Cross-allergenicity and immunogenicity of aztreonam

The immunochemistry of aztreonam, the prototype of the new monobactam class of beta-lactam antibiotics, was studied in a series of experimental and clinical investigations. Rabbit antibodies to aztreonam and naturally occurring human antibodies that recognize aztreonam were found to have negligible cross-reactivity with benzylpenicillin, cephalothin, and cefotaxime. Aztreonam likewise displayed negligible cross-reactivity (less than or equal to 0.001%) with antibodies to penicillin (including human IgE antibodies to major and minor penicillin determinants) and to cephalothin. These studies suggest that aztreonam may be well tolerated by penicillin-allergic individuals, and this possibly is now being evaluated in clinical trials. Seven (6.25%) of 112 healthy persons tested had preexisting IgG antibodies to aztreonam in low titer, presumably as a result of exposure to naturally occurring cross-reacting moieties. Only two of seven patients with preexisting IgG antibodies to aztreonam had a rise in titer following aztreonam treatment. No IgE antibody to aztreonam was detected in serum specimens obtained on day 10 during any of the 112 courses of therapy. These clinical observations suggest but do not prove that aztreonam has only weak potential to elicit a drug-specific immunologic response.