[Transdermal drug delivery systems].

Transdermal drug delivery systems are pharmaceutical preparations, intended to be applied to the unbroken skin in order to deliver the active ingredient(s) to the systemic circulation after passing through the skin barrier. Transdermal patches are formulated in different ways, but normally they consist of release liner, adhesive layer and backing layer. Active ingredient(s) can be incorporated in reservoir, matrix, adhesive, membrane-matrix and microreservoir. The releasing rate of active substances from patches is controlled by membrane, matrix and adhesive. Only several transdermal systems are available on the market today, because for the penetration of most substances skin represents a strong barrier. With transdermal systems it is possible to obtain a controllable and sustained plasma levels, to minimaze the risk of undesirable side effects and to avoid the hepatic first- pass metabolism. These devices are easy to apply and also to remove from the skin. Of a great pharmaceutical interest are also socalled cosmetic patches. They are applied with aim of cleaning and protecting the skin.