MODELING DRUG RELEASE FROM DYNAMICALLY SWELLING POLY(HYDl?OXYETHYL METHACRYLATE-CO-METHACRYLIC ACID) HYDROGELS

Drug release from a swelling hydrogel matrix is a complicated process where diffusion of drug molecules is coupled to the swelling kinetics. The swelling influences the diffusional flux of drug molecules by increasing the diffusion coefficient and diffusional pathlength. Release of phenylpropanolamine from apoly(hydroxyethy1 methacrylate-co-methacrylic acid) hydrogel, initially at low pH, is highly influenced by swelling in a neutral pH medium. Swelling in these ionizing gels is a very long process, even in the absence of a glassy core, indicating that the swelling is not a simple Fickian process. In this paper, a novel approach is introduced to model the phenylpropanolamine release from these swelling gels. Through a free volume relationship, the experimentally determined swelling kinetics are coupled to a diffusion mechanism for the drug molecules. This model was shown to give an accurate prediction of phenylpropanolamine release from poly(hydroxyethy1 methacrylate-co-methacrylic acid) gels.