Penicillin allergy rates may be wildly overestimated

Many people who have not undergone penicillin skin testing falsely believe they are allergic to penicillin when they are not, according to research presented at the American College of Allergy, Asthma and Immunology Annual Scientific Meeting^[1]
on 9 November 2014.

All patients attending the Mayo Clinic’s pre-operative clinic in Florida between August 2012 and August 2013 who said they had a penicillin allergy were given a skin test, accepted as the primary, safe way to determine whether someone is allergic. Of the 384 patients tested, 94% received a negative result.

“These results have a significant bearing on physicians’ prescriptions of antibiotics in a pre-surgical setting to ward off infection,” says Thanai Pongdee, an allergist who practises at the Mayo Clinic in Florida and the lead author of the study. “When patients tell their healthcare provider they are allergic to penicillin, the physician must substitute another antibiotic. These treatment alternatives may be more toxic, more expensive and less effective than penicillin or antibiotics related to penicillin, such as cephalosporins.”

Pongdee suggests that the reason most of the participants wrongly claim to be allergic is because they might have experienced an unfavourable response to penicillin in the past, such as hives, swelling, difficulties in breathing and anaphylaxis.

“Many people, after having experienced a minor reaction to penicillin, are either told by their physicians that they are allergic, when this had never been clinically established, or the patient just assumes he is allergic,” he says. “Even more common is the likelihood that patients did indeed have a clinically established allergic reaction to penicillin but, over time, that allergy went away, which is not atypical for allergies.”

People who have experienced a minor reaction to penicillin expected future reactions would also be minor, he adds whereas “allergic reactions to penicillin tend to be progressive in terms of severity, which is why it’s so important for people who have had bad responses to this antibiotic be clinically tested.”

The ongoing study has been expanded to estimate the cost implications of using an alternative to penicillin or cephalosporins simply because a patient has reported an allergy to them.

“If we have given patients one of the three antibiotics often used as penicillin substitutes — vancomycin, levofloxacin and clindamycin — we can look at data tied to financial utilisation, for example, whether patients who receive these substitutes will have a longer hospital stay or develop resistant bacteria,” he says. He notes that these three antibiotics may have higher rates of adverse effects than penicillin or cephalosporins.

Given that pre-surgical treatments with penicillin and related antibiotics are generally considered first-line therapies with the fewest side effects, Pongdee encourages people who believe they have an allergy to request a penicillin skin-allergy test. He and his team are considering collaborating with pharmacists to educate their patients about the benefits of such testing.