INTRODUCTION:

One of the methods of controlling the rate of drug release is by microencapsulation. Microspheres can be defined as solid spherical particles ranging from 1-5000 µm. These particles consist of core material having drugs coated by polymer material.

Metformin hydrochloride was selected as model drug. In conventional dosage form it is frequently administered as it has a short half-life. It gets readily absorbed throughout the length of gastrointestinal tract. Eudragit S100, ethylcellulose and cellulose acetate were the polymers used for the preparation of microcapsules of metformin hydrochloride. Eudragit S100 a co-polymer of acrylic and methacrylic acid esters have been widely used to prepare microspheres with a view to modulate the drug release.¹ Eudragit is characterized by the presence of relatively higher content of charged quaternary ammonium groups which makes it capable of absorbing aqueous fluid while simultaneously releasing the embedded drug.² Ethylcellulose coated dosage form can be controlled by diffusion through film coating, high viscosity grade of ethylcellulose were used in drug microencapsulation and the release of the drug depends upon the wall thickness and the surface area.³ Cellulose acetate is widely used in controlling the drug release by solvent evaporation technique.⁴ Thus, the objective of the presented work was to formulate the microcapsules of highly water-soluble drug metformin hydrochloride using these polymers.

Characterization of the microcapsules was done by particle size analysis, determination of drug content and drug release studies to get optimized formula. Thus the purpose was therefore; to investigate the effect of these different polymer coatings with different ratio to obtain the best optimized formula.

MATERIALS AND METHODS:

Materials:

Metformin hydrochloride (RPG Life sciences, Mumbai) and Eudragit S100 (Rohm Pharma, West Germany) were obtained as a gift sample. Ethylcellulose (S d Fine Chemicals, India) Cellulose acetate (S d Fine Chemicals, India), Span 80, acetone, petroleum ether and other chemical used were of analytical reagent grade.

Evaluation of raw materials:

Identification and Standardization of drug and other excipients were carried out as per the official procedures mentioned in respective monographs.

Preparation of microsphere:

Microspheres were prepared by o/o emulsion solvent evaporation technique. Homogenous polymer solution was prepared using acetone. Solution with D: P ratio of 1:1, 1:2, 1:3, and 1:4 (Table 1) were prepared and emulsified into liquid paraffin (250 ml) containing dissolved emulsifier span 80. The solution was stirred at 500 rpm for 2.5 hr at room temperature to allow complete evaporation of the solvent. The microsphere formed were collected, filtered and washed with petroleum ether. The Product so obtained was evaluated for particle size, drug entrapment efficiency and drug release. The above procedure was followed for all the three polymers that is Eudragit S100, ethyl cellulose and cellulose acetate.

Table 1: Formulae of different batches of microcapsules of metformin hydrochloride

Sr. no.	Drug (g)	Eudragit S100 (g)	Ethyl cellulose (g)	Cellulose acetate (g)
F1	1	1	---	---
F2	1	2	---	---
F3	1	3	---	---
F4	1	4	---	---
F5	1	---	1	---
F6	1	---	2	---
F7	1	---	3	---
F8	1	---	4	---
F9	1	---	---	1
F10	1	---	---	2
F11	1	---	---	3
F12	1	---	---	4

Characterization of prepared microcapsule:

Determination of particle size:

The particle sizes of the prepared microcapsule were determined by employing sieving method. The microcapsule that passes through one sieve but retained on the next finer sieve was collected, weighed and the percentage retained on each sieve was determined.⁴

Determination of drug content:

Microcapsules equivalent to 100 mg of metformin hydrochloride were weighed and powdered, mixed with 70 ml of water for 15 minutes and diluted to 100 ml with water, filtered.10 ml of the filtrate was diluted to 100 ml with water, further 10 ml diluted to 100 ml with water. The absorbance of the resulting solution was measured at maximum 232 nm.⁵

In vitro dissolution studies of microcapsules of metformin hydrochloride:

In vitro drug release was determined using USP XXIII Type I (basket) dissolution apparatus at 100 rpm in 900 mL of phosphate buffer pH 6.8, maintained at 37^O±0.5^O. From each vessel at every hour 5.0 mL of sample was withdrawn filtered, diluted and analyzed spectrophotometrically at 232 nm. An equal volume of fresh medium which was prewarmed at 37^O was replaced in to the dissolution medium after each sampling to maintain the constant volume throughout the test.⁶ Percentage drug release was calculated by using the standard calibration curve of drug in same dissolution medium. Based on the above results most promising formulation was selected and evaluated.

FTIR Spectroscopy:

The physicochemical compatibility between drug and polymer was studied by using FTIR spectrophotometer (AVATAR 320, Nicolet instrumental co-operation).⁷

X-Ray Diffraction:

To study any polymorphic changes in the drug in the dosage form, X-Ray Diffraction study was carried out on the sample by using X-Ray diffractometer (Philips PW1710).^8,9

Scanning Electron Microscopy (SEM) study:

The microcapsules were observed under a Scanning Electron Microscope, (JXA-840, JEOL, Tokyo, Japan). The samples were mounted on brass specimen mount using double sided adhesive tape. A conducting layer of gold of 30 nm is coated on specimen using JFC 1500 iron spluttering device. An accelerating voltage of 20 kV was generated the electron to beam at a working distance of 39 nm. The microscopy was carried out at probe current 3 x 10^-11 current.¹⁰

Fig.1: Peppas plot showing the release of metformin hydrochloride microcapsule of F2

Fig. 2: Infrared spectra of metformin hydrochloride loaded Eudragit S100 microsphere in the ratio of 1:2

Stability Study:

The optimized formulation were stored at 25±1⁰ and 50±1⁰ for a period of 30 days and observed for any change in morphology or percentage residual drug content. Samples were analyzed for drug content at time interval of 10 days for one month.¹⁰ The dissolution studies were carried out at the end of 30 days to check whether there is any change in drug release pattern after the stability test.

Table2: Percentage release of metformin hydrochloride at various times interval with Eudragit S 100, ethylcellulose and cellulose acetate as coating materials in different ratio

Sr. No.	Formulation	Percentage drug release (hr)
Sr. No.	Formulation	1	2	3	4	5	6	7	8	9	10
1	F1	10	17	23	35	47	59	67	75	80	-
2	F2	15	26	49	60	72	80	87	93	96	-
3	F3	13	23	50	58	63	68	72	84	88	-
4	F4	20	22	29	35	47	59	63	75	80	-
5	F5	12	17	23	32	42	59	65	72	-	-
6	F6	12	26	49	60	72	80	87	90	-	-
7	F7	7	13	28	36	55	68	72	84	-	-
8	F8	9	14	20	35	47	59	63	75	-	-
9	F9	12	16	23	32	41	59	61	72	-	-
10	F10	15	20	32	40	47	55	67	75	-	-
11	F11	9	13	28	34	55	67	73	81	-	-
12	F12	6	13	20	33	47	59	62	74	-	-

Fig. 3: X-ray diffraction pattern of metformin Hydrochloride loaded Eudragit S100 microsphere in the ratio 1:3

RESULTS AND DISCUSSION:

The aim of present study was to prepare microcapsules of metformin hydrochloride by using different coating material with the help of solvent evaporation technique. For preparation of microcapsules of metformin hydrochloride Eudragit S100, ethylcellulose, cellulose acetate were chosen as a coating material, which forms the semipermeable film over the drug. Solvent evaporation technique was used for preparation of microcapsules. During the course of study, various formulations with different ratio of Eudragit S 100, ethylcellulose and cellulose acetate with metformin hydrochloride were prepared and studied in order to observe their percentage drug content, size and shape, in-vitro release profile, drug polymer interaction and stability study.

From all these formulations prepared of different polymer in different ratio with drug, the best-optimized formula was selected and evaluated further. It was observed that as the polymer concentration increases there is retardation in the rate and extent of drug release (Table 2). Metformin hydrochloride and Eudragit S100 in ratio of 1:2 gave the best result and was further evaluated

The drug content of all the formulations was around 90%. The drug release kinetic study explains the mechanism of drug release of the optimized formula. The values of coefficient of correlation (r) calculated for Zero order, First order, and Higuchi’s and Peppas equation (Table 3).

Table 3: Drug release kinetic of optimized formula

Formulation	Zero order equation	First order equation	Matrix equation	Peppas equation
F2	0.9848	0.9451	0.9277	0.9863

Table 4: Release of metformin hydrochloride from the optimized formula after 30 days of stability study

Formulation	% drug release (hr)
F2	1	2	3	4	5	6	7	8	9
F2	15	26	48	60	72	80	87	93	95

It was observed that the release of metformin hydrochloride followed the Peppas equation (Fig. 1). This explains that the release of drug occurs by diffusion following non-Fickian transport mechanism. The entrapment efficiency and percentage drug release study indicated from the optimized formula gave a good pattern of release.

The FTIR spectral data (fig. 2) of microcapsules loaded with drug were almost in agreement with that of pure Eudragit S100 clearly indicates that there is no interaction between the drug molecule and the coated polymer employed in microcapsule preparations. The FTIR data obtained of microcapsule where drug polymer ratio is 1:2 shows the presence of drug molecule and thereby confirms the drug molecule has been entrapped in the polymer film.

X-ray diffraction pattern (fig. 3) ruled out any polymorphic changes of the drug in the dosage forms. SEM photograph indicated that the microcapsules are discrete spherical and covered with continuous coating of Eudragit S100 polymer (fig. 4).

Stability data (table 4) suggested that all formulation of ratio 1:2 of Metformin hydrochloride and Eudragit S100 microcapsules were stable on 30th day and there was no evidence of color changes, up to 95 % of drug release was seen after 30 days stability studies.

CONCLUSION:

After summarizing the results, it can be concluded that the ratio 1:2 of Metformin hydrochloride and Eudragit S100 produced the microcapsules with desired characteristics like flow property, packing property, particle size, shape, drug content and sustained release of Metformin hydrochloride. Proper monitoring and validation of the optimized batch results into microcapsules of water-soluble drug.

ACKNOWLEDGEMENT:

The authors thanks to Rohm Pharma, Gmbh Darmatad, West Germany for the supply of Eudragit S100 polymer; RPG life sciences for the gift sample of Metformin hydrochloride.

D

Fig. 4: Scanning Electron Micrograph of metformin hydrochloride various magnifications A) Single uniform microsphere of D: P, 1:2 of metformin hydrochloride loaded Eudragit S-100 polymer. (B) Single uniform microsphere of D: P, 1:2 of metformin hydrochloride loaded ethylcellulose polymer. (C) Single uniform microsphere of D: P, 1:2 of metformin hydrochloride loaded Cellulose acetate polymer. (D) and (E) showing various size of microcapsules which are spherical and discrete

A B

D E

REFERENCES:

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2. Eudragit S100 data sheet, Rohm Pharm., GmBh., West Germany

3. Reynolds., Pharmaceutical Excipient, Marcel Dekker, 3rd ed ., 117-119.

4. Choudhary, K.P.R., and Ramesh, K.V.R.N., INDIAN DRUGS, 1995, 32(10)., 477-483.

5. Indian Pharmacopeia. Ministry of Health and Family Welfare Government of India, 1996, 1496.

6. Sreenivas B. and Murthy Ramana K.V., INDIAN DRUGS 1996, 33(8), 398.

7. Samatha, M.K., Dube, R. and Suresh, B., Indian Journal of Pharmaceutical Sciences, Nov-Dec., 1999, 61(6), 371-372.

8. Sa. Biswanath. and Tamilvanan., INDIAN DRUGS, 1995, 32(4), 176-183.

9. Ramesh, K.V.R.N. and Chowdhary, K.P.R., INDIAN DRUGS, 1995, 32(10), 478.

10. Rai, G. and Jain, K., Pharmaceutical Technology, 2004, 66-71.

Received on 18.03.2009 Modified on 15.04.2009

Research J. Pharm. and Tech.2 (3): July-Sept. 2009,;Page 559-562