Health A to Z
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from reproducing and spreading. But they don’t work for everything. When it comes to antibiotics, take your doctor’s advice.
Antibiotics don't work for viral infections such as colds and flu, and most coughs and sore throats.
Many mild bacterial infections also get better on their own without using antibiotics.
Taking antibiotics when you don’t need them encourages dangerous bacteria that live inside you to become resistant. That means that antibiotics may not work when you next need them most. This puts you and your family at serious risk.
Antibiotics may be used to treat bacterial infections that:
People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis.
Read more about when antibiotics are used.
Take antibiotics as directed on the packet or the patient information leaflet that comes with the medication, or as instructed by your GP or pharmacist.
Doses of antibiotics can be provided in several ways:
It's essential to finish taking a prescribed course of antibiotics, even if you feel better, unless a healthcare professional tells you otherwise. If you stop taking an antibiotic part way through a course, the bacteria can become resistant to the antibiotic.
If you forget to take a dose of your antibiotics, take that dose as soon as you remember and then continue to take your course of antibiotics as normal.
But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Don't take a double dose to make up for a missed one.
There's an increased risk of side effects if you take two doses closer together than recommended.
Accidentally taking one extra dose of your antibiotic is unlikely to cause you any serious harm.
But it will increase your chances of experiencing side effects, such as pain in your stomach, diarrhoea, and feeling or being sick.
If you accidentally take more than one extra dose of your antibiotic, are worried or experiencing severe side effects, speak to your GP or call NHS 111 as soon as possible.
As with any medication, antibiotics can cause side effects. Most antibiotics don't cause problems if they're used properly and serious side effects are rare.
The most common side effects include:
Some people may have an allergic reaction to antibiotics, especially penicillin and a type called cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis), which is a medical emergency.
Read more about the side effects of antibiotics.
Some antibiotics aren't suitable for people with certain medical conditions, or women who are pregnant or breastfeeding. You should only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member.
Some antibiotics can also react unpredictably with other medications, such as the oral contraceptive pill and alcohol. It's important to read the information leaflet that comes with your medication carefully and discuss any concerns with your pharmacist or GP.
Read more about:
There are hundreds of different types of antibiotics, but most of them can be broadly classified into six groups. These are outlined below.
Both the NHS and health organisations across the world are trying to reduce the use of antibiotics, especially for conditions that aren't serious.
The overuse of antibiotics in recent years means they're becoming less effective and has led to the emergence of "superbugs". These are strains of bacteria that have developed resistance to many different types of antibiotics, including:
These types of infections can be serious and challenging to treat, and are becoming an increasing cause of disability and death across the world.
The biggest worry is that new strains of bacteria may emerge that can't be effectively treated by any existing antibiotics.
Antibiotics are used to treat or prevent some types of bacterial infections. They aren't effective against viral infections, such as the common cold or flu.
Antibiotics should only be prescribed to treat conditions:
Antibiotics are no longer routinely used to treat infections because:
Read more about antibiotic resistance.
Antibiotics may also be recommended for people who are more vulnerable to the harmful effects of infection. This may include:
Antibiotics are sometimes given as a precaution to prevent, rather than treat, an infection. This is known as antibiotic prophylaxis.
Antibiotic prophylaxis is normally recommended if you're having surgery on a certain part of the body which carries a high risk of infection or where infection could lead to devastating effects.
For example, it may be used if you're going to have:
Your surgical team will be able to tell you if you require antibiotic prophylaxis.
Antibiotic prophylaxis may be recommended for a wound that has a high chance of becoming infected – this could be an animal or human bite, for example, or a wound that has come into contact with soil or faeces.
There are several medical conditions that make people particularly vulnerable to infection, making antibiotic prophylaxis necessary.
For example, the spleen plays an important role in filtering out harmful bacteria from the blood. People who have had their spleen removed, people having chemotherapy for cancer, or those with the blood disorder sickle cell anaemia, where their spleen doesn't work properly, should take antibiotics to prevent infection.
In some cases, antibiotic prophylaxis is prescribed for people who experience a recurring infection that's causing distress or an increased risk of complications, such as:
There are some important things to consider before taking antibiotics.
This page contains information on the six main classes of antibiotics:
Don't take one of the penicillin-based antibiotics if you've had an allergic reaction to them in the past. People who are allergic to one type of penicillin will be allergic to all of them.
Penicillins may need to be used at lower doses and with extra caution if you have:
Most penicillins can be used during pregnancy and breastfeeding in the usual doses.
Tell your healthcare professional if you're pregnant or breastfeeding, so they can prescribe the most suitable antibiotic for you.
If you previously had an allergic reaction to penicillin, there's a chance that you may also be allergic to cephalosporins.
Cephalosporins may not be suitable if you have kidney disease, but if you need one you will probably be given a lower than usual dose.
If you're pregnant or breastfeeding, or have acute porphyria, check with your doctor, midwife or pharmacist before taking cephalosporins.
Aminoglycosides are normally only used in hospital to treat life-threatening conditions such as septicaemia, as they can cause kidney damage in people with pre-existing kidney disease.
They're only used during pregnancy if your doctor believes they're essential.
The use of tetracyclines isn't usually recommended unless absolutely necessary in the following groups:
You shouldn't take macrolides if you have porphyria – a rare inherited blood disorder.
If you're pregnant or breastfeeding, the only type of macrolide you can take is erythromycin (Erymax, Erythrocin, Erythroped or Erythroped A) unless a different antibiotic is recommended by your doctor.
Erythromycin can be used at the usual doses throughout your pregnancy and while you're breastfeeding.
Other macrolides shouldn't be used during pregnancy, unless advised by a specialist.
Fluoroquinolones aren't normally suitable for women who are pregnant or breastfeeding.
The most common side effects of antibiotics affect the digestive system. These occur in around 1 in 10 people.
Side effects of antibiotics that affect the digestive system include:
These side effects are usually mild and should pass once you finish your course of treatment.
If you experience any additional side effects other than those listed above, you should contact your GP or the doctor in charge of your care for advice.
Around 1 in 15 people have an allergic reaction to antibiotics, especially penicillin and cephalosporins. In most cases, the allergic reaction is mild to moderate and can take the form of:
These mild to moderate allergic reactions can usually be successfully treated by taking antihistamines.
But if you're concerned, or your symptoms don't respond to treatment, you should call your GP for advice. If you can't contact your GP, call NHS 111.
In rare cases, an antibiotic can cause a severe and potentially life-threatening allergic reaction known as anaphylaxis.
Initial symptoms of anaphylaxis are often the same as above and can lead to:
Anaphylaxis is a medical emergency and can be life-threatening if prompt treatment isn't given. Dial 999 immediately and ask for an ambulance if you think you or someone around you is experiencing anaphylaxis.
Tetracyclines can make your skin sensitive to sunlight and artificial sources of light, such as sun lamps and sunbeds.
You should avoid prolonged exposure to bright light while taking these drugs.
Antibiotics can sometimes interact with other medicines or substances. This means it can have an effect that is different to what you expected.
Some of the more common interactions are listed below, but this isn't a complete list.
If you want to check that your medicines are safe to take with your antibiotics, ask your GP or local pharmacist.
Some antibiotics need to be taken with food, while others need to be taken on an empty stomach. You should always read the patient information leaflet that comes with your medicine.
You should completely avoid alcohol while taking the antibiotics metronidazole or tinidazole, and for 48 hours afterwards, as this combination can cause very unpleasant side effects, such as:
It's recommended that you don't drink alcohol while taking antibiotics. However, as long as you drink in moderation, alcohol is unlikely to interact significantly with your medication.
Read more information about drinking alcohol while taking antibiotics.
Some antibiotics, such as rifampicin and rifabutin, can reduce the effectiveness of the combined oral contraceptive pill.
If you're prescribed rifampicin or rifabutin, you may need to use additional contraception, such as condoms, while taking antibiotics. Speak to your GP, nurse or pharmacist for advice.
Some of the medications you may need to avoid, or seek advice on, while taking a specific class of antibiotic are outlined below.
It's usually recommended that you avoid taking penicillin at the same time as methotrexate, which is used to treat psoriasis, rheumatoid arthritis and some forms of cancer. This is because combining the two medications can cause a range of unpleasant and sometimes serious side effects.
However, some forms of penicillin, such as amoxicillin, can be used in combination with methotrexate.
You may experience a skin rash if you take penicillin and allopurinol, which is used to treat gout.
If you need treatment with cephalosporins, you may need to have your dose of anticoagulants changed or additional blood monitoring.
The risk of damage to your kidneys and hearing is increased if you're taking one or more of the following medications:
The risk of kidney and hearing damage has to be balanced against the benefits of using aminoglycosides to treat life-threatening conditions such as septicaemia.
In hospital, blood levels are carefully monitored to ensure the antibiotic is only present in the blood in safe amounts. If aminoglycosides are used properly in topical preparations, such as ear drops, these side effects don't occur.
You should check with your GP or pharmacist before taking a tetracycline if you're currently taking any of the following:
It's highly recommended that you don't combine a macrolide with any of the following medications unless directly instructed to by your GP, as the combination could cause heart problems:
You should check with your GP or pharmacist before taking a fluoroquinolone if you're currently taking any of the following:
Some fluoroquinolones can intensify the effects of caffeine (a stimulant found in coffee, tea and cola), which could make you feel irritable, restless and cause problems falling asleep (insomnia).
You may need to avoid taking medication that contains high levels of minerals or iron, as this can block the beneficial effects of fluoroquinolones. This includes: