ARTIFICIAL MEMBRANES 249 (21) W. Abraham and D. T. Downing, Interaction between corneocytes and stratum corneum lipid liposomes in vitro, Biochim. Biophys. Acta, 1021, 119-125 (1990). (22) P. W. Wertz, D.C. Swartzendruber, D. J. Kitko, K. C. Madison, and D. T. Downing, The role of the corneocyte lipid envelopes in cohesion of the stratum corneum,J. Invest. Dermatol., 93, 169-172 (1989). (23) D.C. Swartzendruber, P. W. Wertz, D. J. Kitko, K. C. Madison, and D. T. Downing, Molecular models of the intercellular lipid lamellae in mammalian stratum corneum, J. Invest. Dermatol., 92, 251-257 (1989). (24) C. Surber, P. Wilhelm-Klaus, M. Hori, H. I. Maibach, and R. H. Guy, Optimization of topical therapy: Partitioning of drugs into the stratum corneum, Pharm. Res., 7, 1320-1324 (1990).

j. Soc. Cosmet. Chem., 43, 251-258 (September/October 1992) Investigation of the in vitro interaction of various vehicles with hairless mouse skin MOHAMMAD S. RAHMAN, MICHAEL A. GALLO, THOMAS H. UMBREIT, and JOEL L. ZATZ, College of Pharmacy, Rutgers University, P.O. Box 789, Piscataway, NJ 08854 (M.S.R., J.L.Z.), and UMDNJ-RWJ Medical School, 675 Hoes Lane, Piscataway, NJ 08854 (M.A.G., T.H.U.). Received May 14, 1992. Presented in part at the 1989 Annual Scientific Meeting of the Society of Cosmetic Chemists, New York, December 7-8, 1989. Synopsis The interaction of a series of donor solvents including water, propylene glycol, two alcohols, four hydro- carbons, and light mineral oil with hairless mouse skin was studied in vitro by following the dermal absorption of caffeine as a reference compound. Steady-state flux at saturation (J*) of caffeine was calculated for different donor solvents using solubility, donor concentration, and steady-state flux. The value of J* varied markedly with the donor solvent, indicating that caffeine permeation was significantly affected by vehicle/skin interactions. n-Propanol provided the highest value of J* among the various solvents. In the hydrocarbon series, the value of J* decreased exponentially as the chain length was increased. Propylene glycol yielded a lower value of J* compared to water. Light mineral oil provided the lowest value of flux at saturation, suggesting minimal interaction between this vehicle and mouse skin. INTRODUCTION In skin permeation studies, vehicles (solvents) are frequently employed to apply the test material(s) to the membrane surface. The physical and chemical properties of the vehicle play a major role in determining the rate of uptake and penetration of the medicament through the membrane (1). Vehicles can modify either the thermodynamic activity of the drug (2) or the barrier properties of the skin (3). Thus, a thorough understanding of the interaction of the solvent with the drug or the membrane is essential before its selection in any formulation for transdermal drug delivery as well as for dermal toxi- cological evaluation. Mohammad S. Rahman's present address is ManTech Environmental Technology, Inc., 2 Triangle Drive, Research Triangle Park, NC 27709. Thomas H. Umbreit's present address is ATSDR, Atlanta, GA 30333. 251