ABSTRACT
Percutaneous absorption, excretion kinetics, and metabolism of dithranol triacetate (2) have been investigated in Wistar rats. By the use of two differently labelled molecules--3H in the anthracene nucleus and 14C in the acetoxy groups of 2, resp.--the fate of the different parts of the dithranol triacetate molecule could be followed. After injection, large amounts of 2 are cleaved under the influence of enzymes into acetate and dithranol. These deacetylated metabolites lose half their 3H label with formation of 3H2O. In urine, 1,8-diacetoxy-9-anthrone, 1-acetoxy-8-hydroxy-9-anthrone, 1,8-dihydroxy-9,10-anthraquinone and its diacetate were found as metabolites. After dermal application, unchanged 2 is practically not absorbed at all. Arylesterases which, according to in vitro studies, are present in or on the skin, hydrolyse dithranol triacetate to give free dithranol. Up to 33% of the latter are absorbed from under an occlusive dressing. Dithranol triacetate, therefore, shows pro-drug characteristics for the treatment of psoriasis.
