On the release mechanism from coated swellable minimatrices

The approximately in vitro constant release rate shown by 'multiple unit' modified release systems that consist in coated minimatrices seems to depend on swelling properties of the cores and on permeability and/or mechanical characteristics of the applied polymeric film. The present study investigates the overall release mechanism by comparing the release kinetics of systems based on inert or swellable cores and by measuring the permeability of isolated membranes whose composition is identical to that of the applied coating. The results indicate that said coating is not capable of working as a limiting diffusional step; consequently, the release control can reasonably be ascribed to the physical restriction exerted by the film on core swelling.