Preparation and study of the characteristics of dithranol:polyvinylpyrrolidone coevaporates

Dithranol:polyvinylpyrrolidone (Di:PVP) 1:2, 1.4, 1:9, 1:14, 1:25 and 1:40 coevaporates were prepared to increase the aqueous dispersibility of this hydrophobic and water insoluble drug, used for the topical treatment of psoriasis. The coevaporates contained small crystals of Di as well as nanoparticles of Di, embedded in the PVP matrix. This submicron fraction increased with increasing PVP, up to a DI:PVP ratio of 1:25. The coevaporates exhibited a hydrophilic character, allowing easy dispersion in water. This dispersion contained very small particles of submicron size (average diameter 0.1 mu m) and an insoluble part consisting of small Di crystals. When the insoluble fraction nias eliminated by filtration, an aqueous stable colloidal dispersion of Di was obtained. This extreme particle size reduction, combined with an enhanced hydrophilic character should provide Di with interesting characteristics for topical treatment of psoriasis. (C) 1998 Elsevier Science B.V. All rights reserved.