Drug delivery across the skin

For more than two decades, researchers have attempted to find a way to use the skin as a portal of entry for drugs in order to overcome problems associated with traditional modes of drug administration. This has been a complicated task due to the highly effective barrier properties of the skin. In order to deliver drugs through the skin, most compounds require various degrees of permeation enhancement. Classic enhancement methods focused primarily on chemical enhancement or modulation of interactions between the drug and the vehicle. More recent research makes use of innovative vesicular carriers, electrically assisted delivery and various microinvasive methods, some incorporating technologies from other fields. These new and exciting methods for drug delivery are already increasing the number and quality of dermal and transdermal therapies. This review discusses the different types of permeation enhancement, both classic and innovative, and summarises the current strengths and shortcomings in the field with an emphasis on those that have led to products on the market or in the pipeline.