Selective coating of cylindrical matrices with a central hole. II. An interpretation of the release process

A swellable perforated matrix was prepared and coated on one or more of its surfaces. Two drugs having different water solubility were chosen to load the matrix. To clarify the effect of the matrix swelling on the release process, the release rate was analysed according to the swelling area, i.e., the surface area from which the drugs could be released. According to the experimental release data, the drug solubility usually predominated at the beginning and the matrix swelling at the end of the release process. When the interior hole was the only uncoated surface, pseudo-zero order kinetics were obtained when the drug solubility allows the control of the drug release by the matrix swelling.