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Antibiotics are used to treat or prevent some types of bacterial infection. They kill bacteria or prevent them from reproducing and spreading.

What are antibiotics used for?

Antibiotics may be used to treat bacterial infections that:

  • are unlikely to clear up without antibiotics
  • could infect others unless treated
  • could take too long to clear without treatment
  • carry a risk of more serious complications

Preventing infection

Antibiotics are sometimes given as a precaution to prevent an infection. This is known as antibiotic prophylaxis.

Antibiotics may be needed to prevent infection if you:

  • are having surgery where there’s a higher risk of infection
  • are more vulnerable to infection, for example, you’re over 75 or have a weakened immune system
  • have a wound like an animal bite that has a high chance of becoming infected
  • have a medical condition that makes you more vulnerable to infection
  • you have a recurring infections like cellulitis or a urinary tract infection (UTI)

What antibiotics are not used for

Antibiotics do not work against viral infections. This includes the common cold, flu, most coughs and sore throats.

Antibiotics are not often prescribed for mild bacterial infections. This is because your immune system can usually clear these on it’s own.

Types of antibiotics

There are different types of antibiotic. Most can be put into 6 different groups. These are:

  • penicillins – widely used to treat infections including skin infections, chest infections and urinary tract infections (UTIs)
  • cephalosporins – used to treat more serious infections including septicaemia and meningitis
  • aminoglycosides – usually only used in hospital to treat very serious illnesses including septicaemia
  • tetracyclines – commonly used to treat acne and rosacea
  • macrolides – used to treat lung and chest infections, and as alternative to penicillin
  • fluoroquinolones – used to treat a wide range of infections

Tell your healthcare professional if you’re pregnant, breastfeeding, have a health condition, or have ever had an allergic reaction to antibiotics. Some types of antibiotic may not be suitable for you.

How to take antibiotics

Antibiotics can be given in different ways, including:

  • oral – tablets, capsules or liquids that treat most mild to moderate infections
  • topical – creams, lotions, sprays or drops that treat skin infections
  • injections – given directly into the blood or muscle for more serious infections

Your healthcare professional or pharmacist will tell you how to take your antibiotic. You should follow the directions on the label. Read the patient information leaflet that comes with your medicine too. If you have any questions about taking an antibiotic, ask your pharmacist for advice.

You must finish taking your course of antibiotics, even if you feel better. If you stop taking your antibiotics early, bacteria can become resistant to it.

Missed or extra doses

If you forget to take a dose of your antibiotics, take that dose as soon as you remember. You should then continue to take your course of antibiotics as normal.

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 2 doses closer together than recommended.

If you accidentally take 1 extra dose of your antibiotic, it’s unlikely to cause serious harm. But, it will increase your chances of side effects like:

  • pain in your stomach
  • diarrhoea
  • feeling or being sick

Speak to your pharmacist or GP if:

  • you accidentally take more than 1 extra dose of your antibiotic
  • you experience severe side effects after taking an extra dose

If your GP or pharmacy is closed, phone 111.

Possible side effects

Antibiotics can have side effects. These side effects are usually mild and should pass once you finish your course of treatment.

Common side effects

The most common side effects of antibiotics affect the digestive system. Symptoms can include:

  • vomiting
  • nausea (feeling sick)
  • diarrhoea
  • bloating
  • indigestion
  • abdominal pain
  • loss of appetite

If you experience any other side effects, contact your GP or the doctor in charge of your care for advice.

Allergic reactions

Some people have an allergic reaction to antibiotics, especially penicillin and cephalosporins. In most cases, the allergic reaction is mild to moderate. It can cause:

  • a raised, itchy skin rash (urticaria, or hives)
  • coughing
  • wheezing
  • tightness of the throat, which can cause breathing difficulties

Mild to moderate allergic reactions can usually be treated by taking antihistamines.

In rare cases, an antibiotic can cause anaphylaxis. This is a severe and potentially life-threatening allergic reaction. Anaphylaxis is a medical emergency and should be treated quickly.

Phone 999 or go to A&E if:

You or someone else has taken antibiotics and has:

  • a rapid heartbeat
  • difficulty breathing caused by swelling and tightening of the lips, tongue or neck
  • a sudden intense feeling of apprehension and fear
  • a sharp and sudden drop in blood pressure causing light-headedness and confusion
  • lost consciousness

Warnings and precautions

Some antibiotics can interact with:

  • alcohol – you should not drink alcohol while taking antibiotics, or for 48 hours after finishing them
  • combined oral contraceptives – you may need to use additional contraception like condoms while taking certain antibiotics
  • other medications

If you want to check that your medicines are safe to take with your antibiotics, ask your GP or local pharmacist.

Antibiotic resistance

Antibiotics are no longer routinely used to treat infections. This is because:

  • many infections are caused by viruses, so antibiotics aren’t effective
  • antibiotics are often unlikely to speed up the healing process
  • antibiotics can cause side effects

The overuse of antibiotics also means they’re becoming less effective. This has led to the emergence of ‘superbugs’. These are strains of bacteria that have developed resistance to many different antibiotics. These types of infections can be serious and challenging to treat.

New strains of bacteria may develop that antibiotics won’t be able to treat.

Read more about antibiotic resistance

Last updated:
31 May 2024