Modeling and numerical computation of drug transport in laminates: model case evaluation of transdermal delivery...

This study reports on the modeling and numerical computation of drug transport from a laminated system into the skin. The model is based on the diffusion equation, on partitioning of the drug between individual layers of the device, and on continuity conditions for diffusive flux across the material interfaces of the system. Numerical computation of concentration profiles across the system was performed using a sophisticated software package designed for a general class of kinetics-diffusion problems, including time variable diffusion coefficients and interface conditions in case of nonhomogeneous media. This program is demonstrated by a model case evaluation of a transdermal delivery system for nitroglycerin and applies previous data on drug diffusion and partitioning in this system. The layers involved in drug transport are: a polymer film to carry the drug depot; a microporous membrane, the pores of which are filled with nonpolar liquids and solids; an adhesive layer; and a final layer representing the skin. Transport kinetics in the delivery system and the skin are being followed by plots of concentration profiles as a function of application time. Major concentration gradients indicate sites of release control. For practical purposes, the package is intended to serve for preformulation studies of laminated drug delivery systems.