Concepts and Applications in Topical and Transdermal Drug Delivery

Abstract

Topical and transdermal drug delivery involves crossing the main barrier of the skin, the stratum corneum (SC). Basically, the SC is the outermost layer of the skin, formed by dead comeocytes immersed in a lipid matrix which limits the skin penetration and permeation of drugs. Some characteristics are needed for the drug to be delivered passively, like adequate lipophilicity and limited molecular weight. These requirements have limited the number of commercially available products based on 4transdermal or topical delivery. Briefly, the transdermal delivery system is capable of delivering the drug through the skin into the blood circulation, preferentially at a constant rate. Topical administration is responsible for delivery in different skin layers, depending on the drug’s physicochem-ical characteristics and desired effect. Nowadays, many strategies have emerged to improve skin delivery to or through the skin, and these can be categorized into passive and physical methods. For passive delivery of drugs, chemical penetration enhancers can be used to improve skin penetration and/or permeation of drugs. Instead, physical methods such as iontophoresis, sonophoresis, and microneedles can be used to overcome the skin barrier. In this chapter, we will present an overview of skin structure and focus on the most used approaches to overcome the SC, with special attention to topical and transdermal drug delivery aiming at different health sciences applications. Finally, some clinical applications will be presented and discussed.