Dapsone is a leprostatic agent commonly prescribed for the treatment of patients with leprosy, malaria, and a variety of blistering skin diseases, including dermatitis herpetiformis. Methemoglobinemia, a potentially life-threatening condition in which the oxygen-carrying capacity of blood in body tissues is reduced, is a known adverse effect of dapsone use. The authors report a case of dapsone-induced methemoglobinemia observed in the emergency department during routine workup for contact dermatitis in a patient with celiac disease. The pathophysiologic mechanisms, diagnosis, and management of dapsone-induced methemoglobinemia are discussed
