ABSTRACT

The skin covers a total surface area of approximately 1.8m2 and provides the contact between the human body and its external environment (1). This large and outermost layer of the human body is easily accessible and hence attractive as a noninvasive delivery route for selected drug compounds. Dermal and transdermal drug delivery can have many advantages as compared to other routes of drug administration. Dermal drug delivery is the topical application of drugs to the skin in the treatment of localized skin diseases. The advantage of dermal drug delivery is that high concentrations of drugs can be localized at the site of action (i.e., the skin), reducing the systemic drug levels and therefore also reducing the systemic side effects. Transdermal drug delivery, on the other hand, uses the skin as an alternative route for the delivery of systemically acting drugs. This drug delivery route for systemic therapy can have several advantages as compared to conventional oral drug administration. First of all, it circumvents the variables that could influence gastrointestinal absorption such as pH, food intake, and gastrointestinal motility. Secondly, it circumvents the first-pass hepatic metabolism and is therefore suitable for drugs with a low bioavailability. Thirdly, transdermal drug delivery can give a constant, controlled drug input. This would reduce the need for frequent drug intake, especially of drugs with a short biological half-life. Furthermore, variations in drug plasma levels can be avoided, reducing the side effects in particular of drugs with a narrow therapeutic window. Finally, transdermal drug delivery is easy and painless, which in turn will increase patient compliance (2).