How often is penicillin allergy misdiagnosed?

Doctors can try skin prick testing and oral penicillin under observation to check

Most patients who report having a penicillin allergy are not really allergic to the antibiotic, and they may be missing out on the best treatment for their condition as a result, according to a report in the Journal of the American Medical Association.

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Although one in 10 patients has a penicillin allergy noted in their medical record, many have been misdiagnosed as children or are no longer allergic, the authors write.

Dr Erica Shenoy of Massachusetts General Hospital in Boston, coauthor of the report, says about 95% of those in the US with a recorded penicillin allergy don't truly have the allergy.

"The 'penicillin allergy' label affects the antibiotic options available to patients, resulting in the use of alternative and often less effective antibiotics that can expose patients to unnecessary risks," Dr Shenoy says. 

Most patients with a documented allergy are diagnosed as children because of a rash that was likely caused by a virus rather than an allergy.

For those who do have a true penicillin allergy, about eight in 10 are no longer allergic after a 10-year period, the authors write.

Another source of confusion is that the term "allergy" is often used to include intolerances and side effects.

A companion report, published in the same issue of JAMA, outlines recommendations for doctors to evaluate and manage penicillin allergies in their patients.

Skin testing might be helpful for patients with a history of hives, rash, swelling or shortness of breath.

If an initial skin prick test is negative, a second intradermal test can be used to place the penicillin under the skin, which can be examined after 15-20 minutes.

If that test is also negative, doctors can test an oral dose of penicillin while observing the patient to monitor the reaction.

For patients with "low-risk" reactions — such as headache, nausea, vomiting, itching or a family history of the allergy — skin tests might not be necessary, and doctors can start with an oral dose of penicillin under observation.

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