Which local anesthetic is more likely to cause allergic reactions?

Ester anesthetics are more likely to cause allergic reactions due to their chemical structure and the presence of para-aminobenzoic acid (PABA) in their metabolic pathway. When esters are metabolized, they are broken down into PABA, which can trigger hypersensitivity reactions in susceptible individuals. This allergic potential is a significant characteristic of ester local anesthetics, making them a concern in patients with a known sensitivity to PABA.

In contrast, amide local anesthetics are less frequently associated with allergic reactions. Their metabolism does not involve PABA, which significantly reduces the risk of allergic responses. While it is still possible for some patients to have allergic reactions to amides, the incidence is considerably lower compared to esters. Hence, the distinctive structural and metabolic features of ester anesthetics make them more likely to be associated with allergic reactions.