Transdermal treatments.

Percutaneous absorption has now been largely demonstrated and is defined as the passage of a molecule applied to the skin from the external environment to the blood. This phenomenon takes place in two main steps: penetration and actual absorption. Percutaneous absorption avoids the first-pass effect to which orally and rectally administered molecules are submitted, although these molecules can be metabolized in the skin, but to a much lesser degree that by hepatic metabolism. Transdermal devices present many advantage compared to forms administered by other routes: improved patient compliance, easy self-administration, prolonged plasma plateau levels. However, it depends on the skin type and, in the case of allergic reactions, other classical forms designed for the cutaneous route, such as ointments or gels. There are two types of transdermal device: so-called matricial forms, which are semi-solid or solid preparations in which the active ingredient(s) can be dispersed or dissolved; reservoir systems, in which one of the walls is a membrane, placed directly on the skin. In the case of the nitroglycerin, plasma curves are essentially identical regardless of the type of device used. The active ingredients currently available on the market in the form of transdermal devices are scopolamine, nitroglycerin, 17-beta-oestradiol, nicotine, and, for the future, forms containing fentanyl, timolol, ephedrine... are currently being developed.