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Allergic to penicillin? You might want to get that checked

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On paper, penicillin allergy is a common condition, with about 10 per cent of Canadians having one noted in their medical record. In fact, it's the most frequently reported drug allergy, according to research published in the Canadian Medical Association Journal.

It's often diagnosed early in life, around the time babies and children receive their first dose of an antibiotic for an infection. However, the reality is that very few of these diagnoses are accurate.

According to the B.C. Centre for Disease Control (BCCDC), less than one per cent of Canadians actually experience adverse effects from taking penicillin, and the Mayo Clinic reports 90 per cent of people diagnosed with penicillin allergy can be safely treated with the antibiotic.

Moreover, the Mayo Clinic reports about 50 per cent of people will outgrow a penicillin allergy within five years, and 80 per cent will outgrow it within 10 years.

Pediatric allergist Dr. Amiirah Aujnarain says it's important to know if you might not be allergic to penicillin after all, since penicillin-based antibiotics like amoxicillin are the best line of treatment for many infections.

"Penicillin is a huge antibiotic. It covers a lot of different things, and so sometimes you'll have a bacteria you actually want to use amoxicillin for, and then you're using something that's not as good," she told CTV's Your Morning on Friday, "and that creates antibiotic resistance. You're causing yourself to have other side effects that you don't need to."

People mistakenly listed as having a penicillin allergy may be prescribed a more powerful antibiotic with greater side effects for an infection that could be treated with penicillin.

The BCCDC reports that people labelled as allergic to penicillin also face a greater risk for C. difficile infection. C. difficile is a bacterium that causes mild to severe diarrhea and can damage the colon, and it's linked to prolonged usage of high doses of antibiotics.

A true penicillin allergy can be serious, especially when it's severe enough to trigger anaphylaxis. In other patients with an allergy to penicillin, exposure can trigger skin rashes and other less severe reactions.

Aujnarain said people are sometimes falsely diagnosed with a penicillin allergy when patients or health-care providers confuse symptoms of an infection with symptoms of an allergic reaction.

"Most of the time it's not the antibiotic itself – it's actually the infection that you have," she said.

"So people think, 'Oh, I took this antibiotic, I got a rash. It must be the antibiotic.' But most of the time, 89 per cent, it's actually the infection. So you don't actually have the allergy in the first place."

Aujnarain said anyone who wants to know if they are truly allergic to penicillin should ask their doctor or primary care provider for a referral to an allergist, who can use one of several tests to find the answer.

"We have different tools in our toolbox," she said. "The first thing is we can do intradermal testing, so it goes under the skin and we actually see if you react. But most of the time nowadays we actually go directly to what we call an oral challenge."

In an oral challenge test, healthy patients receive an oral dose of liquid amoxicillin and are monitored for signs of allergy, such as hives, swelling or wheezing.

"We wait and make sure you don't have a reaction, and then you go home," she said. "So it's actually painless and you don't have to keep writing 'amoxicillin allergy' forever." 

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