Are you still allergic to penicillin?

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Penicillin and drugs in the penicillin family are some of the most used antibiotics in the world. About 10% of people in the U.S. think they're allergic to it, but more than nine out of 10 of them aren't allergic at all.

The Centers for Disease Control says that's a concern, because they could take an antibiotic that either doesn't work or has bad side effects. But there is a simple test that could hold the answers.

Barbara Clements wants to know if she's allergic to penicillin. Both her husband and daughter believe they are. Her dad too.

"I remember as a child, growing up, he was very careful about it," Clements said. "And so I was just wondering if it was hereditary."

Infectious disease specialist Dr. Seth Cohen says the nine out of 10 people who wrongly think they're allergic to penicillin may be putting themselves at risk. This is especially true for patients who are elderly, immunosuppressed, pregnant or need surgery.

"If you're labeled as having a penicillin allergy, you may be unnecessarily placed on a broad-spectrum antibiotic that can lead to side effects or may be less effective than something in the penicillin family," Cohen said.

A skin scratch test can reveal whether a patient has a penicillin allergy in a little less than an hour.

"Skin testing is a rapid, office-based procedure where we can delist somebody's penicillin allergy," Cohen said. "That means we can tell them in the office that they do not have a penicillin allergy."

He puts penicillin or saline on the skin, scratches it in, marks it and waits for a reaction, if there is one.

That means Clements is not allergic. Now, she wants to get her husband and daughter tested.

Cohen says the skin test is safe and cost-effective, as it reduces the risk of complications in the hospital. Also, many people lose penicillin allergies in about 10 years, so he and the CDC suggest being reevaluated.

REPORT: MB #4586

BACKGROUND: Penicillin's are widely used antibiotics that have important roles in treating bacterial infections. The label of penicillin allergy is commonly attached in childhood where common childhood infections may themselves contribute to or be confused with allergy. In addition, even in those with true allergy, over 90% will lose this tendency over a ten year period. Consequently, although approximately 10% of the population is labeled as being allergic to penicillin, over 90% of these individuals actually are negative on allergy testing and can tolerate penicillin. Immediate allergic reactions to penicillin's typically occur quickly after receiving a dose of the medication, and often occur in patients who have tolerated previous courses of penicillin without issue. Symptoms frequently involve the skin and include hives or swelling which occurs around the face and extremities such as hands and feet. (Source:

SYMPTOMS: People with a penicillin allergy on their medical record are not given penicillin's and may not be given any beta-lactam antibiotics because of concern that the allergy is shared across the antibiotic class. Instead, the antibiotics prescribed may be broader-spectrum. Broad-spectrum antibiotics may be as effective, but they often have more side effects and toxicities, such as increased risk of developing infections. Confirming or ruling out a penicillin allergy through allergy testing could justify the risk, or potentially avert it by allowing your doctor to prescribe beta-lactams. In other cases, your doctor may have to prescribe less-effective drugs than penicillins and cephalosporins because of a documented penicillin allergy.

SKIN TEST: A skin test is used to diagnosis a penicillin allergy. Seth Cohen, MD, MSc, Medical Director, Infection Prevention and Employee Health from the University of Washington says, "Penicillin skin testing has two steps. The first is taking a very thorough history. Then we can decide whether skin testing is actually necessary. Then we move on to a second visit where the patient can undergo skin testing. The skin testing itself takes about an hour and it's composed of two different types of testing. There's a skin prick and then there's an intra dermal portion. The needles are very small that we use. And after the tests are read at 15 minutes, we do another round of testing and we read the second round of tests at 15 minutes. And if the patient does not have any reaction then we typically proceed to give them either a pill of penicillin or amoxicillin and then we watch them for another hour. And if they do great after taking the pill then we go into their medical record and remove the label of penicillin allergy right there in the office." (Source: Seth Cohen, MD, MSc)