(A) 5 mL
(B) 10 mL
(C) 15 mL
(D) 20 mL
(E) 25 mL

The correct response is Option B.

In otherwise healthy children older than 3 years of age who have normal lean body mass, the maximum safe dose of lidocaine (Xylocaine) that can be administered is determined by the child's age and weight. The maximum safe dosage in a 22-kg 5-year-old child is 22 multiplied by 4.5, or 100 mg of lidocaine. At a 1% concentration, which contains 10 mg lidocaine per milliliter (mL), the maximum dose is 10 mL, according to the manufacturer's recommendation.

Reference
1. Physicians' Desk Reference. Montvale, NJ: Medical Economics Co; 2000:638.

In a 50-year-old woman who has a history of allergic reaction to tetracaine, which of the following anesthetics should NOT be used?

(A) Bupivacaine
(B) Etidocaine
(C) Lidocaine
(D) Mepivacaine
(E) Procaine

The correct response is Option E.

All local anesthetics can be classified as either ester- or amide-type. Ester-type local anesthetics, including procaine, benzocaine, chloroprocaine, and tetracaine, can produce allergic reactions. These anesthetics are metabolized by pseudocholinesterase, forming para-aminobenzoic acid (PABA). This compound triggers antibody formation and lymphocyte stimulation to elicit a hypersensitivity reaction. In one study of patients who had no known history of allergy to local anesthetics, 30% of patients developed a positive skin reaction following intradermal injection of an ester-type anesthetic.

Amide-type local anesthetics, including bupivacaine, etidocaine, lidocaine, and mepivacaine, are used more frequently for local infiltration than ester-type agents. These are stable solutions that do not cause true allergic reactions. Any "allergic" reaction to amide-type local anesthetics is most likely caused by methylparaben, a preservative that is structurally related to PABA. Preservative-free local anesthetics are currently available for use in any patient who has sensitivity to methylparaben. In the same study mentioned above, there were no allergic reactions to the amide-type agents. A trick to help remember which complexes belong to which group is that all amides have an "i" in the prefix before the "caine" (ie, bupivacaine, etidocaine, lidocaine, and mepivacaine).

References
1. Aldrete JA, Johnson DA. Evaluation of intracutaneous testing for investigation of allergy to local anesthetic agents. Anesth Analg. 1970;49:173.
2. Berde CB, Strichartz GR. Local anesthetics. In: Anesthesia. 5th ed. New York, NY: Churchill Livingstone, Inc; 2000:516.
3. deShazo RD, Nelson HS. An approach to the patient with a history of local anesthetic hypersensitivity: experience with 90 patients. J Allergy Clin Immunol. 1979;63:387.
4. Giovannitti JA, Bennett CR. Assessment of allergy to local anesthetics. J Am Dent Assoc. 1979;98:701.
5. Incaudo G, Schatz M, Patterson R, et al. Administration of local anesthetics to patients with a history of prior adverse reaction. J Allergy Clin Immunol. 1978;61:339.