A controlled porosity drug delivery system

The relationship between the drug release rate constant (K-o) and the physicochemical properties of porosity modifiers incorporated in the polymer coat of a proposed compression coated drug delivery system was investigated. The effects of particle size, hygroscopicity, solubility, absolute density and powder specific surface area on K-o were related to their influence on the pore structure created. In general, porosity modifiers with larger particle sizes, smaller specific surface areas, greater hygroscopicity coefficients or higher solubilities caused faster drug release, by creating more conducting channels. The porosity modifier particle size and load were related to changes in the coat volume (V-coat), coat porosity (epsilon(final)) and increased specific surface area (SSA(d)). The V-coat decreased with an increased loading or particle size, promoting faster release. K-o increased very slowly until epsilon(final) and SSA(d) reached critical values (approximately 38% and 0.1 m(2) g(-1), respectively), after which K-o increased very rapidly. This information allows the selection of a porosity modifier with the appropriate characteristics to provide a delivery system with the desired release rate. Alternatively, one can specify the necessary coat characteristics after porosity modifier release that will yield the desired release rate. (C) 1998 Elsevier Science B.V. All rights reserved.