Transdermal Patches as Noninvasive Drug Delivery Systems

Abstract

The most common pharmaceutical dosage forms applied to the skin to deliver an exact dose of active substance through the skin into the bloodstream are self-adhesive transdermal drug delivery systems or transdermal patches. There have been many attempts to manufacture transdermal patches that deliver many different active substances, but this process has proved to be quite tedious and difficult, as active substances must meet a long list of strict criteria for their transdermal delivery to be possible. Transdermal patches as physical devices differ in their composition and manufacturing method. They are designed and manufactured as multi-layered, single-dose pharmaceutical preparations. Components of a solid adhesive transdermal patch are: backing layer, liner, reservoir or polymeric matrix with the incorporated active substance, rate controlling membrane (in reservoir-type transdermal patches, mostly), and the pressure-sensitive adhesive. Most of these components are made of different polymers, which allows adjustment of a transdermal patch’s mechanical and adhesive properties, among others. Transdermal patches release active substances through various mechanisms. In order for the active substances to be released from a transdermal patch, solubilization of active substances needs to occur, followed by diffusion. This diffusion follows first-order kinetics and is usually represented by the two- or five-compartmental kinetic model of the skin.