Penicillin allergy: less common than people think

Knowing your penicillin allergy status could make a big difference if you end up in hospital, a new study has found.

As many as 18-25 per cent of Australian hospital inpatients report they have an antibiotic allergy, with about half of these against the most frequently used beta-lactam antibiotics, commonly known as “penicillin allergies”.

Patients with reported penicillin allergies tend to have poorer outcomes in hospital: longer stays, higher chances of infection with antibiotic-resistant “superbugs”, and higher mortality.

Penicillin allergies are also bad news for the health system, necessitating the use of broad-spectrum second-line or third-line antibiotics, which are expensive and contribute to antimicrobial resistance.

However, the study from UNSW found that most people with a self-reported penicillin allergy have no reaction when they are tested via skin tests and oral administration (known as “challenge” or “provocation testing”).

These people can then be labelled non-allergic, in a process is known as penicillin allergy “delabelling”.

“When you go to the trouble of skin testing and challenging people, around 90 per cent don’t actually have penicillin allergy,” Dr Winnie Tong, an allergy researcher at UNSW Medicine & Health and a clinical immunologist at St Vincent’s Hospital Sydney, said.

“One problem is it’s so much work to do all of that safely.”

Delabelling is important to give people a more accurate idea of their penicillin allergy status, which could be important if they end up in hospital.

But it is often a complicated, expensive process, which patients and healthcare providers do not fully understand.

Dr Tong said many Australians began believing they had a penicillin allergy in childhood.

“Many patients say their parents told them. For example, one person has a reaction and the parents are concerned others in the family could be allergic, even though penicillin allergy is not inherited.”

However, if more than a decade has passed since that initial reaction, 80 per cent of people will have no longer have the allergy over time.

There are several other reasons why someone could be incorrectly labelled as allergic to penicillin, including experiencing drug side effects mistaken as an allergic reaction.

“It’s very easy to label someone as allergic, and tell them to avoid penicillins for the rest of their life,” Dr Tong said. “But it’s very difficult then to safely say to someone, you can take away that label, and you can have penicillins.”

Delabelling usually occurs in a hospital setting with a specialist immunologist.

Once a patient’s allergy label is removed, breakdowns in communication can mean that patients are still concerned about their penicillin allergy status despite a negative result during testing.

“The problem is you do all this testing and the patient still won’t take penicillin. Maybe they didn’t understand the results, or their GP didn’t get the results letter,” Dr Tong said.

The study’s findings suggest clear, standardised communication with patients is crucial so they understand their penicillin allergy status.