Transdermal drug delivery: 30+ years of war and still fighting!

By any measure, transdermal drug delivery (TDD) is a successful controlled release technology. Over the last 30+ years, a steady flux of transdermal products have received regulatory approval and reached the market. For the right compounds, TDD is an effective and preferred route of administration; for others, delivery across the skin makes no sense at all. Currently, the "rules" that govern (passive) TDD feasibility are clearly understood, and research activity is focused on novel approaches that strive to subvert skin's excellent barrier function, and broaden the range of active species amenable to percutaneous administration.