Chitosan and chondroitin microspheres for oral-administration controlled release of metoclopramide

This study investigated the usefulness of chitosan and chondroitin sulphate microspheres for controlled release of metoclopramide hydrochloride in oral administration. Microspheres were prepared by spray drying of aqueous polymer dispersions containing the drug and different amounts of formaldehyde as cross-linker. Drug release kinetics were investigated in vitro in media of different pH. Chondroitin sulphate microspheres scarcely retarded drug release, regardless of cross-linker concentration and medium pH, and were thus not further characterized. Chitosan microspheres prepared with more than 15% formaldehyde (w/w with respect to polymer) showed good control release (more than 8 h), and release rates were little affected by medium pH. Release from chitosan microspheres prepared with 20% formaldehyde was independent of pH, suggesting that this may be the most appropriate formulation. The size distribution of the chitosan microparticles was clearly bimodal, with the smaller-diameter subpopulation corresponding to microsphere fragments and other particles. Electron microscopy showed the chitosan microspheres to be almost-spherical, though with shallow invaginations. The kinetics of drug release from chitosan microspheres were best fitted by models originally developed for systems in which release rate is largely governed by rate of diffusion through the matrix.