Penicillin Allergy

Penicillin Allergy


Penicillins are a group of antibiotics and include:

  • Penicillin
  • Ampicillin
  • Amoxicillin
  • Cloxacillin
  • Piperacillin-Tazobactam

Cross Reactivity

Cross reactivity between the penicillins is primarily due to shared common antigenic determinants based on similarities in their core ring structure that is common to all penicillins and their side chains that distinguish between the penicillins. Therefore, cross reactivity cannot be based on side chain similarities alone. If a patient has a true allergy to penicillin, all penicillins should be avoided.

Cross reactivity between the penicillins and cephalosporins is primarily due to similarities in side chains and not similarities in the beta-lactam ring strucutre. If a patient has a true penicillin allergy, a cephalosporin with different side chains can be safely administered. Note cefazolin does not share a similar side chain with any other beta-lactam commonly used in Canada. Please refer to the cross reactivity chart to determine if cross allergy is possible between beta-lactams.

Cross reactivity between penicillins and carbapenems is very low. Carbapenems would be a reasonable option when antibiotics are required in patients with an allergy to penicillins.