Swelling-activated drug delivery systems.

A previous paper dealt with the preparation of an in vitro programmable zero-order drug delivery system in which the area of the surface exposed to the dissolution medium and the macromolecular relaxation of polymer controlled the release of the drug. In the present study, the preparation of similar delivery systems is described, in which differing drugs and polymers were used to ascertain the mechanism governing the drug-release kinetics. The movement of the interfaces between solvent and system was measured during drug release in systems with varying composition. The results indicate that the synchronization of the movement of swelling and eroding fronts at the solvent-system interface determines the achievement of the linear-release kinetics of such swelling activated systems and that the swelling and dissolution characteristics of the polymer employed for core preparation govern front movement.