Dapsone intoxication: two case reports

Two patients with dapsone intoxication, an adult and a 16-month-old child, are reported. Both developed symptomatic methemoglobin concentrations, of 35% and 37%, respectively, and improved with intravenous methylene blue. Methemoglobin levels subsequently rose in both cases to 25% at 24 and 37 hours, respectively. The recurrence of elevated methemoglobin levels resulted from either continued absorption of dapsone or its toxic metabolite from the gastrointestinal tract. Both patients were begun on serial oral activated charcoal and the child received a second methylene blue treatment. During the intoxication, serum hemoglobin concentrations dropped 2 gm with an increase in the reticulocyte count. Review of 20 cases of dapsone overdose from the literature showed that the major toxic manifestations are methemoglobinemia and hemolysis. Delayed sulfhemoglobinemia, reported in only one case, resolved spontaneously. The treatment of dapsone intoxication is intravenous methylene blue for symptomatic methemoglobinemia, gastric decontamination, and early administration of serial oral activated charcoal. Hemolysis is mild but transfusions may be required for patients with a glucose-6-phosphate dehydrogenase deficiency.