A 6-month dermal toxicity test with dithranol and butantrone in miniature swine.

Continuous topical administration of dithranol and butantrone for 6 months caused different irritation profiles in miniature swine. In paraffin wax sticks in white petrolatum, butantrone gave rise to much less initial irritation than dithranol, but after 2-3 weeks the situation had equalized. In gel formulations, butantrone was initially more irritant than dithranol. The vehicles themselves induced significant irritation. Signs of skin hyperplasia (parakeratosis and acanthosis) and inflammation were frequent histopathological findings at the end of the study, but no malignant changes were found. Dithranol and butantrone did not produce any chemical, hematological or serious histological abnormalities during the treatment, suggesting a lack of systemic toxicity. No evidence of systemic absorption was found. This long-term study did not predict delayed irritation of butantrone observed in about 1/3 of the psoriatic patients after treatment for 1-2 months.