Dapsone-Induced Methemoglobinemia

OBJECTIVE: To report a case of methemoglobinemia in a patient receiving dapsone for prophylaxis of Pneumocystis carinii pneumonia (PCP). CASE SUMMARY: A 69-year-old white woman was hospitalized to rule out sepsis. Two years prior to this admission, the patient received an orthotopic liver transplant after which she required hemodialysis three times weekly. Because of intolerance to trimethoprim/ sulfamethoxazole and aerosolized pentamidine, she was prescribed dapsone therapy on hospital day 13, that was continued for 11 days. On hospital day 45 the patient received a cadaveric kidney transplant, and dialysis treatments were scheduled only as needed. One week after the transplant, dapsone therapy was resumed. Nine days into this course of dapsone, the patient developed dyspnea and oxygen desaturation of unknown etiology. The patient was evaluated for and diagnosed with methemoglobinemia. She received two doses of intravenous methylene blue and one dose of oral activated charcoal due to fluctuating methemoglobin concentrations. DISCUSSION: The elimination of dapsone is not completely understood. Several case reports of dapsone-induced methemoglobinemia are present in the literature. Most have occurred in patients who have accidentally or deliberately overdosed. Cases of methemoglobinemia in patients receiving therapeutic doses of dapsone are discussed. CONCLUSIONS: The growing numbers of immunosuppressed patients due to transplantation of HIV may result in increased dapsone use for the prevention of PCP. Clinicians should be aware of the adverse effects associated with dapsone therapy, and patients with dyspnea and hypoxemia of unclear etiology should be evaluated for methemoglobinemia.