Abstract

Dithranol is a valuable agent in the treatment of chronic discoid psoriasis. Properly used it can clear the lesions in most patients without any of the adverse effects of the strong topical corticosteroids.¹ Dithranol inactivates various enzymes, binds with DNA, and inhibits mitosis, but the basis for the therapeutic effect is not fully understood.² The main drawbacks of dithranol preparations, which often make patients reluctant to treat themselves, are dose-related irritancy, especially affecting normal skin, and staining of skin, clothing and bedclothes. To reduce the spread to normal skin, dithranol is usually applied accurately to psoriatic plaques in a stiff base (Zinc and Salicylic Acid Paste BPC). The salicylic acid in this preparation appears to prevent oxidation of the dithranol to an inactive compound.²