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Is it prudent to use regional anesthesia in a patient who reports a Novocain allergy?
Details of the patient’s previous reaction are critical to the decision process. Many patients reporting a Novocain allergy received local anesthesia for a dental procedure. The term Novocain is frequently used by laymen to refer to all local anesthetics. Novocain is the trade name for procaine, an ester-type local anesthetic. Most dentists today use lidocaine, mepivacaine, or bupivacaine, with or without epinephrine. Although true allergic reactions to local anesthetics are uncommon, when they occur, episodes are usually the result of exposure to the ester-type local anesthetics. These agents are metabolized to para-aminobenzoic acid, a known allergen. The agents most often used by dentists are amides. Allergic reactions are mediated by antibodies and/or complement activation and are characterized by urticaria, pruritus, angioneurotic edema, hypotension, and/or bronchospasm. Frequently, patients reporting adverse reactions from local anesthetics actually experienced the effects of high blood levels of local anesthetics or epinephrine rather than true allergic reac-tions. Elevated blood levels of local anesthetics often lead to circumoral numbness, dizziness, tinnitus, blurred vision, drowsiness, or frank seizures. Tachycardia, hyper-tension, and hypotension may also occur as side-effects. Differentiation between an allergic reaction and the recog-nized side-effects of high blood levels becomes critical. Allergy skin testing has met with inconsistent results and remains an unreliable technique. Cross allergenicity between ester and amide local anesthetics does not seem to exist.
Although amide local anesthetics rarely produce true allergic reactions, the preservative methylparaben may be detrimental in some patients. Methylparaben is an aller-gen similar to para-aminobenzoic acid and may also produce allergic reactions. Therefore, it is advisable to use preservative-free solutions whenever possible.
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