Systematic review of methemoglobinemia in acetaminophen poisoning

Acetaminophen (N-acetyl-p-aminophenol paracetamol (APAP)) toxicity is one of the commonly encountered poisonings by emergency physicians. Methemoglobinemia is an uncommon association and rarely seen in APAP poisoning. The study involves the retrospective analysis of all the published reports on APAP-induced methemoglobinemia from 1968 to 2019. In total, there were 14 cases with nine females and six males. The median age of the study cohort was 59 years. The most common presenting feature was altered mentation (nine patients) followed by cyanosis (three patients). The intent of consumption was therapeutic (seven cases) vs. suicidal (five cases) attempt. In most cases, the dose of APAP consumption was not known. Aspirin, sulfasalazine, benzocaine spray, nitrate preservative, contaminated water, detergents, and so on where the other agents consumed by the patients in addition to APAP before developing methemoglobinemia. The median MethHb level of the study cohort was 15.85%. Patients were treated with NAC, hemodialysis, methylene blue and ascorbic acid and continuous renal replacement therapy in various combinations. Full recovery was seen in nine patients while four patients died. APAP toxicity is a well-known and a common entity with multiple sequelae that presents with a variable spectrum of mild to fulminant multiorgan failure. Awareness of non-classical presentations like methemoglobinemia is essential to ensure timely intervention.