Research at Royal Perth Hospital (RPH) has found that 90 per cent of people who believe they are allergic to penicillin are not, and it means they are missing out on highly effective treatment for infections.
RPH infectious diseases department head Claire Italiano said that 10 to 20 per cent of patients admitted to the hospital reported being allergic to penicillin, but of that cohort, about 90 per cent did not, in fact, have the allergy.
In the past, an allergy reported by a patient meant that doctors had "generally erred on the side of caution and just avoided the [penicillin] antibiotics," Dr Italiano told Nadia Mitsopoulos on ABC Radio Perth.
"But we know now that avoiding penicillin antibiotics often ends up in worse outcomes for patients," she said.
"What we find is sometimes people are getting an inferior antibiotic because we're avoiding what they're allergic to."
How allergy mistakes arise
The reasons people come to believe that they are allergic to penicillin are multifold and often relate to an incident in childhood, experts say.
Maryam Sherkat Masoum, an antimicrobial stewardship pharmacist at RPH, said sometimes people mistook a symptom from an illness for an allergic reaction.
"Sometimes people receive penicillin antibiotics for viral infections, and viral infections, especially in childhood, can cause a rash," Ms Sherkat Masoum said.
"Sometimes the penicillin can be mistakenly blamed for this."
The other common reason she saw was people mistaking a side effect of penicillin for an allergic reaction.
"Antibiotics, including penicillins, can have side effects and these can include things like nausea, so feeling like you're going to vomit, vomiting or diarrhoea, headache or thrush," Ms Sherkat Masoum said.
"These are all common side effects, but they're not allergies.
"Quite often, we can help you manage the side effects and actually complete your course of antibiotics and also not report it as an allergy."
Ms Sherkat Masoum says that people can grow out of a previous allergy.
"We now know that penicillin allergies are not lifelong," she said.
"Similar to food allergies, you can grow out of your penicillin allergy.
"The figures are quite impressive — after about 10 years, 80 per cent of people who had a penicillin allergy don't have it anymore."
Why persist with penicillin?
Dr Italiano said until recently, the prevailing belief was that if a patient reported they were allergic to penicillin, it should be avoided at all costs to prevent a potentially life-threatening reaction, and alternative antibiotics were prescribed.
"We considered risking an allergy as being one of the worst things that we can do," she said.
"But we know that that actually isn't the case anymore."
Dr Italiano said when a person was diagnosed with an infection, the most desirable treatment option was to use a highly targeted antibiotic rather than a broad-spectrum drug that did not contain penicillin.
But she said it was less likely to be effective.
"It's really only a last resort, or when people are very sick, and we're not sure what's going on that we use broad antibiotics," Dr Italiano said.
"But sometimes we're stuck a bit when people report a penicillin allergy because we can't use those narrow ones, those targeted ones."
She said the wider use of broad-spectrum antibiotics also had implications for antibiotic resistance and the potential to create superbugs.
"We have some antibiotics that are very broad," Dr Italiano said.
"They treat a lot of bacteria, and that might sound great, but it also means it's upsetting the individual gut flora and contributing potentially to resistance to those antibiotics forming."
Doctors investigate allergies
Now, when a patient at RPH says they are allergic to penicillin, doctors try to investigate further to see if they can be given the drug safely.
"Our first step is to take a further history from them, try and get more details about what antibiotic it was [they reacted to], what occurred. Sometimes we go back over medical records," Dr Italiano said.
"I had one patient in their 90s who reported a penicillin allergy as a baby. I did the maths. There was no penicillin around then, so we knew they weren't allergic.
"Sometimes we can actually remove the [allergic] label at that point."
Dr Italiano says after taking a medical history, doctors then do a risk assessment.
"If the likelihood of someone having an allergy is very low, we can challenge them," she said.
"The first step would be with a small dose of an oral penicillin antibiotic. Then if people have no problem with that, we'll look to de-label them and put them on the most appropriate antibiotic.
"And then for the more complicated cases, where people do actually have an allergy, we will involve our immunology colleagues."
Dr Italiano says that if people have been told they have a penicillin allergy, they should keep telling their doctor but ask their GP to look into their medical history and investigate whether they may be able to take penicillin safely.
