Preparation and characterization of drug-loaded polymethacrylate microspheres by an emulsion solvent evaporation method

Microspheres containing the anti-hypertension drug, felodipine, were prepared by the emulsion solvent evaporation method (o/o) using acrylate methacrylate copolymers, Eudragit RL PO and Eudragit RS PO, as wall materials. In order to increase the encapsulation efficiency, a mixed solvent system comprising 1:1 proportions of acetonitrile and dichloromethane was used as a dispersed phase. The morphology of the microspheres was evaluated using a scanning electron microscope, which showed a spherical shape with smooth surface. The mean sphere diameter was between 9.5-13.2 mum and the microencapsulation efficiencies ranged from 51.4-80.4%. The release profiles and encapsulation efficiencies depended strongly on the structure of the polymers used as wall materials. The release rate of the Eudragit RS PO microspheres was much lower than that of Eudragit RL PO microspheres. Whereas Eudragit RL PO microspheres followed the Higuchi rule, Eudragit RS PO microspheres exhibited a triphasic release profile. It is concluded that drug release rate can be controlled by choice of polymer type.