Sustained release of a model macromolecule from preparations with erodible core

A series of sustained release tablets were prepared which consisted of a water-soluble core and a highly hydrophobic coat. Release of a macromolecule, Spectrum Orange, from this preparation was studied. It was found that release was controlled by the coat composition and coating solution viscosity. SEM and optical microscopy of the tablets indicated that the coats contained pores on the surface which penetrated in towards the centre of the core. It was deduced that the almost zero order release of macromolecules from these tablets was basically through these pores and not by diffusion through the polymer matrix.