Processes of drug transfer with three different polymeric systems with transdermal drug delivery

The transdermal drug delivery exhibits two main advantages over the conventional oral delivery, by-passing the hepatic first-pass, and maintaining the plasma drug level at a plateau over a long period of time. The role of the transdermal therapeutic systems is to apply a constant drug concentration on the skin for a long time, while the skin acts as a membrane. Thus the drug transfer through the skin reaches a constant rate under stationary conditions after a short time under transient conditions. Three transdermal therapeutic systems are considered: a monolithic device made of a polymer containing the drug; this monolithic device in contact with a drug reservoir; a porous polymer containing the drug. The monolithic device can maintain a constant drug delivery only when the diffusivity of the drug through this polymer is very high. In association with a reservoir, this device becomes more efficient. The system made of a porous polymer with convective transfer of the drug appears to be more effective, providing a constant drug concentration on the skin surface, which is responsible for a constant rate of drug transfer through the skin and a constant plasma drug level over a long period of time.