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.L Soc. Cosmet. Chem., 23, 565-590 (August 17, 1972) Corticoid, Vehicle, and Skin Interaction in Percutaneous Absorption MARTIN KATZ, D.Sc., and BOYD J. POULSEN, Ph.D.* Presented December 1-2, 1970, New Yorh City Synopsis--The PERCUTANEOUS ABSORPTION of a drug applied to the skin surface is influenced by INTERACTION between the DRUG, the VEHICLE, and the SKIN. A sys- tematic procedure has been de,•eloped for evaluating the physical-chemical properties of a topical CORTICOID and for custoln-tai]oring a vehicle to its requirements. A series of in vitro and in vivo tests is used for further screening and evaluation of vehicle efficacy and drug ,availability. The goal has been the design of a dosage form which not only has good physical stability and patient acceptability, but which also provides the optimum environment for the release of the corticoid from the vehicle and its penetration through the skin barrier. A case history is presented to illustrate the utility of such an approach. INTRODUCTION Topical therapy provides a unique opportunity to deliver drugs directly to the disease site, in high concentration, with minimal potential for the provocation of systemic side effects. Frequently, the percutane- ous absorption of a drug is a singularly inefficient process. The goal of the topical formulator should be to design a dosage form which not only has good physical and chemical stability, cosmetic acceptability, etc., but also provides the optimum environment for the painstakingly synthe- sized active ingredient in terms of its ability to reach the intended target * Institute of Pharmaceutical Sciences, Syntex Research, Stanford Industrial Park, Palo Alto, Calif. 94301. 565