BACKGROUND

After penicillins, cephalosporins are the most important beta-lactams inducing IgE-mediated reactions. Responses may be selective or cross-reactive with common beta-lactam determinants. Unlike determinants derived from benzylpenicillin, cephalosporin allergenic determinants have not been properly identified, even though a wide variety of these beta-lactams is currently used.

OBJECTIVE

We sought to evaluate the IgE response in subjects with immediate allergic reactions to injectable cephalosporins and to assess their reactivity to different penicillins and cephalosporins.

METHODS

We studied 30 subjects with immediate reactions to one or more of the following cephalosporins: ceftriaxone, cefotaxime, ceftazidime, and cefuroxime. Skin tests and in vitro-specific IgE antibody assays were performed for major and minor determinants of penicillin G, amoxicillin, and ampicillin, as well as for the culprit cephalosporins. Responses to cephalosporins other than the culprit ones were also studied by using skin testing.

RESULTS

Twenty-six patients (group A, 86.7%) displayed skin test and RAST negativity to penicillin determinants and skin test positivity to cephalosporins, with RAST confirmation in 9 patients. Four subjects (group B, 13.3%) had a positive response to penicillin determinants. In group A two patterns of reactivity were observed: one characterized by a response only to the culprit cephalosporin (n = 15, 57.7%) and the other by positive responses to different cephalosporins, including the responsible cephalosporins (n = 11, 42. 3%).

CONCLUSION

Most patients with a history of immediate reactions to cephalosporins are sensitized to determinants generated only by cephalosporins (group A), although a small percentage react to penicillin determinants (group B). Some patients from group A responded only to the culprit cephalosporin, but others reacted to different cephalosporins. These findings can be explained in terms of either selective response to unique determinants or cross-reactivity.