ABSTRACT
Delivery of drugs into systemic circulation via skin has generated lots of interest during the last decade. Transdermal drug delivery systems offer many advantages over the conventional forms or sustained release delivery systems. When technically feasible, topical delivery of drug products for both local and systemic indications offer many advantages over oral or parenteral routes, such as the need for fewer administration, constant blood level, elimination of the potential for both under and overdosing, and avoidance of first-pass metabolism. Skin structure shows that it is relatively impermeable to exogenous substances and drugs. Understanding this structure will help us to improve drug delivery using prodrugs, chemical enhancers, iontophoresis, electroporation and ultrasound waves. This review will overview the structure and function of skin, the skin routes, the interactions between skin and drug delivery systems and advantageous and disadvantageous of skin as a route for drug delivery. Thus the properties and interactions of three entities-the skin, the drug and the drug delivery excipients-is going to be considered