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Penicillin Allergy Patients Can Safely Take Oral Challenge without Prior Skin Test, Study Finds

Although many patients list a penicillin allergy on medical forms, these allergies are very often either unconfirmed or low-risk, researchers have learned. Emory University scientists are revisiting penicillin allergy labels in these patients, and they’re finding that direct oral amoxicillin challenges in a doctor’s office, even without prior skin testing, are acceptable in individuals with an unconfirmed or low-risk penicillin allergy.

Some 1 in 10 hospitalized patients in the general population reports a penicillin allergy, but new research shows that 98 percent of these individuals are tolerant of penicillin or are not acutely hypersensitive. Emory researchers published their recent findings in Allergy & Asthma Proceedings.

“Penicillin is a very effective drug that we use to treat many illnesses, but many people avoid it because they think they are allergic,” says Merin Kuruvilla, MD, assistant professor of allergy and immunology at Emory University School of Medicine and lead author of the Emory study. “The rate of true penicillin sensitization is very low and has been shown to decline over time,” she adds.

Some pediatric patients may have been initially diagnosed with a penicillin allergy because of symptoms that were caused by the illness that the penicillin was meant to treat, according to Dr. Kuruvilla. “Viruses are known to cause benign rashes that can be mistaken for a penicillin allergy,” she says.

In reality, Kuruvilla explains, penicillin allergies have more severe implications than just rashes. “It is associated with an increased duration of hospitalization, the use of suboptimal antibiotics, and an increased risk of antibiotic-related adverse events, like C diff,” she says.

Evaluating penicillin allergy labels is crucial because if no allergy is present, a patient can be prescribed the highly effective drug. Of late, the medical community is reevaluating its primary testing strategy for penicillin allergies. The skin test, which has a 50 percent false positive rate, is becoming less common for low-risk patients without a history of immediate onset anaphylaxis.

“Now the trend is to perform a direct oral amoxicillin challenge, either as a full dose or graded challenge where you start with a small dose of amoxicillin and increase it,” Kuruvilla says.

The Emory research looked at 50 people labeled with a penicillin allergy. Four of them were de-labeled on the spot because it had been more than 10 years since they last experienced hives or rashes after taking penicillin. A direct oral amoxicillin challenge was given to 20 individuals who’d experienced mild symptoms or had an unknown history associated with their last penicillin exposure more than a year ago. They were all monitored for an hour after the challenge.

None developed hypersensitivity reactions to the researchers’ knowledge. Three patients (15 percent) had dizziness and other self-limited subjective symptoms that were deemed not to be a true penicillin allergy. Overall, 24 of the 50 patients (48 percent) thought to have a penicillin allergy had the label deleted from their medical record.

It’s important for an oral amoxicillin challenge to be performed in an allergist’s office since patients do run the risk, although extremely low, of developing anaphylaxis,  Dr. Kuruvilla says, adding, “In our study, if the history was suggestive of any severe adverse reactions, then the person would screen out of any further penicillin testing.”

All in all, there are some common misconceptions about penicillin allergies.

“One misconception is that many people are allergic to penicillin and these allergy labels are lifelong,” Kuruvilla says. “ Another misconception is that people must have the skin test to determine if they’re truly allergic. In fact, most patients who come through the office are candidates for a direct oral amoxicillin challenge.”

Low- or no-risk penicillin allergy can be confirmed with oral challenge test, Emory Nes Center.
Direct oral amoxicillin challenge without preliminary skin testing in adult patients with allergy and at low risk with reported penicillin allergy, NCBI.

Last updated on 9/30/19.

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