By micronization E. M. Atkinson et al reported reduction in the therapeutic dose of griseofulvin to the extent of 50% and it also produced a constant blood-level; Reduction in particle size also decreased the dose of spironolactone by 50% as reported by G.Levy.

The particle size reduction is usually carried out by:

 Ball-Milling

 Fluid energy Micronisation,

 Controlled precipitation while mixing different solvents at different temperature,

 Administration of liquid solutions which upon dilution precipitate the drug in very fine particles, and

 Administration of water-soluble salts of poorly soluble compounds from which the parent, neutral forms may precipitate in ultra fine forms in gastrointestinal fluids.2,3

In 1961, a new approach of solid-dispersion was devised and demonstrated by Sekiguchi and Obi. This provided a new approach to particle size reduction and increased rates of dissolution. Sekiguchi and Obi proposed the formation of a eutectic mixture of a poorly soluble drug such as Sulphathiasole with a physiologically inert, easily soluble carrier such as Urea. The method involves the preparation of a microcrystalline or molecular dispersion of the drug in a solid-matrix of water soluble physiologically inert carrier like urea. The melted Sulphathiasole and urea was followed by rapid solidification. The fine dispersion of the drug in the solid eutectic mixture and the rapid dissolution of the soluble. The bioavailability of a poorly water-soluble drug is often limited by its dissolution rate, which is in turn controlled by the surface area available for dissolution. The effect of particle size of a drug on its dissolution rate and its biologic activity is well known. Atkinson and associates reported that the therapeutic dose of griseofulvin was reduced by half after micronization. A more constant and reliable blood level profile was also obtained.4 The conventional methods for reducing particle size include trituration and grinding, ball milling, fluid energy micronization and controlled precipitation Alternately, micronized particle formation may be accomplished in situ by one the two following techniques:

(1) Liquid solutions using nonaqueous solvents could be administered from which, upon dilution with gastric fluids, the dissolved drug may precipitate in very fine particles; or

(2) Water-soluble salts of poorly soluble drugs could be administered from which the parent drug may precipitate in ultrafine form in gastrointestinal fluids. Althoughreduction in particle size can be easily and directly accomplished by the first four methods; the anticipated increase in availabity may not be achieved.5 This has been attributed to aggregation and agglomeration or air adsorption, which may result in poor powder wettability that reduces the effective surface area.6

Coprecipitates and melts are solid dispersions that provide a means of reducing particle size to the molecular level. The concept of using solid dispersions to improve bioavailability of poorly water-soluble drugs was first introduced by Sekiguchi and Obi in 1961. They demonstrated that the eutectic of sulfathiazole and physiologically inert water-soluble carrier urea exhibited higher absorption and excretion after oral administration than sulfathiazole alone. Recent work on dispersions has been extended to the development of sustained-release preparations.7

Table1.1 Important pharmacokinetic parameter of allopurinol

Half life	1 to 3 hours
Bioavailability	67 +/- 23%
Protein Binding	Negligible
Metabolism	Hepatic (80% Oxypurinol, 10% Allopurinol Ribosides)
Elimination	Biliary and renal
Food	Minimal/Not significant

EXPERIMENTAL METHODOLOGY:

(1) Preparation of Calibratioin curve of drug:

A] Calibration curve of drug in 0.1N HCL:

Allopurinol (100 mg) was dissolved in 100 ml 0.1N HCL and volume was made up to 100 ml in volumetric flask using 0.1N HCL.sonicate for 30 min.filter the solution. From this stock solution 10 ml solution was withdrawn and diluted up to 100 ml in volumetric flask. Same way solution of 5, 10, 15, 20, 25, 30, 35, 40 m/ml was prepared. Absorption of each solution was measured at 250 nm using shimadzu UV-1700 UV/Vis double beam spectrophotometer and 0.1N HCL as a reference standard.

B] Calibration curve of drug in dist.water:

Allopurinol (100 mg) was dissolved in 100 ml dist.water by use of gentle sonicator for 30 min. and volume was made up to 100 ml in volumetric flask using dist.water. From this stock solution 10 ml solution was withdrawn and diluted up to 100 ml in volumetric flask. Same way solution of 5, 10, 15, 20, 25, 30, 35, 40 m/ml was prepared. Absorption of each solution was measured at 250 nm using shimadzu UV-1700 UV/Vis double beam spectrophotometer and dist.water as a reference standard.

(2) Drug excipients interaction study:

DIFFERENTIAL SCANNING COLORIMETRY (DSC): Drug- excipients interactions play a vital role with respect to release of drug from the formulation. The DSC measurements were performed on a DSC-Shimadzu DSC-60, C304544differential scanning calorimeter with a thermal analyzer. All accurately weighed samples (about 1 mg of allopurinol were placed in sealed aluminum pans, before heating under nitrogen flow (20 mL/min) at a scanning rate of 100C min-1 from 25°C to 3500C.An empty aluminum pan was used as reference.8

INFRA RED SPECTROSCOPY STUDIES (IR):

The FTIR spectra were obtained by using an FTIR spectrometer- BL22OH. The samples (allopurinol or SDs) were previously ground and mixed thoroughly with potassium bromide, an infrared transparent matrix, at 1:1 (sample: KBr) ratio, respectively. The KBr discs were prepared by compressing the powders at a pressure of 5 tons for 5 min in a hydraulic press. Thirty scans were obtained at a resolution of 2 cm-1, from 4500 to 400 cm1.differantfivesample (allopurinol, PVPK30, Poloxamer127, PEG4000, Allopurinol+PVPK30, allopurinol+poloxamer127, Allopurinol+PEG4000 were performed for IR.9

(3) PREPARATION SOLID DISPERSION METHOD

Melt method:

In solid dispersion preparation containing different ratios of allopurinol in PEG4000 (1:1,1:2,1:3)were prepared in melting method allopurinol was added to melted PEG4000 at 75°C and resulting homogeneous preparation was rapidly cooled in freeze.susequently the dispersion was ground in mortar and sieved through a 80 # sieve and stored in a screw-cap vial at room temperature until further use.10

Solvent evaporation: Allopurinol: PVPK30 and PEG4000 solid dispersion:

Allopruinol in PEG4000 and PVPK30 containing different weigh ratios (1:1,1:2,1:3) respectively were prepared by solvent evaporation method.

To solution of allopurinol in ethanol, an appropriate amount of PEG4000 and PVPK30 was added. the solvent was evaporate under reduce pressure at 50°C .Solid product was sieved through 80# and stored in a screw-cap vial at room temperature until further use.

(4) Evaluation techniques:

FLOW PROPERTIES:

Bulk density, tapped density, angle of repose, Carr’s index, housener ratios are important parameter for flow property of powder.

In bulk density and tapped density, powders fill in measuring cylinder and calculate by equation. After 50 tapped of cylinder calculate the tapped density. Carr’s index and housner ratios also important for compressibility and flow property measure by equation.11

IN VITRO DISSOLUTION:

Dissolution studies of allopurinol in powder form, SDs and physical mixtures were Performed by using the U.S. Pharmacopoeia (USP) model Dissolution Test Apparatus 6 Bowl at the basket rotation speed of 50 rpm 900 mL 0.1N HCL containing 0.25% (w/v) of SLS, 0.1 N HCl as a dissolution media at 37°C + 0.5°C. The SD or physical mixture equivalent to 100 mg of allopurinol was weighed using digital balance and add, into basket and wrap with muslin cloth and dip in the dissolution medium. At the specified time (every 10 min for 1 h), 10 mL samples were withdraw and filter through Whatman filter and then assayed for allopurinol content by measuring the absorbance at 250 nm using the UV-Visible spectrophotometer. Fresh medium (10 mL), which was pre warmed at 37°C, was replaced immediately into the dissolution medium after each sampling maintain its constant volume throughout the test. Dissolution studies were performed in triplicate (n=3), and calculated mean values of cumulative drug release were used while plotting the release curves. Previous tests determined that there was no change in the lambda max of allopurinol due to the presence of carrier dissolved in the dissolution medium.12

Concentration (mcg/ml)	abs
0	0
5	0.35
10	0.642
15	0.992
20	1.274
25	1.426
30	1.71

RESULTS AND DISCUSSION:

(1) Calibration Curve⁶

Calibration Curve of Allopurinol in 0.1N HCL at 250.0 nm

Equation of the line:

Absorbance = (0.0565 * Concentration) – 0.0655

Linearity was observed between 1-15mcg/mL.

Results of Weighted Regression:

Slope of the Regression line: 0.0565

Intercept of the Regression line : 0.0655

Calibration Curve of Allopurinol in dist.water at 250.0 nm

conc.(mcg/ml)	absorbance
0	0
2	0.178
3	0.228
4	0.31
5	0.376
6	0.498
7	0.576
8	0.604
9	0.66
10	0.8

Equation of the line:

Absorbance = (0.0769 * Concentration) – 0.0075

Linearity was observed between 1-10mcg/mL.

Results of Weighted Regression:

Slope of the Regression line: 0.0769

Intercept of the Regression line: 0.0075

Allopurinol

(2) Drug polymer interaction study:

Differential scanning colorimetry (DSC)3:

allopurinol+poloxamer

Allopurinol+pvpk30

Allopurinol+PEG4000

DISCUSSION:

Drug- excipients interactions play a vital role with respect to release of drug from the formulation amongst others. DSC curve obtained for pure allopurinol, allopurinol+ poloxamer127, allopurinol+PEG4000, allopurinol+PVPK30, shown in figure. Pure powdered allopurinol showing sharp melting endotherm at 386.17°C. DSC scan of allopurinol+poloxamer127 showed single broad endotherm at 372.14°C due to melting. DSC thermographs of allopurinol+poloxamer127showed melting peak of the polymer at 58.08°C and sharp endothermic peak of drug at 372.14°C. DSC spectra of allopurinol+PEG4000showed single broad endotherm at 380.14°C due to melting. DSC thermographs of allopurinol+PEG4000showed melting peak of the polymer at 62.72°C and sharp endothermic peak of drug at 380.14°C. DSC scan of allopurinol+PVPK30 showed single broad endotherm at 383.07°C due to melting.[10] DSC thermographs of allopurinol+ PVPK30showed melting peak of the polymer at 92.82°C and sharp endothermic peak of drug at 383.07°C. Presence all peak indicates that all ingredients are compatible with each other means there is no incompatibility of selected ingredients.13

INFRA RED SPECTROSCOPY STUDIES (IR)4:

Allopurinol

Allopurinol+PEG4000

Allopurinol+PVPK30

Allopurinol+Poloxamer127

DISCUSSION:

The characteristic peak of allourinol and other exiepient shown in given peak of solid dispersion, which indicate absence of any interaction between drug and carrier upon mixing them together with similar particle size. 16,17

(3) Flow property3:

Flow properties:	Solvent evaporation			Melting method
	(1:1)	(1:2)	(1:3)	(1:1)	(1:2)	(1:3)
Angle of repose	36.12	38.65	41.12	43.33	50.5	54.34
Tapped density	o.465	0.47	0.479	0.487	0.53	0.573
Bulk density	0.425	0.4	0.432	0.445	0.42	0.389
% carrs index	8.6	14.89	9.81	8.62	20.7	32.12
Hausner ratio	1.094	1.17	1.11	1.094	1.26	1.473

From above table we were observed that PVP K 30 had good flow property as well as good compressibility. Which has angle of repose 38.65 which is range within 30-40, in case of PEG4000 sticky product was obtain so, PVPK 30 was good in terms of solubility as well as flow properties. 18

Composition of Prepared Tablet from solid dispersion:

Ingredients (in mg)	(for 1 Tablet) Q.T.
Allopurinol:PVP	300
Lactose Monohydrate	q.s
Avicel (MCC)	10%, 15%, 17%.
Sodium Starch Glycolate	2%, 4%, 10%.
Cross carmalose sodium	1%, 5%, 7%.
Cross povidone	2%, 5%, 7%.
Magnesium Stearate	1%.
Talc	2%.
Weight of Tablet	500 mg

Optimize formula:

Ingredients (in mg)	(for 1 Tablet) Q.T.
Allopurinol:PVP	300
Lactose Monohydrate	q.s
Avicel (MCC)	10%
Sodium Starch Glycolate	4%
Magnesium Stearate	1%.
Talc	2%.
Weight of Tablet	500 mg

4) IN VITRO DISSOLUTION:

Determination of rate of release of pure allopurinol:

Time(min.)	% Drug release
0	0.00
15	25.96
30	45.37
45	57.02
60	69.43
90	86.12
120	86.73
150	87.98
180	88.59

Dissolution study of tablet solid dispersion:

Drug + PEG (1:2)

Time(min.)	Melting method	Solvent evaporation
0	0	0
15	67.45	72.12
30	73.45	77.65
45	81.11	80.8
60	89.78	93.2
90	95	97.43
120	97.11	99.8
150	98.8	100.3

Drug+ Poloxamer (1:2)

Time(min.)		Melting method	Solvent evaporation
0	0		0
15	76.43		81.23
30	89.4		87.5
45	95.43		96.9
60	98.78		99.43
90	99.5		100.4
120	100.23		100.2

Drug+ PVP K 30(1:2)

Time(min.)	Melting method	Solvent evaporation
0	0	0
15	89.98	99.1
30	93.45	99.5
45	97.23	100.3
60	100.2	100.1
90	100.1	0

PVPk30 which had good dissolution rate than other polymer. So prepared more drug: PVPK30 ratios (1:1, 1:3) by both mehod incuding solvent evaporation and melting.

Optimization of Drug Polymer Combination (Drug: PVP K30):

Time(min.)	Solvent evaporation		Melting method
Time(min.)	(1: 1)	(1:3)	(1: 1)	(1:3)
0	0	0	0	0
15	81.11	98.28	82.34	94.34
30	89.55	98.42	87.34	96.7
45	94.12	98.18	94.12	98.45
60	98.76	102.49	97.78	102.2
90	101.1		101.3	101.1
120	100.9

Comparison of drug: polymer ratio 1:2 and 1:3 solid dispersion prepared by solvent evaporation method

RESULT AND DISCUSSION:

We can increase solubility of poorly water soluble drug by different techniques. Among them solid dispersion method best method to enhance solubility of allopurinol drug. Based on above all the observation, we use peg4000,pvpk30,and poloxamer containing pvpk30 give good dissolution profile and flow property data.PEG4000 has sticky in nature so produce stickyness of tablet and poloxamer has not good compressibility. so we select pvpk30 polymer with 1:2 (drug +polymer) ratio. Solid dispersion prepared by two methods containing solvent evaporation method select for preparation of solid dispersion. Drug-excipients interactions play a vital role with respect to release of drug from the formulation amongst others. DSC curve obtained for pure allopurinol, allopurinol+poloxamer127, allopurinol+ PEG4000, allopurinol+PVPK30, shown in figure. Pure powdered allopurinol showing sharp melting endotherm at 386.17ºC. DSC scan of allopurinol+poloxamer127 showed single broad endotherm at 372.14ºC due to melting. DSC thermographs of allopurinol+poloxamer127showed melting peak of the polymer at 58.08ºC and sharp endothermic peak of drug at 372.14ºC. DSC spectra of allopurinol+PEG4000showed single broad endotherm at 380.14ºC due to melting. DSC thermographs of allopurinol+PEG4000showed melting peak of the polymer at 62.72ºC and sharp endothermic peak of drug at 380.14ºC. DSC scan of allopurinol+PVPK30 showed single broad endotherm at 383.07ºC due to melting. DSC thermographs of allopurinol+PVPK30showed melting peak of the polymer at 92.82ºC and sharp endothermic peak of drug at 383.07ºC. Presence all peak indicates that all ingredients are compatible with each other means there is no incompatibility of selected ingredients.

The figure shows characteristics shoulders of allopurinol in IR are at 790cm-1and 1245cm-1,denoting CH in plane deformation:1590cm-1 representating ring vibration, 1700cm-1 indicating CO stretching vibration of keto form of 4-hydroxy tatomer.the carbonyl stretching band of allopurinol that appeared at 1700cm-1 shifted in its poloxamer 127,PEG4000, PVPK30,.the band was reduce its intensity and shifted other range. The characteristic peak of allourinol and other exiepient shown in given peak of solid dispersion, which indicate absence of any interaction between drug and carrier upon mixing them together with similar particle size.

CONCLUSION:

The solubility and dissolution rate of allopurinol can be enhanced by the use of SDs of allopurinol with PVPK30. The solubilization effect of PVPK30, reduction of particle aggregation of the drug, absence of crystallinity, and alteration of the surface properties of the drug particles might be responsible for the enhanced solubility and dissolution rate of allopurinol from its SD. From FTIR spectroscopy, it was concluded that there was no well defined interaction between allopurinol and PVPK30, since no new peaks or shift of peaks could be observed. The absence of an endothermic peak of allopurinol in the DSC thermograms of SDs with PVPK30showed the conversion of allopurinol from crystalline to amorphous state. It can be concluded that the preparation SDs of allopurinol with P provides a promising way to enhance its solubility and dissolution.

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