Abstract

Dapsone is used for Pneumocystis jirovecii pneumonia (PCP) prophylaxis in patients with human immunodeficiency virus (HIV) infection who cannot tolerate trimethoprim–sulfamethoxazole (TMP-SMX), the first-line agent. Methemoglobinemia is a known adverse effect of dapsone, usually associated with glucose-6-phosphate dehydrogenase (G6PD) deficiency, but it may also occur in patients with normal enzyme activity. We report a case of early-onset methemoglobinemia in a newly diagnosed HIV-infected patient without G6PD deficiency receiving dapsone for PCP prophylaxis. A 24-year-old male with a CD4 T-cell count of 32/mm³ developed decreased oxygen saturation approximately 72 hours after starting dapsone. Despite minimal symptoms, methemoglobin levels increased up to 11.5%. Dapsone was discontinued, and the patient was treated with methylene blue with rapid improvement. Although dapsone-induced methemoglobinemia is well described, reports in HIV-infected patients receiving dapsone for PCP prophylaxis are limited. This case highlights that methemoglobinemia may occur without G6PD deficiency and emphasizes early recognition.