Permeation of drug and swelling agent through polymeric membranes

The permeation of drug (benzocaine) and swelling agent (ethanol) through th e polymeric [poly(ethylene-co-vinylacetate) and polyurethane] membranes was investigated theoretically and experimentally. Based on the Flory-Huggins and Yasuda theories, the swelling effect on permeant diffusivity was descri bed by expressing the permeant diffusivity in powers of the activity of the swelling agent. The experimental results suggest that the leading-order te rm (first order of activity) is accurate enough to describe the diffusiviti es of benzocaine and ethanol in the poly(ethylene-co-vinylacetate) and poly urethane membranes. The linear dependence of permeant diffusivity on swelli ng-agent activity was further used to analyze the drug diffusion in a membr ane subject to a swelling gradient. With the knowledge of the dependence of benzocaine and ethanol diffusivities on ethanol activity the activity prof ile of ethanol across the membrane can be calculated, and the effective dif fusivity of benzocaine can then be predicted. Experiments carried out to de termine the variation in the effective benzocaine diffusivity corresponding to different swelling gradients agreed well with the calculated results.