Hydroxylamine-metabolites of dapsone cause methemoglobinemia. The use of this drug has been shown to reduce dapsone-induced methemoglobinemia.
Cimetidine partially inhibits the conversion of dapsone into its hydroxylamine metabolites through CYP 3A inhibition. Coleman MD et al. co-administered 1200 mg cimetidine to six patients receiving dapsone therapy. The co-administration of cimetidine resulted in a sustained decrease in dapsone mediated methemoglobin formation by 25%.
Coleman MD et al. The use of cimetidine to reduce dapsone-dependent methemoglobinemia in dermatitis herpetiformis patients. Br J Clin Pharmacol 1992; 34: 244-249.