Introduction

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

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

Many mild bacterial infections can also be cleared by your immune system without using antibiotics, so they aren't routinely prescribed.

It's important that antibiotics are prescribed and taken correctly to help prevent the progression of antibiotic resistance. This is when a strain of bacteria no longer responds to treatment with one or more types of antibiotics.

When antibiotics are 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

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.

How do I take antibiotics?

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:

  • oral antibiotics – tablets, capsules or a liquid that you drink, which can be used to treat most types of mild to moderate infections in the body
  • topical antibiotics – creams, lotions, sprays or drops, which are often used to treat skin infections
  • injections of antibiotics – these can be given as an injection or infusion through a drip directly into the blood or muscle, and are usually reserved for more serious infections

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.

Missing a dose of antibiotics

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 2 doses closer together than recommended.

Accidentally taking an extra dose

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 24 111 service as soon as possible.

Side effects of antibiotics

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:

  • being sick
  • feeling sick
  • bloating and indigestion
  • diarrhoea

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.

Considerations and interactions

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 how antibiotics interact with other medicines

Types of antibiotics

There are hundreds of different types of antibiotics, but most of them can be broadly classified into six groups. These are outlined below.

    • penicillins (such as penicillin and amoxicillin) – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections
    • cephalosporins (such as cephalexin) – used to treat a wide range of infections, but some are also effective for treating more serious infections, such as septicaemia and meningitis
    • aminoglycosides (such as gentamicin and tobramycin) – tend to only be used in hospital to treat very serious illnesses such as septicaemia, as they can cause serious side effects, including hearing loss and kidney damage; they're usually given by injection, but may be given as drops for some ear or eye infections
    • tetracyclines (such as tetracycline and doxycycline)– can be used to treat a wide range of infections, but are commonly used to treat moderate to severe acne and rosacea
    • macrolides (such as erythromycin and clarithromycin) – can be particularly useful for treating lung and chest infections, or an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria
    • fluoroquinolones (such as ciprofloxacin and levofloxacin) – broad-spectrum antibiotics that can be used to treat a wide range of infections

Antibiotic resistance

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.

Accessing medicines self-help guide

Visit our self-help guide on accessing medicines if you have difficulty getting the medicines you need.

Self-help guide: Accessing medicines

Uses

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:

  • that aren't especially serious but are unlikely to clear up without the use of antibiotics – such as moderately severe acne
  • that aren't especially serious but could spread to other people if not promptly treated – such as the skin infection impetigo or the sexually transmitted infection chlamydia
  • where evidence suggests that antibiotics could significantly speed up recovery – such as a kidney infection
  • that carry a risk of more serious complications – such as cellulitis or pneumonia

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 and can cause side effects
  • the more antibiotics are used to treat trivial conditions, the more likely they are to become ineffective for treating more serious conditions

For example, antibiotics are no longer routinely used to treat chest infections, ear infections in children and sore throats.

Read more about antibiotic resistance.

People at risk of bacterial infections

Antibiotics may also be recommended for people who are more vulnerable to the harmful effects of infection. This may include:

  • people aged over 75 years
  • babies less than 72 hours old with a confirmed bacterial infection, or a higher than average risk of developing one
  • people with heart failure
  • people who have to take insulin to control their diabetes
  • people with a weakened immune system – either because of an underlying health condition such as HIV infection or as a side effect of certain treatments, such as chemotherapy

Antibiotics to prevent infection

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:

  • some types of eye surgery – such as cataract surgery or glaucoma surgery
  • joint replacement surgery
  • breast implant surgery
  • pacemaker surgery
  • surgery to remove the gall bladder
  • surgery to remove the appendix

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

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, 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: 

Special considerations

There are some important things to consider before taking antibiotics.

This page contains information on the 6 main classes of antibiotics:

penicillin 

cephalosporins 

aminoglycosides 

tetracyclines 

macrolides

fluoroquinolones

Penicillin

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.

People with a history of allergies, such as asthma, eczema or hay fever, are at higher risk of developing a serious allergic reaction (anaphylaxis) to penicillins, although cases are rare.

Penicillins may need to be used at lower doses and with extra caution if you have:

Pregnancy and breastfeeding

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.

Cephalosporins

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

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.

Tetracyclines

The use of tetracyclines isn't usually recommended unless absolutely necessary in the following groups:

  • people with kidney disease – except doxycycline, which can be used
  • people with liver disease
  • people with the autoimmune condition lupus – which can cause skin problems, joint pain and swelling, and fatigue (feeling tired all the time)
  • children under the age of 12
  • pregnant or breastfeeding women

Macrolides

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

Fluoroquinolones aren't normally suitable for women who are pregnant or breastfeeding.

Last updated:
05 July 2021