Pelling, D., J. C. Phillips and M. E. Cunninghame. Absorption of Hydrophilic and Lipophilic Compounds through Epidermal and Subepidermal Strata of Rat Skin In Vitro. Toxic. in Vitro 1998. 12: 47-55. [Reprinted with permission from Elsevier Science]

benzoic acid - 00065-85-0; di(2-ethylhexyl)phthalate - 00117-81-7

The absorption of a model hydrophilic compound (benzoic acid) and a model lipophilic compound [di(2-ethylhexyl)phthalate; DEHP] was measured through separated epidermal membranes and through the residual stripped 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 increase (40- to 80-fold) using 50% ethanol/water as receptor fluid compared with using PBS, but with the stripped dermis only a small difference (approximately two- to threefold) was detected. The use of 50% ethanol/water as receptor fluid also promoted the penetration of benzoic acid through the epidermis, but only to a limited extent (two- to three-fold increase). As with DEHP, the penetration of benzoic acid through the dermis was also increased. The permeability to ³H₂O of epidermal, but not dermal membranes was also increased by the use of a 50% ethanol/water receptor fluid. It was concluded that 50% ethanol/water can increase the permeability of rat skin strata to both lipophilic and hydrophilic compounds. Further work is needed to provide a basis for selecting suitable receptor fluid formulations for in vitro dermal absorption studies.