What is the approximate overall cross-reactivity rate between penicillins and cephalosporins?

What is the approximate overall cross-reactivity rate between penicillins and cephalosporins?

• A. 0%
• B. 1-2%
• C. 5-10%
• D. 20%

Answer: (B)

Cross-reactivity between penicillins and cephalosporins exists, but it is relatively small. The immune response is mostly driven by side-chain similarities, not just the shared beta-lactam ring, so most cephalosporins can be used safely in patients with a penicillin allergy—especially when the penicillin allergy is not severe and the cephalosporin’s side chain differs. The approximate overall cross-reactivity rate is about 1-2%. However, if the cephalosporin has a side chain similar to the penicillin that caused the reaction, or if there is a history of a severe IgE-mediated penicillin allergy, the risk can be higher.

Cross-reactivity between penicillins and cephalosporins exists, but it is relatively small. The immune response is mostly driven by side-chain similarities, not just the shared beta-lactam ring, so most cephalosporins can be used safely in patients with a penicillin allergy—especially when the penicillin allergy is not severe and the cephalosporin’s side chain differs. The approximate overall cross-reactivity rate is about 1-2%. However, if the cephalosporin has a side chain similar to the penicillin that caused the reaction, or if there is a history of a severe IgE-mediated penicillin allergy, the risk can be higher.