NANOCRYSTALLIZATION: A NOVEL SOLUBILITY …. RPA131400222014.pdfNANOCRYSTALLIZATION: A NOVEL SOLUBILITY ENHANCEMENT TECHNOLOGY FOR POORLY WATER SOLUBLE DRUGS T. SUDHAMANI *, K. ABOOBAKKARSIDHIQ,

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

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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:

[email protected]

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.

mailto:[email protected]

- 540 - | P a g e International Standard Serial Number (ISSN): 2319-8141


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



• 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).



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.



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



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.



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.



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

.



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



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



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



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.



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



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.



• 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



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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NANOCRYSTALLIZATION: A NOVEL SOLUBILITY …. RPA131400222014.pdfNANOCRYSTALLIZATION: A NOVEL SOLUBILITY ENHANCEMENT TECHNOLOGY FOR POORLY WATER SOLUBLE DRUGS T. SUDHAMANI *, K. ABOOBAKKARSIDHIQ,