Transdermal Drug Delivery: More Than Skin Deep

The idea of taping an adhesive patch filled with a drug or rubbing a drug-laced cream into the skin makes intuitive sense. Such products are easy to use, noninvasive, nonintrusive, don't upset the stomach, and with long-release formulations one application lasts many hours or even days. The first blockbuster transdermal drug, the nicotine patch, suppresses a smoker's craving for cigarettes with a steady 16-hour trickle of nicotine; the fentanyl patch provides 72 hours of pain relief; and women who use contraceptive patches apply them just once a week. However, at present only 20 marketed drugs come in FDA-approved transdermal patches and about 100 more are absorbed through the skin in ointment or gel formulations. The limitations of present transdermal drug delivery systems – particularly the skin's imperviousness to macromolecules – hold back growth. Several recent moves by Big Pharma, though, indicate a continuing and possibly growing interest in coming up with transdermal formulations for new and existing drugs, and numerous biotechs, including the four profiled in this issue, believe they can find exciting new ways to capitalize on the transdermal opportunity, particularly as specialty pharmaceuticals have increasingly come to the fore.

Stuck to the skin, patches work passively to diffuse a drug across the stratum corneum, the lipid and remnant epidermal...