539 | P a g e International Standard Serial Number (ISSN): 2319-8141
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International Journal of Universal Pharmacy and Bio Sciences 2(5): September-October 2013
INTERNATIONAL JOURNAL OF UNIVERSAL
PHARMACY AND BIO SCIENCES IMPACT FACTOR 1.89***
ICV 2.40***
Global Impact Factor: 0.406*** Pharmaceutical Sciences REVIEW ARTICLE……!!!
NANOCRYSTALLIZATION: A NOVEL SOLUBILITY ENHANCEMENT
TECHNOLOGY FOR POORLY WATER SOLUBLE DRUGS
T. SUDHAMANI *, K. ABOOBAKKARSIDHIQ, DANDE JEEVAN KUMAR,
V. GANESAN
Department Of Pharmaceutics, The Erode, College Of Pharmacy, Erode, Tamil Nadu, India-
638112.
KEYWORDS:
Nanocrystals, BCS II,
solubility, dissolution,
particle size.
For Correspondence:
Mrs. T. SUDHAMANI *
Address:
Department Of
Pharmaceutics, The
Erode, College Of
Pharmacy, Erode, Tamil
Nadu, India-638112.
Email-ID:
ABSTRACT
Drugs of the biopharmaceutical specification class II (BCS II) shows
poor water solubility and high permeability. The challenging problems
in formulating BCS II drugs are mainly due to the poor solubility is
associated to poor dissolution characteristics and thus to poor oral
bioavailability. In order to enhance these characteristics, formulation of
BCS II drugs has been achieved by getting nanocrystals using
Nanocrystallization technology. Drug nanocrystals are pure solid drug
particles with a mean diameter below 1000 nm. Nanocrystal
dispersions comprise water, active drug substance and a stabilizer. The
use of drug Nanocrystals is a universal formulation approach to
increase the therapeutic performance of these drugs. There are several
advantages of Nanocrystal formulations such as, enhanced oral
bioavailability, improved dose proportionality, reduced food effects,
suitability for administration by all routes and possibility of sterile
filtration due to decreased particle size range. Different methods can be
used to prepare Nanocrystal formulations of a drug powder such as
bottom up, top down, combination technology and other techniques.
Nanocrystals were characterized in terms of particle size, shape and
surface charge, drug content, saturation solubility, dissolution
characteristics, surface hydrophilicity/hydrophibicity, crystalline state
and stability studies. Through this review article, it has been shown
that the Nanocrystal technology can be used as a novel formulation
approach to enhance the solubility of poorly water soluble drugs. The
method being simple and easily scaled up, this approach should have a
general applicability to many poorly water soluble drug entities.
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INTRODUCTION:
The number of newly developed drugs having a poor solubility and thus exhibiting bioavailability
problems after oral administration is steadily increasing. Estimates by the pharmaceutical companies
are that about 40% of the drugs in the pipelines are poorly soluble, and as high as 60% of the
compounds come directly from the synthesis route. Therefore, since a number of years the
pharmaceutical development is focused on formulation approaches to overcome solubility and
related bioavailability problems, so that these new compounds are available for clinical use1. Often
forgotten, the problem of poor solubility arises even before the preclinical phase, which means that
when screening new compounds for pharmacological activity a test formulation needs to be able to
lead to sufficiently high blood levels. Therefore, there is an urgent need to come up with a smart
formulation approach.
Nanocrystallization is defined as a way of diminishing drug particles the size range of 1-1000
nanometers. The produced particles don‘t necessarily have to be crystalline; they can be amorphous
as well. Drug nanocrystals are pure solid drug particles with a mean diameter below 1000 nm.2 Drug
nanocrystals, by definition, are nanoparticles being composed of 100% drug without any matrix
material and mean particle size is below 1μm (i.e. approximately between 200-500 nm).
A nanosuspension consists of drug nanocrystals, stabilizing agents such as surfactants and/or
polymeric stabilizers, and a liquid dispersion medium. The dispersion media can be water, aqueous
solutions, or non-aqueous media. The term ―drug nanocrystals‖ implies a crystalline state of the
discrete particles, but depending on the production method they can also be partially or completely
amorphous3.
Fig.1. Images for Nanocrystals
There are many advantages of nanocrystal formulations designed for oral administration and they
are as follows,
• Increased surface area
• Enhanced solubility
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• Increased rate of dissolution
• Increased oral bioavailability
• Rapid effect
• Improved dose proportionality
• Reduction in required dose
• Reduced food effects
• Reduction in fed/fasted variability
• Rapid, simple and cheap formulation development
• Possibility of high amounts (30-40 %) of drug loading
• Applicability to all routes of administration in any dosage form. Contrary to micronized drugs,
nanocrystals can be administered via several routes. Oral administration is possible in the form of
tablets, capsules, sachets or powder; preferably in the form of a tablet4.
• Increased reliability. Usually side effects are proportional to drug concentration, so decreasing the
concentration of active drug substances leads to an increased reliability for patients.
• Improved stability. They are stable systems because of the use of a stabilizer that prevents re-
aggregation of active drug substances during preparation. Suspension of drug nanocrystals in liquid
can be stabilized by adding surface active substances or polymers.
• Applicability to all poorly soluble drugs because all these drugs could be directly disintegrated into
nanometre-sized particles5.
• Sustained crystal structure. Nanocrystal technology leads to an increase in dissolution rate
depending on the increase in surface area obtained by reduction of the particle size of the active drug
substance down to the nano size range preserving the crystal morphology of the drug.
• Possibility of sterile filtration due to decreased particle size range
There are few limitations only as follows,
•Nanotoxicity may be attributed to the small size (below about 150 nm) of nanocrystals, due to
which they can have access to any cell of the body via pinocytosis. This increases the risk of
cytotoxicity.
•This technology requires expensive equipments which increase the cost of the final product. •The
use of this technique is restricted to BCS class II drugs only.
•The production of nanocrystals and their stability is dependent on the molecular structure of the
drug. Due to this, only certain categories of drugs will be suitable candidates for this technique6.
INFLUENCE OF NANOCRYSTALS ON SOLUBILITY ENHANCEMENT
Most differentiating features of drug nanocrystals are the increased saturation solubility and the
accelerated dissolution velocity. It is explained by following equations. Nernst Brunner/Noyes-
Whiteny equation, Prandtl equation and Freundlich-Ostwald equation. A drug specific constant
which depends only on the solvent and the temperature is called as the saturation solubility (Cs).
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1) Nernst Brunner/Noyes-Whiteny equation
The solid API dissolution rate is proportional to the surface area available for dissolution as
discussed below7.
Where,
Dx⁄dt = dissolution rate, Xd = amount dissolved, A= particle surface area,
D =dissolution, V = volume of fluid available for dissolution, Cs =saturation solubility,
h = effective boundary layer thickness.
2) Prandtl equation
Decrease in the particle size in the sub-micron range will further increase dissolution rate because of
increase in surface area. Which is explained by the Prandtl equation, the diffusion layer thickness
will also be reduced, thus resulting in an enhanced dissolution rate8.
3) Freundlich-Ostwald equation
An increase in saturation solubility of the nanosized API has also been explained by the Freundlich–
Ostwald equation:
Where, S = saturation solubility of the nanosized API, S∞= saturation solubility of an infinitely
large API crystal, = crystal-medium interfacial tension, M = molecular weight of the compound, r =
particle radius, ρ = density, R = gas constant, T =temperature.
Finally, surface wetting increment by surfactants in nanosuspension formulations, in comparison to
conventional micronized formulations results in further enhancement of dissolution rates9. Hence,
better therapeutic drug efficacy was obtained. Also, the rejection of new drug entities because of
poor solubility can be prevented.
NANOCRYSTALLIZATION METHODS
Several preparation methods developed today, implemented preparation methods of nanocrystal
formulations can be classified as ―bottom up‖, ―top-down‖, ―top down and bottom up‖(combination
techniques) and ―other techniques‖.―Bottom up‖ technology begins with the molecule; active drug
substance is dissolved by adding an organic solvent, and then, solvent is removed by precipitation.
―Top down‖ technology applies dispersing methods by using different types of milling and
homogenization techniques10
. ―Top down‖ technology is more popular than ―Bottom up‖
technology; it is known as ―nanosizing‖. In other words, it is a process which breaks down large
crystalline particles into small pieces. In ―top down and bottom up‖ technology, both methods are
utilized together.
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Nanocrystallization Methods
Bottom up Top down combination techniques other techniques
1. BOTTOM UP
1.1 Precipitation methods:
The drug is dissolved in a solvent and subsequently added to a non solvent, leading to the
precipitation of finely dispersed drug nanocrystals. Nanocrystals can be removed from the solution
by filtering and then dried in air. The size and shape of the produced nanocrystals can be controlled
by varying the precipitation conditions such as temperature and concentration. XRD analyses have
proven that the crystal structure in nanocrystals produced by precipitation is similar to that of the
bulk material used. One must consider in mind that these nanocrystals need to be stabilized in order
when they are not allowed to grow to the micrometre range. In addition, the drug needs to be soluble
in at least one solvent, which creates problems for newly developed drugs that are insoluble in both
aqueous and organic media11
.
1.2 Sonocrystallization:
Recrystallization of poorly soluble material using liquid solvents and antisolvents has also been
employed successfully to reduce particle size. The novel approach for particle size reduction on the
basis of crystallization by using ultrasound is sonocrystallization. Sonocrystallization utilizes
ultrasound power characterized by a frequency range of 20-100 kHz for inducing crystallization. It
not only enhances the nucleation rate but also an effective
means of size reduction & controlling size distribution of the active pharmaceutical ingredient
(API). Most applications used ultrasound in the range 20 khz - 5mhz.
Sonocrystallization technique or technology has also been studied to modify the undesirables of
NSAID‘S I) i.e. poor solubility and dissolution rate and consequently the poor bioavailability.
Flurbiprofen was poured in deionized water at 25°C and sonicated for 4 minutes at an amplituted of
60% and cycle is 40 sec on and 10 sec off. The particle size of treated flurbiprofen was significantly
reduced and the increased solubility of treated flurbiprofen was about 35%. The intrinsic dissolution
rate of treated flurbiprofen increased by 2-fold. The dissolution studies obtained that 90% of the
drug was released within 20 minutes for treated flurbiprofen as compared to untreated flurbiprofen
obtained 60% release of the drug.
1.3 Gas antisolvent recrystallization-GAS
This processing requires drug polymer mixture be solubilized via conventional means into a solvent
i.e. then sprayed into an SCF (supercritical fluid), the drug should be miscible with the organic
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solvent. The SCF diffuses into the spray droplets, causing expansion of the solvent present and
precipitation of the drug particles. The low solubility of poorly water-soluble drugs and surfactants
in supercritical CO2 and the high pressure required for these processes restrict the utility of this
technology in the pharmaceutical industry12.
2. TOP DOWN
2.1 Milling methods:
The classical Nanocrystal technology uses a bead or a pearl mill to achieve particle size diminution.
Ball mills are already known from the first half of the 20th century for the production of ultra fine
suspensions. Milling media, dispersion medium (generally water), stabilizer and the drug are
charged into the milling chamber13
. Shear forces of impact, generated by the movement of the
milling media, lead to particle size reduction. In contrast to high pressure homogenization, it is a low
energy milling technique. Smaller or larger milling pearls are used as milling media. The pearls or
balls consist of ceramics (cerium or yttrium stabilized zirconium dioxide), stainless steel, glass or
highly cross-linked polystyrene resin-coated beads14
. Erosion from the milling material during the
milling process is a common problem of this technology. To reduce the amount of impurities caused
by erosion of the milling media, the milling beads are coated. Another problem is the adherence of
product to the inner surface area of the mill.
There are two basic milling principles. Either the milling medium is moved by an agitator, or the
complete container is moved in a complex movement leading consequently to a movement of the
milling media. When one assumes that 76% of the volume of the milling chamber is to be filled with
milling material, larger batches are difficult to produce when moving the new container, so mills
using agitators are used for large sized mill for large batches. The milling time depends upon many
factors such as the surfactant content, hardness of the drug, viscosity, temperature, energy input, size
of the milling media.
2.2 High Pressure Homogenization methods:
a) Microfluidization (IDD-P™ technology)
The microfluidizer is a jet stream homogenizer of two fluid streams collided frontally with high
velocity (up to1000m/sec) under pressures up to 4000 bar. There is a turbulent flow, high shear
forces, particles collide leading to particle diminution to the nanometer range. The high pressure
applied and the high streaming velocity of the lipid can also lead to cavitation additionally,
contributing to size diminution. To preserve the particle size, stabilization with phospholipids or
other surfactants and stabilizers is required. A major disadvantage of this process is the required
production time. In many cases, 50 to 100 time- consuming passes are necessary for a sufficient
particle size reduction. SkyePharma Canada, Inc. (previously RTP, Inc.) applies this principle for its
IDDP ™ technology to produce submicron particles of poorly soluble drugs15.
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b) Piston-gap homogenization in water (Dissocubes):
Drug nanocrystals can also be produced by high-pressure homogenization using piston gap
homogenizers. Depending on the homogenization temperature and the dispersion media, there is a
difference between the Dissocubes technology and the Nanopure technology. Dispersion medium of
the suspensions was water. A piston in a large bore cylinder creates pressure up to 2000 bar. The
suspension is pressed through a very narrow ring gap. The gap width is typically in the range of 3-15
micrometres at pressures between 1500-150 bar. There is a high streaming velocity in the gap
according to the Bernoulli equation. Due to the reduction in diameter from the large bore cylinder to
the homogenization gap which increases the dynamic pressure (streaming velocity) and
simultaneously decreases the static pressure on the liquid. When the liquid starts boiling at that time
gas bubbles occur which subsequently implode, when the suspension leaves the gap and is again
under normal pressure (cavitation). Gas bubble formation and implosion lead to shock waves which
cause particle diminution16
. The patent describes cavitation as the reason for the achieved size
diminution.
Piston gap homogenizers which can be used for the production of Nanosuspensions are e.g. from the
companies APV Gaulin, Avestin or Niro Soavi. The technology was acquired by Skye pharma PLC
at the end of the 90s and employed in its formulation development. The use of water as dispersion
medium is associated with some disadvantages. Hydrolysis of water-sensitive drugs can occur, as
well as problems during drying steps. In cases of thermo labile drugs or drugs possessing a low
melting point, a complete water removal requires relatively expensive techniques, such as
Lyophilization. For these reasons, the Dissocubes® technology is particularly suitable if the
resulting nanosuspension is directly used without modifications, such as drying steps. Many
different drugs have been processed byhigh-pressure homogenization to product DissoCubes. Up to
now each drug investigated could be converted into ananosuspension17
.
c ) Nanopure® XP technology:
This is the registered trade name given by the company PharmaSol GmbH/Berlin. Similar effective
particle size reduction can also be obtained in non aqueous or water reduced media. The production
of nanocrystals in non-homogenization media is a very effective method to obtain direct
formulation. The nanocrystals of the drug dispersed in liquid polyethylene glycol (PEG)or various
oils can be directly filled as drug suspensions into HPMC capsules or gelatin. Cavitation is the major
force in particle size reduction. Against this theory, this technology was developed. Even in non
aqueous media, the particle size diminution can be achieved. Tablets, pellets and capsules must be
formed.
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The advantages of this method are that the dispersion medium need not be removed. Evaporation is
faster and under milder conditions (when water and water miscible liquids are used).This is useful
for temperature sensitive drugs. For i.v. injections, isotonic nanosuspension is obtained by
homogenizing in water-glycerol mixtures. Water reduction causes decrease in the energy required
for the various steps carried out such as fluidized bed drying, spray drying or layering of suspension
onto the sugar spheres. The IP owned by Pharmasol covers water mixtures and water– free
dispersion media (e.g. PEG, oils). When developing the second generation of drug nanocrystals
nanopure, just opposite was done as described in the literature. Suspensions of the drug in the non-
aqueous media were homogenized. This process was done at 0˚C as well as below freezing point
(e.g. -20˚C), along with performing it at room temperature. This was, hence, also called as the ‗deep-
freeze homogenization18
.
3. COMBINATION TECHNOLOGIES:
In this technology, both methods are used together. Nano-Edge is a product obtained by such a
combination technology. Nano-edgetechnology described the formulation method for poorly water-
soluble drugs19
. It is a useful technology and high n- octanol-water partition coefficients. It is
based on direct homogenization, micro precipitation, and lipid emulsions.
3.1 Nanoedge® Technology: Nanoedge technology (Baxter Healthcare Corporation, Deerfield, IL)
described the formulation method for poorly water-soluble drugs. It is a useful technology for active
ingredients that have high melting points and high octanol-water partition coefficients, logP. It is
based on direct homogenization, micro-precipitation, and lipid emulsions. In microprecipitation, the
drug first is dissolved in a water-miscible solvent to form a solution. Then, the solution is mixed
with a second solvent to form a pre-suspension and energy is added to the pre-suspension to form
particles having an average effective particle size of 400 nm to 2 μ. The energy-addition step
involves adding energy through sonication, homogenization, counter current flow homogenization,
micro-fluidization, or other methods of
providing impact, shear, or cavitation forces. A drug suspension resulting from these processes may
be administered directly as an injectable solution, provided water-for-injection is used in the
formulation and an appropriate means for solution sterilization is applied. Nanoedge technology
facilitates small particle sizes (<1000 nm [volume weighted mean]), high drug loading (10–200
mg/mL), long-term stability (up to 2 years at room temperature or temperatures as low as 5 °C), the
elimination of co solvents, reduced levels of surfactants, and the use of safe, well-tolerated
surfactants [21]NANOEDGER process is particularly suitable for drugs that are soluble in non
aqueous media possessing low toxicity, such as N-methyl-2-pyrrolidinone20
.
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3.2 Rapid expansion from a liquefied-gas solution (RESS):
This process is applicable to the substances those are soluble in supercritical fluids. This process
offers a solvent free final product. In this process, first the solute is dissolved in a supercritical fluid
then it is passed through a nozzle at supersonic speed. Pressure reduction of solution in a nozzle
leads to a rapid expansion. This RESS leads to super saturation of the solute and subsequent
precipitation of solute particles with narrow particle size distributions Pathak et al., 2004 applied
SCF processing technique i.e. rapid expansion of super critical solution in a liquid solvent
(RESOLV) for the nanosizing of water insoluble drug particles. The drugs used for nanosizing were
anti-inflammatory Ibuprofen and Naproxen for which CO2 and CO2–co solvent system were used
due to its favorable processing characteristics‘ like its low critical temp (TC=31.1-C) and pressure
(PC=73.8 bar). The RESOLVE process produced exclusively nanoscale (less than 100nm) particles.
Ibuprofen and Naproxen particles suspended in aqueous solution and the aqueous suspension of the
drug nanoparticle are protected from agglomeration and precipitation by using common polymeric
and oligomeric stabilizing agents21
.
4. OTHER TECHNIQUES:
4.1Spray Drying:
One of the preparation methods of nanocrystals is spray drying. This method is usually used for
drying of solutions and suspensions. In a conical or cylindrical cyclone, solution droplets are
sprayed from top to bottom, dried in the same direction by hot air and spherical particles are
obtained. Spraying is made with an atomizer which rapidly rotates and provides scattering of the
solution due to centrifugal effect. The solution, at a certain flow rate, is sent to the inner tube with a
peristaltic pump, nitrogen or air at a constant pressure is sent to the outer tube. Spraying is provided
by a nozzle. Droplets of solution become very small due to spraying; therefore, surface area of the
drying matter increases leading to fast drying Concentration, viscosity, temperature and spray rate of
the solution can be adjusted and particle size, fluidity and drying speed can be optimized. The
dissolution rate and bioavailability of several drugs, including hydrocortisone, COX-2 Inhibitor
(BMS-347070) were improved utilizing this method22
.
4.2 Spray Freezing into Liquid (SFL):
The University of Texas (Austin) was the first to develop and patent the SFL method in the year
2003. This technique was first commercialized by Dow Chemical Company (Midland, MI). Here in,
the atomization of an aqueous, organic, aqueous organic cosolvent solution, aqueous organic
emulsion or suspension containing drug occurs directly into either a compressed gas (i.e. CO2,
propane, ethane or helium), or a cryogenic liquid (i.e. argon, nitrogen or hydrofluoroethers). These
frozen particles are then lyophilized to obtain free flowing and dry micronized powders. The drying
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time for lyophilisation was decreased by acetonitrile and also it increased the drug loading23
. Better
results were obtained, i.e. highly effective wettability and high surface area, enhanced dissolution
rates were obtained from the SFL powder which contained the amorphous nanostructured
aggregates. The micronized bulk danazol exhibited a slow dissolution rate; only 30% of the danazol
dissolved in 2 minutes. Then 95% of the danazol was dissolved in only 2 minutes for the SFL highly
potent powders. In a study, SFL danazol/PVP K-15 powders with high surface areas and high glass
transition temperatures remained amorphous and exhibited rapid dissolution rates even after 6
months long storage24
.
Table 1.Advantages and Disadvantages of Different Methods For The Production of
Nanocrystals25
Technology Advantages Disadvantages
Precipitation
•Simple method
•produce fine form of crystals
•size and shape can be
controlled
•drug needs to be soluble atleast one
solvent, therefore only applicable to
few drugs.
•needs stabilization
• organic solvent need to be removed
Sonocrystallization
•novel approach
•size reduction by
crystallization.
•effective in controlling size
distribution
•utilizes ultrasound power
•high cost
GAS
•uses both solvent and gas
•fine form of products are
available
•drug need to be soluble in
supercritical co2, therefore its
application is limited
•drug needed to be miscible with
organic solvent
Media milling
•quick process
•low cost
•rapid production capacity
•loss of drug due to adhesion in the
inner surface of milling chamber
•not suitable for drug powders having
elasticity
Microfluidization
•used to produce submicron
particles
•time consuming
•needs stabilization to preserve particle
size
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Piston-gap
homogenization
•many different drugs can be
processed
•product can be directly
used without modification
•water sensitive drugs cant be used
• thermolabile and low melting point
drugs needed water removal, very
expensive
Nanopure
technology
•The diameter of product
should be between 200-600
nm
•homogenization can be perfo
rmed in non-aqueous phases
•uses high power
Nanoedge
technology
•small particle sizes
•high drug loading
•long term stability
•elimination of cosolvents
•high cost
• high power consuming
RESS
•applicable for drugs soluble
in supercritical fluids
•produces<100nm articles
•application is limited
Spray drying •used for solutions and
suspensions
•not a universal method
Spray freezing into
liquid
•high drug loading
•increased dissolution
•complicated process like
lyophilisation is involved.
CHARACTERIZATION OF NANOCRYSTALS
The essential characterization parameters for nanocrystals include:
Particle size, shape and surface charge
Drug content
Saturation solubility
Dissolution characteristics
Surface hydrophilicity/hydrophobicity
Crystalline state
Stability studies
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Table 2 :Parameters and its methods for characterization of nanocrystals26,27
Parameter Characterization method
Particle size, shape and surface
charge
Zetasizer (Malvern Zetasizer 3000HS, United Kingdom)
Laser diffraction(LD), Scanning electron microscopy(SEM),
Transmission electron microscopy(TEM) and electrophorosis
Drug content
Quantitative determination by UV spectrophotometer
Saturation solubility UV determination
Dissolution characteristics Paddle , basket methods(USP30) and film dialysis
Surface
hydrophilicity/hydrophobicity
Hydrophobic interaction chromatography
Crystalline state DSC, XRD
Stability studies
As per ICH guidelines and polydispersity index
Particle Size, Shape and Surface charge
The mean size and size distribution (polydispersity index) are important parameters because they
govern properties such as saturation solubility, dissolution velocity, physical stability, and certain
biological performances. Zetasizer which is based on Photon correlation spectroscopy (PCS) or
dynamic light scattering technique (DLS) are employed, but limited to measuring sizes of 3 nm to 3
μm, therefore laser diffractrometry (LD) is used to detect aggregates of drug nanocrystals. LD able
to measure particles of 0.05 μm to 2000 μm. Scanning (or transmission) electron microscopy(SEM,
TEM) may also be used for size evaluation.
Surface charge is an important parameter also governing the stability of the nanosuspensions. It is
measured by means of electrophoresis and is expressed as electrophoretic mobility or converted to
zeta potential. This measurement allows for the prediction of storage stability of the nano-
dispersions. Usually the particles with sufficient zeta potential are less likely to aggregate. Literature
states that a zeta potential of at least -30 mV for electrostatic and -20 mV for sterically stabilized
nanoparticles is desirable for physically stable suspensions.
Determination of drug content
The drug content of the samples was checked by UV & other spectrophotometer to confirm the
purity of the prepared samples. For quantitative determination of drug content in formulations
aqueous dispersions of formulations were passed through 0.8 <m filter. The concentration of drug
was determined spectrophotometrically at a specific nm. The amount of drug in filtrate relative to
the total amount of drug in the dispersion was calculated and expressed as nanocrystal yield.
Saturation Solubility:
Saturation solubility was measured through UV absorbance determination at their corresponding
nanometre range using an UV-Visible spectrophotometer.
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Dissolution characteristics: Dissolution studies were performed using Paddle, basket (USP30) and
film dialysis method. Phosphate buffer of pH ranging in between 6-7 was selected as the testing
media. Test preparations were added to 900 ml of the dissolution medium which was maintained at a
temperature of 37 ± 0.5 ºC. Automatic withdrawals at fixed times were filtered in line and assayed
through UV absorbance determination at specific nanometric range.
Surface hydrophilicity/hydrophobicity
In vivo behaviour of the drug depends on organ distribution, which in turn depends on its surface
properties such as hydrophibicity and interactions with plasma proteins. Hydrophobic interaction
chromatography is able to evaluate the surface hydrophobicity of nanocrystals.
Crystalline state
Evaluation of crystalline character is performed by using Differential scanning calorimetry (DSC)
and X-ray diffraction analysis (XRD) techniques. These are required to ensure that crystallinity of
the drug has been retained upon nanonization because fabrication procedures may alter the
polymorphic state of the drug. For instance high pressure homogenization may generate nanocrystals
with amorphous fraction. may be used to evaluate the polymorphic state.
Stability studies
The polydispersity index (PDI) is an important index of physical stability of the nanocrystal. PDI
values vary between 0 (monodisperse particles) to 1 (broad distribution), however lower values
(.0.3) are usually more appreciable for long-term stability of the nanosuspension.
All the formulations were subjected to stability study as per ICH guidelines the formulations were
divided into two parts and stored at 300 ± 2
0 C and 65% ± 5% RH and 40
0 ± 2
0 C and 70% ± 5% RH.
FORMULATION OF NANOCRYSTAL DOSAGE FORMS
Nanocrystallization is a method in which drug nanocrystals are composed of 100% drug there is no
carrier material as in polymeric nano-particles. Dispersion of the drug nan ocrystal in liquid media
leads to so called ―nanosuspension‖ . Nanocrystal technology can be used to formulate and improve
compound activity and final product characteristics of poorly water-soluble compounds.
Nanocrystals are formulated into all oral and parentral dosage forms including solid, liquid, fast
melt, pulsed release and controlled release dosage forms28
.
Table 3. Currently available nanocrystal formulation products in the market is listed in the
following table29
Product Drug Company
Megace ES Megestrol acetate Par pharm
Rapamune Sirolimus Wyeth
Emend Aprepitant Merck
Tricor Fenofibrate Abbott
Triglide Fenofibrate SkyePharma/FirstHorizon pharmaceuticals
Invega sustenna Paliperiodne palmitate Johnson and Johnson
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Focalin XR DexmethylphenidateHCl Novartis
Ritalin LA Methylphenidate HCl Novartis
Zanaflex Capsule TizanidineHCl Acorda
Avinza Morphine sulphate King Pharmaceuticals
CLINICAL APPLICATIONS OF NANOCRYSTALS:
Clinical application of drug nanocrystals is explained by giving the various route of administrations.
•Oral Administration
Being the most preferred route of administration, the formulation of drug nanocrystals can increase
the solubility and bioavailability of per-orally administered poorly water soluble drugs.
Nanosuspension methods on Danazol and found an increase of bioavailability from 5.1 ± 1.9% for
conventional suspension to 82.3 ± 10.1% for nanosuspension30
. Naproxen, which is an example of
an analgesic drug, has also been formulated as a nanosuspension. Its nanosuspension showed
threefold increase in AUC and a decrease in t-max as compared to the conventional suspension
(Naprosyn®)31
. Along with that, reduced gastric irritancy and a faster onset of action has also been
reported. Some other authors reported that increase in bioavailability for noncrystalline aprepitant
(MK-0869) the active ingredient in Emend®, in beagle dogs and prepared mucoadhesive
nanosuspensions for bupravaquone32
.
• Parentral Administration:
In a carrier-free nanosuspension approach, high drug loading is achieved. Also, the volume of
injection can be decreased to a large extent 33
. Various toxic side effects occurring for the poorly
soluble drugs when administered via the parentral route can be overcome by this approach. They can
be prepared using surfactants and polymeric stabilizers in accepted range for i.v injection. But high
cosolvents and surfactant contents are used in other approaches which cause unwanted side effects
e.g. Cremophor EL in Taxol . Intravenous injectable and chemically stable aqueous omeprazole
nanosuspension formation were developed by Moschwitzer and co-workers34
. Production, no drug
loss or discolouration occurred even after formulating at 0˚C. Hence,it can be proved that production
by nanosuspensions high pressure homogenization is suitable for increasing drug bioavailability and
preventing labile drugs degradation.
• Pulmonary Drug Delivery
Nanosuspension drug delivery for important corticosteroids such as beclamethasone dipropionate
and budesonide for local and systemic treatment of many respiratory diseases proved helpful.
Nebulized nanosuspension is given. An increase in mucoadhesiveness was achieved35
. An increase
in mucoadhesiveness was achieved causing an increase in the residence time at the mucosal surface
of the lung. Physically stable nanosuspension of bupravaquone were prepared which delivered the
drug at the site of action. It was used to treat Pneumonia.
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• Dermal Drug Delivery
If conventional nanocrystals fail, then dermal nanosuspensions come into play. They lead to an
increased concentration gradient between skin and the formulation. This increased saturation
solubility leads to supersaturated formulations and hence, drug absorption through skin also
increases. Positively charged polymers, used as stabilizers for drug nanocrystals, can be used to
enhance the effects. Since the stratum corneum is negatively charged, hence the positively charged
polymers increase the affinity (unpublished data).
• Ophthalmic Drug Delivery
Due to their adhesive properties, nanoparticles have prolonged residence time in the eye. Hence,
nanosuspension formulation for poorly soluble drug for eye diseases was a good option.
Modification of the quasi-emulsion solvent diffusion technique was used and some formulation
parameters were varied such as total drug and polymer amount, drug-polymer ratio and stirring
speed. The mean size of the nanosuspension was around 100 nm and zeta potential of ±40/±60 mV.
This makes them suitable for ophthalmic drug delivery. Rabbit eye was used for the in vivo studies.
Ocular trauma (paracentesis) was induced in rabbit eye. Mitotic response inhibition to the surgical
trauma was achieved and it was comparable to an aqueous eye drop formulation used as a control. In
the aqueous humour, drug levels were higher from the nanosuspension and no toxicity on the ocular
tissues was noted 36
.
•Targeted Drug Delivery
As the surface properties of the nanosuspensions and changing the stabilizer can easily alter in vivo
behaviour, they can be easily used for targeted drug delivery. They have ease of scale up and
commercial production and their versatility enables the development of commercially viable
nanosuspensions which can be used for targeted drug delivery. When macrophages are not the
desired targets, the natural targeting process could pose numerous hurdles. Hence, the surface
potential needs to be altered in order to bypass the phagocytic uptake of drugs. The formulation of
aphidicolin was developed as a nanosuspension for improving the drug targeting effect against
Leishmania-infected macrophages37
. It was concluded that aphidicolin was highly active at a
concentration in the microgram range . The peptide dalargin was successfully targeted to brain by
employing surface modified polyisobutyl cyanoacrylate. To conclude, nanosuspensions are an
effective means of administering poorly soluble drugs to brain with a potential reduction of the side-
effects.
CONCLUSION:
The use of drug nanocrystals is found to be a universal formulation approach to increase the
therapeutic performance of BCS II drugs in any route of administration. Nanocrystal formulation of
poorly aqueous soluble drugs shows a significant increase in the solubility and dissolution
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characteristics. These new technologies are designed to produce final dosage forms with higher
drug loadings, better redispersability at their site of action and an improved drug targeting. Overall,
it was confirmed that nanocrystallization is a promising novel solubility enhancement technique for
poorly water soluble drugs.
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