Novel hydrophilic matrix system with non-uniform drug distribution for zero-order release kinetics

A decrease in the release rate over time is typically encountered when dealing with hydrophilic matrix systems for oral prolonged release due to progressive increase of the distance the drugmolecules have to cover to diffuse outwards and reduction of the area of the glassy matrix at the swelling front. In order to solve this issue, a novel formulation approach based on non-uniformdistribution of the active ingredient throughout the swellable polymer matrix was proposed and evaluated. Various physical mixtures of polymer (high-viscosity hypromellose) and drug tracer(acetaminophen), having decreasing concentrations of the latter, were applied by powder-layering onto inert core seeds. The resulting gradient matrices showed to possess satisfactoryphysico-technological characteristics, with spherical shape and consistent thickness of the layers sequentially applied. The non-uniform matrix composition pursued was confirmed by Raman mappinganalysis. As compared with a system having uniform distribution of the drug tracer, the multi-layer formulations were proved to enhance linearity of release. The simple design concept, advantageoustechnique, which involves no solvents nor high-impact drying operations, and the polymeric material of established use make the delivery platform hereby proposed a valuable strategy to improve theperformance of hydrophilic matrix systems.