Transdermal drug delivery involves the controlled time-release of medication through the skin to the bloodstream, usually from a patch that is adhered to the body. Advantages include steady and mild drug delivery rates that reduce shock to the system as might occur with intravenous infusions, the ability to deliver medication to nauseated or unconscious patients that would be otherwise delivered in oral form, and ease of use.
Consider a square patch of length and width L = 50 mm that consists of a host medium containing an initial, uniform density of medication, pA,p,i = 100 kg/m3. The patch is applied to the skin, which contains an initial drug concentration of pA,s,i = 0. At the patch-skin interface located at x = 0, the ratio of the medication density on the patch side to the medication density on the patient side is described by a partition coefcient of K = 0.5.