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Study seeks to disprove cephalosporin allergies

Jul. 7, 2022, 9:10 AM


by Nancy Humphrey

Cephalosporin antibiotics are widely prescribed for common infections such as bronchitis, otitis media, pneumonia and cellulitis. They are also administered as first-line prophylaxis for many types of surgical procedures.

Patients who report an allergy to one of these drugs can therefore face major barriers when their doctors are trying to decide what antibiotic to use. Cephalosporin allergies are reported by about 1-2% of the population, which is less than the number who report penicillin allergies (10-15%).

Previous research by Grace Koo, MD, and Cosby Stone Jr., MD, MPH, assistant professor of Medicine in the Division of Allergy, Pulmonary and Critical Care Medicine, showed 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 who are recovering from critical illness.

Up to 95% of labeled penicillin allergies reported by 10-15% of the U.S. population may be inaccurate, they said.

Similarly, most patients who report cephalosporin allergies are unlikely to actually have an allergy to these antibiotics, which are commonly used in both the inpatient and outpatient settings.

Vanderbilt University Medical Center research has previously shown that only 8-9% of patients who believed they were allergic to cephalosporins tested positive to one of the drugs.

But determining whether someone is allergic to a medication currently requires time consuming and expensive monitored testing conducted in an allergy clinic, which is not readily available in all settings.

Grace Koo, MD

To address this, a new VUMC study done in the Drug Allergy Clinic and reported recently in the Journal of Allergy and Clinical Immunology: In Practice, shows that taking a careful history in patients who report allergies to cephalosporins and separating them into risk categories can help identify which patients are at low risk to be truly allergic to these antibiotics.

“Cephalosporins, like penicillin, are used in the intensive care unit setting and to treat infection in outpatient settings, and surgeons often prescribe them prior to surgeries and during surgery,” said Koo, first author of the study and a clinical fellow in the Allergy Immunology Fellowship program who will join the VUMC faculty next month. “These two sets of drugs are our go-to as far as first-line antibiotic treatment,” she said.

“We know from research that has been done so far that the risk of cephalosporin allergies and whether patients truly have this allergy, mirrors what we know about penicillin allergies,” she said.

Koo said someone whose history puts them in a low-risk category for a cephalosporin allergy is less likely to be allergic. “A low-risk history would include things that happened when they took the medication that are least concerning to us — a mild reaction a long time ago, or a rash that resolved by itself, or if a relative had a cephalosporin allergy, or if someone’s stomach was upset after they took it,” she said.

“This led to our observation that patients who report having reacted to an oral cephalo-sporin with a low-risk history are exceedingly unlikely to be allergic (less than a 1% chance), and could potentially go straight to an observed test dose to disprove their allergy when they have a need for these medicines, without the need for as much testing.”

However, there was one caveat in the study. The researchers noted that people who had previously reacted to IV cephalosporins rather than oral cephalosporins were more likely to test positive, and that such patients should be treated with greater caution if a test dose was being considered.

Further studies to define the safety and benefits of directly challenging patients who report a low-risk cephalosporin allergy with a test dose are being planned.

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