Between Penicillins and Cephalosporins

Risk of cross-reactivity is about 0.5% between first-generation cephalosporins and penicillins, but this lowers with each subsequent generation of cephalosporins.

Cross-reactivity amongst cephalosporins is low, due the heterogeneity of side chains. Therefore a patient with a cephalosporin allergy may be prescribed another cephalosporin, if it contains both dissimilar C3 and C7 side chains.

Cefazolin does not share a side chain with any beta-lactam and is not expected to cross react with other agents

Cross reactions are possible within the same group

Penicillin, Cephalothin, Cefoxitin

Amoxicillin, Ampicillin, Cephalexin, Cefprozil,Cefaclor

Cefepime, Cefotaxime, Ceftriaxone

Cross reactions are possible within the same group

Cefotaxime, Cephalothin

Cefuroxime, Cefoxitin

Ceftazidime, Aztreonam