The selection and design of topical and transdermal agents: a review

One of the major problems in topical and transdermal drug delivery is the efficiency of the barrier property of the stratum corneum. Topical and transdermal agents were often originally designed as drugs to be given orally. In this paper a mechanistic evaluation of skin penetration shows that topical and transdermal drugs should be designed using different strategies. The relative effects of basic physicochemical parameters are examined. An understanding, at a molecular level, of the permeation process will enable us to produce more effective topical agents and to extend the repertoire of transdermal drugs.