Formulation and evaluation of ethyl cellulose microspheres prepared by the multiple emulsion technique

The aim of this study was to formulate and evaluate microencapsulated controlled release preparations of metformin hydrochloride using ethyl cellulose as the retardant material with high entrapment efficiency and extended release. Microspheres were prepared by the double emulsion solvent diffusion method. A mixed solvent system consisting of acetonitrile and dichloromethane in 1 : 1 ratio and light liquid paraffin were chosen as the primary and secondary oil phases, respectively. Span (R) 80 was used as the surfactant for stabilizing the secondary oil phase. The prepared microspheres were characterized by drug loading, optical microscopy and scanning electron microscopy (SEM). The in vitro release studies were performed in a series of buffer solutions with variable pH. The drug loaded microspheres showed 55-85% of entrapment and the release was extended for up to 12 h. SEM studies revealed that the microspheres were spherical and porous in nature. Data obtained from in vitro release studies were fitted to various kinetic models and high correlation was obtained with the Higuchi model. The drug release was found to be diffusion controlled. Oral administration of the microspheres to the albino mice provided decreased plasma glucose for more than 10 h.