The most common antibiotics given perioperatively are penicillins, cephalosporins, gentamicin, and vancomy-cin (in patients with methicillin-resistant Staphylococcus aureus) (Thong and Yeow-Chan 2004). (3-Lactam antibiotics are estimated to cause 400-800 fatal anaphylactic episodes per year. The skin test is the most reliable method for evaluating suspected anaphylaxis to penicillin; 97% of patients with a negative skin test reaction will tolerate penicillin administration. Thus the skin test has a high negative predictive value. With the presence of a positive history and a positive skin test reaction, the patient has at least a 50 % risk of an immediate reaction to penicillin (Bernstein et al. 1999). Positive drug-specific IgE test results may suggest a diagnosis of penicillin allergy; however, negative tests are unreliable. Thus, skin tests are preferred.

The cross-hypersensitivity between penicillins and cephalosporins is less than 5%-10%. Skin tests for cephalosporins are not standardized, and the negative predictive value is unknown.

Desensitization maybe considered for patients with a positive skin test reaction to penicillin who require penicillin or cephalosporin in absence of suitable non-P-lactam alternatives (Borish et al. 1987; Kelkar and Li 2001).

Vancomycin hypersensitivity usually leads to skin flush (red man syndrome) and commonly occurs from direct mast cell histamine release. Diagnosis is made from clinical history. If the flush does not respond to a slower rate of infusion, a protocol similar to desensitization maybe considered (Wazny and Daghigh 2001).

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