Blue in the Face: Dapsone-Induced Methemoglobinemia in a Woman with Minimal Change Disease

Introduction: Dapsone is a sulfone antibiotic effective for Pneumocystis jiroveci pneumonia (PJP) prophylaxis. It can induce methemoglobinemia, a potentially life-threatening condition marked by impaired oxygen delivery. While glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is a risk factor for developing methemoglobinemia, this complication can develop in its absence. Case Description: A 23-year-old female with minimal change disease flare and a previous allergic reaction to trimethoprim-sulfamethoxazole was placed on prednisone 30 mg daily with concurrent dapsone for PJP prophylaxis. G-6-PD level measured prior to starting therapy was elevated at 15.8U/g Hb (9.8-15.5 U/g Hb). She immediately developed progressively worsening perioral cyanosis, burning sensation of her lips and face and difficulty concentrating. On evaluation 4 days later, pulse oximetry revealed 92% on room air. PaO2 was 93 mm Hg. There was no "saturation gap," however arterial methemoglobin was 7.3%. Dapsone was discontinued, and intravenous methylene blue administered, leading to rapid clinical improvement and resolution of methemoglobinemia. Discussion: This case emphasizes the potential for dapsone-induced methemoglobinemia even in young individuals without classic risk factors, like G-6-PD deficiency or underlying respiratory disease. Early recognition of clinical features is crucial for prompt diagnosis and treatment. Methylene blue remains the first-line therapy for symptomatic methemoglobinemia. This case underscores the need to vigilantly monitor patients taking dapsone, regardless of age or traditional risk factors. A high index of suspicion for methemoglobinemia in the setting of unexplained cyanosis or hypoxia can potentially prevent more serious complications.