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Is This Patient Really Penicillin Allergic?

February 22, 2019

Written by Clay Smith

Spoon Feed
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.

Another Spoonful

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.

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From Nebraska Medicine. Download PDF.

From Nebraska Medicine. Download PDF.

What are your thoughts?