ABSORPTION OF HYDROPHILIC AND LIPOPHILIC COMPOUNDS THROUGH EPIDERMAL AND SUBEPIDERMAL STRATA OF RAT SKIN IN-VITRO

The absorption of a model hydrophilic compound (benzoic acid) and a mo del lipophilic compound [di(2-ethylhexyl)phthalate; DEHP] was measured through separated epidermal membranes and through the residual stripp ed dermis of rat skin. Absorption was determined using both phosphate buffered saline (PBS) and 50% ethanol/water as the receptor fluid. The rate and extent of DEHP absorption through epidermis was greatly incr eased (40- to 80-fold) using 50% ethanol/water as receptor fluid compa red with using PBS, but with the stripped dermis only a small differen ce (approximately two-to threefold) was detected. The use of 50% ethan ol!water as receptor fluid also promoted the penetration of benzoic ac id through the epidermis, but only to a limited extent (two-to threefo ld increase). As with DEHP, the penetration of benzoic acid through th e dermis was also increased. The permeability to (H2O)-H-3 Of epiderma l, but not dermal membranes was also increased by the use of a 50% eth anol/water receptor fluid. It was concluded that 50% ethanol/water can increase the permeability of rat skin strata to both lipophilic and h ydrophilic compounds. Further work is needed to provide a basis for se lecting suitable receptor fluid formulations for in vitro dermal absor ption studies. (C) 1998 Elsevier Science Ltd.