Transdermal drug delivery: problems and possibilities.

Transdermal drug delivery has, in recent years, attracted considerable interest. However, despite the obvious advantages of this novel route of drug administration to achieve systemic therapeutic effect, there remain important, and sometimes severe, limitations on the physiochemical and pharmacological properties of the agent to be delivered. This article reviews the present status and accomplishments of transdermal drug delivery. The benefits, disadvantages, and, as yet, unresolved problems inherent to drug input via the skin are addressed. Deficiencies in our knowledge of the percutaneous absorption process in man are identified, and approaches to elucidate these unknowns are discussed. Finally, with respect to the future potential of transdermal drug delivery, experimental and modeling techniques, which can be employed to assess the feasibility and promise of a therapeutic candidate, are described and illustrated with pertinent examples.