Formulation optimization of double emulsification method for preparation of enzyme-loaded Eudragit S100 microspheres

The present study aimed to develop an oral sustained release microparticulate system for acid labile enzyme-Serratiopeptidase. A 3(2) full factorial experiment was designed to study the effects of the external aqueous phase volume and stabilizer (Tween(R) 80) concentration on the entrapment and size of Eudragit S100 microspheres prepared by a modified double emulsion solvent evaporation technique. The results of analysis of variance tests for both effects indicated that the test is significant. The effect of external aqueous phase volume was found to be higher on the entrapment efficiency of microspheres (SSY1 = 1362.63; SSY2 = 250.13), whereas Tween(R) 80 produced a significant effect on size of microspheres (SSY1 = 944.01; SSY2 = 737.26). Scanning electron microscopy of microspheres demonstrated smooth surface spherical particles. The effect of formulation variables on the integrity of enzyme was confirmed by in vitro proteolytic activity. Microspheres having maximum drug encapsulation (81.32 +/- 3.97) released 4-5% enzyme at pH 1.2 in 2 h. The release of enzyme from microspheres followed Higuchi kinetics (R-2 = 0.987). In phosphate buffer, microspheres showed an initial burst release of 25.65 +/- 2.35% in 1 h with an additional 62.96 +/- 4.09% release in the next 5 h. Thus, formulation optimization represents an economical approach for successful preparation of Eudragit S100 microspheres involving fewest numbers of experiments.