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INTERNATIONAL JOURNAL OF REVIEW ARTICLE PHARMACEUTICAL INNOVATIONS ISSN 2249-1031

19 | P a g e Volume 3, Issue 6, November ₋ December 2013 http://www.ijpi.org

A REVIEW ON SOLID ORAL DOSAGE FORM OF ANTIEPILEPTIC DRUGS

BY PELLETIZATION TECHNIQUES Kundu Subrata*1, Srinivasan Ganga2

1Shri JJT University, Rajasthan 2Vivekananda College of Pharmacy, Mumbai University

ABSTRACT:

Epilepsy is one of the severe diseases and it has wide scope in research. Various Antiepileptic

drugs are available in market in the form of Tablet, Capsule, Solution, Suspension, Gel etc.

Whereas, the Multiple unit dosage form manufactured by Pelletization technique gain a lot of

popularity due to its advantages like increased surface area and dissolution, easy to fill in

capsule, higher distribution in GI track, and flow of pellets. Pelletization is the growing

technique in pharmaceutical field. Most of the drugs are now a day available in pellet forms.

The current review focuses on Pelletization technique, coating of these pellets and the release

of the drug from these coated pellets. Brief focus on different types of release patterns such as

immediate release, sustained release, extended release, controlled release are mentioned.

Need of Pelletization in formulation of antiepileptic drugs is also discussed. Coating of the

pellets can be done in the fluidized bed processor and different parameters are discussed like

Polymeric particle size, Film-forming temperature, Plasticizer, Blend polymer, Hydration of

polymer, Properties of the core surface and other parameters like spray rate, product

temperature, Atomization pressure etc. Also the theories of film formation like Wet sintering

theory, Capillary pressure theory, sintering theory are discussed. Mechanism of drug release

from the coated pellets is described.

Key words: Antiepileptic drugs, Pelletization, Multiparticulate.

INTRODUCTION:

Epilepsy, a disease that has been in

existence for ages, continues to affect

approximately 50 million individuals

worldwide. The disease is often

accompanied by neurobiological,

cognitive, psychological, and behavioral

changes that may heighten susceptibility to

seizures and affect quality of life.

Anti-epileptic drugs (AEDs) are the

primary option for the management of

epilepsy. Anti-epileptic drugs (AEDs) are

also known as the anticonvulsant drugs or

anti seizure drugs. Now a day’s new drugs

are developed to treat the epilepsy as well

as the existing drugs are designed in novel

forms like pellets filled in capsule etc.

Dosage Forms of Antiepileptic Drugs:

Various drugs are available for the

treatment of epilepsy. Specific use of a

drug in treatment of epilepsy is not

possible it depends upon the type of

Corresponding Author*

Kunda Subrata



epilepsy, drug properties and also on the

patient compliance [1, 2]

. Various dosage

form available for different antiepileptic

drugs are summarized in table 1.

Table 1: Dosage Forms of Antiepileptic Drugs

Tablet Capsule Injectable Suspension Solution Gel

Acetazolamide Acetazolamide Acetazolamide Carbamazepine Gabapentin Diazepam

Carbamazepine Carbamazepine Diazepam Felbamate Oxcarbazepine

Clonazepam Clorazepate Lorazepam Phenytoin Valproic acid

Clorazepate Divalproex

Diazepam Ethosuximide

Divalproex Gabapentin

Ethosuximide Phenytoin

Felbamate Pregabalin

Gabapentin Topiramate

Oxcarbazepine Valproic acid

Lamotrigine Zonisamide

Phenytoin

Primidone

Tiagabine

Topiramate

Trimethadione

Pharmacokinetics:

Antiepileptic drugs are slightly soluble and

exert good absorption i.e. 80-100% of drug

reaching to the circulation. All drugs have

penetration in to CNS. So they are

administered by oral route [3]

.

Mechanism of Action:

Mechanism of various antiepileptic drugs

is schematically mentioned in the

following figure- 1[4]

;



Figure 1: Mechanism of various antiepileptic drugs

DIFFERENT RELEASE PATTERN

FOR ORAL SOLID DOSAGE FORMS:

Various antiepileptic drugs are available

with different release profile. Immediate

release dosage forms are either uncoated or

coated with immediate release film

forming polymers. Modified release

(delayed, extended, sustained and/or

extended release) dosage forms are either

matrix based and/ or coating based with

dissolution rate controlling hydrophilic or

hydrophobic polymers. Based on the

pharmacodynamic and pharmacokinetic

Properties of the Antiepileptic drugs,

dosage form design are decided.

Advantages of Extended release

products:

1. Maintain therapeutic concentrations.

2. Avoids the high blood concentration.

3. Extended release formulations have the

potential to improve the patient

compliance.

4. Drug absorption is slower so it reduces

the toxicity.

5. Protect the drug from hydrolysis or

other degradative changes in

gastrointestinal tract.

6. Minimize the local and systemic side

effects.

7. Improvement in treatment efficacy.

8. Minimize drug accumulation with

chronic dosing.

9. Improve the bioavailability of some

drugs.

Disadvantages of Extended release

products:

1. Expensive in preparation.



2. The release rates are varied by various

factors such as food and the rate of

transit through the gut.

3. Some differences in the release rate

from one dose to another dose.

4. Extended release formulation contains a

higher drug load and thus any loss of

integrity of the release characteristics of

the dosage form.

5. Sometimes the target tissue will be

exposed to constant amount of drug

over extended period results in drug

tolerance.

WHAT IS PELLETS?

In pharmaceutical application, an

agglomeration process that results in

agglomerates of a rather wide size

distribution within the range of 0.1 – 2.0

mm, with a high intra-agglomerate

porosity (about 20 – 50 %) is named a

granulation process, and the agglomerates

are called granules.

If the final agglomerates are spherical, free

flowing, and of a narrow size distribution

in the size range of 0.5 – 2.0 mm, and a

low intra-agglomerate porosity (about 10

%), the process is often referred to as

pelletization process, the agglomerates are

called pellets.

Advantages:

Pellets can disperse freely

throughout an area of the

gastrointestinal tract after

administration and consequently

the drug absorption is maximized

as a large gastrointestinal surface

can be involved in this process.

Peak plasma level of the drug can

be reduced by the use of spherical

particles with different release

rates; potential side effects are

minimized without markedly

lowering drug bioavailability;

The wide distribution of spherical

particles in the gastrointestinal tract

limits localized build-up of the

drug, avoiding the irritation effect

of some drugs on the gastric

mucosa;

Modified-release multiparticulates

delivery systems are less

susceptible to dose dumping than

single-unit dosage forms.

Disadvantages:

Often pellets cannot be pressed into

tablets because they are too rigid.

In that case, pellets have to be

encapsulated into capsules [5]

.

The production of pellets is often

an expensive process and / or

requires highly specialized

equipment.

The control of the production

process is difficult (e.g. the amount

of water to be added is critical for

the quality of the pellets and over

wetting can occur very easily).

REASONS FOR PELLETIZATION

Pelletization is very important area of

interest in pharmaceutical industry due to

various reasons:

Prevention of segregation of co-

agglomerated components,

resulting in an improvement of the

uniformity of the content;

Prevention of dust formation,

resulting in an improvement of the

process safety, as fine powders can

cause dust explosions and the



respiration of fines can cause

health problems;

Increasing bulk density and

decreasing bulk volume;

The defined shape and weight

improves the appearance of the

product;

Improvement of the handling

properties, due to the free-fl owing

properties;

Improvement of the hardness and

friability of pellets;

Controlled release application of

pellets due to the ideal low surface

area-to-volume ratio that provides

an ideal shape for the application of

film coatings.

All these aspects can be considered as

technological advantages of pelletization.

METHODS OF PELLETIZATION:

Pelletization involves the agglomeration of

active pharmaceutical ingredients and

excipients in spherical beads called pellets.

Variety of techniques is available for pellet

manufacturing [6]

.

Powder layering

Solution/Suspension layering

Extrusion-Spheronization

Spherical agglomeration or Balling

Spray congealing/Drying

Cryo Pelletization

Melt spheronization

Freeze Pelletization

Hot melt extrusion

THEORY – PELLET FORMATION

AND GROWTH:

It is necessary to understand the formation

and growth of pellets before selecting the

pelletization procedure. Numbers of

theories are available for the mechanism of

growth and formation of pellets. Some of

them are derived from research while

others are postulated from visual

observations [7, 8]

.

Pelletization process mainly involves 3

steps:

Nucleation

Transition

Ball growth

But based on experiments on the

pelletization technique steps proposed are

Nucleation, coalescence, layering &

abrasion transfer.

Figure 2: Pelletization process



COATING OF

MULTIPARTICULATES:

Mainly the coating of pellets can be done

by polymeric solutions as well as

polymeric dispersion. In such type of

coating the mechanism in film formation is

the critical step.

MECHANISM OF FILM

FORMATION:

Coating is achieved mainly by spraying

and drying process of the dispersion which

is composed of three phases: gas phase,

aqueous phase, and polymeric particles.

Water is evaporated leaving the polymeric

solid. These residual solid composed of

discrete particle, become a homogenous

film.

Muroi[9]

reviewed many proposed theory

for film formation and its application in

pharmaceuticals was discussed by

Lehmann[10]

and Steuernagel [11]

. Fusion

and film formation of polymeric particles

can be explained by following theories:

Wet sintering theory[12]

Capillary pressure theory[13]

Dry sintering theory[14,15]

FORMULATION AND PROCESSING

FACTORS

[A] Polymeric particle size:

The film formation is stronger with

decreased size of polymer and difficult

film formation from large size dispersion

polymer. Latexes and pseudo latexes are

easier for film formation due to its

submicron size. Nakagami et al[16]

reported

effect of particle size on film formation of

2-methyl-5-vinyl-pyridine-methylacrylate-

methacrylic acid copolymer suspension

and observed film formation from

polymeric particles.

[B] Film-forming temperature:-

Polymers are deformable above Ts which

is necessary for film formation. The

softening of polymer films is related to

glass transition of polymer. And both

correspond to sharp increase in polymer

chain mobility[17]

. Amer et al[18]

reported

relation between Tg and bed temperature.

They concluded that when coating is done

at 10ᵒC or less above the Tg the film

formation was certain but such operation

may lead to agglomeration which is

minimized by dusting powder directly into

the coating chamber.

[C] Plasticizer:-

Plasticizer is used to decrease Ts and Tg

values. The degree of decrease in Ts

depends on the plasticizer concentration

and physiochemical properties of

plasticizer. In order to promote polymer

mobility and flexibility plasticizer must be

compatible with the polymer.

Toyoshima[19]

evaluated the capacity of

plasticizer to break the bond between

molecules by dissolving temperature of the

polymer in plasticizer and interaction force

between polymer and plasticizer molecules

by the cloud point (CP).

[D] Blend polymer:-

Blending of polymer is done to adjust the

softening temperature of the polymer. For

example: Eudragit NE30D has low Ts at

18°C and is blended with Eudragit RS30D.

Upto 40% of Eudragit NE30D, there is

slight decrease in temperature but above

40% of NE30D there is drastic change in

temperature. The blend of Eudragit RS30D

/ Eudragit NE30D are in the ratio of 2:3

with Ts of 53ᵒC. Release profile of this



blend was very fast indicating poor film

formation.

[E] Hydration of polymer:-

For excellent film formation hydration of

polymer is important apart from polymer

particle size. For example: Eudragit L30

D55 shows excellent film forming ability

due to its small size and also it contains

hydrophilic methacrylate (MA) of 50% as

the molar fraction of monomer[20]

. The

hydrogen bond between the polymer and

pendent ester can be broken by water

molecules and hydration causes lowering

of mechanical strength of particle and

polymer particle to deform. Hydrogen

bond between water and carboxyl groups

act as driving force for film formation.

[F] Properties of the core surface:-

Core used must be porous granules.

Protiman and Brown et al[21]

reported that

application of an aqueous dispersion of

Copolymer of ethyl acrylate-methyl

methacrylate (EA-MMA) to porous

surface resulted in higher minimum flim

forming temperature (MFT) values which

indicates lesser period for capillary

pressure to act due to water penetration

resulted in incomplete film formation.

Since most drugs are surface active they

migrate from core to film layer which

decreases the capillary pressure (driving

force for film formation). Yang and

Ghebre-Sellassie reported this problem [22]

resulted in poor film former. Migration of

drug can be avoided by slow coating at

initial stage or seal coating of cores.

[G] Additives:-

Solid additives that are insoluble in water

are used as pigments (TiO2, food dyes) in

coloring the coating, membrane diluents to

thicken the membrane, example: talc or

magnesim stearate [23]

and also act as

antiadherent, anticoagulant used to

separate interactive polymeric particle and

avoid coagulation. The fumed silica in

surelease formulation and oily acetylated

monoglyceride in aquateric formulation act

as antiadherent and anticoagulant

respectively. Small amount of additives

suppress membrane permeability but

excessive additives result in discontinuous

film structure [24, 25]

.

[H] Coating of fine powders:-

Preparation of multiparticulate dosage

form by spray coating process, resulting of

agglomeration problem especially with

fine powder. In fine powder case the

interparticulate bridge of membrane

material is formed leading agglomeration

[26]. This interparticulate bridge need to be

separated in order to avoid agglomeration

but conventional top sprayed fluidized bed

usually cannot generate that much strength

to separate this bridge, so Wurster process

which is best suited for fine powder

coating is used where particles smaller

than 100µm may be coated discretely, and

smallest size particle that can be coated by

Wurster process depends on the binding

strength of membrane material. The

condition that is maintained in Wurster

process for fine powder is: the mass

median diameter is kept at 12µm at spray

pressure of 2.3 atm and a spray rate of

4ml/min. This is the spray condition with a

pneumatic nozzle can normally be used. In

aqueous produces intense separation of

particles due to the collision of particles

against the partition. Brittle crystals are

easily fractured and even lactose crystal

becomes roundish [27]

.



APPROACHES TO FORMULATING

COATING SOLUTION

Advantage of film coating is to modifying

the release characteristic of drug from a

dosage form. Approaches to formulate

modified release coating are:

Film – forming material dissolved

in organic solvent.

Aqueous polymer dispersion.

Hot melts.

Table 2: List of Process variables in film coating

Variables Has influence on :

Coating equipment

Coating dispersion solids content

Spray rate

Atomizing air pressure / volume

Quantity of coating applied

Drying conditions (air volume, temperature,

and humidity)

With organic solvent-based solutions

With aqueous polymeric dispersions.

Quality and functionality of coating

Economics

Membrane structure

Uniformity of distribution of coating

Processing costs

Membrane structure


Processing costs

Membrane structure


Drug release rate


Processing costs

Membrane structure

Drug release rate

Coalescence of film

Drug leaching

Tackiness of the coating

Drug release rate

MECHANISM OF DRUG RELEASE

FROM COATED PELLETS:

Pellets are coated with the various

polymers which are insoluble in GI track

as well as soluble in GI track. Here we will

focus on mechanism of release to predict

the in vivo behaviour of the pellet dosage

form. The major mechanism by which

drug is release in pellets dosage form

depends on the type of coating material

and method of coating. Kinetics of release

depends on the solubility behaviour of

coating material in GI condition and core

formation. Behaviour is classified

according to three general types:



(1) Coating is insoluble in all

physiologically relevant conditions.

(2) Solubility changes at some point in GI

tract.

(3) Coating slowly erodible under GI

condition.

1. Coating is insoluble in all

physiologically relevant conditions:

[A] Solution / diffusion through the

continuous plasticized polymer phase:-

The mechanism assumes that polymers

forms continuous phase with the

plasticizer and additives are homogenously

dispersed. Diffusion of solute within

amorphous polymer phase involves co-

operative movement of drug and polymer

chain segment around it [28]

. Thermal

fluctuation between adjacent chains

permits the passage of a drug. Another

mechanism of release is configurational

diffusion. Frequency of diffusion of drug

depends on (i) size and shape of drug, (ii)

force of attraction between adjacent

polymer chain, and (iii) stiffness of

polymer chains. In general if the film is

continuous i.e. lacks pores and flexible and

drug has high affinity for polymer relative

to water, promote the diffusion mechanism

of release.

[B] Solution / Diffusion through

plasticizer channels:-

When plasticizer is uniformly distributed

and is in high concentration then it forms a

continuous phase in the form of patches

channels. Diffusitivity in plasticizer is

lower than in water as it is more viscous

than water. Ozturk et al[29]

estimated K

value from solubility ratio to the

distribution coefficient for

phenylpropanolamine HCl between water

and four plasticizer and K value ranges

from 1.694 / 40 for triacetin to 3.954 / 40

for Myvacet, which suggested that this

mechanism is too slow to explain the

release rate observed.

[C] Diffusion through aqueous pores:

This coating is not homogenous and

continuous but is provided with pores.

These pores are filled with solution when

it comes in contact with aqueous medium,

thus facilitating diffusion of drug. This

mechanism is seen in coating done with

aqueous dispersion as pseudo-latexes than

organic solvent as pseudo-latexes particles

do not fuse completely, thus creating pores

in the coating.

[D] Osmotically driven release:

When the coating is porous, release of

drug may be due to osmotic difference

between the core materials and release

environment source of osmotic pressure in

core formulation include low molecular

weight excipients (example: the sugar

constituting Nu – Pareil seeds) and the

drug. Drug released through osmotic

pressure must be highly water soluble and

must be of low molecular weight.

Osmotically driven release act when

pellets come in contact with water it

imbibes water to the core drug and

excipients get dissolved in water

generating interior osmotic pressure. The

osmotic pressure difference between the

core and external medium provides force

to efflux through pores in the coating.

2. Solubility changes at some point in

GI tract.

Coating which are pH sensitive have

increased solubility at some point in the GI

tract which is used to prevent release in the



stomach but complete release in the

intestine. The pH difference is about 5 pH

units[30]

between stomach and small

intestine at fasted state but it is reduced

when food is ingested as gastric fluid

become buffered with food. Thus narrow

range is provided over which the coating

solubility must change. Achieving release

in colon is difficult as compared to small

intestine, as the pH difference between

ileum and proximal colon is much less

than between stomach and small intestine.

3. Bioerodible coating:-

To achieve prolong release using enteric-

coating one can employ heterogenous

coating such as shellac [31]

. Acidic nature

of hydrolysate explains enteric properties

of shellac coatings, while the heterogeneity

of composition explains prolong release of

drug. Triglycerides and ether wax / fat is

also utilized as coating to provide prolong

drug release and their digestion and

dissolution is facilitated by lipase released

in pancreatic juice and by bile salts. To

predict invivo release from invitro

experiments, incorporate physiological

amount of pancreatin and bile salts in

release media. High degree of colonization

of colon by bacteria favours designing of

site-specific release to colon [32]

. This is

used for treating inflammatory bowel

disease as high concentration of the drug is

achieved in local tissue. The

Azoreductases is used in colon- specific

delivery and studies are going on use of

glycosidic linkage. In bioerodible coating,

the polymer includes catalyst like

polyorthoesters to speeden the release as

bioerodible polymer alone erode too

slowly in GI tract. By adding phthalic

anhydride in the polyorthoester matrix,

surface erosion mechanism is achieved

resulting in zero- order release because

rate of water penetration into the polymer

becomes the rate limiting step of its

erosion. The advantage of this type of

design is three folds:

1. Release relatively independent of

GI condition.

2. Manipulating release rate by

modifying the level of catalyst

used. And

3. Complete release is possible if

polymer degrade completely

within GI transit time.

Example: Cyclobenzaprine HCl

formulation, produce release over a period

of 10 to 15 hours. This design for short –

term release formulation has been

discussed by Heller et al [33]

.

Marketed Examples of sustained release

antiepileptic drugs:

1. Formulation of Topiramate pellets

(Patent No. – US 8,298,580,B2 ):

Sugar spheres are used in the

formulation of Topiramate pellets. It

is one of the extended release type

dosage form. In this the spheres were

firstly seal coated then the drug

layering is done by using fluidized

bed processor. Then pellets were

subjected for rate controlling layer

coating using polymers like ethyl

cellulose, methylcellulose at level of

2-4% coating. This formulation

reduces the adverse effects related to

the CNS which are shown by

immediate release dosage form of

Topiramate [34]

.

2. Formulation of Carbamazepine

Pellets: (US 2007/0071819 A1)



Extended release formulation

containing carbamazepine is

formulated by blending

carbamazepine with rate controlling

polymer and pharmaceutically

acceptable excipients by granulation

followed by sieving, extrusion and

marumerization or spheronization,

pelletization, micropelletization etc.

Then these pellets coated with

enteric polymer using fluid bed

processor. The rate controlling

polymers include cellulose

derivatives, starch, PVP, alginates,

acrylic acids. Suitable enteric

polymer such as cellulose acetate

phthalate, cellulose acetate

trimellitate, HPMC phthalate acetate,

HPMC acetate succinate,

Methacrylic acid copolymer such as

Eudragit L100-55, D-55 etc. These

pellets were filled in capsule. The

resultant capsule show its release in

intestine it will not show its release

in stomach[35]

.

3. Formulation of Acetazolamide

Pellets: (EP 0540 813 B1)

In this patent the Acetazolamide

Pellets were prepared by the

Extrusion Spheronization method.

Acetazolamide itself act as a binder

so binder free pellets were prepared

and then these pellets were coated

with rate controlling membrane.

Rate controlling membrane consists

of polymers like ethyl cellulose,

waxes etc. and MCC as a moisture

controlling agent. Acetazolamide

containing pellets can be filled into

soft or hard gelatin capsules

otherwise presented in a unit dosage

form [36]

.

Table 3: Composition of Pellet Core

Ingedient % Composition, dry basis

Acetazolamide 80.0

MCC 19.94

SLS 0.06

Table 4: Composition of Coated Pellets

Ingredients % Composition, Dry basis

Acetazolamide Pellets 94.52

Ethylcellulose(100 cps) 0.72

HPC (6 cps) 2.86

Mineral oil 0.41

Colorant 1.46

CONCLUSION:

This short review on drug delivery of

antiepileptic drugs by pelletization

concludes that drug delivery using

multiple units like pellets in a single

dosage form is one of the novel concepts.



Major advantage of such system is that

drugs which degrade in gastric fluid can be

protected because pellets cannot be

stopped in stomach so it will not show

release in stomach. Such type of pellets

can be filled in capsule as well as

compressed in tablets. Extended release

dosage form show reduced side effects and

maintenance of drug in body for longer

time so the dosing frequency is also

reduced. Patient compliance and flexibility

is also there. Pelletization technique is now

a day very fast growing technique. Various

newer drugs administered by this

technique.

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