Irritation and staining by dithranol (anthralin) and related compounds: I. Estimation with chamber testing and contact thermography.

Irritation and staining by dithranol and some related compounds was studied with the chamber-testing technique in a series of 62 psoriasis patients. Suitable to routine testing of the individual tolerance to dithranol is the use of 0.05 and 0.5 per cent concentrations in petrolatum, exposure of the mid-back skin for 24 hours, and reading of the reactions (erythema, brown staining, edema) on the second day after the application. Contact themography was used when the brown stain hampered the extimation of erythema. Low concentrations of 10 acetyldithranol elicited weaker reactions than dithranol but at the 0.5 per cent level the acetylderivative tended to give stronger reactions than the parent compound. Ten per cent dithranol triacetate caused only occasionally slight erythematous reactions, whereas 10,10'-bis-(formylethyl) dithranol and dithranol anthraquinone elicited no reactions at all. The mechanisms of the staining and inflammatory reactions and possibilities of their reduction are discussed. The use of the chamber-testing technique is recommended to screening of new less irritating and staining hydroxyanthrones for clinical trial.