Mechanistics aspects of the release of drugs from hydrophilic polymer matrices

Abstract

Hydrophilic polymers, which both swell and erode, are widely used to produce sustained release of drugs from monolithic matrices, and have been extensively reviewed in the literature (Alderman 1984), (Peppas and Korsmeyer 1987). In the present work gravimetric swelling and erosion studies were completed on such matrices, since the extent of water uptake and thus swelling is an indication of the extent of soluble drug release by diffusion. The rate of erosion of the polymer is an indication of the extent of poorly soluble drug release by erosion. It was attempted to describe any relationships noted mathematically, as a preliminary step to future development of a simple mathematical model describing drug release based on swelling and erosion of a monolithic swellable polymer matrix, since the models already in the literature show a number of approximations. The extent of swelling and erosion of pure hydroxypropylmethylcellulose (HPMC) matrices was found to be significantly influenced by the use of different polymer molecular weights and by increases in agitation rate, but to a lesser extent by changes in dissolution medium. Dissolution medium uptake followed square root of time kinetics, and erosion followed cube root kinetics.