updated 6/25/2005 1:27:34 PM ET 2005-06-25T17:27:34

A study by University of Pennsylvania researchers casts doubt on the conventional wisdom that most penicillin allergies are forever.

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The researchers found that the number of people who had an allergic symptom after taking penicillin and then had another episode after taking the antibiotic again was far fewer than expected.

However, the researchers stressed that more study is needed before doctors start writing penicillin prescriptions for patients who say they’re allergic.

Previous smaller studies had concluded that about 60 percent of people who have an allergic reaction once to penicillin will have another one if they take the antibiotic again. However, the Penn researchers’ review of 3.4 million electronic medical records for people in Great Britain who were prescribed penicillin from 1987 to 2001 found the number of second allergic responses to be less than 2 percent.

Benefit to public health
Researchers are trying to find out just how common the allergy really is and better understand the risk of re-prescribing penicillin, said Dr. Andrea J. Apter, a Penn allergist and associate professor of medicine. While more work is necessary before that happens, the study suggests that some patients labeled as allergic can safely take the antibiotic if there’s an emergency or alternatives would be inferior, she said.

Of the 6,000 patients who had an allergic response such as a rash or wheezing after the first prescription, about half — 3,014 — received a second dose. Among those patients, only 57 — 1.9 percent of the total — had a similar recurrence.

If it turns out that a larger number of people can safely take penicillin, which is highly effective and relatively inexpensive, it would benefit public health as well as patients’ wallets, said Penn professor and senior researcher Dr. Brian L. Strom.

Penicillin skin testing is currently imperfect and typically unavailable to doctors because some of the testing materials aren’t widely available, Apter said.

The limitation of the study is that people who think they’re allergic to penicillin may not be, said Dr. Clifford W. Bassett, a New York City allergist and a spokesman for the American Academy of Allergy, Asthma and Immunology.

“It’s very important to understand that the history of penicillin allergy is anecdotal. A lot of those probably were not true positives,” he said. The Penn study didn’t involve actual blood or skin tests on patients, so it’s hard to determine how many truly were allergic, he said.

Some people may have had a rash or hives that came from their illness and not the medicine. Also, every year that an allergic person avoids penicillin may reduce their sensitivity, Bassett said.

The study appears in this month’s Journal of Allergy & Clinical Immunology.

© 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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