Book excerpt: This authoritative volume explores advances in the techniques used to measure percutaneous penetration of drugs and chemicals to assess bioavailability and bioequivalence and discusses how they have been used in clinical and scientific investigations. Seven comprehensive sections examine topics including in vitro drug release, topical drugs products, clinical studies, and guidelines and workshop reports, among others. The book also describes how targeted transdermal drug delivery and more sophisticated mathematical modelling can aid in understanding the bioavailability of transdermal drugs. The first edition of this book was an important reference guide for researchers working to define the effectiveness and safety of drugs and chemicals that penetrated the skin. This second edition contains cutting-edge advances in the field and is a key resource to those seeking to define the bioavailability and bioequivalence of percutaneously active compounds to improve scientific and clinical investigation and regulation.