Abstract
Various biological membranes (barriers) at the sites of drug administration have increased in interest in drug delivery. Epithelial barriers such as gastrointestinal, dermal, nasal, and pulmonary barrier are reviewed at a cellular, biochemical, and anatomical level. Several factors, enzymatic metabolism and membrane permeability, are concerned in drug delivery, Penetration enhancers, for example, act on the various biological barriers at a different extent. Thus absorption enhancers are overviewed, and their enhancing mechanism is presented and discussed from the point of drug delivery system.
