So, you think you’re allergic to penicillin?

Penicillin allergy test.
A simple allergy test performed by a trained professional can determine whether you are really allergic to penicillin.

Did you know that most people who think they are allergic to penicillin actually aren’t allergic at all?

Approximately one in 10 Americans say they have a serious allergy to penicillin or other closely related drugs. But the number of people who are actually allergic to penicillin is far, far lower.

For the vast majority, penicillin-based medications are safe and cost-effective antibiotics. Avoiding them if you aren’t really allergic could have both financial and health-related downsides.

Studying penicillin allergies

In a recent study Justin Chen, M.D. and his colleagues conducted at UT Southwestern, about 90 percent of the individuals they surveyed whose health records indicated a penicillin allergy did not actually have a reaction to the antibiotic in an allergy test.

That means only a very small percentage of patients who tell their doctor about a penicillin allergy are actually allergic. In addition, most people “grow out” of penicillin allergy in about 10 years after the initial allergy symptoms. While some people do in fact have this serious allergy, the number of people affected by it in the United States is likely far fewer than previously thought. 

We aren’t the only ones to notice a discrepancy. UT Southwestern’s findings have been backed up by similar studies performed from San Diego to Florida.

Some of the people who reported a penicillin allergy might have been allergic as a child but outgrew it over time. Sometimes, a rash caused by an infection can be mistaken as a reaction to the antibiotic. And, often, reported penicillin allergies are based on hazy, incorrect recollections.

Why it matters

As far as antibiotics go, penicillins are some of the safest and cheapest antimicrobial medications available. Patients who are allergic to penicillin must take broad-spectrum antibiotics, which can be costlier and more toxic.

Being treated with broad-spectrum antibiotics can knock out beneficial bacteria in our body, setting the stage for harmful bacteria that are tough to treat. People who have a reported penicillin allergy are more likely to be hospitalized for C. difficile and MRSA, bacteria that are resistant to multiple antibiotics and can cause life-threatening infections. 

In short, patients who think they are allergic to penicillin but aren’t are both missing out on a host of medications and taking riskier antibiotics.

About the allergy test

The process of being tested for a penicillin allergy is the same for children and adults. A trained specialist will perform a skin test, which takes about 30 minutes, followed by a test dose of penicillin (also called an oral challenge). You will then be observed for one hour for signs of allergic reaction. The whole process takes an hour and a half to two hours.

During the skin test, the physician will scratch the surface of the skin to allow some penicillin to make contact and also introduce a small amount underneath the skin. If you are truly allergic, the area of the skin tested will get red, itchy, and bumpy. If not allergic, the skin will remain the same.

If the skin test is negative and shows no reaction to the penicillin, this suggests your body is not allergic to penicillin. That’s when we would give the test dose of penicillin in the office to make sure you can tolerate taking the medication. The skin test followed by the oral penicillin challenge is very good at detecting true allergy to penicillin, with about 97 percent accuracy.

We recommend that this sensitive test should only be performed by an allergy specialist or in an allergy clinic and cannot be done by your primary care physician.

Get tested today

Following the process above, an allergist can easily check you (or a loved one) for a penicillin allergy.     

A good time for penicillin-allergy testing to take place is before a child transitions from pediatric care to adult medical care. Even if a child was allergic 10 or 15 years ago, he or she may not be now, and it’s a good time to get the label removed from his or her health records.

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