Penicillin allergy and antibiotic resistance

Jenny Firman
Chief Health Officer 
Department of Veterans’ Affairs 

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Many people reading this will have been told they have a penicillin allergy. Up to one in five of Australians who are admitted to hospital say they have a penicillin allergy. This is not surprising, as antibiotics in the penicillin family are very commonly prescribed – nearly everyone will have taken a penicillin at some time in their life. 

In the past this has not caused too many problems as there have been many other antibiotics to choose from. But antibiotic resistance has rapidly increased at the same time as development of new antibiotics has decreased. This has started to cause problems when choosing an antibiotic for people with a penicillin allergy. 

True penicillin allergy 

However, researchers have found true penicillin allergy is much lower than people think. When researchers do allergy skin testing on people in hospital they have found only 10-20% of those who say they have a penicillin allergy actually have a true allergy. 

People may think they have a penicillin allergy for several reasons. They may have been told by their parents that they had a penicillin allergy as a small child but don’t know the full details of what happened. They may have had a side effect to penicillins such as nausea or diarrhoea, which is not a true allergy but means their doctor may avoid giving penicillins again for minor illnesses. Or they may have developed a rash after taking penicillins – this may be because of the antibiotics, a viral illness that causes a similar rash, or a virus such as glandular fever interacting with the penicillin. 

Sometimes people or their doctors have avoided penicillins due to someone in their family having a severe penicillin allergy, even though there is no evidence this allergy is inherited. 

Knowing if someone has a true and severe allergy can be important because if they have a serious or life-threatening infection, or need certain surgeries, a penicillin may be the first choice for them. 

Some people do have serious allergic reactions to penicillins and shouldn’t take them. These reactions may be delayed and include things like serious blistering, extensive skin rashes, severe mouth ulcers, kidney, liver and blood conditions. Other people may have immediate reactions such as anaphylaxis, swelling of the mouth, throat, lips or tongue, low blood pressure, and hives (urticaria). People who have these reactions after penicillin should avoid penicillins for their whole life and will be offered other options. 

If your doctor considers it is important for you to find out if you have a true penicillin allergy, you can be referred for specialist allergy testing. Such testing may involve allergy skin testing or sometimes an oral penicillin challenge where you are given a dose of penicillin in a hospital setting where any serious reactions can be treated. 

The history of antibiotics 

Penicillin was discovered nearly 100 years ago by Alexander Fleming when he noticed that bacteria weren’t growing near a particular mould. However, it took another 10 years to purify a small amount of penicillin from the mould and prove it could treat infection in humans. Howard Florey, an Australian pharmacologist and pathologist, and a team of researchers at Oxford University did this in 1940. 

By then, England was at war, and people were dying of wound infections, so they needed to work to make enough to be useful. There was limited medicine manufacturing happening in England so Florey and a member of his team travelled to Chicago where they were able to work with the US Government and dramatically ramp up production. 

By September 1943, there was enough penicillin to meet the needs of the entire Allied Armed Forces. The large scale availability of such a useful antibiotic revolutionised the treatment of infectious disease and injuries in servicemen, and aided the Allied victory in the Second World War.

Antibiotic resistance 

The methods used to discover and develop penicillin then led to the discovery of other antibiotics, including many used today to treat bacterial infections and prevent infections after surgery. These were developed as bacteria became resistant to the existing antibiotics. Using antibiotics means bacteria develop resistance as a defence. Some bacteria can also share their resistance genes with different types of bacteria. 

There are several ways to slow down the development of antibiotic resistance: 

• Prevent infections by washing your hands and keeping up to date with vaccinations. 
• Only take an antibiotic when necessary (e.g. not for viral infections). 
• Choose the right antibiotic for the right infection and take the course for the prescribed period of time. 

This last one is important for people with a possible penicillin allergy as penicillin is very effective against many common infections and, importantly, doesn’t impact the ‘good’ bacteria living in the gut. Other ‘broader spectrum’ antibiotics do affect these gut bacteria and are more likely to lead to resistance developing. Hospital patients who report antibiotic allergy are more likely to have longer stays in hospital and suffer multi-resistant infections. 

If your doctor assesses that you need a penicillin allergy test, DVA funds this for veterans with a Gold Card or a White Card with a relevant accepted condition. 

The discovery of antibiotics revolutionised medicine in the 20th century. It’s up to all of us to use them wisely and help to limit the development of antibiotic resistance whenever we can.