Percutaneous egression: What do we know?

Background: The process by which drugs leave the bloodstream to enter the skin compartments is important in determining appropriate routes of delivery and developing more efficacious medications. We conducted a general literature review on percutaneous egression mechanisms. Summary: Studies demonstrate that the stratum corneum (SC) is a compartment for systemically delivered drugs. Upon reviewing the available literature, it became apparent that there may be multiple mechanisms of percutaneous egression dependent upon drug physiochemical properties. These mechanisms include, but are not limited to, desquamation, sebum secretion, sweat transport and passive diffusion. While drugs often utilize one major pathway, it is possible that all mechanisms may play a role to varying extents. Key Messages: Available literature suggests that hydrophilic substances tended to travel from blood to the upper layers of the skin via sweat, whereas lipophilic substances utilized sebum secretion to reach the SC. Upon reaching the skin surface, the drugs spread laterally before penetrating back into the skin as if they were topically administered. More data are warranted to identify additional percutaneous egression mechanisms, precise drug action sites and accelerate drug development.