Benzocaine-Induced Methemoglobinemia Attributed to Topical Application of the Anesthetic in Several Laboratory Animal Species

Case reports of benzocaine-induced methemoglobinemia following application of topical anesthetics have been noted for man, cats, dogs, and sheep. Elevated levels of methemoglobin (MHb) could be a possible confounding variable for several types of experimental studies. We designed a screening study using a common topical benzocaine-containing anesthetics. Response to benzocaine spray occurred in most individuals tested, with response peaking between 15 and 30 min after dosing. A positive MHb response ranged from 3.5% to 38% and occurred in over 95% of individual animals and occurred from 15-60 min after drug administration. Responses were quite variable due to the screening nature of the study and the topical route of drug administration but the highest responses occurred in rabbits and cats, the lowest in mice and dogs. MHb could be a confounding variable for several types of studies; investigators should consider this toxicity of benzocaine-containing topical anesthetics and use appropriate alternative methods or drugs (i.e. lidocaine). Pub. in American Jnl. of Veterinary Research, v54 n8 p1322-1326, Aug 1993.