Lack of cross-reactivity between aztreonam , a monobactam antibiotic, and penicillin in penicillin-allergic subjects.

Monobactam antibiotics are a new class of beta-lactam antibiotics. In contrast to penicillins or cephalosporins, monobactams possess a monocyclic beta-lactam structure. IgE or immediate hypersensitivity cross-reactivity between aztreonam (a monobactam) and penicillin was investigated, since this will be an important consideration when therapy is chosen. The maximum concentration of aztreonam reagents not giving false-positive skin tests was determined in normal subjects who were not allergic to penicillin. Subsequently, 41 subjects with IgE antibody to one or more penicillin moieties, as determined by positive skin reactions, were tested with the aztreonam reagents. Thirty-seven of these persons showed no reactivity while four showed equivocal tests. Repeat tests in those four persons were negative to the aztreonam reagents, while their penicillin tests remained unchanged. These in vivo data suggest that there is no cross-reactivity between IgE antibodies to penicillin and aztreonam and provide a basis for investigating the therapeutic use of monobactams in patients who are allergic to penicillin.