Many self-reported antibiotic allergies are misdiagnosed

Most patients who self-report they have an antibiotic allergy may not actually have a true antibiotic allergy. Rather, the problem may relate to underlying urticaria. The problem is with the limitations of self-reporting. It’s possible “that a majority of these ‘antibiotic’ allergies are actually an activation of mast cells—likely mediated by an infection—and not truly a direct response from the antibiotic to the mast cell. The mechanism is not an IgE mediated mechanism,” said Dr. Joel Liem, director at Windsor Allergy Asthma Education Centre. While true antibiotic allergies are a serious clinical problem, self-reports can be unreliable. Read: QUIZ: Test your knowledge of alopecia areata “Patients who claim they have an antibiotic allergy need to be assessed formally by an allergist. Implications for physicians would be the lack of availability of a good antibiotic if a patient thinks that he or she is allergic,” he said. Dr. Liem was coauthor of study investigating whether self-reported antibiotic allergies are increased in patients with a history of acute urticaria or chronic spontaneous urticaria (CSU). Findings were presented in a poster at the Canadian Society of Allergy and Clinical Immunology Annual Conference. “Ten percent of the population believe that they have a penicillin allergy. The real numbers are likely less than 1%. Based on observation of my clinical practice, patients with chronic spontaneous urticaria appear to state they had antibiotic allergies more frequently than those without CSU,” he told the Medical Post in an email. “We hypothesized that these people’s reactions to the antibiotic or penicillin was likely not from the antibiotic or penicillin, but rather a manifestation of their underlying urticarial disorder,” he said. The study was a retrospective chart review of 950 patients using electronic medical record data from the Windsor Allergy & Asthma Clinic, in Windsor, Ontario. Cases were defined as those with a history of acute urticaria or CSU. Controls were selected for comparison who had an established diagnosis of food allergies, asthma, allergic rhinitis or non-allergic rhinitis. The number of reported medication and antibiotic allergies were compared between the two groups. A total of 42 of 239 (17.6%) patients with a history of urticaria (both acute or chronic) reported they had an antibiotic allergy. This compared to 82 of 711 (12%) of the control group. Additionally, 8 of 239 (3.3%) of cases (acute or chronic) versus 14 out of 711 (2%) of the control group reported they had two antibiotic allergies. In brief, the “patients with a history of urticaria were more likely to report they had an antibiotic allergy than would be by chance,” the poster said. Whether the urticaria was acute or chronic didn’t make a difference in the reporting rates. The mechanisms of chronic spontaneous urticaria, or an acute viral urticaria is not completely known. This study focused only on what patients self-reported and did not allergy-test patients. To determine if patients do have a serious allergy to antibiotics, allergy testing is vital. The findings are not surprising, and underlying urticaria can indeed lead to the misdiagnosis of a drug allergy, said Dr. Eric Macy, an allergist and assistant clinical professor of medicine in the department of medicine at UC San Diego. He has conducted related research but was not part of this study. In general, “almost all individuals with a reported ‘allergy’ to an antibiotic, will actually tolerate another course of that exact antibiotic,” he said. Fewer than 5% of patients with a history of a penicillin allergy will have that intolerance confirmed by formal penicillin allergy testing. Many patients are inaccurately identified as having an antibiotic allergy because they have noted a delayed onset reaction, often hives or other rashes, after receiving an antibiotic. “Hives and other rashes are a common feature of many infections. If an infection is treated—or mistreated in the case of viral infections—with an antibiotic, and something happens, like a rash, an individual is very likely to be labeled ‘allergic’,” he said. Some people with underlying chronic urticaria may have a flare in their urticaria with the immune stimulation associated with an infection. “The history most likely to confirmed it to be a true IgE-mediated drug allergy is new onset hives, or anaphylaxis, occurring within an hour of the first dose of the last exposure to an antibiotic, completely clearing within 24 hours,” Dr. Macy said.

Many self-reported antibiotic allergies are misdiagnosed

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