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 p olymer 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 relate d to their influence on the pore structure created. In general, porosi ty modifiers with larger particle sizes, smaller specific surface area s, greater hygroscopicity coefficients or higher solubilities caused f aster drug release, by creating more conducting channels. The porosity modifier particle size and load were related to changes in the coat v olume (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 wit h the desired release rate. Alternatively, one can specify the necessa ry coat characteristics after porosity modifier release that will yiel d the desired release rate. (C) 1998 Elsevier Science B.V. All rights reserved.