Cephalosporin allergy: Characterization of unique and cross-reacting cephalosporin antigens

Twelve subjects who had developed immediate allergic reactions after the administration of a cephalosporin were studied in order to identify the allergenic determinants involved in the induction of the reactions and to study the cross-reactivity with penicillins and with cephalosporins of different generations. Skin tests and assays of IgE antibodies specific to determinants of benzyl penicillin (BP), amoxicilin (AX) and ampicillin (AMP) were carried out. In addition, skin tests and IgE-radioimmunoassays (RIA) were performed with the cephalosporins responsible. In some patients who presented skin-test positivity only to cephalosporins, cross-reactivity among these drugs was studied by skin testing with a panel of first-, second-, and third-generation cephalosporins. Skin testing for immediate hypersensitivity demonstrated positive reactions to cephalosporins in 10 subjects, with IgE- RIA confirmation in 5. The other two patients presented IgE-RIA positivity with skin test negativity. Six out of the 12 subjects developed a positive response to cephalosporins and to one or mare penicillin determinants, indicating cross-reactivity with penicillins. The other 6 developed a positive response only to cephalosporins. In this group, two patterns of reactivity were observed: one where the specificity seemed to be limited to the cephalosporin responsible and another where cross-reactivity among different cephalosporin structures existed.