Fig. 1: Arithmetic means size of Microspheres of Metformin HCL different formulation

metformin (250 mg) was added and used as the aqueous phase. The oil phase comprised of 20 ml sunflower oil and 5 ml petroleum ether with 1% span 80 (as emulsifier) which were mixed together and allowed to stir for 20 min at 800-1000 rpm on a magnetic stirrer. The aqueous phase was added drop wise to the oil phase and stirred at the same rpm for 30 min to form the primary emulsion. This emulsion was then added to 80 ml of sunflower oil preheated to 65-70ºc using 21 no. needles and stirred at

Fig. 2: Dissolution study of Marketed Tablets Metformin Hydrochloride

1000-2000 rpm for 2 hours to allow to room temperature with continuous. The suspension was then allowed to cool to room temperature with continuous stirring using a magnetic stirrer. On cooling, 100 ml of anhydrous ether was added. The suspension containing the micro sphere was centrifuged for 15 min and the settled micro sphere were washed three times with ether to remove trace of oil on micro-sphere surface .The obtained micro-sphere were then vacuum dried in a desiccator's overnight and stored at 4°C in dark. Further polymer to drug ratio optimized by prepared by four batches, FS-1 to FS-2 (Table I). MH to HPMC was altered ratio from 1:1 to 1:2 and MH to Carbopol ratio from 1:1 to 1:2 for batch FS-3 to FS-4 respectively. The effects of formulation variable on characteristics of microsphere are summarized in a Table-I.

Fig. 3: Dissolution study of Microspheres of Metformin HCL different formulation

Table I Optimization of Drug: polymer ratio

Formu lation	Drug: polymer	% Yield	Mean particle size (μ m)	Entrapment efficiency (%)	Angle of repose
FS-1	1:1	76.02	2.3	41	12.40º
FS-2	1:2	71.72	3.8	55	14.57º
FS-3	1:1	74.17	4.2	62	15.48º
FS-4	1:2	80.82	3.2	55	18.14º

Table II: In-vitro release profile of marketed tablets

S. No.	Time (minutes)	% Drug release
1	5	3.967
2	10	12.505
3	15	27.586
4	20	53.344
5	30	60.852
6	45	64.572
7	60	67.104

Evaluation of microspheres

Micromeritic study

The P article size of all formulation was determined by microscopy(Motic –DMWB, Magnification -4x).The derived properties of the microspheres such as the angle of repose was determined by funnel method.

Determination of drug Entrapment:

Metformin (drug) content in the micro-spheres was estimated by an UV spectrophotometric method based on the measurement of absorbance at 233 nm in phosphate buffer having pH 6.8. About 100mg of microsphere weigh accurately and crushed in glass mortar. Powdered microspheres were suspended in 50 ml of phosphate buffer pH 6.8. After 24 hour, the solution was filtered and filtrate was analyzed for drug content 233 nm. Corresponding drug concentrations in samples were calculated from calibration plot generated by regression of data reported in table I. The method was validated for linearity, accuracy and precision. The method obeyed Beer's law in the concentration range of 5-50 (μ g /ml). Results are show in Table I

Weight of drug in Micro-spheres

% Loading = X 100

Weight of Micro-spheres

Surface Morphology

Scanning electron microscopy of all formulations was show in fig. no-A, B, C and D respectively different magnification were used taking the photo micrograph. Particle size of Metformin HCL micro sphere found to be range from 250-400 micrometer for FS-1, FS-2, FS-3 and FS-4 respectively. Particles of all the formulation were found smooth & discrete where as formulation FS-2 and FS-4 was found to be more spherical, smooth & discrete.SEM analyses were performed on pure Metformin hydrochloride and HPMC & Carbopol (sample) and on equimolar combination obtained by Emulsification-heat stabilizing method, in an order to gain insight about the possible morphological changes by methods. Metformin Hydrochloride particle appeared as lamellar, rather irregular sized crystals, with a tendency to self-agglomerate. Which appeared formed by amorphous around particle of very homogeneous and small dimension (2-5μ m).

Particle size and shape analysis

For size distribution analysis, optical microscope was used to determine the size of the particle that lies within a range from 0.2 um to 100 equal divisions and hence, each division is equal to 10um and the particles are measured along an arbitrarily chosen fixed line across the center of the particle. The particle size is a factor to be considered important in formulation of micro-spheres and shown in Fig. 5.

∑nd ^{p +f}

d mean= [ ---------]

∑nd ^f

Where 'n' is No. of particle in size range whose mid point is 'd', 'p' is an index related to the size of an individual particle while 'f' is frequency index.

In vitro drug release

Microspheres equivalent to 100mg of MH were taken in dialysis tube and placed in 500ml of 6.8 phosphate buffer. The medium was stirred by using the magnetic stirrer and the temperature was maintained at 37±0.5°C. Periodically 1ml of the samples was withdrawn and diluted to 10ml by using phosphate buffer. After each withdrawal the same quantity of fresh medium was replaced immediately. Then the sample was assayed by UV spectrophotometer (Shimadzu 1700) at 233 nm using medium as blank and shown in table II and III and fig 2 and 3.

RESULTS AND DICUSSION:

Controlled release microspheres were prepared by emulsification heat stabilizing method using HPMC and Carbopol.The microscopic studies performed using motic- DMWB microscope at magnification of 4x showed that the prepared microspheres, a shown in figure 1, lamellar,rather irregular sized crystal. It was also found that microspheres weree free flowing with size distribution between 145-234 µm. The mean particle size was found to increases with the significantly with the amount of polymer and the drug used. The mean particle size was between 145μm-234μm (Table I. The microscopic obtained were free flowing and angle of repose was found to be between 12-18°.It was observed that these formulation of microspheres were uniformly spherical shape. mean particle size was determined for the various formulations.).

Table III. Cumulative drug release of FS-1 to FS-4 Formulation

S. No	Time (minutes)	FS-1	FS-2	FS-3	FS-4
1	5	3.545	4.905	4.014	6.40
2	10	6.209	7.425	11.376	8.64
3	15	9.753	11.792	17.244	11.51
4	30	14.659	20.106	20.997	13.0
5	60	20.181	27.675	31.158	27.06
6	120	27.340	36.648	44.451	40.34
7	180	41.727	45.675	49.451	50.69
8	240	47.318	53.316	54.063	63.0
9	300	56.045	60.759	58.69	71.0
10	360	65.795	74.313	67.69	88.0
11	420	84.272	77.589	86.594	95.0
12	480	97.23	95.112	92.75	98.5

Percentage yield and entrapment efficiency was obtained by emulsification heat stabilizing method. The mean percentage yield for the various formulations were 74.72%, maximum yield of 76.02 was obtained FS-1 formulation .The mean entrapment efficiency was 59.02%.

The result indicate was found the percentages drug release of metformin from microspheres and was found to be 97.23, 95.122, 92.75 and 98.5 in 8 hrs from FS-1, FS-2, FS-3 and FS-4 respectively. The Percentage drug release were found to be 20.181, 27.675, 31.158 and 27.06% drug were released from the FS-1, FS-2, FS-3 and FS-4 respectively within 1 hrs where as more than 60% drug was released in 1 hrs from the marketed tablets.¹⁰ Therefore in the study microspheres were followed controlled release Pattern, when compared with marketed formulations.⁹

CONCLUSION

Based on the result obtained it was concluded that HPMC and Carbopol can improve controlled drug delivery. The different ratios of Metformin hydrochloride with respect to stabilizers (HPMC, Carbopol) were showed that microspheres containing Metformin hydrochloride is a concentration dependent and with the increasing the ratio of stabilizer, drug release is decrease from its system. It can provide prolonged action with decreasing its therapeutic dose and improving its therapeutic activity.

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Received on 06.12.2008 Modified on 28.01.2009

Research J. Pharm. and Tech. 2(1): Jan.-Mar. 2009; Page 176-179