Drug Interaction Report

Theoretically, coadministration of dapsone with inducers of CYP450 3A4 such as rifamycins, anticonvulsants, barbiturates, and St. John's wort may increase the formation of dapsone hydroxylamine, a metabolite associated with hemolysis. Dose-related hemolysis is the most common adverse event associated with oral dapsone in both patients with or without glucose-6-phosphate dehydrogenase (G6PD) deficiency. While clinical studies have not demonstrated evidence of clinically significant anemia in patients treated with dapsone 5% gel for acne vulgaris, an increased reticulocyte count and a decreased hemoglobin level were noted to be associated in a G6PD-deficient patient. Exposure to dapsone from the recommended topical dose is about 1% of that from a 100 mg oral dose.

GENERALLY AVOID: Concurrent acute use of barbiturates and ethanol may result in additive CNS effects, including impaired coordination, sedation, and death. Tolerance of these agents may occur with chronic use. The mechanism is related to inhibition of microsomal enzymes acutely and induction of hepatic microsomal enzymes chronically.

MANAGEMENT: The combination of ethanol and barbiturates should be avoided.