Think you’re allergic to penicillin? Think again: Millions may have been wrongly diagnosed in childhood, leaving them vulnerable to superbugs
- 100 years on, penicillin is one of the most powerful drugs in a doctor’s armoury
- However, one in ten are allergic to this original infection-fighting wonder drug
- Or so they think – in reality, around nine in ten of these people aren’t allergic
Nearly 100 years after its discovery changed the medical landscape, penicillin is still one of the most powerful drugs in a doctor’s armoury.
However, about one in ten people is allergic to this original infection-fighting wonder drug. Or so they think.
Penicillin allergy is the most common drug allergy in the UK, but the vast majority — around nine in ten — of those affected aren’t actually allergic.
Not only do they not have an allergy to it, but recent research suggests being mislabelled as allergic could be dangerous.
For people with penicillin allergy are more likely to get antibiotic-resistant infections such as C.difficile or MRSA, which can be life-threatening. This is because doctors are forced to use other antibiotics, which tend to be broad spectrum, targeting more types of bacteria than penicillin does.
Game-changing: 100 years on, penicillin is one of the most powerful drugs for a doctor
‘Unnecessary use of broad-spectrum antibiotics leads to the development of drug-resistant bacteria, including MRSA and other typically hospital-acquired infections such as C.difficile,’ says Dr Pamela Ewan, a consultant allergist at Addenbrooke’s Hospital in Cambridge.
This increases antibiotic resistance in the general population, but also in the patients themselves — if you wipe out the non-resistant strains of bacteria in a person’s body with broad-spectrum antibiotics, then the MRSA can multiply without competition.
A study recently published in the BMJ found that the risk of MRSA in people with ‘penicillin allergy’ on their medical notes increased by 69 per cent and the risk of C.difficile by 26 per cent.
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Patients also stay longer in hospital and are less likely to have their infection treated successfully because the drugs used instead of penicillin are not as effective, says Dr Ewan.
‘The evidence is mounting that it can have a knock-on effect on your long-term health,’ adds Neil Powell, a consultant antimicrobial pharmacist at Royal Cornwall Hospitals NHS Trust.
‘Penicillin is still the best first-line treatment for dangerous infections such as bacterial pneumonia, some sexually transmitted diseases and wound infections, but you won’t be given it for fear of a severe allergic reaction. Alternative antibiotics, such as fluoroquinolones, can be less effective and are more toxic to muscles and the central nervous system than penicillin, causing side-effects such as joint problems, tendon rupture and nerve pain.’
Fact: For people with penicillin allergy are more likely to get antibiotic-resistant infections such as C.difficile or MRSA, which can be life-threatening
And, indeed, earlier this month, the European Medicines Agency — which oversees drug regulation across the EU — ruled that quinolones and fluoroquinolones should be used only when ‘there are no alternatives’.
So, why do people mistakenly believe they have an allergy in the first place? Often, it’s down to penicillin having been wrongly prescribed for viral infections in childhood, suggests Mr Powell.
‘In the past, children would get viral infections and many were given penicillin, even though it wouldn’t have made any difference because penicillin only works against bacterial infections.
‘When the child developed a viral rash on day two or three, the penicillin was often blamed. We erred on the side of caution by noting this as a penicillin allergy, but now we realise that was doing patients more harm than good.’
The common side-effects of penicillin can also lead both patients and doctors to the wrong conclusions. ‘These include diarrhoea and feeling queasy, which can be confused with a systemic anaphylaxis [a severe allergic reaction causing a rapid drop in blood pressure, swelling and sometimes diarrhoea and vomiting],’ says Jacqueline Sneddon, an antimicrobial pharmacist and spokeswoman for the Royal Pharmaceutical Society.
Better recording of notes would help. ‘At the moment, we don’t have enough options to describe reactions to drugs, so sensitivities can be wrongly input as allergies,’ says Mr Powell (see box, above).
Now, the National Institute for Health and Care Excellence (NICE) is advising doctors, nurses and pharmacists to double-check that a patient’s medical notes are accurate, to ensure they receive the best treatment.
Wrong diagnosis: Penicillin allergy is the most common drug allergy in the UK, but the vast majority — around nine in ten — of those affected aren’t actually allergic
Ms Sneddon says: ‘Questions they need to ask include: “When did the reaction happen? What exactly happened? How long after taking penicillin did the reaction occur?” ’ Timing of the last reaction is important, as a proportion of people with sensitivity to penicillin no longer react after ten years.
Mr Powell suggests patients could be proactive ‘and ask what is the best antibiotic for their treatment. If it’s penicillin, ask if they can check you really have an allergy and discuss the risks’.
He adds: ‘It is possible to establish the facts, which can drastically improve treatment options for patients currently getting second-best alternatives. Just asking a few questions can de-label around 20 to 40 per cent of patients who believe they have a penicillin allergy.
‘It may also be possible to be referred to an allergist for a skin test [where a drop of liquid containing penicillin is put onto the skin before pricking the area beneath], or a penicillin challenge test [where the patient is given one dose of a penicillin].’
But this can be prohibitively expensive and there aren’t enough immunologists, says Mr Powell. He believes efforts should be focused on older people, or those with conditions such as diabetes, who are most vulnerable to infections.
MISTAKE EASILY MADE
A sensitivity to penicillin is different from an allergy.
While sensitivity is usually characterised by diarrhoea, thrush or headache, an allergy involves the immune system over-reacting.
This causes classic symptoms ‘including an itchy rash, swelling of the lips and tongue and difficulty breathing’, explains antimicrobial pharmacist Neil Powell. An allergic reaction occurs within an hour — and often much sooner.
An upset stomach with nausea or diarrhoea after a day or two of taking antibiotics is unlikely to be an allergic reaction, but may result from the drug disrupting the gut bacteria.
It’s thanks to these two tests that Josie Eddy, 63, a former bank worker from Truro, Cornwall, can have penicillin, after more than 40 years of thinking (wrongly) she was allergic to it.
At 19, she was treated with it for a urinary tract and chest infection. She says: ‘My GP gave me penicillin but, after a few days, I broke out in a rash with 10p-sized hives all over my body.
‘I went shopping in Truro and collapsed. I woke up in hospital. I just took for granted that I was allergic and so did the doctors who put it in my notes. I didn’t have penicillin for 40 years after that.’
However, her health took a turn for the worse. Josie, who is married to Malcolm, 67, a retired telecoms manager, developed bile duct disease in 2014 — where the tubes that carry bile from the liver become blocked. She is now on the waiting list for a transplant.
In the meantime, she needs daily treatment with antibiotics — importantly, penicillin. Penicillin is also one of the key drugs used after the surgery to stop infection.
The tests showed she didn’t have an allergy to the drug. ‘For all those years, I probably had a sensitivity to it,’ she says. It causes her some side-effects, such as a rash and nausea, ‘but they’re not life-threatening and I’m just grateful penicillin is an option’.
Josie is spreading the word about checking for penicillin allergy among other members of PSC Support, a charity for people with bile duct disease. ‘My advice to anyone with a “penicillin allergy” is to find out if you really are allergic, as you never know what’s around the corner.’
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