Allergic reactions to local anesthetics.

The majority of adverse reactions to local anesthetics are due to high plasma levels from excessive quantities of a drug. These are often blamed on idiosyncrasy, sensitivity, or allergy. The incidence of reactions due to allergy to local anesthetics is low compared to that with other drugs. Allergic reactions may be systemic or local. More than 80% of reactions are cell mediated, resulting in contact dermatitis. The remainder are caused by circulating antibodies that give rise to systemic anaphylaxis. Acute anaphylactic reactions are rare but invariably fatal unless promptly treated. Localized systemic anaphylactic reactions manifested by urticaria, laryngeal edema, and extrinsic asthma are less serious and amenable to treatment. There is no foolproof test for screening of susceptible persons. The intradermal test is of no value for detecting possible systemic sensitivity. The patch test is useful for detecting contact allergy. Systemic reactions are treated with epinephrine, antihistamines, and steroids. Contact dermatitis responds to topical steroids.