Dynamics of the fraction of drug particles near the release boundary

Abstract

We consider a drug release formulation and investigate the evolution of the fraction of drug molecules that are sufficiently close to the release boundary, in order to check the validity of the assumption underlying the theoretical derivation of a stretched exponential (Weibull) release kinetics. Diffusion-controlled drug release from spheres and slabs is considered. Both analytical results and Monte Carlo simulations are used to calculate the evolution of diffusive drug particles. We find that the fraction of drug molecules near to an exit, as a function of time, follows an inverse power-law in a substantial part of the release problem (from around 1–5% up to at least 80% of the release), justifying an approximate description of the release kinetics through a stretched exponential function.