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Allergic reactions to ester anesthetics are primarily attributed to para-amino benzoic acid (PABA), a metabolite of these anesthetics. When ester anesthetics like procaine are metabolized in the body, they break down and release PABA, which has the potential to trigger hypersensitivity reactions in some individuals. This is the reason why individuals who have a known allergy to esters often react specifically to PABA rather than the anesthetic itself.

In contrast, other anesthetics listed, such as lidocaine and bupivacaine, are classified as amides and are generally considered less likely to provoke allergic reactions. They do not metabolize into PABA; thus, they are less associated with this type of allergic response.

Understanding the role of PABA is crucial for practitioners in recognizing and managing potential allergic reactions in patients, particularly those with a history of sensitivity to ester-type local anesthetics.