Dr. Thanai Pongdee’s team tested 384 patients who all reported penicillin allergy. A shocking 94 percent of the tests came back negative. In a second Mayo Clinic study of 38 self-declared penicillin allergic people, no one tested positively for the allergy.
Pongdee, a Mayo Clinic allergist-immunologist, presented the findings at an annual meeting of the the American College of Allergy Asthma and Immunology. Then in 2018, he and a colleague published published an analysis of several studies to conclude that: “80 to 90 percent of individuals with self-reported penicillin allergy are actually able to tolerate penicillins” after a physician’s evaluation.
That paper, published in Mayo Clinic Proceedings, offers guidance to physicians and notes that there are considerable financial and health costs to labeling someone “penicillin allergic”. (That is, unless they truly do have the allergy.) Pongdee and his colleague write that: “Antibiotic costs are 63 percent to 158 percent higher for those with reported penicillin allergy than for those not allergic to penicillin.”
The alternative antibiotics also aren’t as effective, leading to longer hospital stays and higher costs for the patient. Also of considerable concern, the authors say some common alternatives to penicillin “are clearly associated” with antibiotic-resistant infections, along with higher rates of Clostridium difficile.
The Centers for Disease Control and Prevention (CDC) estimates there are 2.8 million antimicrobial-resistant infections per year in the U.S., and 35,000 U.S. deaths a year.
Body of Evidence on Penicillin Allergy
A Canadian study also found that more than 98 percent of patients with a history of penicillin allergy tested negative for the allergy. However, the patients’ new allergy-free status was often not properly recorded on their medical charts.
These findings, along with Pongdee’s study and later analysis, bolster earlier suggestions that the allergy is not as widespread as once thought. It’s clearly worth seeing an allergist to see if you too have outgrown the allergy.
While it’s still unknown why so many people react to penicillin at some point in their lives, one strong association has emerged between infectious mononucleosis and penicillin allergy.
A decade-long Allergy Asthma and Clinical Immunology study followed 10 patients who were being treated for infectious mononucleosis, also known as “mono”. All patients broke out into hives after being treated with penicillin-based antibiotics. Following the allergic reaction, testing revealed an association between developing penicillin sensitivity and the disease.
In cases where patients with infectious mononucleosis react to penicillin, additional testing appears to be necessary. Research shows these patients often won’t react to a skin prick test, but they will react if an intradermal test (deeper under the skin) is conducted.
Article updated: May 2022
