A comparative study of various microencapsulation techniques: effect of polymer viscosity on microcapsule characteristics.

It is a comparative study of salbutamol sulphate-ethylcellulose microcapsules prepared by three different microencapsulation techniques i.e. coacervation thermal change, solvent evaporation and coacervation non-solvent addition by adjusting the ratio of salbutamol sulphate to ethylcellulose. In vitro release profiles of microcapsules were studied using USP XXIV dissolution apparatus-I in 450 ml double distilled water maintained at 37 degrees C at 50 rpm. Scanning electron microscopic results indicated that all microcapsules were aggregated, whitish and irregular in shape with good entrapment efficiency (86.34 to 97.83), production yield (87.91+/-1.34 to 98.33+/-1.37) and flow properties. Initial burst effect was observed in the drug release behavior from all microcapsules. A slight increase in actual drug loading but profound increase in mean diameter of microcapsules was observed with the increase in the viscosity of ethylcellulose. UV and FTIR spectroscopy, x-ray diffractometry and thermal analysis verified the absence of any strong chemical interaction between drugs and polymer. The drug release from all the formulations followed anomalous diffusion mechanism and was best fit to Higuchi's kinetic model. The results suggest coacervation thermal change as an appropriate approach to develop slow-release multi-unit oral dosage form of salbutamol sulphate suggesting at least twice administration in every 24 hours.