When patients with severe allergies to penicillin (urticarial, bronchospasm, anaphylaxis, angioedema) are excluded, the cross reactivity to cephalosporins is very low (approximately 0.1%)
The reaction is related to structures in the side chain, not the cyclical structure as thought in the past.
There are several cephalosporins with IDENTICAL side chains that should not be given to patients with allergies to specific penicillins, namely:
Penicillin: do not give cefoxitin
Ampicillin: do not give cefaclor or cephalexin
Amoxicillin: do not give cefadroxil or cefprozil
References
The Medical Letter on Drugs and Therapeutics • December 24, 2012 (Issue 1406) p. 101.
