Independent anaphylaxis to cefazolin without allergy to other β-lactam antibiotics

Immediate hypersensitivity reactions to beta -lactam antibiotics, such as penicillins, are relatively common and usually caused by IgE antibodies to the major and minor antigenic determinants of penicillin, although side-chain-specific reactions to semi-synthetic penicillins have been described. Although sensitivity to cephalosporins may occur because of cross-reactivity to beta -lactam ring structures, immediate hypersensitivity to these medications can be side-chain-specific. Therefore in most patients who react to cephalosporins with immediate anaphylactic hypersensitivity, there should be either preexisting IgE-mediated allergy to penicillin or prior exposure to the specific cephalosporin that produced the reaction. We report here the occurrence, over a 6-month period, of four cases of immediate anaphylaxis to cefazolin given before surgery, in patients lacking a history of penicillin allergy or documented cefazolin exposure. Skin testing for immediate hypersensitivity demonstrated positive reactions only to cefazolin, with no reactivity to other beta -lactams, indicating preexisting unpredictable and unexplainable side-chain-specific immediate allergy to cefazolin.