Study on multilayer ethylcellulose matrices for controlled release of benzoic acid

Matrix devices based on ethyl cellulose (EC) for controlled release (CR) ap plications were investigated for zero order release. These matrices were pr epared by solvent casting and contained three or five layers arranged in sy mmetrical fashion with benzoic acid (BA) loaded only in inner layers; while the outermost layers were kept free from BA. It was found that three layer matrices maintain high release rates inspite of outer barrier layer and he avy initial release (burst effect) was significantly reduced; but linear re lease profile was not obtained. In five layer matrices four type of drug di stribution profiles were tested and it was found that descending staircase type concentration gradient gave linear release profile, with enhanced rele ase duration and reduced burst effect.