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Allergic Reactions Did You Know. . . Although the incidence of allergic reactions to local anesthetics has decreased, they are still documented. Allergic reactions to local anesthetic agents may occur as a result of sensitivity to 1) either the ester or amide component, 2) the methylparaben used as a preservative in the multiple dose vials, or 3) the antioxidants used in some formulations. Allergic reactions may consist of cutaneous lesions, urticaria, edema, or anaphylactoid reactions. See Table 1 for a comparison of local anesthetics. Ester local anesthetics are associated with a higher incidence of allergic reactions due to one of their metabolites, para-amino benzoic acid (PABA). PABA is structurally similar to methylparaben. Amide local anesthetics do not undergo metabolism to PABA, and therefore hypersensitivity to amide local anesthetics is rare. Because of these possible hypersensitivity reactions, many manufacturers have reformulated some of their products to eliminate methylparaben. Some of these products include: Nesacaine-MPF, Lidocaine-MPF, Polocaine-MPF, and Sensorcaine-MPF. A ruling by the Food and Drug Administration mandated the removal of methylparaben from all local anesthetic dental cartridges. Antioxidants (sodium bisulfite, metabisulfite) are added to local anesthetic products that contain vasoconstrictors (epineprhine, levonordefrin) to prevent biodegradation by oxygen. Some patients may also be allergic to sulfites, and for this reason antioxidants should be avoided. It may be difficult to determine the allergy of the patient and skin testing can be utilized. It is rare that a patient would be allergic to both an ester and amide local anesthetic. However, the following guidelines may assist in selecting an appropriate local anesthetic. Guidelines:
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