ABSTRACT
A transdermal drug product is intended to deliver the drug systemically to treat or prevent disorders in locations distant from the site of topical application. Adhesive patches and transdermal drug delivery systems (TDS) of defined shape and size are marketed for systemic action and are intended for the treatment or prevention of a systemic disease. TDS are regarded as new drugs and therefore have to be approved based on clinical safety and efficacy studies. In vitro testing of TDS is considered important in two key areas, defining skin permeation kinetic studies using a diffusion cell system and cadaver skin during the drug development process, and in vitro drug release kinetics, to be used for batch-to-batch release and as a compendial test. For TDS products, a high flux is desired so that the drug can penetrate the stratum corneum so as to be available in sufficient amounts to the systemic circulation for therapeutic effect.
