Amide and Ester Local Anesthetic Allergy

An ultrasound-guided regional nerve block is an evolving trend in ED procedural sedation. The thought being, local anesthetics could be used instead of benzodiazepines, ketamine or propofol, which could allow for earlier patient discharge from the ED and lower risk of complications (respiratory depression).

Navigating the library of local anesthetics can be complex, particularly if your patient reports some allergy to lidocaine or prilocaine or if the drug is on shortage (an evolving problem in the US). Let’s just pretend it’s an allergy that you concerned enough about to not use that particular drug, but does that mean local anesthetics are off-limits?

Not necessarily.

Local anesthetics are divided into two main groups based on their chemical structure: amides and esters. Generally, allergy or hypersensitivity to an amide local anesthetic does not “cross-react” with ester local anesthetics.

A quick way to remember which agent belongs in which category is that amides generally have two “I”’s and esters have one “I.” The one exception to this is procainamide, which is classified as an ester.


Bupivacaine, lidocaine, mepivicaine, prilocaine, ropivacaine, etidocaine


Procaine, chloroprocaine, tetracaine, cocaine, benzocaine, novocaine, procainamide


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