Sodium alginate microspheres of metformin HCl: formulation and in vitro evaluation

Metformin microspheres with sodium alginate alone and in combination with gellan were prepared using an emulsion-cross linking method. The prepared microspheres were evaluated for their physico-chemical characteristics like particle size, morphology using SEM, incorporation efficiency, equilibrium water content (swelling) and in vitro drug release. The effect of various formulation variables like polymer concentration (sodium alginate; and proportion of gellan in microspheres prepared by a combination of sodium alginate and gellan), drug loading, crosslinking agent concentration and cross-linking time on the in vitro dissolution of the prepared microspheres were evaluated. The results showed that both the particle size and the incorporation efficiency were proportional to the polymer concentration. In case of microspheres containing both sodium alginate and gellan, the mean diameter and the incorporation efficiency were higher than the corresponding microspheres containing only alginate, both increasing with an increase in proportion of gellan. The prepared microspheres were found to be discrete and spherical in shape and were successful in sustaining the drug release for 8 hours. Incorporation of gellan caused a significant decrease in drug release. The release followed a biphasic profile, in all cases, characterized by an initial phase of moderate drug release followed by a phase of higher release. Further, the kinetic treatment of the dissolution data revealed the prevalence of matrix diffusion kinetics.