Transdermal drug delivery: progress and challenges

There are a number of advantages associated with transdermal drug delivery. With this route of administration, it is possible to avoid pain and presystemic metabolism. In addition, pharmacokinetic profile of the drug is more uniform with fewer peaks and troughs. However, the outermost layer of the skin. the stratum corneum. constitutes a strong barrier making it difficult for permeants to cross the skin at clinically relevant rates. This review examines progress made over the last 4 decades and challenges ahead. Over this period, about 35 transdermal products have been approved by regulatory authorities. About 19 drugs have been formulated into transdermal patches and approved by the Food and Drug Administration. The main challenge lies with the formulation of macromolecules- proteins, small interfering RNA and other products of biotechnology into transdermal delivery systems. This challenge is being met with approaches such as microneedles, iontophoresis, sonophoresis and electroporation.