UMEM Educational Pearls

Category: Pharmacology & Therapeutics

Title: Cephalosporin Side Chains and Allergies

Keywords: Cephalosporin,penicillin,anaphylaxis,urticaria,cross sensitivity (PubMed Search)

Posted: 11/7/2013 by Ellen Lemkin, MD, PharmD (Updated: 5/29/2024)
Click here to contact Ellen Lemkin, MD, PharmD

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


The Medical Letter on Drugs and Therapeutics • December 24, 2012 (Issue 1406) p. 101.