EM Perles: For your ED pharmacology pearls
Clinical Conundrum:
A patient comes in with a laceration that needs repairing but the patient reports an allergy to the local anesthetic Tetracaine, What do you do?
Background:
Currently available local anesthetics fall into 2 general categories, esters and amides. Local anesthetics that are considered an "ester" (ie, benzocaine, chloroprocaine, cocaine, procaine, tetracaine) may be more likely to result in an allergic reaction since the para-aminobenzoic acid (PABA) metabolite of ester anesthetics have been associated with allergic reactions.
However, allergic reactions to "amides" (ie, bupivacaine, lidocaine, mepivacaine, prilocaine, ropivacaine) have also been reported but to a lesser extent.
Answer:
A true confirmed IgE-mediated reaction to an ester or amide containing agent should prevent use of other agents in the same structural group, but agents from the other group may be safe to use.
In practice, cross-sensitivity between ester and amide agents has been rarely reported and is usually attributed to preservatives. If an allergy to both classes of local anesthetics is confirmed, alternative anesthetic options should be considered such as diphenhydramine given as a local anesthetic.
Written by:
Joanne C. Routsolias, PharmD, RN, BCPS
Clinical PharmD Specialist - Emergency Medicine/Toxicology
Cook County Health
References:
Eggleston, Lush LW. Understanding allergic reactions to local anesthetics. Ann pharmacother. 1996;30(7-8):851-57.
Bhole MV, Manson AL. Seneviratne SL, et al. IgE-mediated allergy to local anesthetics: separating fact from perception: a UK perspective. Br J Anaesth. 2012:108(6):903-11.
Green SM, Rothrock SG, Gorchynski J: Validation of diphenhydramine as a dermal local anesthetic. Ann Emerg Med 1994; 23:1284-1289.
Ernst AA, Marvez-Valls E, Mall G, et al. 1% Lidocaine versus 0.5% diphenhydramine for local anesthesia in minor laceration repair. Ann Emerg Med 1994; 23:1328-1332.