Dapsone-Induced Methemoglobinemia in a Patient with Acute Lymphocytic Leukemia Admitted with Severe Legionella Pneumonia

Dapsone is an antibacterial medication used as an alternative to the first-line therapy (sulfamethoxazole-trimethoprim) for Pneumocystis pneumonia prophylaxis. Methemoglobinemia is a known toxicity of dapsone. However, dapsone-induced methemoglobinemia in an acute lymphocytic leukemia (ALL) patient with severe Legionella pneumonia has not been previously reported. We describe a 37-year-old male with ALL who was admitted for severe Legionella pneumonia sepsis, rhabdomyolysis, and multiple organ failure. The patient was started on broad-spectrum antibiotics and subsequently intubated for respiratory failure. The patient's methemoglobin level was 24.5%. The repeat methemoglobin level was 28.7%; intravenous methylene blue 100 mg was given for a total of 2 doses after which the methemoglobin level decreased to 2.5%. The patient was extubated 4 days after the second dose of methylene blue. He was later discharged home in stable condition. This patient developed severe sepsis with multiorgan failure, which resulted in acute liver and renal insufficiencies. The decreased metabolism and excretion of dapsone and its toxic metabolite is the likely cause of methemoglobinemia in this patient. Immunocompromised oncology patients who develop severe sepsis require careful monitoring for dapsone-induced methemoglobinemia. Liver dysfunction and renal failure may both potentiate toxicity with prophylactic doses of dapsone.