Further studies on the interaction between anthralin salicylic acid and zinc oxide in pastes.

Abstract

The interaction of ZnO, salicylic acid, and anthralin in various forms of paste and in hexane solution was studied, as well as the interaction of pastes with various solid surfaces. In zinc oxide paste (P.Z.O.) anthralin is rapidly converted into therapeutically inactive compounds. The deterioration of anthralin paste is initiated on the surface of ZnO or, in the presence of water, also on other—chemically rather inert—surfaces. The deteriorating effect of ZnO can be greatly reduced by the addition of salicylic acid, but none of the attempts to eliminate the deteriorating effect of other surfaces (skin, lint, glass wool etc.) were successfull. It is shown that the protective effect of small amounts of salicylic acid is achieved by deactivation of the surface of ZnO, due to the formation of surface zinc salicylate. A zinc oxide paste containing salicylic acid, an Amylum paste, and Lactacyd pH 2 were found to be good vehicles for anthralin in the clinical treatment of psoriasis vulgaris.