Membrane transport of alkyl homologs: role of fluid flow in aqueous diffusion region.

Passive drug transport across a membrane involves the resistances in series offered by the membrane and the liquid layer immediately adjacent to it. The liquid layers generally are referred to as unstirred aqueous diffusion layers, suggesting that solute transport across these layers occurs solely by molecular diffusion. In accord with convective diffusion theory, recent studies showed that the transport from either a dissolving surface or a membrane surface depends not only on molecular diffusion but also on fluid convection inthe liquid adjacent to the membrane. Membrane permeation rates were determined for a series of alkyl p-aminobenzoates, and the results correlated with a model comprised of membrane diffusion and convective diffusion in the adjacent liquid region.