Methylene blue-A double-edged sword in the treatment of methemoglobinemia in a patient with emamectin benzoate poisoning: A case report

Abstract

Emamectin benzoate (EB), a widely used avermectin-derived pesticide, rarely causes mammalian toxicity but can induce severe methemoglobinemia following acute exposure. We report a case detailing the management of EB-induced methemoglobinemia, complicated by methylene blue-induced hemolytic anemia in a non-G6PD-deficient patient. A 34-year-old male presented with altered sensorium, hypoxemia, and severe methemoglobinemia (63%) 6 h post-ingestion of 15 mL EB (1.9%). While early intubation and targeted pharmacotherapy (methylene blue and Vitamin C) successfully normalized his methemoglobin levels, his clinical course was complicated on day six by non-G6PD-deficient hemolytic anemia (hemoglobin drop: 13.8–6.5 g/dL). The patient recovered fully following supportive therapy and red blood cell transfusion. This case demonstrates that while methylene blue effectively reverses 
EB-induced methemoglobinemia, it can precipitate severe, delayed hemolytic anemia even in G6PD-normal patients. This suggests a potential synergistic hematologic toxicity between EB and methylene blue. Clinicians should maintain prolonged vigilance for hemolysis and carefully weigh alternative therapies for methemoglobinemia.