Metahemoglobinemia asociada a primaquina en paciente pediátrico con anemia severa tratada con ácido ascórbico: reporte de caso

Primaquine-associated methemoglobinemia is an uncommon condition that requires clinical suspicion. We present the case of a 10-year-old girl admitted with severe bothropic snakebite. During hospitalization, she was diagnosed with malaria and severe anemia (hemoglobin 4.2 g/dL), requiring red blood cell transfusion and treatment with chloroquine and primaquine. On the eight day, she developed respiratory distress, with an oxygen saturation of 80% and requiring supplemental oxygen. Arterial blood gas analysis showed a methemoglobin level of 10.5%, with a PaO2 of 158 mmHg with an FiO2 of 50%, leading to a diagnosis of methemoglobinemia. Primaquine was discontinued, and intravenous ascorbic acid was administered, followed by clinical improvement. Glucose-6-phosphate dehydrogenase (G6PD) levels were measured to assess the potential use of methylene blue, the result was reported as normal after clinical improvement, and therefore methylene blue was not required. This case highlights the importance of recognizing the discrepancy between oxygen saturation and PaO2 as a finding suggestive of methemoglobinemia, promptly identifying and discontinuing the causative drug, and preventing complications. It also emphasizes the need to consider this adverse drug reaction even in patients with normal G6PD levels and recognize the contraindication of methylene blue in patients with G6PD deficiency.