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What are antibiotics?

Antibiotics are a group of medicines used to treat infections caused by bacteria and are sometimes referred to as antibacterial or antimicrobials. They work by either killing bacteria or preventing their growth.

There are different types of antibiotics that are used to treat different infections.

If you have been admitted to hospital with an infection antibiotics are often given via a vein (intravenously) for the first 48-72hours. They may then be changed to an antibiotic that is given by mouth (tablet, capsule, liquid).

When should antibiotics be used?

Antibiotics are only effective against infections caused by bacteria and some parasites. They do not work against viruses such as the common cold or fungal infections.

Your doctor will only prescribe antibiotics if you need them. They can be life-saving for some serious infections such as meningitis.

If you are having an operation, you may be given an antibiotic in theatre to prevent infection. This is known as prophylaxis and will depend on the type of surgery you are having.

How should I take my antibiotics?

It is important that you take your antibiotics in the correct way. If you do not it may reduce how well they work.

Some antibiotics have special instructions for example take on an empty stomach. Remember to always read the instructions on the label.

You should complete the entire course as directed by your doctor even if you start you feel better.

Antimicrobial resistance

Overuse of antibiotics has led to some bacteria altering their structure and developing resistance to some antibiotics, meaning that the antibiotic will no longer work against that infection.

If we continue to overuse antibiotics and bacteria continue to develop resistance we may exhaust ways to treat serious infections. With fewer new antibiotics being developed we must look after the antibiotics we have by using them carefully.

You can help the cause by becoming an antibiotic guardian:

Side effects

As with any medicine there is the possibility of side effects, but they may not occur in everyone. There is a full list of potential side effects within the patient information leaflet that comes with your antibiotics.

The most common side effects with antibiotics are diarrhoea, nausea and vomiting.

If you have concerns about a possible side effect please discuss with your pharmacist or doctor.

Allergic reactions

  • Some people develop allergic reactions to antibiotics:
  • Rash
  • Swelling of face and tongue
  • Difficulty in breathing

If these symptoms rapidly progress and become worse, this is known as anaphylaxis. Urgent medical assistance is required. Always give clear details of previous reactions before being prescribed antibiotics.

Other medication

Some antibiotics interact with other medication causing unwanted reactions or changing the way that medicine works.

Therefore it is important that you tell your doctor or pharmacist of all your other medication, including those that you buy over the counter. Complementary therapies also have the ability to interact with antibiotics.

What to do with unwanted antibiotics?

If you have any unwanted antibiotics, please take them to your local pharmacy for safe disposal.

You should not:

  • Save them for another time
  • Share them with anybody else
  • Flush them down toilets or sinks

Further information

If you have any questions about the antibiotics you have been prescribed then you can speak to one of our pharmacists by calling our Pharmacy Medicines Hotline:

0151 529 3208

(Monday – Friday 08:30 – 17:00)

The following website also provides further information:

Key Points

  • Antibiotics DO NOT work for viral infections
  • Always tell your doctor and pharmacist of any previous allergies and the nature of the reaction before being given any antibiotic
  • Always complete the course prescribed
  • Always follow the instructions on the label or packaging

We must all use antibiotics responsibly - Misuse of antibiotics causes bacteria to become resistant to the antibiotic. So when you need antibiotics in the future they may no longer work.


  • Last Updated:
    01 October 2020
  • Review Date:
    01 October 2024
  • Author:
    Sian Davison
  • Summary:

    Antibiotics are a group of medicines used to treat infections caused by bacteria and are sometimes referred to as antibacterial or antimicrobials.

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