Acute toxic methemoglobinemia caused by a topical anesthetic.

A case is presented in which respiratory distress resulted from the production of methemoglobin Following application of topical benzocaine to a child’s oral mucous membrane. Modern local anesthetics are among the safest of administered agents, with few reported cases of morbidity or mortality. The use of topically applied local anesthetic agents is important in the atraumatic administration of regional block anesthesia and for performing minor procedures. Topical anesthetics poorly penetrate intact tissue but can penetrate abraded skin or injured mucous membranes. Concentrations of agents used for topical application are considerably higher than those of the same agent when used for injection. The higher concentration of these agents also leads to a greater potential toxicity. Because topical anesthetics generally are vasodilators, vascular absorption can be rapid, and levels in the blood quickly may reach those achieved by direct intravenous administration. Topical anesthetics are available in ointments, gels, or pressurized spray containers. These dosage forms can present difficulties in determining accurately the amount of anesthetic a patient receives during a procedure. This report presents just such a situation -a case in which severe systemic effects resulted from application of the topical anesthetic benzocaine.