UMEM Educational Pearls

Category: Pharmacology & Therapeutics

Title: Carbapenem Cross-Reactivity in Penicillin-Allergic Patients

Keywords: carbapenem, penicillin, allergy, skin test, cross-reactivity (PubMed Search)

Posted: 8/26/2012 by Bryan Hayes, PharmD (Emailed: 9/1/2012) (Updated: 9/4/2013)
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Carbapenems (meropenem, ertapenem, doripenem, imipenem/cilastatin) are broad-spectrum antibiotics that have good gram-negative and anaerobic coverage and are used to treat resistant bacterial infections.

  • Early retrospective studies showed ~10% cross-reactivity in penicillin-allergic patients.

  • More recent prospective studies verified penicillin allergy by the accepted standard (ie, skin test to the major and minor penicillin determinants) and tested for carbapenem allergy by administering a full therapeutic dose to carbapenem skin test-negative patients.

  • The cross-reactivity between skin tests appears to be around 1%, with all carbapenem skin test-negative patients tolerating the challenge.

Key point: Remember that only 10% of patients reporting penicillin allergy actually have a true IgE allergy. It's like a built-in, 10-fold safety factor.
Bottom line: In a patient reporting a penicillin allergy, the incidence of cross-reactivity to a carbapenem is probably around 0.01%. With cross-reactivity this low, it is likely that if a patient does have a reaction to the carbapenem, they are independently allergic to that drug too.


Frumin J, Gallagher JC. Allergic cross-sensitivity between penicillin, carbapenem, and monobactam antibiotics: what are the chances? Ann Pharmacother 2009;43(2):304-15.

Herbert ME, Brewster GS, Lanctot-Herbert M. Medical myth: ten percent of patients who are allergic to penicillin will have serious reactions if exposed to cephalosporins. West J Med 2000;172:341.

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