Adverse drug reactions (ADRs) are a major clinical issue which can prolong hospitalization and increase overall healthcare costs. JCAHO requires hospitals to have a concurrent ADR monitoring system in place.

Drug Therapy will be featuring potentially avoidable examples of ADRs in this and upcoming issues for education purposes.

Cases:
Three patients undergoing transesophageal echocardiograms developed symptoms of methemoglobinemia (acute desaturation, gray skin color, and lethargy) shortly after the administration of topical benzocaine spray. Two of the patients were treated with methylene blue. The third was treated with O2 and oral ascorbic acid.

Topical benzocaine spray 20% is commonly used where local anesthesia of the oropharynx is required. There are a number of case reports of methemoglobinemia secondary to benzocaine administration. The severity of the methemoglobinemia symptoms has a direct correlation with methemoglobin concentration. Symptoms usually become apparent when levels reach 10% to 30% of the total hemoglobin. The symptoms range from fatigue and dizziness to tachycardia, dyspnea, and cyanosis. At greater than 50% levels, patients can be seen to experience seizures, coma, arrhythmias, metabolic acidosis, and even death. Treatment should be prompt, with airway management including 100% O2, intubation, and ventilation. In more severe cases, methylene blue 1-2mg/kg 1% solution may be injected slow IV push over 5 minutes. This dose may be repeated after 30 minutes if the patient is symptomatic or if the methemoglobin level is >30.

"Here's Our Reaction":

• The potential for methemoglobinemia exists from the use of topical benzocaine.
• Topical administration should be limited to a 1-second spray. Note: MGH will be transitioning to a benzocaine 20% metered spray containing 50 mg per activation.
• Benzocaine spray should not be used for general sore throat or throat discomfort. Good alternatives in this instance are cetylpyridinium lozenges (1 lozenge every 4 hours prn throat discomfort) or Chloraseptic Spray (1 spray every 4 hours prn).

Ultimately, ADR reporting will lead to positive patient outcomes.

Report ADRs by:

• Paging your floor pharmacist
• Filing an incident report
• Calling the ADR Hotline at 6-1575.

Selected References:

1. Spielman FJ, Anderson JA, Terry WC. Benzocaine-induced methemoglobinemia during general anesthesia. J Oral Maxillofac Surg 1984; 42:740-743.

2. Wright RO, Lewander WJ, Woolf AD. Methemoglobinemia: etiology, pharmacology, and clinical management. Ann Emerg Med. 1999; 34: 646-656.

3. Guerriero SE: Methemoglobinemia caused by topical benzocaine. Pharmocotherapy 1997; 17:1038-1040.

4. Slaughter MS, Gordon PJ, Roberts JC et al. An unusual case of hypoxia from benzocaine-induced methemoglobinemia. Ann Thorac Surg 1999; 67:1776-1778.

5. Stoiber TR: Toxic methemoglobinemia complicating transesophageal echocardiography. Echocardiography 1999; 16: 383-385.

6. Walker JP, Houston H, Miller S et al. Acute methemoglobinemia secondary to topical benzocaine spray. Advanced Studies in Medicine. 2003; 3:45-48.

7. Byrne MF, Mitchell RM, Gerke H et al. The need for caution with topical anesthesia during endoscopic procedures, as liberal use may result in methemoglobinemia. J Clin Gastroenterol 2004; 38:225-229.

8. Rodriguez LF, Smolik LM, Zbehlik AJ. Benzocaine-induced methemoglobinemia: report of a severe reaction and review of the literature. Ann Pharmacother 1994; 28: 643-649.