[Pharmacokinetics and efficacy of skin medications]

Topical therapy of the skin begins with the liberation from a carrier substance and results in a subsequent diffusion of the drug into the horny layer, depending on the physical and chemical properties of the respective agents. By permeating the epidermis the drug may be taken up by the inner compartment, namely the blood. A rediffusion to the skin is possible following systemic application. Although equivalent processes are induced by systemic and topical application, the latter application form limits the permeability including the first pass effect to the skin and its microcirculation. The characteristics are influenced by the type of dermatoses and by the condition of the horny layer as a barrier. The binding of these drugs to the skin's fibers and cells as well as the intensity and degree of permeation in the microcirculation is also of importance. The topical application of antihistamines, corticosteroids, heparin, coffein and nicotinic acid esters are used to describe the relationship between pharmacokinetics and effectiveness in view of clinical-experimental aspects. This pharmacoanalysis is based for the most part on factors which influence the microcirculation, namely the development of erythema, edema and thermography. The pharmacokinetics of topically applied substances are altered by the therapeutic effectivity of these agents and by the resulting changes in the structures of the skin.