Table 1: Clinically relevant cross-reactivity among beta-lactam antibiotics

Cross-reactivity among beta-lactam antibiotics with similar or identical side chains has been documented. For patients with an immediate allergy to one beta-lactam, it is reasonable to avoid agents with similar side chains.

Note: There are no shared side-chains between penicillins and cefazolin, ceftriaxone or ceftazidime.

Shared side-chains: penicillins and cephalosporins

  • Amoxicillin, ampicillin and cefadroxil, cefprozil, cephalexin, cefaclor*

Shared side-chains: cephalosporins

Please note there are 3 groups of cephalosporins with shared side chains. Antibiotics listed within each group demonstrate cross-reactivity

  • Cefadroxil, cefprozil, cephalexin, cefaclor*
  • Cefepime, ceftriaxone, cefotaxime
  • Cefuroxime, cefoxitin

Shared side-chains: cephalosporins and monobactam

  • Ceftazidime and aztreonam

*no longer available in Canada

Last updated: June 2019

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