About antibiotics

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

Antibiotics aren't effective against viral infections. This includes the common cold, flu, most coughs and sore throats.

Antibiotics aren't routinely prescribed for mild bacterial infections. This is because the immune system can usually clear these on it's own.

When are antibiotics used?

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

Antibiotics to prevent infection

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


Antibiotic prophylaxis is normally recommended if you're having surgery in a certain area. This is because there could be a higher risk of infection.

Your surgical team will be able to tell you if you need antibiotic prophylaxis.

People vulnerable to infection

Antibiotics may be recommended for people who are more vulnerable to infection. This includes:

  • people aged over 75 years
  • babies less than 72 hours old with a confirmed bacterial infection
  • babies with a high risk of developing a bacterial infection
  • people with heart failure
  • people who have to take insulin to control their diabetes
  • people with a weakened immune system

Bites or wounds

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.

Medical conditions

There are several medical conditions that make people particularly vulnerable to infection. This makes antibiotic prophylaxis necessary.

The spleen plays an important role in filtering out harmful bacteria from the blood. If your spleen doesn't work properly, this means antibiotics can help prevent infection.

People more vulnerable to infection include those:

  • who've had their spleen removed
  • having chemotherapy for cancer
  • with the blood disorder sickle cell anaemia

Recurring infection

Antibiotic prophylaxis may also be recommended for a recurring infection, like:

Types of antibiotics

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


These are widely used to treat a variety of infections, including:

  • skin infections
  • chest infections
  • urinary tract infections


These can be used to treat a wide range of infections. Some are also effective for treating more serious infections, like:

  • septicaemia
  • meningitis


These are usually used in hospital to treat very serious illnesses like septicaemia. This is because they can cause serious side effects like hearing loss and kidney damage.

Aminoglycosides are usually given by injection. They may also be given as drops for some ear or eye infections.


These can be used to treat a wide range of infections. They are commonly used to treat moderate to severe acne and rosacea.


These can be particularly useful for treating lung and chest infections.

Macrolides are used as an alternative for people with a penicillin allergy. They can also be used to treat penicillin-resistant strains of bacteria


These are broad-spectrum antibiotics that can be used to treat a wide range of infections.

Accessing medicines self-help guide

Visit our self-help guide on accessing medicines if you have difficulty getting the medicines you need. This is suitable for patients who are prescribed long-term or repeat antibiotic courses. This is not appropriate for short-term courses that are not regularly prescribed for you.

Self-help guide: Accessing medicines

Taking antibiotics

Your GP or pharmacist will tell you how to take your antibiotic. It will come labelled with the dose you should take and other relevant information. You should follow the directions on the label and 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.

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

It's essential to finish taking your antibiotics, even if you feel better. You should only do differently if your healthcare professional tells you to.

If you stop taking your course of antibiotics early, bacteria can become resistant to it.

Missing a dose of antibiotics

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.

Accidentally taking an extra dose

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

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

Non-urgent advice: Speak to your pharmacist or GP if you:

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

If your GP or pharmacy is closed, phone 111.

Antibiotic resistance

Antibiotics are no longer routinely used to treat infections 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 in recent years 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. Superbugs include:

These types of infections can be serious and challenging to treat.

The worry is that new strains of bacteria will develop that antibiotics won't be able to treat.

Side effects and interactions of antibiotics

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

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

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

Antibiotic allergic reactions

Some people have an allergic reaction to antibiotics, especially penicillin and cephalosporins. In most cases, the allergic reaction is mild to moderate and 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 prompt treatment should be given.

Non-urgent advice: Speak to your GP if:

  • you're concerned about your symptoms
  • your symptoms don't respond to treatment

If your GP is closed, phone 111.

Urgent advice: 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 neck
  • a sudden intense feeling of apprehension and fear
  • a sharp and sudden drop in blood pressure causing
  • light-headedness and confusion
  • lost consciousness


Some antibiotics can interact with other substances and medicines.


You should not drink alcohol while taking the antibiotics, especially metronidazole or tinidazole.

You shouldn't drink alcohol for 48 hours after stopping your antibiotics.

This combination can cause very unpleasant side effects, like:

  • feeling and being sick
  • stomach pain
  • hot flushes
  • headaches

Combined oral contraceptives

Some antibiotics can reduce the effectiveness of the combined oral contraceptive pill. This includes the antibiotics rifampicin and rifabutin.

If you're prescribed these antibiotics, you may need to use additional contraception like condoms. Speak to your GP, nurse or pharmacist for advice.


Antibiotics can sometimes interact with other medicines or substances. This means it can have an effect that is different from what you expected.

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


There are some important things to consider when taking antibiotics.


Don't take a penicillin-based antibiotic 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.

People with allergies are at higher risk of developing a serious allergic reaction to penicillins. This includes people with:

Penicillins may also 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. They'll be able to prescribe the most suitable antibiotic for you.


If you've had an allergic reaction to penicillin, you may also be allergic to cephalosporins.

Cephalosporins may not be suitable if you have kidney disease. If you need this antibiotic and have kidney disease you'll probably be given a low dose.

Check with your doctor, midwife or pharmacist before taking cephalosporins if you:

  • are pregnant
  • are breastfeeding
  • have acute porphyria

Aminoglycosides are normally only used in hospitals to treat life-threatening conditions like septicaemia. This is because 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.


Tetracyclines aren't usually recommended unless absolutely necessary if you:

  • have kidney disease – except doxycycline, which can be used
  • have liver disease
  • have lupus
  • are under the age of 12
  • are pregnant
  • are breastfeeding

Tetracyclines can make your skin sensitive to sunlight and artificial sources of light, like sun lamps and sunbeds. This means you should avoid prolonged exposure to bright light while taking these drugs.


You shouldn't take macrolides if you have porphyria. This is 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 whilst 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.

Last updated:
30 May 2023