INFECTIONS
November 11, 2014

Allergic to Penicillin?

If you've had a reaction to a course of penicillin and thought it meant you were allergic, think again.

If you have developed a rash or other reaction during the course of being treated with penicillin, you may have decided, or been told, you have an allergy to this antibiotic. But two recent studies suggest that many people who believe they are allergic to penicillin are not.

The findings suggest that people who think that they have a penicillin allergy might want to discuss this more fully with their doctor or allergist. You can be tested to determine whether you are truly allergic or not.

Penicillin allergies may fade over time. And a rash or hives that may suggest an allergic reaction to penicillin is not conclusive evidence.

Up to 10% of the adult U.S. population has had an allergic response to penicillin at some time in their life.

The first study looked at 384 people with upcoming surgery who believed they were allergic to penicillin. Fully 94% tested negative for a penicillin allergy.

“They may have had an unfavorable response to penicillin at some point in the past, such as hives or swelling, but they did not demonstrate any evidence of penicillin allergy at the current time. With that in mind, their doctors prescribed different medications prior to surgery,” the study's lead author, Thanai Pongdee, MD, said in a statement.

In the second study, 38 people who thought they were allergic to penicillin were given penicillin skin tests. All 38 tested negative. Doctors then changed the prescriptions for 29 participants, which significantly lowered their prescription costs.

Penicillin is one of the least expensive antibiotics on the market. Substitute antibiotics that are prescribed to people who cannot take penicillin are almost always more expensive, often considerably so.

In some cases, penicillin is clearly the drug of choice but cannot be prescribed to a patient because of their allergy. Many of the substitute antibiotics are more toxic or carry the risk of more serious side effects.

Confirmation of a penicillin allergy starts with a skin test, typically given by an allergist. A negative penicillin skin test usually indicates the person is at low risk for an immediate allergic response to penicillin.

According to the CDC, up to 10% of the adult U.S. population has had an allergic response to penicillin at some time in their life. These two studies strongly suggest that the real number of allergic people is much, much lower.

Both studies were presented at the American College of Allergy, Asthma and Immunology (ACAAI) 2014 Annual Scientific Meeting, held in Atlanta.

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