A Vanderbilt study shows that physicians can safely identify and disprove low-risk penicillin allergies using an oral amoxicillin challenge in consenting patients, even those in the intensive care unit (ICU) who are recovering from critical illness.

This finding, reported in The Journal of Antibiotic Allergy and Clinical Immunology: In Practice, shows that similar approaches can be made in other settings where patients are likely to benefit, said Cosby Stone Jr. MD, MPH, assistant professor of Medicine in the Division of Allergy, Pulmonary, and Critical Care Medicine and senior author of the study.

“Up to 95% of labeled penicillin allergies reported by 10-15% of the U.S. population may be inaccurate. They don’t test positive for allergy. Unnecessary penicillin allergies are often a barrier to giving the right antibiotic at the right time,” Stone said.

“When a penicillin drug is the first-line antibiotic allergy of choice to treat a patient, and we are avoiding using it because of unnecessary allergy, it can result in treatment failures, prolonged hospitalizations and may increase the chance of surgical infections and multidrug-resistant infections. The second line of antibiotics are often less effective. You can imagine how bad this is for the patient, their doctors, hospitals and the health care system overall in terms of bad outcomes, drug resistance and increased costs,” he said.

Based on previous research, Stone and colleagues involved in penicillin allergy research estimate that patients labeled with a penicillin allergy who are “exceedingly unlikely” to test positive for penicillin allergy comprise between 60-70% of all patients reporting a label of penicillin allergy.

So, they turned their attention to the ICU setting, where patients were in a safe environment in the event of a reaction, and also at higher need for antibiotics.

They offered those low-risk penicillin allergy patients the opportunity to take a dose of amoxicillin to disprove their allergy, without taking a penicillin allergy skin test first.

The 205 low-risk consenting patients were watched carefully for an hour after they were given the amoxicillin. Tolerating that dose over an hour disproves the chance that they will have anaphylaxis during a future penicillin treatment, though patients were reminded that they can still have delayed onset rashes, which were observed in less than 1% of the patients during the challenge or during a subsequent penicillin treatment. A few patients reported stomach upset.

“Over two years, our testing program has already enabled 100 penicillin treatments for these patients that would not have happened otherwise,” Stone said.

“ICU patients often have immunocompromising conditions that predispose them to infections,” said Grace Koo, MD, a clinical fellow in the Allergy Immunology Fellowship program and first author of the study. “Unfortunately, many of these patients also have multiple antibiotic allergy labels, which makes it difficult for providers to choose the best antibiotics to treat these infections. Penicillins are first-line antibiotics for many infections. Therefore, having access to penicillin is particularly beneficial for this patient population, and delabeling is key.”

“Point-of-care direct oral challenge as a delabeling method is safe for patients with low-risk penicillin labels and allows them to be delabeled during their current hospitalization. Our data show that many of these patients are able to tolerate penicillins soon after their delabeling, some during the same hospitalization and others during subsequent health care encounters,” Koo said.

Stone said a challenge is the most definitive way to prove that someone is not allergic to something. “If you put the substance you are worried about into your body in a safe observed setting and nothing major happens, that rules out an allergy.”

Incidentally, Stone said, they discovered during their research that patients have often taken amoxicillin before and didn’t realize that tolerating amoxicillin disproves their penicillin allergy.

The penicillin delabeling research was funded by the federal Agency for Healthcare Research and Quality and the Patient-Centered Outcomes Research Institute.

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