What to do when patients say they are PCN allergic?
- determine whether an IgE-mediated response (i.e. anaphylaxis) occurred
- If so
- third- and fourth-generation cephalosporins can be used generously
- first- and second-generation cephalosporins with R1 side chains similar to PCN should be avoided (see table below)
- first- and second-generation cephalosporins with different R1 side chains can be given (see table below)
- If so
- Skin testing not recommended for determining safety of administering cephalosporins to PCN-allergic patients (because it is unreliable)
- Skin testing does predict true PCN allergy
Penicillin and cephalosporins known to have a risk of allergic cross reaction:
Patients who are allergic to amoxicillin or ampicillin should avoid the cephalosporins listed, because they have similar R1-group side chains.
Myth: ~10% of patients with history of PCN allergy will have an allergic reaction if given cephalosporin.
True: Overall cross-reactivity rate is ~1% when using first gen cephalosporins or cephalosporins with similar R1 chains. PCN-allergic patients, use of 3rd or 4th generation cephalosporins carries a negligible risk of cross allergy.
Campagna, James D. et al. “The Use Of Cephalosporins In Penicillin-Allergic Patients: A Literature Review”. The Journal of Emergency Medicine 42.5 (2012): 612-620.