Preparation and In-vitro Evaluation of Metformin Microspheres Using Non-Aqueous Solvent Evaporation Technique

Purpose: To prepare and evaluate metformin microspheres for prolonged release. Methods: Metformin microspheres were prepared by non-aqueous solvent evaporation method using various polymers, including ethylcellulose (EC), hydroxypropyl methylcellulose (HPMC), carbopol 934P (CA) and chitosan (CH). The effect of process variables, viz, drug/polymer ratio, stirring rate and type of polymer on the mean particle size, drug entrapment efficiency, yield, drug content, micromeritic properties and drug release of the microspheres were studied. Results: It was observed that as the stirring speed increased from 600 to 1800 rpm, microsphere size decreased and hence drug release rate increased. Drug release rate at 1:2 drug: polymer for microspheres produced at a stirring rate of 1200 rpm was in the following order: carbopol 934P > HPMC > ethyl cellulose > chitosan. The formulations containing carbopol 934P (CA3) and HPMC (HPMC3) released drug faster than chitosan microspheres (CH3). Conclusion: Amongst the developed microspheres, CH3 formulation (with chitosan as the polymer) exhibited maximum prolonged drug release at gastrointestinal pH or at least 15 h. This oral sustained metformin formulation could potentially improve the bioavailability of the drug as well as patient compliance.