Methemoglobinemia secondary to benzocaine topical anesthetic

An 80-year-old white woman with a history of hypertension presented to the Emergency Department with bright red bleeding from the rectum, She was treated with 5 mg of midazolam and benzocaine topical anesthetic spray prior to undergoing colonoscopy and esophageal gastroduodenoscopy. Thirty minutes after endoscopy, the patient became cyanotic and dyspneic; she was suffering from methemoglobinemia, a rare complication secondary to the use of benzocaine topical anesthetic spray. After i.v. administration of methylene blue, 120 mg (2 mg/kg) in 100 cc of normal saline solution, the cyanosis and dyspnea resolved.