Chemical enhancement of percutaneous absorption in relation to stratum corneum structural alterations

The outermost layer of the skin, stratum corneum (SC), provides an outstand ing barrier against the external environment and is also responsible for sk in impermeability toward most solutes. The barrier function is related to t he unique composition of the SC lipids and their complex structural arrange ment. The lipoidal matrix of the SC, therefore, is a target of penetration enhancer action. The literature on the skin barrier structure and function and on the mechanisms of action of some well established permeation promote rs, with a focus on their impact on SC structural alterations, is reviewed. Data obtained from infrared, thermal, and fluorescence spectroscopic exami nations of the SC and its components imply enhancer improved permeation of solutes through the SC is associated with alterations involving the hydroca rbon chains of the SC lipid components. Data obtained from electron microsc opy and X-ray diffraction reveals that the disordering of the lamellar pack ing is also an important mechanism for increased permeation of drugs induce d by penetration enhancers. (C) 1999 Elsevier Science B.V. All rights reser ved.