Testing of controlled-release transdermal dosage forms. Product development and clinical trials.

In vitro techniques have been developed that are predictive of drug permeation through skin. Methods also have been developed to determine the skin irritation potential of a drug substance during the preclinical stages of transdermal dosage form development. Clinical studies are performed to test for skin irritation, contact sensitization, plasma levels of drug, and efficacy of the dosage form. In theory, these studies should be predictive of a dosage form's performance in routine clinical use. This may not be the case, however; contact sensitization cannot be predicted with absolute certainty beforehand in animals. This article discusses various aspects of testing transdermal dosage forms and how the results of these tests correlate with what happens when a transdermal dosage form is put into routine clinical use.