A Case Report of Benzocaine-Induced Methemoglobinemia

Methemoglobinemia is a serious medical condition characterized by the disrupted binding of oxygen to iron on hemoglobin, with a consequent impaired oxygen delivery to body tissues. Various drugs including the local anesthetics such as benzocaine can cause acquired methemoglobinemia. The reported case describes methemoglobinemia that occurred in association with the use of topical benzocaine spray and lozenges in a previously healthy 51-year-old female who had undergone colon surgery to remove a bleeding polyp. Pulse oximetry revealed the patient was hypoxic and a measured methemoglobin (MetHB) serum concentration was 32.4%, well above the normal of less than 2%. Treatment with intravenous methylene blue resulted in a rapid improvement in the patient's respiratory status. The case emphasizes the need for practitioners to appreciate that topical benzocaine products can cause potentially fatal methemoglobinemia.