A Case of Topical Benzocaine-Induced Methemoglobinemia

Abstract

The author reports a case of topical benzocaine-induced methemoglobinemia. Benzocaine is a topical anesthetic commonly used during minor surgical and cannulation procedures. Although not widely reported, benzocaine has the potential to induce severe or life-threatening methemoglobinemia. Clinical practitioners should be cognizant of this complication associated with benzocaine use and its appropriate management. The following report describes a case of topical benzocaine-induced methemoglobinemia in a 74-year-old, Caucasian woman who had undergone transesophageal echocardiography and who received topical benzocaine for local anesthesia. Ten minutes after the administration of benzocaine, her oxygen saturation levels decreased to 71%, requiring immediate attention. Co-oximetry (multiple wavelength spectrophotometry) measured methemoglobin levels indicated the presence of methemoglobinemia. The patient was subsequently treated with 60 mg of intravenous methylene blue. Within 10 minutes, the patient’s condition had improved. The primary etiology of methemoglobinemia is from exposure to oxidizing agents. Benzocaine is an oxidizing agent commonly used as a topical anesthetic. Topically applied benzocaine, in the patient described here and in other reported cases, produced elevated methemoglobin levels requiring treatment with a reducing agent. Methylene blue, within a specified dosage range, can serve as a reducing agent to reverse the effects of topically applied benzocaine-induced methemoglobinemia.