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.

Total radioactivity in the blood of rats for 5 hr following rectal administration of 3H-benzocaine in oleaginous, absorption, emulsion (water-in-oil and oil-in water), and water-soluble ointment vehicles was measured. The release was greatest from the water-soluble vehicle and followed the same relative order as seen in an earlier in vitro experiment. No intact benzocaine was found in the blood using radiochromatography. In vitro hydrolysis of benzocaine by rat blood did not occur as determined with the techniques of this experiment.