Irritation and staining by dithranol (anthralin) and related compounds. III. Cumulative irritancy and staining during repeated chamber testing.

Irritation and staining, the side effects of dithranol and related compounds have previously been studied after a single chamber-exposure. To mimic the therapeutic situation, the chamber application was repeated for 3 weeks on the uninvolved back skin of 17 psoriasis patients. In equimolar concentrations corresponding to 0.05% dithranol, dithranol caused markedly more erythema and staining than 10-propionyl dithranol and 10-butyryl dithranol, whereas 10-butyryl dithranol irritated and stained less than 10-propionyl dithranol. To reach the irritation and staining level of dithranol, a 4-fold higher concentration of 10-butyryl dithranol was required. During the first week the irritation culminated, declining later despite repeated applications, possibly because of exhaustion of anthrone-induced inflammatory mediators.