Cross Reactivity:See the comprehensive B-lactam cross-reactivity chart for groups of ß-lactams that may cross-react.
- Cross reactivity between penicillins is related to the ß-lactam ring ± side chains.
Between penicillin & cephalosporins:
~ 1% in patients who report a penicillin allergy
2.55% in those with a confirmed penicillin allergy
Cross reactivity between penicillins and cephalosporins is related to the similarity of the side chain structure.
NB: Cefazolin is NOT expected to cross-react with any penicillin or cephalosporin as it does not have a similar side chain as any other β-lactam.
Between penicillins and carbapenems:
[Clin Infect Dis 2014;59:1113-22]
4.3% for any type of hypersensitivity reaction
2.4% for IgE-mediated reactions
Among cephalosporins, and between cephalosporins and carbapenems:
- The degree of cross reactivity is unknown but is thought to be very low.
(not commercially available in Canada)
- Minimal cross reactivity except with ceftazidime (common side chain).