions

and a complete clinical response in 56 for the subset

of most frequently treated tumors Another example of

delivery to the disease site was reported by Zhang et


8202019 1-s20-S0169409X04000687-main


al [62] They showed in vitro release of ceftiofur

could be changed by varying the Poloxamer 407

concentrations or including polyvinyl pyrrolidone

carboxymethylcellulose or hydroxylpropyl methylcel-lulose The formulations were developed to treat deep

bovine foot infections No in vivo data was presented

Besides extending the release gelled formulations

may also improve the drugsrsquo stability as shown with

deslorelin when formulated in Pluronic 127 [63]

Drugs that are lipid-soluble can be administered as

oil-in-water emulsions Since the continuous phase in

these systems is aqueous it should be absorbed

rapidly at the injection site to leave a depot of drug

dissolved in small oil droplets Norden et al [64]

describe a high dependence of drug concentration on

dispersed droplet size of a submicrometer ow emul-

sion stabilised with phospholipid A minimum droplet

size was observed (about 60 nm) as the clomethiazole

concentration increased then further increase in the

drug concentration resulted in an increase in droplet

size The mechanism of this effect was thought to be

due to the depression of the phospholipid chain

melting transition and interaction of the drug at the

phospholipid interface reducing the emulsifying ac-

tion of the phospholipid In comparison with coarse

emulsions microemulsions are also reported that have

improved physical stability on storage These too can be used to prolong drug absorpt ion following paren-

teral administration Bello et al [65] reported delayed

absorption of pertechnetate following subcutaneous

injection of a microemulsion formulation in compar-

ison to an aqueous solution The pertechnetate disap-

pearance rate as measured by the loss of radioactivity

was 10 times faster if the aqueous solution was

administered von Corwant et al [66] describe another

injectable microemulsion system comprising soybean

phosphatidylcholine and poly(ethylene glycol) (660)-

12-hydroxystearate (Solutol HS15) medium chaintriglyceride ethanol and polyethylene glycol 400

and water On injection intravenously dilution with

water results in formation of an ow emulsion with

droplet size smaller than IntralipidR Use of ow emul-

sions may have beneficial effects on injection tolera-

bility for lipo philic drugs as precipitation at the

injection site may be minimized if drug is slowly

released from the oil This was noted by Lee et al [67]

who reported pain on injection of intravenous clonixic

acid (a poorly water-soluble drug) was reduced on

formulation as a microemulsion consisting of castor

oilTween 20Tween 85

Liposome particulates can also be injected in

aqueous media to provide prolonged release of t her-apeutic or vaccine agents MacEwen et al [68]

describe liposome encapsulated muramyl tripeptide-

phosphatidylethanolamine (MTP-PE) as a treatment

option for dogs with metastasis undergoing amputa-

tion for osteosarcoma The liposomal treatment in-

creased the median survival time from 77 days for

control dogs treated with empty liposomes to 222

days f or dogs treated with liposomal MTP-PE Kruth

et al [69] review the utilization of liposomes for the

delivery of biological response modifiers (cytokines)

for the treatment of cancer in dogs Again signifi-

cantly longer survival times were found in dogs with

liposomal formulations Differences in the pharmaco-

kinetics of drugs administered in liposomes have been

reported with subcutaneous and intramuscular injec-

tion A lower maximum plasma concentration (C max)

of meglumine antimonite a compound used to treat

canine leishmaniasis was reported following subcu-

taneous compared with intramuscular injection of a

liposomal formulation This is consistent with an

expected slower absorption rate at the subcutaneous

site [70] In this case intramuscular administration

was recommended because higher C max for meglu-mine antimonite rather than sustained levels appears

to give improved therapeutic outcomes in canine

leishmaniasis

412 Oily systems (oily solutions suspensions and

wo emulsions)

Oily systems include those in which an oil phase

constitutes the external phase and thus include oily

solutions suspensions and water-in-oil emulsions

Larsen et al [71] showed a dependence of in vivo

release rates on apparent oilwater partition coeffi-cients for a series of nicotinic acid derivatives (methyl

to hexyl esters) The rate of attainment of equilibrium

between oil and aqueous phases was also linearly

related to the apparent partition coefficients so that

compounds with a high apparent partition coefficient

were more slowly released

Dispersibility of oily suspensions is often difficult

to achieve in the field so that dose non-uniformity can

be an issue with these products Foster and Kiefer [72]

patented the inclusion of small volumes of water in


8202019 1-s20-S0169409X04000687-main


oily suspensions to aid suspension redispersibility

Small amounts of water from the active ingredients

excipients or by direct addition can be used to control

flocculation and thus the redispersibility of oil suspensions After 6 months storage suspensions of

ceftiofur HCl in cottonseed oil with 039 water

could be uniformly redispersed in a 10-s mechanical

shaking test In comparison equivalent suspensions

with 020 water were not adequately re-dispersed

after the 6-month storage

42 In situ forming solid formulations

In situ forming systems have been a recent

technology developed for the production of sustained

release systems These systems are fluid on injection

and rely on a change in the local environment to

produce a high viscosity or solid depot at the

injection site Changes that cause solidification fol-

lowing injection include increase in temperature to

37 jC loss of organic solvent from the injected

material by diffusion or hydration with water from

the injection site The rheological properties of these

systems must remain consistent with injection prior

to and during the injection process to be acceptable

delivery systems Systems developed in this area have

included the sucrose acetate isobutyrate (SABER R)and polyester organic solution (AtrigelR) systems An

excellent review of this topic strictly focused on

veterinary medicine was completed by Matschke

et al [73]

Control and synchronization of estrus has been

demonstrated in mares [7475] and in gilts and sows

[76] with a sucrose acetate isobutyrate (SAIB

SABER k) delivery system containing progesterone

and estradiol or deslorelin The gel systems formed

by diffusion of organic solvent from the site can be

sterilized by gamma irradiation [7778] and can bemodified to provide the appropriate delivery duration

Evaluation of SABER k systems in mares have

resulted in in vivo estradiol levels similar to pol-

y(DL-lactide) microsphere formulations [79] without

the associated scale-up difficulties for the simple lsquolsquomix

and fillrsquorsquo operation

Examples of significant weight gains achieved

following injections of a growth agent in Atrigel

systems are given in Table 3 Implants formed in vivo

were flat oval smooth discs conforming to the in

vivo cavity with morphology ranging from single

spheres to multiple small spheres However it was

noted that welts formed at the injection site within 24

h and remained through the 28-day study Histopath-

ological evaluation of the injection site was indicative

of granulomatous myositis and panniculitis

43 Solid formulations

Solid implant formulations have demonstrated sus-

tained release for periods ranging from weeks to yearsImplants include those manufactured from biodegrad-

able or bioabsorbable polymers silicone or silastic

rubber implantable osmotic pumps and reservoir

systems Each formulation approach has advantages

which may include the ability to retrieve the device

research and manufacturing costs drug release rate

and duration and drug compatibility with the matrix

Short-term implants containing deslorelin in an inert

biocompatible matrix have been shown to significantly

accelerate follicular growth [80] Implantation resulted

in ovulation for 93 of treated mares within 48 h Theresponse was not diminished with repeated treatment

[8182] and treatment did not affect pregnancy rates

[83] Longer-term implants (1ndash12 months) have also

been shown to effectively release actives Drummond

et al [84] reported effective treatment of ticks for

periods ranging from 40 to 80 days by utilizing

sustained release of ivermectin from polyethylene

glycol implants whereas Miller et al [85] demonstrat-

ed 10ndash12 weeks control of horn flies with similar

implants Efficacious serum ivermectin levels have

Table 3

In situ forming implants prepared Atrigel formulations containing a

growth agent

Treatment Average daily

gain (kgday)

Placebo 114a

NMP solvent 116a

Atrigel-A (Poly-lactide-co-

caprolactone 2575 42)

125ab

Atrigel B (Poly-lactide-co-

glycolide 5050 60)

143 bc

Atrigel C (Polylactide 53) 158c

IP-Atrigel A 143 bc

Pharmacia control 151c

Positive control 154c

abcMeans with a common superscript are not different P gt010


8202019 1-s20-S0169409X04000687-main


been reported [86] after 4 months following implanta-

tion of a methylcellulose implant in free-range bighorn

sheep Shih et al [87] demonstrated sustained release

of ivermectin consistent with a bulk erosion mecha-nism in both dogs and rats from cross-linked poly

(ortho ester) matrices for periods greater than 12

months

Silastic and silicone rubber implants impregnated

with melengestrol acetate (MGA) or progesterone

have been shown to be effective for the long-term

suppression and synchronization of estrus in cattle

[8889] Kesler et al [90] determined that synchroni-

zation was more effective with sustained release of

norgestomet from silicone implants compared to

hydron implants Release of estrogens from polyhy-

droxy polymer systems [91] was effective in control-

ling estrus in cattle only when norethandrolone was

incorporated into the matrix with synchronization

ranging from 89 to 100 when the implant was

given in combination with injections of estradiol

valerate Woody et al [92] determined that both 9-

and 16-day treatments with polyhydroxy polymer

systems containing norethandrolone were unsatisfac-

tory in synchronization of estrus when heifers are

implanted early or late in their estrous cycles Intra-

vaginal silicone and polyurethane implants have been

used extensively for the control of estrus in cattlesheep goats deer pigs and horses and ar e available

in a variety of drug delivery systems [4] A distinct

advantage of rubber type implants is that the intact

implant may be withdrawn when desired

In vitrondashin vivo correlation of release of norges-

tomet from hydrophilic (hydrogel) implants for the

control of estrus in cattle was described by Chien and

Lau [93] to follow a matrix controlled process Poly-

merization of the water-soluble monomers of hydrox-

yethyl methacrylate to an alcohol-soluble linear

polymer was followed by crosslinking with ethylenedimethacrylate to generate the gels Control of the

amount of cross-linking agent the monomer-to-water

ratio and the polymerization conditions resulted in a

range of polymer masses from compact gel to cellular

sponge

Endocrine changes in gilts were examined [94]

during and after administration of progesterone with

implantable osmotic pumps designed to deliver 115

mgday Sustained plasma progesterone levels effec-

tively inhibited estrus Following device removal

preovulatory endocrine changes continued in a normal

fashion Osmotic implant pumps have also been

investigated for the delivery of porcine somatotropin

to allow a one-t ime administration during the swinefinishing phase [95] For further information on por-

cine and bovine somatotro pin delivery a review

article by Foster is available [96]

Jaffe et al [97] have demonstrated the controlled

release of insect steroid analogues through 3 months

from poly( q-caprolactone) implantable resevoir sys-

tems with control of ticks in rabbits The reservoir

devices were prepared by sealing lengths of poly( q-

caprolactone) tubing (254 mm OD 019 mm wall

thickness) and filling with ecdysteroid suspensions

This work supported data previously reported [9899]

with release of insect growth regulators from poly( q-

caprolactone) reservoir devices for the control of

grubs in cattle

New drug delivery technology has been developed

to deliver solid implants van de Wijdeven [100]

described a hollowed-out mini projectile which can

be loaded with drug The device is held 3 ndash 10 mm

from the animalsrsquo skin during delivery thus avoiding

cross-contamination between handler and animal

Other ballistic devices include the darted devices used

in wildlife management

Microparticulate systems have been investigated to provide sustained release of drug moieties for periods

of as little as 1 week to greater than 1 year Several

methods of preparation are utilized including solvent

evaporation techniques and melt technologies which

eliminate the need for removal of organic solvents

Solvent evaporation techniques have been utilized by

Burns et al [101] to formulate poly(DL-lactide) micro-

spheres for the short-term (12ndash14 days) delivery of

progesterone and estradiol-17h for the control of

estrus and ovulation in mares Blanchard et al [102]

have also shown a significant reduction in variation indays to estrus for treated mares Intervals to estrus and

ovulation were shown to be dose-dependent [103]

Slightly longer duration (16 ndash 30 days) delivery of

estradiol-17h from polylactide microsphere formula-

tions was demonstrated by Cushman et al [104] to

successfully induce pseudopregnancy and thus allow

for synchronization of estrus in gilts Miller et al

[105] have reported the efficacy of long-term delivery

of ivermectin to cattle and goats for the control of

cattle ticks and horn flies utilizing a series of bio-


8202019 1-s20-S0169409X04000687-main


absorbable poly(lactide-co-glycolide) (PLAPGA)

copolymer microsphere formulations Microspheres

were formulated with approximately 30 ivermectin

loading utilizing a solvent-evaporation process and5050 PLAPGA copolymer (90000 MW) 9010

PLAPGA copolymer (5000 MW) or a PLA monomer

(20000 MW) All formulations exhibited an initial

burst with sustained ivermectin release dependent on

the composition of the polymer The formulations

showed near 100 control of both ticks and horn

flies for up to 9 weeks post injection Further inves-

tigation [106] with formulations containing a combi-

nation of 5050 PLAPGA (75000 MW) and 6535

PLAPGA (100000 MW) confirmed the earlier stud-

ies with control of ticks for greater than 11 weeks

Weight gain in treated cattle was also significantly

increased Vitamin B12 has also been successfully

administered to lambs and sheep as PLGA micro-

spheres in peanut oil (SMARTShot k B12) [107ndash

109] When administered subcutaneously to lambs

grazed on cobalt deficient pastures at doses of 3

45 or 6 mg B12 significantly greater weight gains

were seen in the treated lambs from the time of

weaning at 60ndash 187 days compared with untreated

controls Serum vitamin B12 levels were greatly

elevated compared with controls on days 25 and 60

then only slightly higher at other sampling times over 91ndash243 days while liver B12 was elevated in treated

lambs when measured at 124 days (158ndash227 nmolkg

fresh tissue) and returned to baseline ( lt 70 nmolkg

fresh tissue) by 215 days [109]

5 Recent advances

The top four marketed CR-PDF (Table 1) represent

well the types of depot controlled release veterinary

products implants suspensions and solutions Thecarrier vehicles in these products include water oil

propylene glycol polyethylene glycol and n-methyl-

2-pyrrolidone Controlled release parenteral dosage

forms for food animals must be cost-effective so the

dosage forms and vehicles mentioned above are

logical choices However improvements to these

conventional CR-PDF can provide additional value

to both consumers and pharmaceutical companies

alike Adding a fast-release pellet containing the

anti-infective tylosin tartrate to the standard implant

presentation (Component R with TylanR) has practi-

cally eliminated implant site infection and abscesses

minimizing implant loss and improving absorption

and efficacy [110] With formulations introduced inlate 1999 and early 2000 the products have quickly

gained ground in the feedlot industry growth promo-

tant field The manufacturer Ivy Animal Health has

seen sales increase from $16 million in 1998 to $324

million in 2000 with their feedlot market share

increasing from 17 to 34 [111]

The companion animal market quite different from

the food producing market is often focused on treat-

ing lsquolsquomembers of the familyrsquorsquo This enables the

research and development of more expensive dosage

forms As the markets expand for companion animals

and vaccines new CR-PDF will continue to be

developed ProgramR 6-Month Injectable for Cats

(Novartis) is a recent example of a long-term delivery

system The injectable sterile suspension provides for

the control of flea populations for a full 6 months by

preventing the development of flea eggs thus disrupt-

ing the flea life cycle Presented in 04 and 08 ml

preloaded unit-dose syringes it is indicated for use in

cats 6 weeks in age and older Injected subcutane-

ously once every 6 months the ProgramR formulation

provides an alternative to monthly tablet or oral

suspension dosing ProHeart R6 (Fort Dodge) alsoexemplifies the current trend of controlled release

parenteral dosage forms The microsphere technology

delivery system provides 6 months of continuous

protection from heartworm disease and treatment of

existing larval and adult hookworm Presented as a

two-part 20 ml vial product each package includes a

vial containing 10 moxidectin sterile microspheres

and a specifically formulated sterile vehicle for con-

stitution of the microsphere vial Indicated for use in

dogs six months and older with treatment every six

months ProHeart R

6 eliminates owner complianceissues associated with daily or monthly oral dosing

6 Concluding remarks

To meet future market requirements expectations

for formulations continue to increase For the food

animal market products must continue to minimize

costs both of the product and those associated with

handling and dosing of the animals while exhibiting


8202019 1-s20-S0169409X04000687-main


superior efficacy and minimal residue For the com-

panion animal market future product development

must continue to be convenient for the owners with

treatment programs expanding to include many areasfound in human health (eg arthritis cancer) For

both markets one-time or infrequent dosing is de-

sired with products exhibiting sustained release over

a period of time as short as a couple of days to 12

months Site-specific delivery can also provide added

benefits To meet these needs additional technologies

being studied include microspheres (eg polyesters

alginates) implants (polyesters silicone collagen) in

situ forming implants (eg sucrose acetate isobuty-

rate polyesters) and osmotic pumps These formula-

tions are used to eliminate parasites synchronize

estrus enhance growth reduce tumors control diabe-

tes and vaccinate animals

References

[1] RG Arnold Controlled-release new animal drugs J Con-

trol Release 8 (1988) 85ndash90

[2] DH Carter M Luttinger DL Gardner Controlled release

parenteral systems for veterinary applications J Control

Release 8 (1988) 15 ndash 22

[3] SM Cady Status of control release technology in the animalhealth industry Proc Int Symp Control Rel Bioact Mater

Boston MA 1999

[4] MJ Rathbone KL MacMillan W Jochle MP Boland

EK Inskeep Controlled-release products for the control of

estrus in cattle sheep goats deer pigs and horses Crit Rev

Ther Drug Carr Syst 15 (1998) 285ndash380

[5] JD Baggot Clinical pharmacokinetics in veterinary medi-

cine Clin Pharmacokinet 22 (1992) 254ndash273

[6] H Mawhinney SM Oakenfull TJ Nicholls Residues from

long-acting antimicrobial preparations in injection sites in

cattle Aust Vet J 74 (1996) 140ndash142

[7] R Rule L Moreno JM Serrano AG Roman R Moyano

J Garcia Pharmacokinetics and residues in milk of oxyte-

tracyclines administered parenterally to dairy goats AustVet J 79 (2001) 492ndash496

[8] S Brown Administration of an injectable antibiotic in the

ear of an animal US Patent 6074657 (2000)

[9] NJ Medlicott IG Tucker Pulsatile release from subcuta-

neous implants Adv Drug Deliv Rev 38 (1999) 139ndash149

[10] N Washington C Washington CG Wilson Physiological

pharmaceutics Barriers to Drug Absorption 2nd ed Taylor

and Francis London 2001

[11] PL Williams R Warwick M Dyson LH Bannister (Eds)

Grayrsquos Anatomy 37th ed Churchill Livingstone Edinburgh

UK 1989

[12] EN Maried Human Anatomy and Physiology 3rd ed The

BenjaminCummings Publishing California USA 1995

[13] P Dandona D Hooke J Bell Exercise and insulin absorp-

tion from subcutaneous tissue BMJ 1 (1978) 479ndash480

[14] S Bjerregaard H Pedersen H Vedstesen C Vermehren ISoderberg S Frokjaer Parenteral wateroil emulsions con-

taining hydrophilic compounds with enhanced in vivo re-

tention formulation rheological characterisation and study

of in vivo fate using whole body gamma-scintingraphy Int

J Pharm 215 (2001) 13ndash27

[15] BE Ballard E Nelson Absorption of implanted solid drug

J Pharm Sci 51 (1962) 915ndash924

[16] J Zuidema FAJM Pieters GSMJE Duchateau Release

and absorption rate aspects of intramuscular injected phar-

maceuticals Int J Pharm 47 (1988) 1ndash12

[17] J Zuidema F Kadir HAC Titulaer C Oussoren Release

and absorption rates of intramuscularly and subcutaneously

injected pharmaceuticals II Int J Pharm 105 (1994)

189ndash207

[18] RG Morris A Karatassas A Orfanos Regional blood flow

as a determinant of drug absorption description of an animal

model J Pharmacol Toxicol Methods 30 (1993) 39ndash45

[19] F Kadir J Zuidema A Pijpers A Vulto JHM Verheijden

Drug lipophilicity and release pattern of some h-blocking

agents after intra-apidose and intramuscular injection in pigs

Int J Pharm 64 (1990) 171ndash180

[20] F Kadir J Zuidema A Pijpers R Melendez A Vulto

JHM Verheijden Pharmacokinetics of intra-apidosely and

intramuscularly injected carazolol in pigs J Vet Pharmacol

Ther 13 (1990) 350ndash355

[21] MK Al-Hindawi KC James PJ Nicholls Influence of

solvent on the availability of testosterone propionate fromoily intramuscular injections in rats J Pharm Pharmacol

39 (1987) 90ndash95

[22] F Tse PG Welling Bioavailability of parenteral drugs I

Intravenous and intramuscular doses J Parenter Drug

Assoc 34 (1980) 409ndash421

[23] Y Cheng-Der JS Kent Effects of propylene glycol on

subcutaneous absorption of benzidamole hydrochoride J

Pharm Sci (1982) 476ndash478

[24] E Duncan Biomaterials What is a biomaterial Med De-

vice Diagn Ind 12 (1990) 138ndash142

[25] H Park K Park Biocompatibility issues of implantable

drug delivery systems Pharm Res 13 (1996) 1770ndash1775

[26] JM Anderson H Niven J Pelagalli LS Olanoff RD

Jones The role of the fibrous capsule in the function of implanted drugndash polymer sustained release systems

J Biomed Mater Res 15 (1981)

[27] FD Anderson DF Archer SM Harman RJ Leonard

WH Wilborn Tissue response to bioerodible subcutaneous

implants a possible determinant of drug absorption kinetics

Pharm Res 10 (1993) 369ndash380

[28] JM Anderson In vivo biocompatibility of implantable de-

livery systems and biomaterials Eur J Biopharm 40 (1994)

1ndash8

[29] AL Daugherty JL Cleland EM Duenas RJ Mrsny

Pharmacological modulation of the tissue response to


8202019 1-s20-S0169409X04000687-main


implanted polylactic-co-glycolic acid microspheres Eur J

Pharm Biopharm 44 (1997) 89ndash102

[30] JH Eldridge JK Staas JA Meulbroek TR Tice

RM Gilley Biodegradable and biocompatible poly(DL-

lactide-co-glycolide) microspheres as an adjuvant for sta- phlococcal enterotoxin B toxin which enhances the level

of toxin-neutralizing antibodies Infect Immun 59 (1991)

2978ndash2986

[31] T Uchida S Martin TP Foster RC Wardley S Grimes

Dose and load studies for subcutaneous and oral delivery of

poly(lactide-co-glycolide) microspheres containing ovalbu-

min Pharm Res 11 (1994) 1009ndash1015

[32] A Kidane P Guimond TR Ju M Sanchez J Gibson A

North H HogenEsh TL Bowersock Effects of cellulose

derivatives and poly(ethylene oxide)ndash poly(propylene ox-

ide) tri-block copolymers (PluronicR surfactants) on the

properties of alginate based microspheres and their interac-

tions with phagocytic cells J Control Release 85 (2002)

181ndash189

[33] C Oussoren G Storm Role of macrophages in the local-

isation of liposomes in lymph nodes after subcutaneous ad-

ministration Int J Pharm 183 (1999) 37ndash41

[34] R Marchant A Hiltner C Hamlin A Rabinovitch R

Slobodkin JM Anderson In vivo biocompatibility stud-

ies I The cage implant system and a biodegradable

hydrogel J Biomed Mater Res 17 (1983) 301ndash 325

[35] SF Bernatchez A Merkli C Tabatabay R Gurny QH

Zhao JM Anderson Biotolerance of a semisolid hydropho-

bic biodegradable poly(ortho ester) for controlled drug deliv-

ery J Biomed Mater Res 27 (1993) 677ndash681

[36] KW Reed SH Yalkowsky Lysis of human red blood cells

in the presence of various cosolvents J Parenter Sci Tech-nol 39 (1985) 64ndash68

[37] PD Williams BG Masters LD Evans DA Laska GH

Hottendorf An in vitro model for assessing muscle irritation

due to parenteral antibiotics Fundam Appl Toxicol 9

(1987) 10ndash17

[38] DA Laska PD Williams JT Reboulet RM Morris The

L6 muscle cell line as a tool to evaluate parenteral products

for irritation J Parenter Sci Technol 45 (1991) 77ndash82

[39] GA Brazeau H Fung An in vitro model to evaluate muscle

damage following intramuscular injections Pharm Res 6

(1989) 167 ndash 170

[40] H Kranz GA Brazeau J Napaporn RL Martin W

Millard R Bodmeier Myotoxicity studies of injectable

biodegradable in-situ forming drug delivery system IntJ Pharm 212 (2001) 11ndash 18

[41] GA Brazeau HL Fung Use of an in vitro model for the

assessment of muscle damage from intramuscular injections


[42] MJ Rathbone MN Martinez Modified release drug de-

livery in veterinary medicine Drug Disc Today 7 (2002)

823ndash829

[43] I Ahmed K Kasraian Pharmaceutical challenges in veter-

inary product development Adv Drug Deliv Rev 54 (2002)

871ndash882

[44] JL Cleland Solvent evaporation processes for the produc-

tion of controlled release biodegradable microsphere formu-

lations for therapeutics and vaccines Biotechnol Prog 14

(1998) 102 ndash 107

[45] J Hanes JL Cleland R Langer New advances in micro-

sphere-based single-dose vaccines Adv Drug Deliv Rev 28(1997) 97 ndash 119

[46] MA Tracy Development and scale-up of a microsphere pro-

tein delivery system Biotechnol Prog 14 (1998) 108ndash115

[47] P Herbert K Murphy O Johnson N Dong W Jaworowicz

MA Tracy JL Cleland SD Putney A large-scale process

to produce microencapsulated proteins Pharm Res 15 (1998)

357ndash361

[48] S Calis S Bozdag HS Kas M Tuncay AA Hincal

Influence of irradiation sterilization on poly(lactide-co-gly-

colide) microspheres containing anti-inflammatory drugs

Farmaco 57 (2002) 55 ndash 62

[49] G Spenlehauer M Vert JP Benoit A Boddaert In vitro

and in vivo degradation of poly(DL lacticglycolide) type

microspheres made by solvent evaporation method Bioma-

terials 10 (1989) 557ndash563

[50] DS Greco JD Broussard ME Peterson Insulin thera-

py Vet Clin North Am Small Anim Pract 25 (1995)

677ndash689

[51] EH Bertoy RW Nelson EC Feldman Effects of lente

insulin for treatment of diabetes mellitus in 12 cats J Am

Vet Med Assoc 206 (1995) 1729 ndash 1731

[52] PA Graham AS Nash QA McKellar Pharmacokinetics

of a porcine insulin zinc suspension in diabetic dogs J Small

Anim Pract 38 (1997) 434ndash438

[53] TP Foster WM Moseley JF Caputo GR Alaniz MW

Leatherman X Yu WH Claflin DR Reeves DL Cleary

M Zantello LF Krabill JR Wiest Sustained elevated se-rum somatotropin concentrations in Holstein steers following

subcutaneous delivery of a growth hormone releasing factor

analog dispersed in water oil or microspheres J Control

Release 47 (1997) 91ndash 99

[54] TP Foster WM Moseley JF Caputo MJ Hageman Aque-

ous prolonged release formulation US Patent 6150330

(2000)

[55] DS MacLean JD Robertson M Jay DJ Stalker Nonin-

vasive measurement of protein release from subcutaneous

depo formulations in vivo using X-ray fluorescence J Con-


[56] C Tardi M Brandl R Schubert Erosion and controlled

release properties of semisolid vesicular phospholipid disper-

sions J Control Release 55 (1998) 261ndash270[57] R Perez-Soler G Lopez-Berestein M Jahns K Wright

LP Kasi Distribution of radiolabelled multilamellar lipo-

somes injected intralymphatically and subcutaneously Int

J Nucl Med Biol 12 (1985) 261ndash266

[58] T Kim J Kim S Kim Extended-release formulation of

morphine for subcutaneous administration Cancer Chemo-

ther Pharmacol 33 (1993) 187ndash190

[59] K Schwach-Abdellaoui M Moreau M Schneider B Bois-

ramc R Gurny Controlled delivery of metoclopramide us-

ing an injectable semi-solid poly(ortho ester) for veterinary

application Int J Pharm 248 (2002) 31ndash37


8202019 1-s20-S0169409X04000687-main


[60] Y Sun Y Peng N Aksornkoae JR Johnson JG Boring

D Scruggs RC Cooper SC Laizure AJ Shukla Con-

trolled release of oxytetracycline in sheep J Control Re-

lease 85 (2002) 125ndash134

[61] EK Orenberg EE Luck DM Brown BE Kitchell Im- plant delivery system intralesional delivery of chemothera-

peutic agents for treatment of spontaneous skin tumors in

veterinary patients Clin Dermatol 9 (1991) 561ndash568

[62] L Zhang DL Parsons C Navarre UB Kompella Devel-

opment and in-vitro evaluation of sustained release Polox-

amer 407 (P407) gel formulations of ceftiofur J Control


[63] JGW Wenzel KSS Balaji K Koushik C Navarre SH

Duran CH Rahe UB Kompella PluronicR F127 gel for-

mulations of deslorelin and GnRH reduce drug degradation

and sustain drug release and effect in cattle J Control Re-

lease 85 (2002) 51ndash59

[64] TP Norden B Siekmann S Lundquist M Malmsren

Physiochemical characterisation of a drug-containing phos-

pholipid-stabilised ow emulsion for intravenous administra-

tion Eur J Pharm Sci 13 (2001) 393ndash401

[65] M Bello D Colangelo MR Gasco F Maranetto S Morel

V Podio GL Turco I Viano Pertechnetate release from a

water oil microemulsion and an aqueous solution J Pharm

Pharmacol 46 (1994) 508ndash510

[66] C von Corswant P Thoren S Engstrom Triglyceride-based

microemulsion for intravenous administration of sparingly

soluble substances J Pharm Sci 87 (1998) 200ndash208

[67] J-M Lee K-M Park S-J Lim S-J Lee C-M Kim

Microemulsion formulation of clonixic acid solubility en-

hancement and pain reduction J Pharm Pharmacol 54

(2002) 43ndash49[68] EG MacEwan ID Kurzman DM Vail RR Dubielzig

K Everlith BR Madewell CO Rodriguez Jr B Phillips

CH Zwahlen J Obradovich RC Rosenthal LE Fox M

Rosenberg C Henry J Fidel Adjuvant therapy for melano-

ma in dogs results of randomized clinical trials using sur-

gery liposome-encapsulated muramyl tripeptide and

granulocyte macrophage colony-stimulating factor Clin

Cancer Res 5 (1999) 4249ndash4258

[69] S Kruth Biological response modifiers interferons interleu-

kins recombinant products liposomal products Vet Clin

North Am Small Anim Pract 28 (1998) 269 ndash 295

[70] JE Valladares J Freixas J Alberola C Franquelo C

Cristofol M Arboix Pharmacokinetics of liposome-encap-

sulated meglumine antimonate after intramuscular and sub-cutaneous administration in dogs Am J Trop Med Hyg 57

(1997) 403 ndash 406

[71] SW Larsen AE Thomsen E Rinvar GJ Friis C Larsen

Effect of drug lipophilicity on in vitro release from oil

vehicles using nicotinic acid esters as model prodrug deriv-

atives Int J Pharm 216 (2001) 83ndash93

[72] TP Foster DL Kiefer Antibiotic oil suspension US Patent

5736151 (1996)

[73] C Matschke U Isele P van Hoogevest A Fahr Sustained-

release injectables formed in situ and their potential use for

veterinary products J Control Release 85 (2002) 1ndash15

[74] P Burns DJ Thompson F Donadue L Kincald B Leise

J Gibson R Swaim A Tipton Pharmacodynamic evalua-

tion of SABER k delivery system for the controlled release

of the GnRH alanlgue desorelin acetate for advancing ovu-

lation in cyclic mares Proc Int Symp Control ReleaseBioact Mater (1997) 737ndash738

[75] J Fleury EL Squires R Betschart J Gibson S Sullivan

A Tipton PJ Burns Evaluation of the SABER k delivery

system for the controlled release of deslorelin for advancing

ovulation in the mare effects of formulation and dose Proc

Int Symp Control Release Bioact Mater (1998) 657 ndash 658

[76] R Barb R Kraeling G Rampacek DJ Thompson J Gib-

son S Sullivan B Simon PJ Burns Evaluation of the

SABER delivery system for the controlled release of deslor-

elin effect of dose in estrogen primed ovarectomized gilts

Proc Int Symp Control Release Bioact Mater (1999)

1170ndash1171

[77] R Betschart J Fleury EL Squires T Nett J Gibson S

Sullivan A Tipton PJ Burns Evaluation of the SABER k

delivery system for the controlled release of the GnRH ana-

logue deslorelin for advancing ovulation in mares effect of

gamma irradiation Proc Int Symp Control Release Bioact

Mater (1998) 655ndash656

[78] SA Sullivan JW Gibson PJ Burns L Franz EL Squires

DL Thompson AJ Tipton Sustained release of progester-

one and estradiol from the SABER k delivery system in vitro

and in vivo release rates Proc Int Symp Control Release

Bioact Mater (1998) 653ndash 654

[79] CA Johnson DLJ Thompson SA Sullivan JW Gibson

AJ Tipton BW Simon PJ Burns Biodegradable delivery

systems for estradiol comparison between poly(DL-lactide)

microspheres and the SABER delivery system Proc IntSymp Control Release Bioact Mater (1999) 74ndash 75

[80] C Meinert JF Silva I Kroetz E Klug TE Trigg HO

Hoppen W Jochle Advancing the time of ovulation in the

mare with short-term implant releasing the GnRH analogue

deslorelin Equine Vet J 25 (1993) 65 ndash 68

[81] K Wilhelm J Graham EL Squires TE Trigg W Jochle

Repeated use of deslorelin STI for accelaeration of ovulation

in mares without loss of effectiveness Reprod Domest

Anim 29 (1994) 247

[82] EL Mumford EL Squires E Jochle LA Harrison

TM Nett TE Trigg Use of deslorelin short-term implants

to induce ovulation in cycling mares during three consecu-

tive estrous cycles Anim Reprod Sci 39 (1995) 129ndash140

[83] W Jochle TE Trigg Control of ovulation in the mare withovuplant k A short term release implant (STI) containing

the GnRH analogue deslorelin acetate studies from 1990 to

1994 J Equine Vet Sci 14 (1994) 632ndash644

[84] RO Drummond JA Miller Control of ticks systemically

with sustained-release implants of ivermectin in DA Grif-

fiths CE Bowman (Eds) Acarology VI Ellis Horwood

West Sussex UK 1984 pp 1274ndash1279

[85] JA Miller RO Drummond DD Oehler A sustained re-

lease ivermectin implant for livestock pest control in TJ

Roseman SZ Mansdorf (Eds) Controlled Release Delivery

Systems Marcel Dekker New York 1983 pp 223ndash236


8202019 1-s20-S0169409X04000687-main


[86] WM Boyce JA Miller DA Jessup RK Clark Use of

ivermectin implants for the treatment of psoroptic scabies in

free-ranging bighorn sheep J Zoo Wildl Med 23 (1992)

211ndash213

[87] C Shih J Fix RL Seward In vivo and in vitro release of ivermectin from poly(ortho ester) matrices I Crosslinked

matrix prepared from ketene acetal end-capped prepolymer

J Control Release 25 (1993) 155ndash162

[88] PF Scanlon TD Burgess Subcutaneous and oral applica-

tions of progestagens for control of estrus in heifers Can J

Anim Sci 51 (1971) 540ndash541

[89] JF Roche JP Crowley The long-term suppression of heat

in cattle with implants of melengestrol acetate Anim Prod

16 (1973) 245ndash250

[90] DJ Kesler RJ Favero In vitro and in vivo secretion of

norgestomet from matrix silicone and hydron implants and

pregnancy rates of females synchronized with norgestomet


435ndash436

[91] JN Wiltbank JC Sturges D Wideman DG LeFever

LD Faulkner Control of estrus and ovulation using subcu-

taneous implants and estrogens in beef cattle J Anim Sci

33 (1971) 600ndash606

[92] CO Woody RA Pierce Influence of day estrous cycle at

treatment on response to estrous cycle regulation by nore-

thandrolone implants and estradiol valerate injections J


[93] YW Chein EPK Lau Controlled drug release from poly-

meric delivery devices IV In vitrondashin vivo correlation of

subcutaneous release of norgestomet from hydrophilic

implants J Pharm Sci 63 (1976) 488ndash492

[94] S Mukai Y Mori H Nagashima K Hoshino Changes in plasma gonadotrophins ovarian steroids and inhibin concen-

trations in gilts following progesterone treatment with im-

plantable osmotic pumps Anim Reprod Sci 20 (1989)

287ndash297

[95] MJ Azain KD Bullock TR Kasser JJ Veenhuizen

Relationship of mode of porcine somatotropin administra-

tion and dietary fat to the growth performance and carcass

characteristics of finishing pigs J Anim Sci 70 (1992)

3086ndash3095

[96] TP Foster Somatotropin delivery to farmed animals Adv

Drug Deliv Rev 38 (1999) 151ndash165

[97] H Jaffe DE Sonenshine DK Hayes WH Dees M

Beveridge MJ Thompson Controlled-release reservoir

systems for the delivery of insect steroid analoguesagainst ticks (Acari Ixodidae) J Med Entomol 23

(1986) 685 ndash 691

[98] H Jaffe PA Giang DK Hayes JA Miller BH Stroud

Implantable systems for the delivery of insect growth in

DH Lewis (Ed) Controlled Release of Pesticides and Phar-

maceuticals Plenum New York 1981 pp 303ndash310

[99] H Jaffe JA Miller Implantable systems for delivery of

insect growth regulators to livestock in R Baker (Ed)

Controlled Release of Bioactive Materials Academic Press

New York 1980 pp 237 ndash 250

[100] GGP van de Wijdeven Development and assessment of

mini projectiles as drug carriers J Control Release 85

(2002) 145 ndash 162

[101] PJ Burns TR Tice DW Mason DF Love RR Foss F

Sarver JA Woods TR Sissener AV Heitland K Wil-

helm ME Farlin EL Squires Control of estrus and ovula-tion in mares using progesterone and estradiol biodegradable

microspheres in a multicenter clinical trial Proc Int Symp

Control Release Bioact Mater (1994)

[102] TL Blanchard DD Varner PJ Burns KA Everett SP

Brinsko L Boehnke Regulation of estrus and ovulation in

mares with progesterone or progesterone and estradiol bio-

degradable microspheres with or without PGF2a Therioge-

nology 38 (1992) 1091ndash1106

[103] J Fleury JB Costa-Neto PJ Burns Regulation of estrus

and ovulation in cyclic mares with progesterione and estra-

diol biodegradable microspheres effects of different doses of

estradiol J Equine Vet Sci 13 (1993) 525ndash528

[104] R Cushman JH Britt P Davis U Boonyaprakob V

Hedgpeth J Gibson B Hudson P Burns Pharmacody-

namic evaluation of biodegradable estradiol-17betamicro-

spheres and prostaglandin F2alpha for the control of

estrus and ovulation in gilts Proc Int Symp Control

Release Bioact Mater (1998) 251ndash 252

[105] JA Miller DD Oehler JM Pound Delivery of ivermec-

tin by injectable microspheres Vet Entomol 91 (1998)

655ndash659

[106] JA Miller RB Davey DD Oehler JM Pound JE

George EH Ahrens Control of Boophilus annulatus (Ac-

ari Ixodidae) on cattle using injectable microspheres con-

taining ivermectin J Econ Entomol 92 (1999) 1142ndash 1146

[107] ND Grace DH Lewis An evaluation of the efficacy of

injectable microencapsulated Vitamin B12 in increasing andmaintaining the serum and liver Vitamin B12 concentrations

of lambs N Z Vet J 47 (1999) 3ndash7

[108] ND Grace The effect of increasing the Vitamin B12 status

of Romney ewes on foetal liver Vitamin B12 milk Vitamin

B12 and liver Vitamin B12 concentrations in suckling lambs

N Z Vet J 47 (1999) 97 ndash 100

[109] ND Grace SO Knowles GR Sinclair J Lee Growth

response to increasing doses of microencapsulated vitamin

B12 and related changes in tissue vitamin B12 concentra-

tions in cobalt-deficient lambs N Z Vet J 51 (2003)

89ndash92

[110] TL Stevens SR Spurlin Pellet implant system US Patent

5874098 PJB Publications Ltd (1999)

[111] Ivyrsquos star performer in growth spotlight Anim Pharm 473(2001) 17

[112] GH Ward SH Yalkowsky Studies in phlebitis V Hemo-

lysis as a model for phlebitis J Parenter Sci Technol 47

(1993) 44ndash46

[113] GH Ward SH Yalkowsky The role of the effective con-

centration in interpreting hemolysis data J Parenter Sci

Technol 46 (1992) 161ndash162

[114] K Reed SH Yalkowsky Lysis of human red blood cells in

the presence of various cosolvents II The effect of differing

NaCl concentrations J Parenter Sci Technol 40 (1986)

88ndash94


8202019 1-s20-S0169409X04000687-main



in the presence of various cosolvents III The relationship

between hemolytic potential and structure J Parenter Sci


[116] NJ Medlicott KA Foster KL Audus S Gupta VJStella Comparison of the effects of potential parenteral

vehicles for poorly water soluble anticancer drugs (or-

ganic co-solvents and cyclodextrin solutions) on cul-

tured endothelial cells (HUV-EC) J Pharm Sci 87

(1998) 1138ndash 1143

[117] GA Brazeau H-L Fung Physiochemical properties of bi-

nary organic cosolventndash water mixtures and their relationship

to muscle damage following intramuscular injection

J Parenter Sci Techol 43 (1989) 144 ndash 149

[118] GA Brazeau H-L Fung Effect of organic cosolvent-in-

duced skeletal muscle damage on the bioavailability of intra-

muscular [14

C]Diazepam J Pharm Sci 79 (1990) 773 ndash 777[119] GA Brazeau HL Fung Mechanisms of creatine kinase re-

lease from isolated rat skeletal muscles damaged by propylene

glycol and ethanol J Pharm Sci 79 (1990) 393 ndash 397

[120] GA Brazeau SS Watts LS Mathews Role of calcium

and arachidonic acid metabolites in creatine kinase release

from isolated rat skeletal muscles damaged by organic cosol-

vent J Parenter Sci Technol 46 (1992) 25 ndash 30


8202019 1-s20-S0169409X04000687-main


5 Recent advances 1360

6 Concluding remarks 1360

References 1361

1 Introduction

Sustained release dosage forms (SRDF) are impor-

tant products in veterinary medicine [1ndash4] For certain

prophalytic and treatment uses one-time or infrequent

administration has become the standard procedure

For example monthly administration is available in

most heartworm preventatives such as HeartguardR

SentinelR and Interceptor R To compete in this mar-

ket new products will need to have similar or better

administration schemes In addition the companionanimal market will continue to increase and the busy

lives of pet owners preclude frequent administration

The SRDF possess advantages over conventional

dosage forms such as improved patient compliance

thus creating more effective products Other potential

advantages include reduced side effects to the animal

and added convenience to the animal owner Stress is

often reduced for both the animal and owner by the

infrequent dosing associated with SRDF administra-

tion The SRDF also have advantages for the phar-

maceutical industry through increased sales andextended patent protection

While oral drug delivery continues to be the pri-

mary route of administration the parenteral route does

offer advantages when oral administration is difficult

The advantages can be quite varied such as overcom-

ing the physical challenge of orally dosing cats to the

logistical difficulties with controlling estrus in herds of

domesticated livestock Also interspecies variability

caused by differences in oral absorption especially

between ruminant and non-ruminant animals may be

minimized with parenteral administration [5] Con-

trolled release parenteral dosage forms (CR-PDF) may

be difficult to develop because of the need to under-

stand injection site absorption tissue drug residues

tissue irritation injectability and retention extended

efficacy testing product stability formulation manu-

facturing analytical methods and packaging

This article will provide an overview of the

veterinary medicine CR-PDF market highlight chal-

lenges in bringing these products to the market

discuss the types of dosage forms available for development and explain some of the recently

marketed CR-PDF used in veterinary medicine

2 Controlled release dosage form market

Of the total $7 billion market in 1998 for veter-

inary pharmaceuticals around $1 billion may be

attributed to controlled release dosage forms [3]

Parenteral sustained release products account for an

estimated 40 ($04 billion) Top parenteral con-trolled release products include PosilacR MicotilR

Nuflor R and Revalor R (Table 1) The main treat-

ment areas are respiratory diseases feed efficiency

improvementgrowth and milk enhancement

3 Formulation development challenges

CR-PDFs are typically administered into muscle

(intramuscular injections) or subcutaneous sites [2]

Table 1

Top animal health parenteral controlled release pharmaceuticals in 1999

Product Drug Dosage form Indication Species 1999 sales

($ million)

PosilacR Zinc bovine growth hormone Oil suspension Milk enhancer Dairy cattle 225

MicotilR Tilmicosin Solution (propylene glycolwater) Parasiticide Cattle 85

Nuflor R Florfenicol Solution (n-methyl-2-pyrrolidone

propylene glycol polyethylene glycol)

Antibiotic Cattle 64

Revalor R

CompudoseR

SynovexR

Trenbolone estradiol

progesterone testosterone

Solid implants Growth Cattle 90


8202019 1-s20-S0169409X04000687-main








































damage

31 Injection site















8202019 1-s20-S0169409X04000687-main

































































8202019 1-s20-S0169409X04000687-main










































8202019 1-s20-S0169409X04000687-main




































d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN













8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main








































damage

31 Injection site















8202019 1-s20-S0169409X04000687-main

































































8202019 1-s20-S0169409X04000687-main










































8202019 1-s20-S0169409X04000687-main




































d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN













8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main

































































8202019 1-s20-S0169409X04000687-main










































8202019 1-s20-S0169409X04000687-main




































d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN













8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main










































8202019 1-s20-S0169409X04000687-main




































d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN













8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main




































d A

dt frac14

cSs

M 1=2 1 thorn

K a

frac12Hthornd

eth1THORN

d A

dt frac14

cSs

M 1=2 1 thorn

K b

frac12OHd

eth2THORN













8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main








8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main











































































permission


8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main













5 Fibrosis














































































8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main






































































Table 2




Red blood cell

haemolysis



haemaglobin on


compounds

[36112ndash115]


(L6 muscle cells

human umbilical

cord endothelial

cells)

Cell toxicity is

determined by cell



(MTT assay) and


damage (leakage of




for other cells)

[3738116]


muscle model




injection of system

[39ndash41117ndash

120]


8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main
























































































8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main





























































































8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main
















































oilTween 20Tween 85


























leishmaniasis


wo emulsions)
















8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main




























et al [73]













































Table 3


growth agent


gain (kgday)

Placebo 114a

NMP solvent 116a



125ab


glycolide 5050 60)

143 bc


IP-Atrigel A 143 bc





8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main







months


































sponge






















grubs in cattle






























8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main































5 Recent advances
















































months ProHeart R









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main


















References







Boston MA 1999






















UK 1989









J Pharm 215 (2001) 13ndash27









189ndash207











Ther 13 (1990) 350ndash355



39 (1987) 90ndash95



Assoc 34 (1980) 409ndash421

















1ndash8




8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main








2978ndash2986











181ndash189

















(1987) 10ndash17






(1989) 167 ndash 170









823ndash829



871ndash882




(1998) 102 ndash 107








357ndash361











677ndash689















(2000)



















8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main





lease 85 (2002) 125ndash134









































(1997) 403 ndash 406






5736151 (1996)



















1170ndash1171























Anim 29 (1994) 247

















8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main





211ndash213









16 (1973) 245ndash250





435ndash436




33 (1971) 600ndash606












287ndash297





3086ndash3095






(1986) 685 ndash 691











(2002) 145 ndash 162










nology 38 (1992) 1091ndash1106













655ndash659











N Z Vet J 47 (1999) 97 ndash 100





89ndash92






(1993) 44ndash46







88ndash94


8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









8202019 1-s20-S0169409X04000687-main










(1998) 1138ndash 1143







muscular [14









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