Pharmacokinetic considerations in the use of newer transdermal formulations.

This review addresses the pharmacokinetics and pharmacodynamics of transdermally delivered drugs. The systemic input of drugs via the skin has attracted considerable interest over the past 15 years. The early promise of the administration route has, to some extent, been realised with the approval and successful launching of transdermal formulations of hyoscine (scopolamine), glyceryl trinitrate (nitroglycerin), clonidine and oestradiol. The further application of transdermal delivery, however, will require additional effort. While other molecules (e.g. testosterone, fentanyl, nicotine) may ultimately be administered in this way, important questions pertaining to pharmacology (tolerance), toxicity (irritation, sensitisation) and dose sufficiency (penetration enhancement) remain. These problems are illustrated using information which has been published in the literature. Overall, while the enthusiasm for attraction and benefits of transdermal delivery remain evident, it is clear that future successes will demand a heightened level of commitment and skill from the pharmaceutical scientist.