Floating microspheres have emerged as a potential candidate for gastroretentive drug delivery system. For developing a desired intragastric floatation system employing these microspheres, it is necessary to select an appropriate balance between buoyancy and drug releasing rate. These properties mainly depend on the polymers used in the formulation of the microspheres. Hence it is necessory to study the effect of these polymer concentrations on the various physicochemical properties of the microspheres. Floating microspheres were prepared by emulsion solvent evaporation technique utilising different polymers such as ethyl cellulose, Eudragit® RS and Eudragit® RL by dissolving them in a mixture of dichloromethane and methanol. Release modifiers studied were hydroxypropyl methylcellulose K4M, hydroxypropyl methylcellulose E50 LV and Eudragit® EPO. Prepared microspheres were analysed for particle size, surface morphology, entrapment efficiency, buoyancy, differential scanning calorimetry and in-vitro drug release. Ethyl cellulose and Eudragit® EPO resulted microspheres with high percentage yield, excellent spherical shape but had very less buoyancies with a high cumulative drug release. Ethyl cellulose microspheres prepared using hydroxypropyl methylcellulose K4M showed more sustained drug release and high buoyancies than that of the microspheres formulated with the hydroxypropyl methylcellulose E50 LV. Amongst these hydroxypropyl methylcellulose E50 LV showed good balance between buoyancy and the drug release.

The aim of present work was to develop a metformin hydrochloride sustained release tablet by aqueous coating. Eudragit RL and Eudragit RS were used for coating of tablets. Eudragit RL having 10% and Eudragit RS having 5% of functional quaternary ammonium groups, which give rise to pH independent permeability of the polymer. Metformin hydrochloride uncoated tablets were prepared by wet granulation technique. Tablets were coated with blends of Eudragit RS30D and Eudragit RL30D in 5:1 and in 3:1 ratios at different coating level viz. 7%, 5%, 3%, 1.5%, 1%. Two dissolution media: pH 1.2 and pH 6.8 phosphate buffer were employed for in vitro release behaviors of metformin hydrochloride tablets. Coating with blends of Eudragit RS 30D and Eudragit RL 30D in 5:1 and in 3:1 ratio at 1% and at 3% showed sustained release effect for 12 h. The two Eudragit polymers with different features as coating materials produced the desired results.