Penicillin: Once Allergic Does Not Mean Always Allergic


Approximately 10% of US patients report having an allergic relation to penicillin, yet only 1% of the population are truly allergic.

According to the US Centers for Disease Control and Prevention (CDC), approximately 10% of US patients report having an allergic reaction to a penicillin antibiotic at some point in their lives, yet only 1% of the population are truly allergic to this class of antibiotics.

The Society of Infectious Diseases Pharmacists has launched a podcast series called The Itch. In a miniseries, the podcast panelists discuss different aspects of penicillin allergies. The panelists discuss trends at their institution and what physicians on the frontline should be doing to correctly evaluate their patients accurately for a penicillin allergy.

In an exclusive interview at ID Week 2018 in San Francisco, California, we sat down with Julie Ann Justo, PharmD, MS, BCPS-AQ ID, an assistant clinical professor at the University of South Carolina College of Pharmacy, and infectious diseases clinical pharmacy specialist at Palmetto Health Richland Hospital, Columbia South Carolina. Dr. Justo, a panelist on the podcast, discussed some gaps in understanding penicillin allergies with Contagion® (see video).

“One of the things I think providers fail to do is dig a little bit deeper and discuss the reaction [and] the timing [of the reaction] during their lifetime,” Dr. Justo stressed.

Many individuals who report having a penicillin allergy have not actually experienced a true Immunoglobulin E (IgE)-mediated reaction, according to the CDC. For individuals who have experienced a true IgE-mediated reaction, the CDC estimates that 80% of those patients will lose their sensitivity to penicillin after 10 years.

Dr. Justo explained to Contagion® what individuals should know about being labeled as penicillin-allergic, especially when presenting to the hospital for an illness or infection.

“One of the things that we very much need to educate our patients on is, trust me, you don’t want to be labeled as penicillin-allergic unless you really are,” she explained, “and the reason why is because that whole family of beta-lactam antibiotics, on the whole, are really the safest and most efficacious antibiotics that we have, and they are first-line recommendations for a wide variety of infectious syndromes.”

These infectious syndromes include urinary tract infections and pneumonia among others, and when broad-spectrum antibiotics are used as an alternative to penicillin, they can have negative consequences. These consequences can include higher health care costs, increased risk for resistance, and suboptimal antibiotic therapy.

Therefore, it is critical to correctly identify penicillin allergies to decrease unnecessary use of broad-spectrum antibiotics.

Dr. Justo discussed different penicillin testing options with Contagion® (see video).

“At my center, located in South Carolina, we actually do pharmacist-driven and pharmacist-performed penicillin skin testing which is somewhat unique. We go through the same immunization training and we perform the skin test and get certified and have to keep up our education in order to do so,” she explained.

Penicillin skin testing and challenge doses are reliable and useful methods for evaluating the existence of IgE-mediated penicillin allergy, according to the CDC. The current standard of care is to perform a skin test with the major determinant peniclloylpolylsine and commercially-available penicillin G.

If the skin test is negative, it is usually followed by oral penicillin class challenges to safely rule out an IgE-mediated penicillin allergy.

To learn more about “The Itch” podcast, visit

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