Free diffusion in drug absorption

Abstract

Absorption is a mass transfer process that involves the passage of intact drug molecules from the site of absorption (which often, but not always, corresponds to the site of administration) to the bloodstream. Free diffusion is the most common absorption mechanism for drugs. In free diffusion across a membrane, the solute molecules move around by random Brownian motion, and the solute flux is the resultant of these separate motions . Whereas the exact path of a single particle cannot be predicted, the net movement (i.e., the flux), down a concentration gradient, is measurable and reproducible.