Finite element analysis of diffusional drug release from complex matrix systems. II. Factors influencing release kinetics.

This work concentrated on the analysis of several factors influencing the kinetics of diffusional drug release from complex matrix devices, such as convex tablets and rings, into a finite volume. These factors include initial drug concentration distribution, anisotropic matrix, and time- and concentration-dependent diffusion coefficients. The individual and comprehensive effects of these factors on the release kinetics were investigated by the finite element method. Errors introduced by neglecting drug diffusion through the ends of edges of cylindrical devices were estimated by comparison of the 1-D models with the 2-D cylinder model. The influence of side-wall coating on the accuracy of the prediction of release profiles by the 1-D slab model for cylindrical devices was studied using various coating materials of different permeabilities. The analyses carried out in this work could assist the design of the complex matrix systems required for controlled drug release.