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Antibiotics and treating infections - Information for patients, carers and visitors

What are antibiotics?

Antibiotics are medicines used to treat infections caused by bacteria. They work by either killing
bacteria or preventing their growth. Different types of antibiotics are prescribed to treat different kinds of infection. In Australia, most antibiotics are only available on prescription from a doctor or a dentist.

When should antibiotics be used?

Antibiotics do not work against infections caused by viruses such as common colds, flu, most coughs or sore throats. Antibiotics are effective only against bacterial infections—they cannot help you recover from infections caused by viruses.

If you are having an operation, you may be prescribed antibiotics to prevent an infection. This is known as prophylaxis and is especially common before surgery to repair broken bones and joints and before bowel surgery.

How to take antibiotics

Antibiotics are usually taken by mouth, but can sometimes be given into a vein (intravenous), into a muscle (intramuscular) or applied to the affected part of the body such as skin, eyes or ears as drops, lotion or ointment (also known as topical).

Some antibiotics should not be taken with certain foods, whilst others are best taken on an empty stomach, usually an hour before or two hours after meals. Alcohol should be avoided with certain antibiotics. Always follow the directions on the label or patient information leaflet.

Antibiotic use causes bacteria to become resistant to antibiotic treatments, therefore, it is important to finish the full course and take the correct dose at the right time in order to kill all the bacteria that are causing the infection.

Do not give your antibiotics to friends, family or pets and do not keep leftover antibiotics. If you have received more doses than you were prescribed ask your pharmacist about
how to dispose of the remaining medicines.

Special care

You should speak to your doctor before taking an antibiotic if you know that you have any liver or kidney problems. Tell your doctor or pharmacist if you are pregnant or breastfeeding before taking any antibiotics.

Side-effects of antibiotics

The most common side effects of antibiotics are diarrhoea, stomach pain, nausea and vomiting. Some antibiotics may make your skin more sensitive to the sun. Often you will get no obvious side effects from antibiotics, however if your symptoms persist, contact your doctor.

After treatment with certain antibiotics, you may get a fungal infection such as oral (in the mouth) or vaginal thrush. This is because antibiotics may destroy your body’s ‘good’ bacteria that help to control overgrowth of microbes like fungi, as well as the ‘bad’ bacteria responsible for the
infection being treated.

Speak with your doctor or pharmacist about treatment for thrush if you develop symptoms such as a painful, white film coated mouth or white, curd-like vaginal discharge.

Occasionally some antibiotics may cause overgrowth of a different type of bacteria in your bowel known as C. difficile. This causes symptoms such as severe watery diarrhoea up to 10 times a day, stomach pain and cramping, fever, loss of appetite and blood or pus in the stool.

This can happen while you are taking antibiotics and even up to some months after completing your prescribed course. If you develop these symptoms, consult your doctor immediately. You may be given a different type of antibiotic to treat this type of infection.


Some people can be allergic to antibiotics, particularly penicillin and similar antibiotics such as cephalosporins, and may experience side effects such as a rash, swelling of the face and tongue and difficulty breathing when they take antibiotics. This is called an anaphylactic reaction and it can be serious or even fatal. Sometimes it can occur even if you have had the same antibiotics in the past and did not experience these symptoms.

Always tell your doctor, nurse or pharmacist if you have had an allergic reaction to an antibiotic and remind them of your allergy before you receive any antibiotics. Seek immediate medical advice if symptoms of an allergy occur after taking antibiotics.

Interactions with other medicines

There are a number of important interactions between antibiotics and other medicines including blood thinners such as warfarin and medicines used to treat high cholesterol such as ‘statins’.

It is important to tell your doctor or pharmacist if you are taking any other medicines or herbal remedies before you start taking antibiotics and ensure that they are safe to take at the same time as your antibiotics. Alcohol should be avoided while taking certain antibiotics, such as metronidazole.

Certain antibiotics can stop the contraceptive pill working properly. If you have diarrhoea or vomiting while taking an antibiotic, your pill might not be properly absorbed. Speak to your doctor or pharmacist if you have any concerns.

Resistance to antibiotics

Bacteria evolve rapidly—they adapt and find ways to survive the effect of antibiotics. They become
‘antibiotic resistant’ so that the antibiotic no longer works. Antibiotic resistance is growing. 

If you take antibiotics when you do not need them, they may lose their ability to kill bacteria. If the
bacteria keep ‘overpowering’ the medicines we have, we may run out of ways to kill these bacteria.
This is a health hazard not just for the person having taken the antibiotics inappropriately, but also for anyone else who might catch the resistant bacteria afterwards.

Taking antibiotics when they are not needed and not taking them correctly, for example, just when
you remember or in a low dose, will lead to more bacteria becoming resistant to them. This is why it is important to finish the course of antibiotics even if you feel better.

Why can’t other antibiotics be used to treat resistant bacteria?

They can, however they may not be as effective and could have more side effects. Eventually the bacteria will become resistant to them too. Only two new types of antibiotics have been found in the past 30 years and there is no guarantee that new ones will be discovered, we must look after the antibiotics that we have by using them carefully.

We cannot stop resistance occurring, but we can do a lot to slow it down and stop it spreading while we work to develop new types of antibiotics.

Some questions you may like to ask your doctor when you are prescribed antibiotics:

• Why have I been prescribed antibiotics?
• When should I expect to get better and what should I do if am not feeling well by this time?
• Are there any treatment options that do not include antibiotics?
• What is the correct way to take these antibiotics and how long do I need to take them for?
• What are the common side effects of these antibiotics and what should I do if they occur?
• Any other questions you may have.

Remind your doctor of any allergies you have to medicines including antibiotics. 

Please inform your doctor if you are taking any other medicines or herbal remedies or if you are pregnant or breastfeeding.


University College London Hospitals NHS Foundation Trust. Antibiotics [pamphlet]. London; 2008 [updated 2013 Dec; cited 2015 Apr 14]. Available from: https://www.uclh.nhs.uk/PandV/PIL/Patient%20information%20leaflets/Antibiotics.pdf

Mater acknowledges consumer consultation in the development of this patient information.
Mater Doc Num: PI-CLN-410035
Last modified 25/9/2019.
Consumers were consulted in the development of this patient information.
Last consumer engagement date: 12/6/2017
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