Written by Clay Smith
Penicillin allergy is a lot less common than patients report. A low-risk history could allow you to prescribe it in the ED or clinic.
Why does this matter?
Penicillin and other β-lactam antibiotics are some of the most effective. Use of alternatives is often unnecessarily broad-spectrum, promotes resistance (including MRSA and VRE), increases side effects, and increases risk of C. difficile. But what can we do if a patient reports an allergy? Quite a lot…
My great grandfather was allergic to penicillin; so, I never take it.
Ten percent of people in the US report allergy to penicillin, but more than 95% of them are actually able to tolerate β-lactams. Cross-reactivity to cephalosporins had been previously reported to be 8% but is actually only ~2% and depends on the R-group side chain. See figure below.*
Low-risk includes: GI side effects only, chills, headache, fatigue, or family history of allergy. Such patients may be prescribed amoxicillin with no period of observation. If they have other low-risk features of pruritus without rash or unknown reaction not suggestive of an IgE-mediated reaction > 10 years ago, they may be given a dose of amoxicillin and observed for an hour. If they tolerate amoxicillin, then they can safely tolerate all β-lactam antibiotics.
Moderate risk includes: urticaria, pruritic rash, or features of IgE-mediated reaction. Such patients need skin testing prior to amoxicillin challenge.
High risk includes: anaphylaxis, positive skin testing, recurrent reactions, or reaction to multiple β-lactam agents. Such patients should be managed by an allergy specialist and not given penicillin.
This JAMA article references Nebraska Medicine’s Penicillin Allergy Guidance Document. This is an excellent resource (screenshot below*).
Evaluation and Management of Penicillin Allergy: A Review. JAMA. 2019 Jan 15;321(2):188-199. doi: 10.1001/jama.2018.19283.
Open in Read by QxMD
Reviewed by Thomas Davis
*Cross-Reactivity of Penicillins and Cephalosporins
Cross reactivity of penicillin-allergic patients to cephalosporins has more to do with the R1 side chain than the β-lactam ring. Carbapenem cross-reactivity is <1%, and there is no cross-reactivity with monobactams.