Challenging the Penicillin Allergy Label

It would be a brave doctor who would ignore the warning ‘allergic to penicillin’ when deciding which antibiotic to prescribe for a patient.

But according to a new review published recently in JAMA, despite up to 10% of the population reporting allergies to penicillin, few have clinically significant reactions.

“Although many patients report they are allergic to penicillin, clinically significant IgE-mediated or T lymphocyte-mediated penicillin hypersensitivity is uncommon (<5%),” the US review authors said.

And the issue is an important one. As the authors point out, not only will patients, labelled as having a penicillin allergy be given alternative antibiotics that are more likely to fail and cause side-effects but the use of these alternatives increase the risk of antimicrobial resistance developing. So for all these reasons, the researchers propose that is worthwhile that all patients labelled as having an allergy to penicillins be re-evaluated.

As a starting point, a comprehensive history should be taken. And while the reviewers acknowledge that, to date no allergy questionnaires have been validated in terms of defining risk levels, there are plenty of features in a history that can give a clue as to whether a person could safely be offered skin prick testing or a drug challenge.

Broadly speaking, patients with a history of a minor rash, that was not significantly itchy that developed over the course of days into the course of the antibiotic are considered low-risk. This is opposed to people who have a history of developing a very pruritic rash within minutes to hours of taking the drug (which tends to indicate an IgE-mediated ...

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