Targets in Dermal and Transdermal Delivery and Classification of Penetration Enhancement Methods

Abstract

The application of drugs via the skin is appealing because it is non-invasive and avoids systemic side effects and numerous problems associated with conventional routes of drug application, i.e. intravenous or oral drug delivery (e.g. hepatic first pass, food enzymes, pH changes, etc.). In addition to this the rate of drug input can be controlled and drugs can be self-administered. The target sites of the body for this mode of drug application can be local tissues, regional tissues and systemic circulation. The drug penetration through the skin includes the route across the stratum corneum (intercellular and transcellular routes) or the route via the hair shafts or sweat pores. The skin’s strong barrier properties make it difficult for drugs to penetrate this barrier and achieve therapeutic doses at the site of disease. There are approximately 20 transdermal products on the market, and this number has not shifted much in the past decade. Many of the drugs need help to penetrate the skin. There are a large number of methods that enhance dermal as well as transdermal drug delivery. These methods are broadly chemical and physical, have different modes of action and can be used alone or synergistically. This chapter is a brief overview of targets in skin delivery of drugs and methods used to enhance drug penetration.