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Published on June 06, 2016

Allergic to penicillin? Give testing a shotAllergic to penicillin? Give testing a shot

It’s the story Paul Sklarew, MD, of the Allergy & Asthma Centers of Cape Cod hears again and again.

“A patient says, ‘I’m 60 and when I was a child my mother told me I was allergic to penicillin.’ That finding is old and vague,” said Dr. Sklarew. “People don’t know that most patients who are labeled penicillin-resistant are not – and even many doctors are not aware.”

The problem with the false allergies is that patients who could use penicillin don’t.

“Compared to the alternatives, penicillin is a less expensive medicine,” said Dr. Sklarew. “It can be more effective for some disorders, and it has fewer side effects.”

About 10 percent of Americans think they’re allergic to penicillin, according to the American College of Allergy, Asthma and Immunology (ACAAI). Dr. Sklarew noted that one study showed that only about one in five patients believed to be allergic had a positive reaction to a skin test.

“It makes sense to have a test, especially people who have a remote or a vague history or a history that doesn’t match an allergic reaction, like someone who says they got a headache after using penicillin,” says Dr. Sklarew. “Also, it could be that they were allergic to penicillin and outgrew the allergy.”

Allergist David Khan, MD, of the University of Texas Southwestern Medical Center, recently presented a study at the ACAAI’s Annual Scientific Meeting. The study “examined the records of 15 patients who, after being told they were penicillin-allergic, tested negative for penicillin allergy, and were then able to be treated with intravenous penicillin on multiple occasions,” according to the ACAAI.

“We found intravenous penicillins to be safe for repeated use in patients who had been told they were allergic,” said Dr. Khan.

“Recent research has shown that patients who are labeled penicillin-allergic and take other antibiotics are more likely to have poor outcomes, such as development of colitis, longer hospital stays and greater numbers of antibiotic-resistant infections,” said Albany, Oregon allergist Roland Solensky, MD, another presenter at the ACAAI meeting.

Penicillin is an antibiotic that’s used to treat a large range of bacterial infections. The most common symptoms of a penicillin allergy are an itchy rash, hives, swelling of the lips or eyes, or breathing difficulties.

“It’s most expeditious if there’s a rash to say maybe it’s the penicillin,” said Dr. Sklarew. “The rash goes away so people assume it was the penicillin that caused it. Once you make the diagnosis, it kind of sticks. Physicians aren’t eager to push patients into taking something they’re worried about.”

The best way to verify a penicillin allergy starts with a skin test. “It’s a little scratch test like we do for pollen or dust or dogs,” said Dr. Sklarew. “If that’s negative, we give them a little injection under the skin, an intradermal. If they get a red, itchy spot, they’re allergic. If they don’t react, then the likelihood is 1 percent that they’re allergic.”

Testing takes about half an hour for the two-step skin test, and the tests are covered by most insurance plans, said Dr. Sklarew.

“If a patient is still concerned, we can do a penicillin challenge, where they get a tablet in the office. I have them wait an hour after taking penicillin. They know that not only are the skin tests negative, but they took a pill and didn’t have a reaction. This provides more reassurance and they can return penicillin to their treatment options,” he said.