Controlled Release of Drugs from Polymer Films

Abstract

Controlled release of drugs from pharmaceutical formulations is an attractive concept. Most controlled-release preparations are formulated in polymer bases in a manner which aims to produce specific rates of drug release. In this thesis, the formulation of controlled-release systems consisting of local anaesthetics in gelatin bases is investigated with a view to elucidating the physico-chemical factors which influence the release of drugs from such formulations. Studies on the release of lignocaine from homogeneous films show that it depended on the dissolution rate of the matrix. The importance of temperature on the mechanism of release of lignocaine from homogeneous gelatin films is shown. The extent to which emulsion systems is modelled by equations describing release from homogeneous films has been found to depend on the drug oil-water partition coefficient. The release of drugs with low partition coefficient from emulsion systems can be satisfactorily simulated by the homogeneous film equations. The use of diffusion equations describing release from suspension systems has also been evaluated for emulsion systems. Predictions of release profiles from emulsion systems using equations developed for estimating the dielectric permeability of heterogeneous media were attempted. No single equation provided entirely reliable prediction for release of lignocaine from a range of alcohol-in-gel emulsions. Zero-order delivery of benzocaine was obtained from formaldehyde-hardened emulsion-type gels. With high formaldehyde levels in the films, a two-phase release profile was observed. The early phase was attributed to fast diffusive release of complexed benzocaine, while the late phase was attributed to slower release of matrix-bound benzocaine.