Dapsone-Induced Methemoglobinemia in a Woman With Multiple Myeloma Without Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency.

Methemoglobinemia is a condition characterized by the presence of abnormal hemoglobin, known as methemoglobin, in the blood, which impairs the ability of red blood cells to carry oxygen effectively. Symptoms include cyanosis, shortness of breath, fatigue, and in severe cases, organ damage or death. We presented a case of a 49-year-old female with multiple myeloma who developed drug-induced methemoglobinemia while on dapsone prophylaxis for Pneumocystis carinii pneumonia (PCP). Despite normal glucose-6-phosphate dehydrogenase (G6PD) levels, the patient exhibited cyanosis and shortness of breath. The case underscores the importance of considering methemoglobinemia in patients with unexplained hypoxemia, especially when associated with medication use. Diagnosis relies on clinical assessment, arterial or venous blood gas analysis with co-oximetry, and a thorough medication history. Methemoglobinemia poses a diagnostic challenge due to its varied presentations and requires a high index of suspicion, particularly in patients with multiple myeloma receiving potentially causative medications such as dapsone. Thorough evaluation, interdisciplinary collaboration, and prompt treatment are essential for favorable outcomes in these complex cases.