5

In recent years, much attention has been focused on lipid-based formulations (Humberstone

et al., 1997) to enhance the solubility of poorly water soluble drugs and improving

bioavailability to administer them through oral route resulting in increasing their clinical

efficacy, cost effectiveness and ease of preparation.

2.1. Lipid based drug delivery systems (Pouton, 2000)

Lipid based drug delivery systems (LBDDS) are one of the most popular approaches to

improve the oral bioavailability of poorly water soluble drugs (Charman, 2000; Gershanik et

al., 2000). Lipid vehicles are known to enhance the absorption of lipophilic drugs and there

are various mechanisms by which LBDDS enhance the absorption of lipophilic drugs:

Enhanced dissolution/solubilization

The presence of lipids in the GI tract stimulates gall bladder contractions, biliary and

pancreatic secretions, including bile salts (BS), phospholipids (PL) and cholesterol (Ch)

(Fleisher et al., 1999). These products, along with the gastric shear movement form a crude

emulsion and promote the solubilization of the co-administered lipophilic drug (Tso, 1985).

Surfactants present in the delivery system may also improve the solubilization of the

lipophilic compound.

Affecting intestinal permeability

A variety of lipids have been shown to change the physical barrier function of the gut wall

and hence, to enhance permeability. For BCS class II compounds, permeability through the

GI wall is not a limiting step towards absorption and hence, this mechanism is not thought to

be a major contributor for the absorption enhancement of lipophilic drugs. However, this may

be helpful for BCS class IV drugs.

Reduced metabolism and efflux activity

Certain lipids and surfactants also reduce the activity of efflux transporters in the GI wall and

hence, to increase the fraction of drug absorbed (Dintaman et al., 1999; Nerurkar et al.,

1996). Because of the interplay between P-gp and CYP3A4 activity this mechanism may

reduce intra-enterocyte metabolism as well.

6

Stimulation of lymphatic transport

Bioavailability of lipophilic drugs may also be improved by the stimulation of the intestinal

lymphatic transport pathway (Trevaskis et al., 2008; Charman et al., 1996).

Prolongation of gastric residence time

Gastric transit time is prolonged with the presence of lipids in GI tract (Van Citters et al.,

1999). As a result, the residence time of the lipophilic drug in the small intestine increases.

This improves dissolution of the drug and thereby improves absorption.

Classification of lipid delivery systems (Pouton, 2000)

The simplest lipid products are those in which the drug is dissolved in digestible oil, usually a

vegetable oil or medium chain triglyceride (fractionated coconut oil). These are safe food

substances and do not present a toxicological risk to formulators. Oil solution has been the

standard way of administering oil-soluble vitamins (A and D) for many years. Bioavailability

from oil solutions is likely to be very good because the triglycerides are rapidly digested to

free fatty acids and 2-mono-glycerides, and these products are solubilised to form a colloidal

dispersion within bile salt-lecithin mixed micelles. A hydrophobic drug is also likely to be

solubilised in mixed micelles resulting in a reservoir of drug in colloidal solution from which

it can partition, allowing efficient, passive (transcellular) absorption. The low solvent

capacity of triglycerides often prevents formulation in oil, but oil solutions may be a realistic

option for potent drugs. Solvent capacity for less hydrophobic drugs can be improved by

blending triglycerides with other oily excipients which include mixed monoglycerides and

diglycerides. Since these are similar to the natural degradation products of triglycerides (the

difference being that their monoglyceride content is mostly 1 monoglyceride rather than 2-

monoglyceride) they do not prevent efficient digestion. As excipients with GRAS status they

have the same advantages as triglycerides, and are useful for blending with triglycerides or

for use as an alternative. Formulations which comprise drug in solution in triglycerides and/or

mixed glycerides are classified here as „Type I‟ (Table 2.1).When an appropriate dose of the

drug can be dissolved, a Type I formulation may well be the system of choice, in view of its

simplicity and biocompatibility.

The inclusion of a lipophilic surfactant (HLB 12) may improve the solvent capacity of the

formulation, but this approach has mainly been used to promote emulsification. Under

7

optimum conditions it is possible to formulate a self-emulsifying drug delivery system

(SEDDS) which emulsifies in aqueous solutions under very gentle conditions of agitation, to

result in a dispersion of colloidal dimensions. If the surfactant is insufficiently hydrophilic to

dissolve and form micelles in aqueous solution, then it exists itself as a dispersed phase,

either with or separated from the oily components. This type of formulation is likely to retain

its solvent capacity for the drug after dispersion and is referred to as Type II (Table 2.3). The

distinguishing features of Type II systems are (a) efficient self-emulsification and (b) absence

of water-soluble components. Formulation of Type II SEDDS has been described in detail

elsewhere (Pouton, 1982, 1984, 1985a, b; Wakerley et al., 1986a,b, 1987; Charman et al.,

1992) and reviewed recently (Pouton, 1997). Hydrophilic surfactants (water soluble with

HLB> 12) and/ or water-soluble cosolvents have also been blended with oils to produce self-

emulsifying systems. When the surfactant content is high (for example 40%, w/w, or more)

or co-solvents are included in addition to surfactants, it is possible to produce very fine

dispersions <100 nm in diameter) under conditions of gentle agitation (Constantinides, 1995;

Constantinides and Scalart, 1997). This approach was used for the reformulation of

cyclosporin A as 'Neoral' (Vonderscher and Meinzer, 1994). Formulations which include

water-soluble components are referred to in Table 2.1 as Type III formulations, and have

been referred to as 'self­ microemulsifying' systems, due to the optical clarity which can be

achieved with Type III systems.

Table 2.1. Classification of lipid delivery system. (Pouton, 2000)

Components Type I Type II Type III Type IV

Triglycerides or

mixed glycerides

100 40-80 40-80 <20

Surfactants - 20-60 (HLB>11) 20-40 (HLB>11) 20-50 (HLB>11)

Hydrophilic

cosolvents

- - 0-40 20-50

Particle size of

dispersion (nm)

Coarse 100-250 100-250 50-100

Significance of

aqueous dilution

Limited

importance

Solvent capacity

unaffected

Some loss of

solvent capacity

Significant phase

changes

Significance of

digestibility

Cruical Not crucial but

likely to occur

Not crucial but

may be inhibited

Not likely to occur

Advantages GRAS status;

simple;excellent

capsule

compatibility

Unlikely to lose

solvent capacity

on dispersion

Clear or almost

clear dispersion

Formulation has

good solvent

capacity for many

drugs

Disadvantages Poor solvent

capacity unless

drug is highly

lipophilic

Turbid o/w

dispersion

Possible loss of

solvent capacity

on dispersion;

less digested

Likely loss of

solvent capacity

on dispersion;may

not be digestible

8

2.2. Self-emulsifying drug delivery systems (SEDDS)

Self-emulsifying drug delivery systems (SEDDS) are defined as isotropic mixtures of natural

or synthetic oils, solid or liquid surfactants, or alternatively, one or more hydrophilic solvents

and co-solvents/surfactants (Wakerly et al., 1986; Craig et al., 1993; Constantinides, 1985;

Craig, 1993). Upon mild agitation followed by dilution in aqueous media, such as GI fluids,

these systems can form fine oil in water (o/w) emulsions or microemulsions (SMEDDS).

Self-emulsifying formulations spread readily in the gastro intestinal tract and the digestive

motility of the stomach and the intestine provide the agitation necessary for self-

emulsification (Shah et al., 1994; Kommuru et al., 2001).

SEDDS typically produce emulsions with a droplet size between 100 and 300 nm while

SMEDDS form transparent microemulsions with a droplet size of less than 50 nm. An

additional advantage of SEDDS over simple oily solutions is that they provide a large

interfacial area for partitioning of the drug between oil and water. Thus, for lipophilic drug

compounds that exhibit dissolution rate limited absorption, these systems may offer an

improvement in the rate and extent of absorption and result in more reproducible blood time

profiles (Charman et al., 1992) and have been shown to enhance the oral bioavailability of

lipophilic drugs (Humberstone et al., 1997; Pouton et al., 1997) such as cyclosporine (Klauser

et al., 1997), halofantrine (Khoo et al., 1998), ontazolast (Jayaraj et al., 1998), and

progesterone (Solomon et al., 1998). The ease of dispersion and the very small particle size of

the resultant colloidal microemulsion have been viewed as the principal reasons for their

utility in the delivery of lipophilic drugs. Consequently, most of the commercially available

lipid formulations are complex mixtures of lipids,surfactants, and cosolvents/cosurfactants

constructed to improve drug solubility in the formulation (and therefore increase drug pay

load) and also to maximize dispersion of the dose form on exposure of the capsule fill to the

GI contents (Porter et al., 2004).

When compared with emulsions, which are sensitive and metastable dispersed forms, SEDDS

are physically stable formulations that are easy to manufacture. Microemulsions are readily

distinguished from normal emulsions by their transperancy, their low viscosity, and more

fundamentally their thermodynamic stability. The dividing line, however, between the size of

a swollen micelle (approx. 10-140 nm) and a fine emulsion droplet (approx. 100-600 nm) is

not well defined, although microemulsions are very labile systems and a microemulsion

9

droplet may disappear within a fraction of a second whilst another droplet forms

spontaneously elsewhere in the system. In contrast, ordinary emulsion droplets, however

small, exist as individual entities until coalescence or Ostwald ripening occurs.

2.2.1. Advantages of SEDDS

Increased stability (Gursay, et al., 2003)

SMEDDS present small particle sizes, thus avoiding the problems of large particle size in

conventional composition.

Efficient transport

The particle sizes in the aqueous dispersions of the SMEDDS are much smaller (l00 nm-250

nm) than the larger particle characteristics of vesicular and emulsion phases. This reduced

particle size enables more efficient drug transport through the intestinal aqueous boundary

layer, and through the absorption brush border membrane.

Less dependence on lipolysis (Chris de Smidt, et al., 2004)

The smaller particle size triglyceride components make SMEDDS less dependent upon

lipolysis and other factors, which affect the rate and extent of lipolysis. The reduced lipolysis

dependence further provides transport, which is less prone to suffer from any lag time

between administration and absorption caused by the lipolysis process, enabling a more rapid

onset of therapeutic action and better bioperformance characteristics.

Non-dependence on biles and meal food contents (Charman & Pouton, 1997)

Food is a major factor affecting the therapeutic performance of the drug in the body. Due to

the higher solubilization potential over bile salt micelles, the SMEDDS are less dependent on

endogenous bile and bile related patient disease states and meal fat contents. These

advantages overcome meal dependence with meal-dosage restriction.

Superior solubilization

SMEDDS enables efficient loading capacity over conventional formulations. In addition, the

particular combination of surfactant used can be optimized for a specific therapeutic agent to

more closely match the polarity distribution of the therapeutic agent, resulting in still further

enhanced solubilization.

10

Faster dissolution and release

Dissolution being the rate limiting step for absorption of drugs, it is a major factor that limits

the bioavailability of numerous poorly water soluble drugs. Due to the robustness of

SMEDDS to dilution, the therapeutic agent remains solubilized and thus does not suffer

problem of precipitation of the therapeutic agent in the time frame relevant for absorption. In

addition, the therapeutic agent is presented in small particle carriers and is not limited in

dilution rate by entrapment in the emulsion carriers. These factors avoid liabilities associated

with the poor partitioning of lipid solubilized drug to the aqueous phase, such as large

emulsion droplet surface area, and high interfacial transfer resistance and enable rapid

completion of the critical partitioning stage.

Consistent performance

Aqueous dispersions of the SMEDDS are thermodynamically stable for the time period

relevant for absorption and can be predictably reproduced, thereby limiting variability in

bioavailability a particularly important advantage for therapeutic agents with a narrow

therapeutic index.

Efficient release

The composition of the SMEDDS are designed using components that help to keep the

therapeutic agent or absorption promoter, such as permeation enhancer, an enzyme inhibitor,

etc., solubilized for transport to the absorption sites, but readily available for absorption, thus

providing a more efficient transport and release.

Less prone to gastric emptying delays

Unlike conventional triglycerides containing formulations, which form bigger droplets on

dispersion, the SMEDDS are less prone to gastric emptying delays, resulting in faster

absorption and avoid unwanted retention in the gastro-intestinal tract.

Small size

Because of small size in aqueous dispersion, the SMEDDS allow for the faster transport of

the therapeutic agent through the aqueous boundary layer.

11

Ease of manufacture and scale up (Patraval, et al., 2003)

Ease of manufacture and scale up are the most important advantages that make SMEDDS

unique when compared to other drug delivery systems like solid dispersions, liposomes,

nanoparticles, etc., for improving bioavailability. SMEDDS require very simple and

economical manufacturing facilities like simple mixer with agitator and volumetric liquid

filling equipment for large scale manufacturing. This explains the interest of industry in the

SMEDDS.

Self-emulsification is a phenomenon, which has been exploited commercially for many years

in formulations of emulsifiable concentrates of herbicides and pesticides. These formulations

are used to produce concentrates of crop sprays which are diluted by users, such as farmer or

household gardner, allowing very hydrophobic compounds to be transported efficiently. In

contrast SMEDDS, using excipients acceptable for oral administration to humans have not

been widely exploited. There are number of reasons why self-microemulsifying drug delivery

system (SMEDDS) is not in common use. Some relate to custom and habit of pharmaceutical

development laboratories and some to genuine reasons (Pouton, C. W., 1997);

1. Most pharmaceutical companies have a commitment to tabletting machinery, which

leads them to favor tablet formulation at early stage often before sufficient data are

available on the bioavailability of the drug. Once the path to formulation of a solid

dosage form is selected, it is difficult to revert to oily formulation at a later stage.

2. Encapsulation of an oily formulation may have to be outsourced.

3. The solvent capacity of oily formulation is not high unless the drug is very

hydrophobic/lipophilic (log P>4), so that formulation in oils is usually limited to

potent compounds.

4. There may be some suspicion that chemically the drug will be unstable in an oily

formulation than in crystalline form, and this may be so, but at present there is

insufficient data to predict chemical stability in self-micro emulsifying drug delivery

system (SMEDDS).

5. The use of high concentration of surfactant is a legitimate concern from a

toxicological standpoint.

12

Additionally, formulators favor utilizing tried and tested materials to prevent problems

surfacing at a later stage of development of new chemical entity. The above are the issues

which will tend to direct a formulator away from SMEDDS, though it is now accepted that

there are a group of compounds for which SMEDDS, is the delivery system of choice,

exemplified by cyclosporin A. The development of this compound by Sandoz has confirmed

the potential of se1f-microemulsifying drug delivery system (SMEDDS) in bringing

hydrophobic compounds to the market place. There are several drugs which are poorly

bioavailable from marketed conventional formulation which could have been formulated in

oily systems, the potential of SMEDDS will not be realized until more human bioavailability

studies have been published and until more information is available on the chronic toxicology

of self-micro emulsifying drug delivery system (SMEDDS).

2.2.2. Applications of SEDDS (Tang et al., 2007)

Supersaturable SEDDS (S-SEDDS)

The high surfactant level typically present in SEDDS formulations can lead to GI side effects

and a new class of supersaturable formulations, including supersaturable SEDDS (S-SEDDS)

formulations, have been designed and developed to reduce the surfactant side-effects and

achieve rapid absorption of poorly soluble drugs (Poelma et al., 1991; Gao et al., 2003; Gao

et al., 2004). The S-SEDDS approach is to generate a protracted supersaturated solution of

the drug when the formulation is released from an appropriate dosage form into an aqueous

medium. Surpersaturation is intended to increase the thermodynamic activity to the drug

beyond its solubility limit and, therefore, to result in an increased driving force for transit into

and across the biological barrier (Gao et al., 2004). The S-SEDDS formulations contain a

reduced level of surfactant and a polymeric precipitation inhibitor to yield and stabilize a

drug in a temporarily supersaturated state. Hydroxypropyl methylcellulose (HPMC) and

related cellulose polymers are well recognized for their propensity to inhibit crystallization

and, thereby, generate and maintain the supersaturated state for prolonged time periods

(Pellet et al., 1994; Pellet et al., 1997; Usui et al., 1997; Yamada et al., 1999; Raghavan et al.,

2000; Lervolino et al., 2000). A supersaturable self-emulsifying drug delivery system (S-

SEDDS) of paclitaxel was developed employing HPMC as a precipitation inhibitor with a

conventional SEDDS formulation. In vitro dilution of the S-SEDDS formulation results in

formation of a microemulsion, followed by slow crystallization of paclitaxel on standing.

13

This result indicates that the system is supersaturated with respect to crystalline paclitaxel,

and the supersaturated state is prolonged by HPMC in the formulation. In the absence of

HPMC, the SEDDS formulation undergoes rapid precipitation, yielding a low paclitaxel

solution concentration. A pharmacokinetic study showed that the paclitaxel S-SEDDS

formulation produces approximately a 10-fold higher maximum concentration (Cmax) and a 5-

fold higher oral bioavailability (F = 9.5%) compared with that of the orally administered

Taxol formulation (F = 2.0%) and the SEDDS formulation without HPMC (F =1%) (Gao et

al., 2003). It is worth emphasizing that the significantly reduced amount of surfactant used in

the S-SEDDS formulation approach provides a better toxicity/safety profile than the

conventional SEDDS formulations. However, the underlying mechanism of the inhibited

crystal growth and stabilized supersaturation by means of these polymers is poorly

understood even although several studies have been carried out to investigate this (Gao et al.,

2003; Raghavan et al., 2001; Pellet et al., 1997; Hasegawa et al., 1988).

Solid SEDDS

SEDDS are normally prepared as liquid dosage forms that can be administrated in gelatin

capsules. An alternative method is the incorporation of liquid self-emulsifying ingredients

into a powder in order to create a solid dosage form (tablets, capsules). A pellet formulation

of progesterone in SEDDS has been prepared by the process of extrusion/spheronization to

provide a good in vitro drug release (100% within 30 min, T50% at 13 min). The same dose

of progesterone (16 mg) in pellets and in the SEDDS liquid formulation resulted in similar

AUC, Cmax and Tmax values (Tuleu et al., 2004). Attama et al. used goat fat and Tween 65

admixtures to formulate self-emulsifying tablets containing diclofenac by pour moulding

using a plastic mould. The tablets showed good release profiles, as well as acceptable tablet

properties. Under mild agitation, such as occurs under gastrointestinal conditions, the release

rates are comparable with those of conventional tablets (Attama et al., 2003). Encapsulating

the emulsion lipid droplets in HPMC by spray-drying has been demonstrated to produce an

improved bioavailability following release of the lipid droplets from the powder in vivo. Tue

et al. (Hansen et al., 2005) have investigated the oral bioavailability of a directly

compressible dry emulsion as a tablet and compared it with an HPMC dry emulsion powder

and a simple lipid solution. Four female beagle dogs received a single dose of each

formulation containing the same amount of MCT and model drug, Lu 28-179. Cyclodextrin

solutions administered orally and intravenously were used as references. The absolute

14

bioavailability decreased in the order: cyclodextrin solution (0.14) > HPMC dry emulsion

(0.11) > technically improved dry emulsion (0.10) > MCT solution (0.06). The directly

compressible dry emulsion tablets were concluded to be comparable with the HPMC dry

emulsion powder in terms of bioavailability (Woo et al., 1961).

SEDDS for TCM

Silybin, the principal component of a Carduus marianus extract, is known to be very

effective in protecting liver cells from harmful effects caused by smoking, drinking,

overworking, environmental contaminants, stress or liver damaging drugs. However, the

bioavailability of orally administered silybin is very low due to its low solubility in water.

Woo et al. discloses an oral microemulsion consisting of a Carduus marianus extract

containing a major amount of silybin, or a silybin derivative as an active ingredient. The

composition of the invention consists of miglyol 812 and ethyl linoleate as oils, HCO 50 and

Tween 20 as surfactant, dimethyl isosorbide as co-surfactant and D-tocopherol as an anti-

oxidant. The formulation provides a greatly increased level of in vivo bioavailability of

silybin, the level being atleast 4-fold higher than that achievable by conventional

formulations (You et al., 2005) Curcuma zedoaria (Berg.) Rose. (Zingiberaceae), also called

„er-zhu‟ in Chinese, has long been used as a folk medicine. The essential oil, zedoary

turmeric oil (ZTO), was extracted from the dry rhizome of C. zedoaria. A series of studies on

ZTO indicated that it exhibits potent pharmacological actions including the suppression of

tumors, antibacterial and antithrombotic activity, increased white blood cell count, and

increased gastric motility (You et al., 2005). To increase the in vivo absorption of zedoary

turmeric oil (ZTO) and develop new formulations of a water insoluble oily drug, Li

formulated SEDDS using ZTO as the oil (Li et al., 2002). Pueraria lobata is a traditional

Chinese medicinal herb. In China, its extract has been used for the treatment of hypertension,

senile ischemic cerebrovascular disease and anginapectoris. Studies of its pharmacology and

clinical application shave shown that the active constituents in the extractare isoflavones,

mainly puerarin. It is known to dilate coronary arteries, reduce myocardial oxygen

consumption and improve microcirculation in both animals and humans suffering from

cardiovascular disease (Li et al., 2002). Yufengningxin tablets are a formulation of total

isoflavones obtained from Pueraria lobata, and are available commercially in China. The

dissolution rate of Yufengningxin tablets is very low and, therefore, a SMEDDS formulation

of Pueraria lobata isoflavone was developed to improve the oral bioavailability. An optimized

15

formulation consisted ethyl oleate, Tween 80 and transcutol P as cosurfactant. The

dissolution of SMEDDS after 10 min was more than 90%, and the dissolution of

Yufengningxin tablets at 60 min was less than 30%. The absorption of puerarin from the

SMEDDS of Puerarialobata isoflavone resulted in a 2.2-fold increase in bioavailability

compared with Yufengningxin tablets Ginkgo biloba L., the last surviving member of a

family of trees (Ginkgoaceae) that appeared more than 250 million years ago, has been

mentioned in the Chinese Materia Medica for more than 2500 years. A standardized Ginkgo

biloba extract (GBE) contains 5-7% terpene lactones (ginkgolides and bilobalide) and 22-

27% ginkgo flavonol glycosides (eg., the flavones quercetin, kaempferol, and isorhamnetin)

(Kleijnen et al., 1992). Many pharmacological and clinical studies have demonstrated that the

extracts of Ginkgo biloba possess antioxidant, antiischemic, neuro protective, cardiovascular

and cerebrovascular activities, and have beneficial effects oncognitive deficits, including

Alzheimer‟s type and multi infarct dementia, as well as peripheral vascular disease

(Kressmann et al., 2002). The dissolution and bioavailability of the active components from

the oral solid preparations of different Ginkgo biloba brands were obviously different and

irreproducible, due to the lower solubility of the active components (Kressmann et al., 2002).

The SEDDS formulation of GBE was accordingly developed to increase the dissolution rate

and thus improve oral absorption and acquire the reproducible blood-time profiles of the

active components of GBE. The prepared SEDDS was compared with the conventional GBE

tablets following administration to fasted dogs. The active components of GBE, terpene

lactones, were determined using liquid chromatography with electrospray ionization mass

spectrometric detection (Tang et al., 2006). The relative bioavailability of SEDDS for

ginkgolide was 154%, compared with the reference tablets.

2.2.3. Formulation of SEDDS (Patel et al., 2010)

SEDDS formulation containing following components

1) Oil phase

2) Surfactant

3) Co-surfactant/Co-Solvent

Self-emulsification has been shown to be specific to the nature of the oil/surfactant pair, the

surfactant concentration and oil/surfactant ratio and the temperature at which self-

16

emulsification occurs (Wakerly et al., 1986; Wakerly et al., 1987; Pouton et al., 1985). In

support of these facts, it has also been demonstrated that only very specific pharmaceutical

excipient combinations could lead to efficient self-emulsifying systems (Charman et al.,

1992; Shah et al., 1994; Chanana et al., 1995; Kimura et al., 1994; Hauss et al., 1998; Karim

et al., 1994).

Oils

The oil represents one of the most important excipients in the SEDDS formulation not only

because it can solubilise marked amounts of the lipophilic drug or facilitate self-

emulsification but also and mainly because it can increase the fraction of lipophilic drug

transported via the intestinal lymphatic system, thereby increasing absorption from the GI

tract depending on the molecular nature of the triglyceride (Gershanik et al., 2000; Lindmark

et al., 1995; Charman et al., 1991; Holm et al., 2002). Both long and medium chain

triglyceride oils with different degrees of saturation have been used for the design of self-

emulsifying formulations. Furthermore, edible oils which could represent the logical and

preferred lipid excipient choice for the development of SEDDS are not frequently selected

due to their poor ability to dissolve large amounts of lipophilic drugs. Modified or hydrolyzed

vegetable oils havebeen widely used since these excipients form good emulsification systems

with a large number of surfactants approved for oral administration and exhibit better drug

solubility properties (Constantinides et al., 1995; Kimura et al., 1994; Hauss et al., 1998).

They offer formulative and physiological advantages and their degradation products resemble

the natural end products of intestinal digestion. Novel semisynthetic medium chain

derivatives, which can be defined as amphiphilic compounds with surfactant properties, are

progressively and effectively replacing the regular medium chain triglyceride oils in the

SEOFs (Constantinides et al., 1995; Karim et al., 1994).

Surfactants

Several compounds exhibiting surfactant properties may be employed for the design of self-

emulsifying systems, the most widely recommended ones being the non-ionic surfactants

with a relatively high hydrophilic−lipophilic balance (HLB). The commonly used emulsifiers

are various solid or liquid ethoxylated polyglycolyzed glycerides and polyoxyethylene 20

oleate (Tween 80). Safety is a major determining factor in choosing a surfactant. Emulsifiers

of natural origin are preferred since they are considered to be safer than the synthetic

17

surfactants (Constantinides et al., 1995; Hauss et al., 199; Yuasa et al., 1994; Georgakopoulos

et al., 1992). However, these excipients have a limited self-emulsification capacity. Non-ionic

surfactants are less toxic than ionic surfactants but they may lead to reversible changes in the

permeability of the intestinal lumen (Swenson et al., 1994; Wakerly et al., 1986). Usually the

surfactant concentration ranges between 30 and 60% w/w in order to form stable SEDDS. It

is very important to determine the surfactant concentration properly as large amounts of

surfactants may cause GI irritation.The surfactant involved in the formulation of SEDDS

should have a relatively high HLB and hydrophilicity so that immediate formation of o/w

droplets and/or rapid spreading of the formulation in the aqueous media (good self-

emulsifying performance) can be achieved. For an effective absorption, the precipitation of

the drug compound within the GI lumen should be prevented and the drug should be kept

solubilized for a prolonged period of time at the site of absorption (Serajuddin et al., 1988;

Shah et al., 1994). Surfactants are amphiphilic in nature and they can dissolve or solubilize

relatively high amounts of hydrophobic drug compounds. The lipid mixtures with higher

surfactant and co-surfactant/oil ratios lead to the formation of SMEDDS (Constantinides et

al., 1995; Karim et al., 1994; Meinzer et al., 1995; Vondercher et al., 1994). There is a

relationship between the droplet size and the concentration of the surfactant being used. In

some cases, increasing the surfactant concentration could lead to droplets with smaller mean

droplet size such as in the case of a mixture of saturated C8-C10 polyglycolized glycerides

(Labrafac CM-10). This could be explained by the stabilization of the oil droplets as a result

of the localization of the surfactant molecules at the oil-water interface (Levy et al., 1990).

On the other hand, in some cases the mean droplet size may increase with increasing

surfactant concentrations (Wakerly et al., 1987; Kommuru et al., 2001; Craig et al., 1995).

This phenomenon could be attributed to the interfacial disruption elicited by enhanced water

penetration into the oil droplets mediated by the increased surfactant concentration and

leading to ejection of oil droplets into the aqueous phase (Pouton et al., 1997).

Co-surfactants

Role of co-surfactant together with surfactant is to lower the interfacial tension to a very

small, even transient, negative value. At this value the interface would expand to form fine

dispersed droplets, and subsequently adsorb more surfactant and surfactant/co-surfactant until

their bulk condition is depleted enough to make interfacial tension positive again. This

process is known as “spontaneous emulsification” forms the microemulsion. However, the

18

use of co-surfactant is crucial not only to formation of microemulsion, but also to

solubilisation in microemulsion. Other variables such as the chemical nature of oil, salinity,

and temperature are also expected to influence the curvature of the interfacial film.

Co-solvents

The production of an optimum SEDDS requires relatively high concentrations (generally

more than 30% w/w) of surfactants. Organic solvents such as, ethanol, propyleneglycol (PG),

and polyethylene glycol (PEG) are suitable for oral delivery, and they enable the dissolution

of large quantities of either the hydrophilic surfactant or the drug in the lipid base. These

solvents can even act as co-surfactants in microemulsion systems. On the other hand,

alcohols and other volatile co-solvents have the disadvantage of evaporating into the shells of

the soft gelatin, or hard, sealed gelatin capsules in conventional SEDDS leading to drug

precipitation. Thus, alcohol free formulations have been designed (Constantinides et al.,

1995), but their lipophilic drug dissolution ability may be limited.

2.2.4. Mechanism of self-emulsification (Gursoy et al., 2004)

Self-emulsification takes place when the entropy change favouring dispersion is greater than

the energy required to increase the surface area of the dispersion (Reiss et al., 1975). The free

energy of a conventional emulsion formulation is a direct function of the energy required to

create a new surface between the oil and water phases. The two phases of the emulsion tend

to separate with time to reduce the interfacial area and thus the free energy of the systems.

The conventional emulsifying agents stabilize emulsions resulting from aqueous dilution by

forming a monolayer around the emulsion droplets, reducing the interfacial energy and

forming a barrier to coalescence. On the other hand, emulsification occurs spontaneously

with SEDDS because the free energy required to form the emulsion is both low and positive

or negative (Constantinides et al., 1995). It is necessary for the interfacial structure to show

no resistance against surface shearing in order for emulsification to take place (Dabros et al.,

1999). The ease of emulsification was suggested to be related to the ease of water penetration

into the various LC or gel phases formed on the surface of the droplet (Wakerly et al., 1986;

Groves et al., 1974; Rang et al., 1999). The interface between the oil and aqueous continuous

phases is formed upon addition of a binary mixture (oil/non-ionic surfactant) to water

(Wakerly et al., 1986). This is followed by the solubilisation of water within the oil phase as a

result of aqueous penetration through the interface. This will occur until the solubilisation

19

limit is reached close to the interphase. Further aqueous penetration will lead to the formation

of the dispersed LC phase. In the end, everything that is in close proximity with the interface

will be LC, the actual amount of which depends on the surfactant concentration in the binary

mixture. Thus, following gentle agitation of the self-emulsifying system, water will rapidly

penetrate into the aqueous cores and lead to interface disruption and droplet formation. As a

consequence of the LC interface formation surrounding the oil droplets, SEDDS become very

stable to coalescence. Detailed studies have been carried out to determine the involvement of

the LC phase in the emulsion formation process (Wakerly et al., 1986; Rang et al., 1999;

Pouton et al., 1987; Wakerly et al., 1987). Also, particle size analysis and low frequency

dielectric spectroscopy (LFDS) were utilized to examine the self-emulsifying properties of a

series of Imwitor 742 (a mixture of mono and diglycerides of capric and caprylic

acids)/Tween 80 systems (Craig et al., 1993; Craig et al. 1995). The results suggested that

there might be a complex relationship between LC formation and emulsion formation (Craig

et al. 1995). Moreover, the presence of the drug compound may alter the emulsion

characteristics, probably by interacting with the LC phase (Craig et al., 1993). Nevertheless,

the correlation between the LC formation and spontaneous emulsification has still not been

established (Craig et al., 1993; Gursoy et al., 2003).

2.2.5. Biopharmaceutical aspects (Tang et al., 2007)

The ability of lipids and/or food to enhance the bioavailability of poorly water soluble drugs

has been comprehensively reviewed and the interested reader is directed to these references

for further details (Humberstone et al., 1997; Charman et al., 1997). Although incompletely

understood, the currently accepted view is that lipids may enhance bioavailability via a

number of potential mechanisms, including (Porter et al., 2001).

a) Alterations (reduction) in gastric transit, thereby slowing delivery to the absorption

site and increasing the time available for dissolution (Porter et al., 2001).

b) Increases in effective luminal drug solubility. The presence of lipids in the GI tract

stimulates an increase in the secretion of bile salts (BS) and endogenous biliary lipids

including phospholipid (PL) and cholesterol (CH), leading to the formation of

BS/PL/CH intestinal mixed micelles and an increase in the solubilisation capacity of

the GI tract. However, intercalation of administered (exogenous) lipids into these BS

structures either directly (if sufficiently polar), or secondary to digestion, leads to

20

swelling of the micellar structures and a further increase in solubilisation capacity

(Porter et al., 2001).

c) Stimulation of intestinal lymphatic transport. For highly lipophilic drugs, lipids may

enhance the extent of lymphatic transport and increase bioavailability directly, or

indirectly via reduction in first pass metabolism (Porter et al., 1997; Porter et al.,

2001; Muranishi et al., 1991).

d) Changes in the biochemical barrier function of the GI tract. It is clear that certain

lipids and surfactants may attenuate the activity of intestinal efflux transporters, as

indicated by the p-glycoprotein efflux pump, and may also reduce the extent of

enterocyte based metabolism (Benet at al., 2001; Dintaman et al., 1999; Nerurkar et

al., 1996).

e) Changes in the physical barrier function of the GI tract. Various combinations of

lipids, lipid digestion products and surfactants have been shown to have permeability

enhancing properties (Aungst et al., 2000; Muranishi et al., 1990). For the most part,

however, passive intestinal permeability is not thought to be a major barrier to the

bioavailability of the majority of poorly water soluble, and in particular, lipophilic

drugs.

Enhanced drug absorption by lymphatic delivery

Charman et al. proposed that drug candidates for lymphatic transport should have a log P >5

and, in addition, a triglyceride solubility >50 mg/ml. The importance of lipid solubility was

illustrated by comparing the lymphatic transport of DDT (log P 6.19) with

hexachlorobenzene (HCB, log P 6.53).

Khoo et al. showed significant lymphatic transport of the poorly lipid soluble (1 mg/ml) HCl

salt of halofantrine (Hf-HCl), following oral post prandial administration to dogs. The authors

suggest that the high level of lymphatic transport of Hf-HCl (43.7% of dose), which was

similar to that of the lipid soluble Hf base, was due to conversion of Hf-HCl in the intestinal

lumen, during lipolysis, to the more lipophilic free base, which then becomes associated with

chylomicron production (Khoo et al., 1999)

21

Although enhanced lymphatic transport has been suggested as a potential mechanism of

enhanced bioavailability, few studies have investigated the lymphotropic potential of

SEDDS.

Haus et al. investigated the effects of a range of lipid based formulations on the

bioavailability and lymphatic transport of ontazolast, following oral administration to

conscious rats. This drug undergoes extensive hepatic first pass metabolism and it has

solubility in soybean oil of 55 mg/ml, and a log P of 4. The formulations of ontazolast

investigated included a suspension (lipid free control), a 20% soyabean o/w emulsion, two

SEDDS containing Gelucire 44/14 and Peceol in the ratios 50:50 and 80:20, respectively, and

a solution of the drug in Peceol alone. All the lipid formulations increased the bioavailability

of ontazolast relative to the control suspension, while the SEDDS promoted more rapid

absorption.

The Effect of excipients on efflux transport

Drug efflux mediated by broad specificity xenobiotic transporters present in the intestinal

epithelium may be an important factor in the poor or variable absorption of orally

administered drugs (Makhey et al., 1998).

Lo et al. have shown that bile salts, fatty acids, phospholipids, and surfactants were potent

absorption enhancers and efflux reducing agents in Caco-2 cells and the rat intestine (Lo et

al., 1998; Lo et al., 2000; Lo et al., 2000).

Other researchers also investigated the non-ionic surfactants, such as Tween 80, Pluronic

P85, and Cremophor EL in vitro and in vivo in animals and in humans for their potential

ability to reverse MDR caused by p-glycoprotein (P-gp) and multidrug resistance-associated

proteins (MRP) (Batrakova et al., 1999; Yamazaki et al., 2000).

Recently, Cremophor, Tween 80, and Solutol HS-15 have been proven to reverse the MDR

phenotype in cultured cells at concentrations likely to be achieved clinically (Yamazaki et al.,

2000; Dudeja et al., 1995)

TPGS (d-alpha-tocopheryl polyethylene glycol 1000 succinate) has been shown to be an

effective inhibitor of P-gp mediated drug resistance and has been used to enhance the

bioavailability of CsA in liver transplant patients as well as significantly improving

22

absorption and reducing the daily drug cost (Dintaman et al., 1999). Inhibition of MDR-

related pumps by various excipients has been proposed to occur due to binding competition,

ATP depletion, and membrane perturbation (Yamazaki et al., 2000; Friche et al., 1990). For

example, Tween 80 has been shown to modulate anthracycline and vinca alkaloid resistance

in MDR cells by inhibiting the binding of these drugs to P-gp (Yamazaki et al., 2000; Friche

et al., 1990). The ability of Pluronic copolymer, one poly (ethylene oxide) block copolymer,

to antagonize P-gp and sensitize MDR cells appears to be a result of ATP depletion, and

inhibition of P-gp and MRP drug efflux proteins (Kabanov et al., 2002). Studies with MDR

modifiers such as bile salts indicated that perturbations of the cell membrane structure may

influence P-gp-mediated drug transport (Lo et al., 1998; Schuldes et al., 2001; Dolderer et al.,

2000). These modifiers may influence cytotoxic drug action by producing structural changes

to the lipid domains in the plasma membrane. The membrane perturbation caused by

pharmaceutical excipients, such as Tween 20, Tween 80, Brij 30, and Myrj 52, may result in

a change in the fluidity of Caco-2 cell membranes, and thus inhibit the activity of membrane

spanning proteins, such as P-gp and MRPs which substantially reduce the basolateral to

apical efflux of epirubicin across Caco-2 monolayers (Lo et al., 2003). Tween 20, Tween 80,

Brij 30, and Myrj 52 may also inhibit protein kinase C (PKC) activity, reduce

phosphorylation of P-gp, and modulate P-gp mediated drug efflux (Komarov et al., 1996).

Inhibition of the efflux and/or enterocyte based metabolism will increase the concentration

and residence time of the intact drug in the cell. This may result in increased drug available

for partitioning into the lymphatics (O‟Driscoll et al., 2002).

Role of lipolysis

Digestion of dietary triglyceride in the small intestine is very rapid, and many other non-ionic

esters, such as mixed glycerides and surfactants, will be substrates for pancreatic lipase

(Embleton et al., 1997). Digestion of formulations will inevitably have a profound effect on

the state of dispersion of the lipid formulation, and the fate of the drug (Macgregor et al.,

1997). Fortunately, the liberation of free fatty acid during lipolysis can be titrated using

NaOH in a pH stat, allowing quantitative data about the kinetics of digestion to be obtained.

The location of the drug can be assayed in various fractions after ultracentrifugation of the

products of digestion, which allows investigation of the likely fate of the drug after lipolysis

(Pouton et al., 2000). The inclusion of highly lipophilic compounds in SEDDS is often

reported to result in strongly enhanced oral absorption although it is still controversial

23

whether further lipolysis of the dispersed lipid material is required for final transfer to the

enterocyte membranes.

In order to assess the relative roles of lipid vehicle dispersion and vehicle digestibility in the

oral absorption of penclomedine (Pcm), a series of formulations of Pcm in medium chain

triglyceride (MCT)/TPGS was developed having three sizes (160 nm, 720 nm, and mm sized

(crude oil); with or without the inclusion of tetrahydrolipstatin (THL), a known lipase

inhibitor. Oral absorption of Pcm was studied after administration of small volumes of these

formulations to conscious rats. Formulations with a particle size of 160 nm had the highest

relative bioavailability (set at F = 1), whereas administration in particle 720 nm in size

resulted in a slightly lower bioavailability (F = 0.79). Co-inclusion of THL yielded similar

bioavailability for these two SEDDS. Crude oil formulations had an F= 0.62 (without THL)

and 0.25 (with THL).

Positively charged SEDDS

Many physiological studies have proved that the apical potential of absorptive cells, as well

as that of all other cells in the body, is negatively charged with respect to the mucosal

solution in the lumen (Corbo et al., 1990; Rojanasakul et al., 1992). A novel SEDDS, which

results in positively charged dispersed oil droplets upon dilution with an aqueous phase,

showed an increase in the oral bioavailability of progesterone in young female rats

(Gershanik et al., 1996). More recently, it has been shown that the enhanced electrostatic

interactions of positively charged droplets with the mucosal surface of the everted rat

intestine are mainly responsible for the preferential uptake of the model drug cyclosporine A

(CsA) from positively charged droplets (Gershanik et al., 1998). The Caco-2 cell model was

used for the investigation of the charge dependent interactions of the SEDDS with human

intestinal epithelial cells. The positively charged emulsions affected the barrier properties of

the cell monolayer at high concentrations and reduced the cell viability. However, at the

dilution with aqueous phase used in the study (1:2000), the positively charged SEDDS did

not produce any detectable cytotoxic effect. The binding of the fluorescent dye DiIC18(3)

was much higher from the positively charged SEDDS, compared with the negatively charged

formulation, suggesting increased adhesion of the droplets to the cell surface due to

electrostatic attraction (Gershanik et al., 2000).

24

Table 2.2. List of SEDDS of various drugs.

Compound Formulation Excipients Observations

Simvastatin (Kang et

al., 2004)

SMEDDS 37% Capryol 90, 28%

Cremophor EL, 28% Carbitol

BA 1.5 fold higher

from SMEDDS

Indomethacin (Kim

et al., 2000)

SEDDS 70% ethyl oleate, 30%

Tween 85

BA significantly

increased from

SEDDS

Progesterone (Tuleu

et al., 2004)

SEDDS Mono-di-glycerides:

polysorbate 80, 50/50 w/w

BA 9 fold higher

from SEDDS

Danazol (Porter et

al., 2004)

SMEDDS Medium chain lipids,

Cremophor EL, ethanol

BA 6 fold higher

from SMEDDS

Carvedilol (Wei et

al., 2005)

SEDDS Labrafil M1944CS, Tween

80, Transcutol

BA 4 fold higher

from SEDDS

Cyclosporin (Trull et

al., 1994)

SEDDS Corn oil, ethanol Increased BA and

Cmax from SEDDS

Vitamin E (Julianto

et al., 2000)

SEDDS Tween 80: Span 80: Palm oil

in 4:2:4

BA 3 fold higher

from SEDDS

Coenzyme Q10

(Kommuru et al.,

2001)

SMEDDS 40% Myvacet, 90%

Labrasol, 10% Lauroglycol

BA 2 fold higher

from SEDDS

Silymarin (Wu et al.,

2006)

SMEDDS Tween 80,ethyl alcohol,

ethyl linoleate, PEG 400

BA 2 fold higher

from SMEDDS

Win 54954 (Charman

et al., 1992)

SEDDS 40% Neobee M5, 25% Tagat

To

Increased Cmax, No

difference in BA

Halofantrine (Khoo

et al., 1998)

SEDDS 47% Captex 355, 23%

Capmul MCM, 15%

Cremophor, Ethanol

High BA

Itraconazole (Hong et

al., 2006)

SEDDS Transcutol, pluronic L64,

tocopherol acetate

Increased BA and

reduced Food effect

Atorvastatin (Shen et

al., 2006)

SMEDDS Cremophor RH 40,

propylene glycol, Labrafil,

Labrafac

BA increased

significantly

Atovaquone (Sek et

al., 2006)

SMEDDS LC lipids, ethanol,

cremophor EL

BA 3 fold higher

from SMEDDS

PNU 91325 (Gao et

al., 2004)

SEDDS 6% LC lipids, 30%

Cremophor, 18% Pluronic

L44, 9% PEG, 5% DMA,

20% HPMC

BA 5-6 fold increase

from SEDDS

25

2.2.6. Characterization of SEDDS (Patel et al., 2010)

Differential scanning calorimetry

Differential scanning calorimetry for SMEDDS can be determined using DSC 60. Liquid

sample and Solid sample should be placed in the aluminum pan and result can be recorded.

Any type of chemical interaction should be determined using DSC (Taha et al., 2004)

Fourier transform-infrared spectroscopy

Fourier transform-infrared for SMEDDS can be determined using FT-IR. Liquid sample

should be placed in the liquid sample holder and result can be recorded. Any type of chemical

interaction should be determined using FT-IR (Nazzal et al., 2002).

Macroscopic evaluation

Macroscopic analysis is carried out in order to observe the homogeneity of microemulsion

formulations. Any change in color and transparency or phase separation occurred during

normal storage condition (37±2 ºC) was observed in optimized microemulsion formulation.

Visual assessment

To assess the self-emulsification properties, formulation is introduced into 100 ml of water in

a glass Erlenmeyer flask at 25 °C and the contents are gently stirred manually. The tendency

to spontaneously form a transparent emulsion is judged as good and it is judged bad when

there was poor or no emulsion formation. Phase diagrams are constructed identifying the

good self-emulsifying region (Shen et al., 2006).

Determination of self-emulsification time

The emulsification time of SMEDDS is determined according to USP XXII dissolution

apparatus. Each formulation is added drop wise to purified water at 37 ºC. Gentle agitation

can be provided by a standard stainless steel dissolution paddle rotating at 50 rpm.

Emulsification time is assessed visually (Wei et al., 2005).

Solubility studies

26

Unknown amount of selected vehicles are added to each cap vial containing an excess of

drug. After sealing, the mixtures are heated at 40 ºC in a water bath to facilitate the

solubilization. Mixing of the systems is performed using a vortex mixer. Formed suspensions

are then shaken with a shaker at 25 ºC for 48 h. After reaching equilibrium, each vial is

centrifuged at 3000 rpm for 5 minutes, and excess insoluble LOV is discarded by filtration

using a membrane filter (0.45 μm, 13 mm, Whatman, India). The concentration of drug is

then quantified (Shen et al., 2006).

Transmittance test

Stability of optimized microemulsion formulation with respect to dilution is checked by

measuring Transmittance through U.V. Spectrophotometer. Transmittances of samples are

measured at 650 nm and for each sample three replicate assays are performed (Shen et al.,

2006).

Droplet size determination

It is a precise method for evaluation of stability. Size of droplet is measured by photon-

correlation spectroscopy (PSC) with Zetasizer. All measurements are carried out at scattering

angle of 90 ° and 25 °C temperatures. Prior to measurement, microemulsion is diluted in two

steps with pure water then it is filtered through a 0.22 µm filter just before it is added to

cuvette. In first step it is diluted with equal amount of water. In second step the mixture is

further diluted to appropriate concentration for the measurement. That depends on droplet

size (Usually diluted 100-200 times) (Zhang et al., 2007).

Zeta potential measurement

Zeta potential for microemulsion is determined using Zetasizer. Samples are placed in clear

disposable zeta cells and results are recorded. Before putting the fresh sample, cuvettes are

washed with the methanol and rinsed using the sample to be measured before each

experiment (Wei et al., 2004).

27

Stability

Temperature

Shelf life as a function of time and storage temperature is evaluated by visual inspection of

the SMEDDS system at different time period. SMEDDS are diluted with purified distilled

water and to check the temperature stability of samples, they are kept at three different

temperature range 2-8 °C (refrigerator), room temperature and observed for any evidences of

phase separation, flocculation or precipitation.

Centrifugation

In order to estimate metastable systems, the optimized SMEDDS formulations are diluted

with purified distilled water. Then microemulsion is centrifuged at 1000 rpm for 15 minute at

0 °C and is observed for any change in homogeneity of microemulsions.

In vitro release

The quantitative in vitro release test is performed in purified distilled water/dissolution

medium, which is based on USP 24 method. SMEDDS are placed in dialysis bag during the

release period to compare the release profile with conventional dosage form. Sample

solutions are withdrawn at predetermined time intervals, filtered through a 0.45 μ membrane

filter, dilute suitably and analyzed spectrophotometrically. Equal amount of fresh dissolution

medium is replaced immediately after withdrawal of the test sample. Percent drug dissolved

at different time intervals is calculated using the Beer Lambert‟s equation (Kang et al., 2004)

2.3. Diabetes mellitus

Diabetes mellitus is a chronic metabolic disorder characterized by a high blood glucose

concentration (hyperglycemia) caused by insulin deficiency, often combined with insulin

resistance. Hyperglycemia occurs because of uncontrolled hepatic glucose output and

reduced uptake of glucose by skeletal muscle with reduced glycogen synthesis. When the

renal threshold for glucose reabsorption is exceeded, glucose spills over into the urine

(glycosurea) and causes an osmosis diuresis (polyurea), which in tum results in dehydration,

thirst and increased drinking (polydipsia). Depending on the etiology of the diabetes mellitus,

factors contributing to hyperglycemia may include reduced insulin secretion, decreased

28

glucose usage and increased glucose production (Davis and Granner, 1996; Nolte and Karam,

2001; Rang et al., 2003).

2.3.1. Complications of diabetes mellitus

Diabetes mellitus leads to various acute and chronic complications. Diabetic ketoacidosis and

nonketotic hyperosmolar state are acute complications of diabetes. Both are associated with

potentially serious complications if not promptly diagnosed and treated. Chronic

complications can be divided into vascular and nonvascular complications. The vascular

complications are further subdivided into microvascular that include eye disease (retinopathy,

macular edema, cataracts and glaucoma), neuropathy (sensory and motor and autonomic) and

nephropathy and macrovascular that include coronary artery disease, peripheral vascular

disease, and cerebrovascular disease and dennatologic complications. Nonvascular

complications include problems such as gastroparesis, sexual dysfunction and skin changes

(Powers et al., 2001).

2.3.2. Classification of diabetes mellitus

Several distinct types of diabetes mellitus exist and are caused by a complex interaction of

genetics, environmental factors and lifestyle choices (Table 2.3). However, there are two

major types of diabetes mellitus. Type 1 diabetes (Insulin Dependent Diabetes Mellitus;

IDDM) is a severe form where there is an absolute deficiency of insulin resulting from

autoimmune destruction of P cells. If untreated, it will ultimately lead to ketosis and death.

The incidence of each type of diabetes mellitus varies widely throughout the world. In the

United States, about 10% of all diabetic patients have IDDM with an incidence of 18 per

100,000 inhabitants per year (Davis and Granner, 1996; Powers, 2001). Type 2 (Non Insulin

Dependent Diabetes Mellitus; NIDDM) diabetes is accompanied both by insulin resistance

and by impaired insulin secretion. Such patients are often obese and usually present in adult

life; the incidence rising progressively with age as P cell function declines. In this case,

insulin secretion may appear normal or even excessive but it is insufficient to compensate for

insulin resistance. Circulatory endogenous insulin is sufficient to prevent ketoacidosis but is

often subnormal or relatively inadequate because of tissue insensitivity. NIDDM is far more

common than IDDM, accounts for 80-90% of all cases of diabetes. The incidence rates of

NIDDM increase with age, with a mean rate of about 440 per 100,000 per year by the sixth

decade in males in the United States. A few patients, perhaps 5 percent, who appear to have

29

NIDDM may actually have a slowly progressive form of IDDM, and eventually become

dependent on insulin. NIDDM further subdivided into non-obese and obese types; the latter is

more common (incidence, approximately 80% of NIDDM patients) (Davis and Granner,

1996; Powers, 2001).

Table 2.3. Different forms of diabetes mellitus (Davis and Granner, 1996)

General

Insulin dependent diabetes mellitus (IDDM, type I)

Non Insulin Dependent Diabetes Mellitus (NIDDM, type II)

Gestational diabetes mellitus

Specific Maturity onset diabetes of youth (MODY, glucokinase gene mutations)

Mutations of the insulin receptor (including leprechunism)

Insulin gene mutations

Tropical diabetes Diabetes secondary to pancreatic disease or surgery

Diabetes associated with genetic syndromes, e.g., Prader-Willi syndrome

Diabetes secondary to endocrinopathies

2.3.3. Drugs used for the treatment of diabetes mellitus

a. Insulin: Insulin is the mainstay for treatment of virtually all IDDM and many NIDDM

patients. Different insulin preparations available depending on their duration of action are:

Ultra-short acting (Insulin Lispro), Short acting (Regular insulin and Prompt insulin zinc

suspension i.e., Semilente), Intermediate acting (Isophane insulin suspension and Insulin zinc

suspension i.e., Lente) and Long acting (Protamine zinc insulin suspension and Extended

insulin zinc suspension i.e., Ultralente) (Davis and Granner, 1996; Nichols, 2000).

b. Oral hypoglycemic agents: Most patients with NIDDM can be treated without insulin

(Gerich, 1989; Davis and Granner, 1996). The oral antidiabetic agents have been proved

efficacious in NIDDM. They can be classified according to their predominant mechanism of

action (Reynolds, 1997; Nichols, 2000; Satoskar et a1., 2001).

1. Stimulators of beta cells, e.g., sulfonylureas, repaglinide

2. Inhibitors of gluconeogenesis, e.g., biguanides

3. Inhibitors of intestinal a gIucosidases, e.g., acarbose, meglitol

4. Drugs which reduce insulin resistance, e.g., glitazones

5. Aldose reductase inhibitors, e.g., epalrestat, sorbinil

30

Sulfonyl ureas

Among the oral hypoglycemic agents listed above, sulfonylureas are an important class

currently available for treating hyperglycemia in NIDDM. They are sulfonamide derivatives

but do not possess antibacterial activity. All members of this class are substituted

arylsulfonylureas. They differ at the para position on the benzene ring and at one nitrogen

residue of the urea moiety. They increase the release of endogenous insulin as well as its

peripheral effectiveness (Davis and Granner, 1996; Nolte and Karam, 2001). The

sulfonylureas are divided traditionally into first and second groups or generations of agents

(Table 2.4) (Reynolds, 1997).

Table 2.4. Different sulfonylurea drugs.

First-generation sulfonylureas Second-generation sulfonylureas

Clorpropamide, tolbutamide, tolazamide,

acetohexamide, carbutamide

Glibenclamide (glyburide), glimipiride,

gliclazide, glipizide , glibunuride,

gliquidone, glisentide, glisolamide,

glisoxepide, glyclopyramide,

glycyclamide

The hypoglycemic activity of synthetic sulphur containing compounds had been known for

some time when researchers found during studies of the antibacterial potency of p-amino-

sulfonamide-isopropyl-thiodiazole in patients with typhoid fever that it could cause severe

hypoglycemia (Gerich, 1989). By the mid-1960s, four compounds- tolbutamide,

acetohexamide, tolazamide and chlorpropamide were in widespread clinical use for the

treatment of NIDDM. In the late 1970s the use of sulfonylureas revived and in 1984 both

glibenclamide and glipizide were approved for use in United States. Both the number and

percentage of the patients whose diabetes is treated with sulfonylureas is increasing. Three

agents, chlorpropamide, glibenclamide and glipizide, account for about 75% of the market

(Gerich, 1989). Some patients who do not respond initially to tolbutamide, acetohexamide or

tolazamide may respond to glibenclamide, glipizide or chlorpropamide. Glibenclamide also

offer a wider dose range as compared to other sulfonylureas. It also offers the theoretical

advantage of fewer pharmacological interactions because of their nonionic binding to plasma

proteins (Gerich, 1989). In comparison to Glibenclamide, gliclazide is comparatively newer

sulfonylurea and has good efficacy, appears of particular benefit in patients previously

untreated with oral antidiabetic drugs and is generally well tolerated. In the long term, it

reduces hepatic gluconeogenesis, and increases insulin effects by acting at receptor or post

31

receptor sites. It also inhibits platelet aggregation and increases fibrinolysis. Because of these

therapeutic effects it has emerged as one of the important and promising drug substances for

diabetes mellitus, especially due to the noticeable improvement of survival rates in patients

with chronic increase in glucose level.

The principal action of glibenclamide and gliclazide is on beta cells, stimulating insulin

secretion from pancreatic cells and thus reducing plasma glucose. High affinity receptors for

sulfonylureas are present on the KATP channels in beta cell plasma membranes and the

binding of various sulfonylureas parallels their potency in stimulating insulin release. The

drugs reduce the K+ permeability of the beta cells by blocking KATP channels causing

depolarization, Ca2+ entry and insulin secretion. These drugs may also inhibit the release of

glucagon in vitro. Reduced plasma glucagon levels have been found in patients with NIDDM

after the long term administration of sulfonylureas in many but not all. They also may further

increase insulin levels by reducing hepatic clearance of the hormone (Gerich, 1989; Davis

and Granner, 1996; Rang et al., 2003). These agents have the potential to cause profound and

persistent hypoglycemia. Hypoglycemia is the major risk that must be weighed against any

benefits of these drugs. It is usually related to delayed meals, increased physical activity,

alcohol intake or renal insufficiency. Most sulfonylureas are metabolized in the liver to

compounds that are cleared by the kidney. Thus their use in individuals with significant

hepatic or renal dysfunction is not advisable. Weight gain, a common side effect of

sulfonylurea therapy, results from the increased insulin levels and improvement in glycemic

control. Gastrointestinal (GI) disturbances such as nausea, vomiting, heartburn, anorexia,

diarrhea and a metallic taste may occur. Skin rashes and pruritus may take place and

photosensitivity has been reported. Other severe side effects may be manifestations of a

hypersensitivity reaction. They include leucopenia, thrombocytopenia, agranulocytosis,

hemolytic anemia and cholestatic jaundice (Gerich, 1989; Davis and Granner, 1996; Satoskar

et al., 200 1). Since glibenclamide and glipizide are usually intended to be taken for a longer

period, patient compliance is also very important (Takahshi et al., 1997). In addition, they

require more than once a day dosing because of the shorter half-life, which adversely, affects

the patient compliance (Gerich, 1989).

Diabetes mellitus, long considered a disease of minor significance to world health, is now

taking its place as one of the main threats to human health in the 21st century (Zimmet et al.,

2000). The past two decades have seen an explosive increase in the number of people

32

diagnosed with diabetes worldwide (Amos et al., 1997; King et al., 1998). Diabetes mellitus

has reached epidemic proportions and affects more than 170 million individuals worldwide.

Global estimates for the year 2010 predict a further growth of almost 50%, with the greatest

increases in the developing countries of Africa, Asia, and South America (Zimmet et al.,

2001). In more developed societies, the prevalence of diabetes mellitus has reached about 6%

(King et al., 1998) and, even more alarmingly, among obese white adolescents 4% had

diabetes and 25% had abnormal glucose tolerance (Sinha et al., 2002). Some 90% of diabetic

individuals have type 2 (non-insulin-dependent) diabetes mellitus, and within this category no

more than 10% can be accounted for by monogenic forms such as maturity onset diabetes of

the young (Fajans et al., 2001) and mitochondrial diabetes (Maassen et al., 2004) or late onset

autoimmune diabetes of the adult, which is actually a late-onset type 1 diabetes (Pozzilli et

al., 2001). Thus, most diabetes in the world is accounted for by “common” type 2 diabetes,

which has a multifactorial pathogenesis caused by alterations in several gene products. The

medical and socioeconomic burden of the disease is caused by the associated complications

(Wei et al., 1998; UKPDS., 1998) which impose enormous strains on healthcare systems. The

incremental costs of patients with type 2 diabetes arise not only when the diagnosis is

established but at least 8 years earlier (Nichols et al., 2000). The devastating complications of

diabetes mellitus are mostly macrovascular and microvascular diseases as a consequence of

accelerated atherogenesis. Cardiovascular morbidity in patients with type 2 diabetes is two to

four times greater than that of non-diabetic people (Zimmet et al., 2001). Over the past 30

years, the status of diabetes has changed from being considered as a mild disorder of the

elderly to one of the major causes of morbidity and mortality affecting the youth and middle

aged people (Huizinga et al., 2006). It is important to note that the rise in prevalence is seen

in all six inhabited continents of the globe (Wild et al., 2004). According to the Diabetes

Atlas 2006 published by the International Diabetes Federation, the number of people with

diabetes in India currently around 40.9 million is expected to rise to 69.9 million by 2025

unless urgent preventive steps are taken. Besides significant mortality, diabetes related

morbidities such as diabetic retinopathy, neuropathy and cardiovascular disease have also

placed a heavy financial burden on society (Henriksson et al., 1998; Warner et al., 1996;

Simell et al., 1996). For example, in the United States alone, the total annual economic cost

of diabetes in 1997 was estimated to be US$98 billion. This included US$44 billion in direct

medical and treatment costs and US$54 billion for indirect costs attributed to disability and

mortality. Healthcare professionals as well as public policy makers are well aware of the

33

public health impact of diabetes. Diabetes is a silent disease – many sufferers became aware

that they have diabetes only when they develop one of its life-threatening complications.

Knowledge of diabetes mellitus can assist in early detection of the disease and reduce the

incidence of complications. Thus, considerable efforts had been put in to inform the public

about diabetes.

2.4. Drugs profile

2.4.1. Gliclazide (BP 2008; Martindale 2006)

Structure:

Chemical formula C15H21N3O3S

Molecular weight 323.41

Category In NIDDM (Sulfonylurea derivative)

Chemical name 1-(3-azabicyclo(3.3.0)oct-3-yl)-3-p-tolylsulphonylurea

pKa 5.8

Log p (Oct/Water) 2.1

Melting point

Appearance White or almost white powder

Solubility Practically insoluble in water, freely soluble in methylene

chloride, sparingly soluble in acetone, slightly soluble in alcohol

Loss on drying Not more than 0.25%, determined on 1.000 g by drying in an

oven at 100 oC to 105

oC for 2h

Content NLT 99.0% and NMT 101.0%

Dosage form Tablet

Strength 20 mg, 30 mg, 40 mg, 80 mg

160 mg daily are given in 2 divided doses

Route of administration Oral

Mechanism Inhibition of ATP-dependent potassium channels(sulfonylurea);

treatment of diabetes mellitus

Indications Noninsulin-Dependent Diabetes Mellitus

T1/2 10-12 h

Tmax (h) 4-6 h

Bioavailability Variable (approx. 60-110%)

34

2.4.2. Glibenclamide (Glyburide) (IP 2007; BP 2008; Martindale)

Structure:

Chemical formula C23H28ClN3O5S

Molecular weight 494.0

Category In NIDDM (Sulfonylurea derivative)

Chemical name 1-{4-[2-(5-chloro-2-

methoxybenzmido)ethyl}benzenesulphonyl}-3-cyclohexylurea

pKa 5.3

Log p (Oct/Water) 4.8

Melting point 172 to 174 °C

Appearance A white or almost white, crystalline powder

Solubility Practically insoluble in water, sparingly soluble in methylene

chloride, slightly soluble in alcohol and in methanol

Loss on drying Not more than 1.0%, determined on 1.0 g by drying in an oven

at 105 oC

Content 99.0% to 101.0% (dried substance)

Dosage form Tablet

Strength 2.5 mg-5 mg daily with breakfast

Increments of 2.5 – 5 mg daily up to 15 mg daily

Route of administration Oral

Mechanism Inhibition of ATP-dependent potassium channels(sulfonylurea);

treatment of diabetes mellitus

Indications Noninsulin-Dependent Diabetes Mellitus

Tmax (h) 2-4 h

Bioavailability Variable (approx. 60-90%)

35

2.5. Excipients profile

2.5.1. Sunflower oil

Chemical Name Sunflower oil

Structural Formula Sunflower oil is classified as anoleic–linoleic acid oil. Its

composition includes linoleic acid (66%), oleic acid

(21.3%), palmitic acid (6.4%), arachidic acid (4.0%), stearic

acid (1.3%), and behenic acid (0.8%). The USP32–NF-27

describes sunflower oil as a refined fixed oil obtained from

the seeds of Helianthus annus Linne (Family: Asteraceae).

The PhEur 6.2 describes sunflower oil as the refined fatty oil

obtained from the seeds of Helianthus annus C. by

mechanical expression or by extraction. A suitable

antioxidant may be added.

Description Sunflower oil occurs as a clear, light yellow-colored liquid

with a bland, agreeable taste

Boiling point

40–60 oC

Density (g/cm3)

0.915–0.919

Hydroxyl value 14–16

Iodine number 125–140

Melting point -18 oC

Refractive index

1.472–1.474

Specific gravity 0.914–0.924

Saponification value 180–200

Functional Category Diluent; emollient; emulsifying agent; solvent; tablet binder.

Stability and Storage

Conditions

Sunflower oil should be stored in an airtight, well-filled

container, protected from light. Stability may be improved

by the addition of an antioxidant such as butylated

hydroxytoluene

36

2.5.2. Palm Oil

Source Kernels of fruits of Elaeis guineensis

Chemical Name Palm Oil

Appearance Liquid

Description Orange-red liquid or solid with a pleasant odor. Insoluble in water

and less dense than water. Hence floats on water. Contains

principally glycerides of palmitic, oleic, and linoleic acids

Melting point

30-40 °C (lit.)

Water

0.3% max

Acid value 251 – 261

Iodine number 16-22

Solubility Soluble in water, 1.141e-011 mg/L @ 25 °C

Saponification value 252 – 262

Stability Stable. Combustible. Incompatible with strong oxidising agents

2.5.3. Polyethylene Glycol 600 (PEG 600)

Chemical Name Structural formula

Emperical formula HOCH2(CH2OCH2)mCH2OH where m represents the average

number of oxyethylene groups.m= 13.2

Molecular weight 570–613

Density

1.11–1.14 g/cm3 at 25

oC

Viscosity (dynamic)

[mPa s (cP)]

15–20

Moisture content Hygroscopic,although hygroscopicity decreases with increasing

molecular weight.

Freezing point

15–25 oC

Refractive index

1.467

Description

Liquid grades (PEG 200–600) occur as clear, colorless or

slightlyyellow-colored, viscous liquids. They have a slight but

characteristic odor and a bitter, slightly burning taste. PEG 600 can

occur as a solid at ambient temperatures

Category Ointment base; plasticizer; solvent; suppository base; tablet

Stability and Polyethylene glycols are chemically stable in air and in solution,

37

Storage Conditions

although grades with a molecular weight less than 2000 are

hygroscopic. Polyethylene glycols do not support microbial growth,

and they do not become rancid.

2.5.4. Tween 20

Chemical Name Polyoxyethylene 20 sorbitan monolaurate

Structural formula

Emperical formula C58H114O26

Molecular weight 1128

Viscosity (mPa s): 400

Moisture content 3.0

Color and Form at

25 oC

Yellow oily liquid

Specific gravity at

25 oC

1.1

HLB value 16.7

Acidity/alkalinity pH 6.0–8.0 for a 5% w/v aqueous solution

Flash point 149 oC

Acid value (%) 2.0

Hydroxyl value 96–108

Saponification

Value

40–50

Description

Polysorbates have a characteristic odor and a warm, somewhat

bitter taste. The absolute color intensity of the products may vary

from batch to batch and from manufacturer to manufacturer

Functional Category

Dispersing agent; emulsifying agent; nonionic surfactant;

solubilizing agent; suspending agent; wetting agent.

38

2.5.5. Tween 80

Chemical Name Polyoxyethylene 20 sorbitan Monooleate

Structural formula

Emperical formula C58H114O26

Molecular weight 1310

Viscosity (mPas): 425

Moisture content 3.0

Color and Form at 25 oC Yellow oily liquid

Specific gravity at 25 oC 1.1

HLB value 15

Acidity/alkalinity pH 6.0–8.0 for a 5% w/v aqueous solution

Flash point 149 oC

Acid value (%) 2.0

Hydroxyl value 65-80

Saponification value 45–55

Description

Polysorbates have a characteristic odor and a warm,

somewhat bitter taste. Absolute color intensity of the

products may vary from batch to batch and from

manufacturer to manufacturer

Functional Category

Dispersing agent; emulsifying agent; nonionic surfactant;

solubilizing agent; suspending agent; wetting agent.