Dermal and Transdermal Novel Drug Delivery Systems

The skin, due to its large surface area and ease of accessibility, is an attractive pathway for both local (dermal) and systemic (transdermal) drug delivery. Drug administration through the skin provides several advantages such as high patient compliance, consistent blood levels of the drug, avoiding drug degradation in the gastrointestinal tract as well as hepatic first-pass metabolism, and reduction of systemic side effects. However, the skin (and particularly, the stratum corneum ) acts as an impervious barrier against drug permeation. Practically, the number of drugs with optimal physicochemical properties to permeate through the skin is very low. Therefore, novel approaches and systems have been developed to conquer this limitation. This chapter first gives a brief introduction to the skin and its barrier properties, as well as the opportunities and challenges ahead, and factors affecting percutaneous drug delivery. Then, we delve into different scenarios for overcoming the skin barrier, including temporal disruption of the stratum corneum , bypassing it, molecular modification of drugs to acquire optimal features to permeate through the skin, and using advanced carriers, formulations, or devices to improve drug delivery. In the following, a variety of novel strategies and systems including chemical and physical permeation enhancement methods, nanocarriers, microneedles, patches, transdermal sprays, and advanced transdermal formulations that have been developed to facilitate the delivery of therapeutics to the skin will be reviewed. Next, the fate of the drug after entering the skin (i.e., dermal and transdermal pharmacokinetics) will be overviewed; and finally, the novel skin products available in the market will be highlighted.