Matrix systems for zero-order release: facile erosion of crosslinked hydrogels

Abstract

Bioerodible matrices are particularly suited for the systemic administration of drugs over extended time periods. Type I-A bioerodible matrices reported in the past degrade either too slowly or too rapidly. The rate of erosion, therefore, has no influence on the kinetics of release. This paper reports kinetics of release of theophylline from a series of crosslinked glassy/swollen hydrogel matrices based on a novel crosslinking monomer, viz. 2-hydroxyethyl glycolate dimethacrylate. The release of theophylline in an alkaline medium is accompanied by the erosion of the crosslinks. Under appropriate conditions, theophylline is released at a constant rate by the erosion of the crosslinks in the bulk of the swollen polymer as well as by the surface erosion of the glassy polymer. The release behaviour has been explained on the basis of the concept of time-dependent diffusivity of the active ingredient and swelling-controlled zero-order release, respectively.