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Antibiotics


Expert reviewer, Dr Adrian Raby, General Practitioner
Next review due October 2022

Antibiotics are medicines used to treat or prevent infections caused by bacteria. Your doctor will only prescribe antibiotics when they’re really needed. This is for your own health and to prevent the increasing problem of antibiotic resistance (where they stop working). It’s very important for everyone to use antibiotics correctly.

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Why has my doctor advised me to take antibiotics?

Your doctor will only offer you antibiotics to treat an infection that’s likely to be caused by bacteria. Some bacterial infections clear up by themselves, so your doctor may want to wait before prescribing antibiotics you may not need. They’ll advise you on other treatment and self-management that could help. For instance, these days antibiotics are not used routinely to treat:


Antibiotics don’t work against viruses, so your doctor won’t normally offer them to treat viral illnesses such as colds, flu or chickenpox. Sometimes, a viral infection may lead to what’s called a secondary bacterial infection, such as pneumonia. If this happens or there’s a risk it might, your doctor may recommend antibiotics to treat or prevent the secondary bacterial infection.

Your doctor may also offer you antibiotics to prevent an infection in certain other situations. These include for certain types of surgery, or if your immune system is low (such as during chemotherapy or if you have HIV infection).

For some medical conditions, antibiotics can ease symptoms and speed up recovery. If you have a serious bacterial infection like pneumonia or meningitis, antibiotics can be life-saving. Some sexually transmitted infections (STIs), for example gonorrhoea and chlamydia, are caused by bacteria and need antibiotics to treat them.

Ask your doctor to explain why antibiotics are the best option for you.

How do antibiotics work?

Some antibiotics work by killing bacteria. They usually do this by preventing them from building their cell walls. Other antibiotics work by stopping bacteria from growing and multiplying. This gives your body’s own defences time to find and kill them.

What are the main types of antibiotic?

There are many different antibiotics, which work in different ways and affect different types of bacteria. The main groups of antibiotics are given here.

  • Penicillins (for example, benzylpenicillin, amoxicillin and flucloxacillin).
  • Cephalosporins (for example, cefalexin and cefaclor).
  • Tetracyclines (for example, doxycycline and minocycline).
  • Aminoglycosides (for example, gentamicin and tobramycin).
  • Macrolides (for example, erythromycin and clarithromycin).
  • Quinolones (for example, ciprofloxacin and levofloxacin).

Other commonly-used antibiotics include nitrofurantoin and trimethoprim, which are often used for urine infections.

Antibiotics can also be put into two groups according to whether they’re broad- or narrow-spectrum. Broad-spectrum antibiotics can treat infections caused by a wide range of different bacteria. Narrow-spectrum antibiotics only work against specific bacteria.

Your doctor will offer you the most suitable antibiotic, taking into account where the infection is and what any laboratory results show. In some circumstances, you may need to take more than one antibiotic. Your doctor will explain why.

The leaflet that comes with your medicine will have more information. It will tell you what type of antibiotic you’re taking and what conditions it’s usually used for.

What forms do antibiotics come in?

Antibiotics come in different forms including:

  • tablets or capsules (most commonly)
  • liquids (if you have difficulty swallowing or when giving to children)
  • ear and eye drops (for example, for conjunctivitis)
  • creams (for skin conditions like eczema and broken skin which gets infected)
  • injections (for serious infections – these are usually given in hospital)

Usually you can only get antibiotics on prescription. However, some you can buy at the pharmacy over the counter (such as eye drops for conjunctivitis).

How to take antibiotics

The leaflet that comes with your medicine will give you lots of important information about when and how to take your antibiotics. Your doctor or pharmacist may also give you advice. It’s important to follow any instructions you’re given.

How long do I take them for?

You’ll need to take antibiotics for a set period of time, which could be days, weeks or even months. Your prescription should tell you how long. Finish the whole course, even if you start to feel better, to make sure all the bacteria are gone and to stop the infection returning.

Using antibiotics correctly

It’s important not to misuse antibiotics.

  • Don’t take someone else’s antibiotics, or share yours with another person.
  • Don’t take antibiotics ‘just in case’ (when you’re travelling abroad, for instance) unless your doctor has advised you to because you’re at particular risk of infection.
  • Don’t keep leftover antibiotics to use later.
  • Don’t flush them down the toilet or sink – hand any unused antibiotics to your pharmacist for disposal.

Special considerations

Not all antibiotics are suitable for everyone. Tell your doctor, nurse prescriber or dentist if:

  • you’re allergic to penicillin or any other antibiotic (see our section on side-effects to antibiotics below)
  • you have other health conditions, such as problems with your liver or kidneys, or are taking other medicines
  • you might be pregnant, or know you are, or are planning to become pregnant. Also if you’re breastfeeding. If you’re pregnant or breastfeeding, your doctor will offer you the antibiotic which is safest for you and your baby

Antibiotic resistance

Some bacteria develop resistance to certain antibiotics. This means that the antibiotic doesn’t work as well, and for some people may not be able to treat their infection. Antibiotic resistance is a serious and growing problem in the world today.

Every time someone takes antibiotics, many bacteria are killed but some resistant bacteria survive and may multiply. These resistant bacteria can then go on to cause a further infection or be spread to other people. Some multi-resistant bacteria are resistant to several antibiotics at the same time. It can be much harder to treat infections with antibiotic-resistant bacteria.

One example of antibiotic-resistant bacteria you may have heard of is MRSA (methicillin-resistant Staphylococcus aureus). These bacteria can cause serious infections and are resistant to most of the usual antibiotics your doctor would prescribe.

Health professionals are trying to slow down the development of resistance, which is caused by the over-use and misuse of antibiotics. They are now very careful to recommend antibiotics only when they’re really necessary. This is why your doctor or pharmacist may advise how you can manage an infection without antibiotics.

You can do your bit to stop antibiotic resistance by working with your doctor to ensure that you only take antibiotics when they’re the best option. And by following the advice we give above on taking your medicines.

Side-effects of antibiotics

Side-effects are the unwanted effects of taking a medicine. It’s not possible to list all the side-effects of all the different antibiotics here. The patient information leaflet that comes with your medicine will have lots of details of these, so you should read this carefully.

Some of the most common side-effects of antibiotics include diarrhoea and feeling sick or vomiting.

As well as killing the harmful bacteria that are causing your infection, antibiotics may also destroy your body’s ‘friendly’ protective bacteria. These normally stop other micro-organisms growing out of control. So, if you take antibiotics you may get overgrowth of fungi causing thrush, for instance in your mouth or vagina. Or you can get an infection with a type of bacteria called Clostridium difficile found in your intestine. This can produce toxins causing severe diarrhoea, and this is a serious problem in hospitals and care homes. It may be fatal, particularly in the elderly or those who are weakened through illness.

If you have side-effects, it’s important to talk to your doctor or the healthcare professional who prescribed your medicine before you stop taking it. Depending on your infection, they may be able to offer you an alternative antibiotic, although this won’t always be possible.

Allergies to antibiotics

A more serious possible side-effect of taking antibiotics is having an allergic reaction, especially to penicillins and cephalosporins. This can range from a mild skin rash to a severe life-threatening reaction. If you’ve had an allergic reaction in the past, be sure to tell your doctor.

If you’re allergic to an antibiotic, typical symptoms include:

  • an itchy rash
  • flushing of your skin
  • sore eyes
  • a blocked or runny nose
  • swelling in any part of your body but especially your face, throat and tongue
  • feeling or being sick

These reactions usually happen very quickly after taking antibiotics. If they happen, stop taking your antibiotic and contact your GP as soon as possible.

Occasionally, a severe allergic reaction, called anaphylaxis, can happen. The symptoms of anaphylaxis include:

  • difficulty breathing (which may sound noisy)
  • wheezing
  • feeling light-headed or faint, even collapsing
  • a fast heartbeat
  • clammy skin

Seek immediate medical attention (call 999) if you think you’re having these symptoms after taking antibiotics or any other medicines.

True allergy to penicillins is quite rare. About one in 10 people think they have an allergy to penicillin, but for many this isn’t the case. They may have just had side-effects like sickness or a headache, or a mild skin rash as a child. If so, and you get a serious infection, your doctor may suggest you take penicillin because it’s the best medicine to treat your illness. They’ll consider this carefully though because a severe allergic reaction is potentially fatal.

Interactions with other medicines, food and drink

Some antibiotics can interact with other medicines, foods or drinks. You’ll find details of these in the patient information leaflet which comes with your medicine. You can ask your pharmacist if you have any questions.

Antibiotics may make the action of other medicines stronger or weaker. Before you take anything else at the same time as antibiotics, including herbal remedies, check with your pharmacist or health professional who prescribed the antibiotics.

Antibiotics and the contraceptive pill

Certain antibiotics (for example, rifampicin) can stop the contraceptive pill from working as well. And some side-effects from taking antibiotics (such as, for diarrhoea and vomiting) may stop your contraceptive pill from being absorbed into your body. If you’re taking antibiotics that affect the contraceptive pill or you’ve vomited or had severe diarrhoea, you should use another method of contraception. Your doctor can talk to you about the best options for you.

Antibiotics and diet

You should also check the patient information leaflet to see if it’s OK to have certain foods or drinks with your antibiotic. For example, dairy products (including milk) can affect how your body absorbs some antibiotics. Alcohol can cause a reaction with some antibiotics – see our FAQ on alcohol and antibiotics below. Dietary supplements or fortified foods and drinks containing calcium may make your antibiotic less effective.

Medicines checklist

Our handy medicines checklist helps you see what to check for before taking a medicine.

Bupa's medicines checklist PDF opens in a new window (0.8MB)

Bupa medicines checklist

Frequently asked questions

  • If you’re feeling unwell, it’s probably best to avoid alcohol for a while. But it’s unlikely that you’ll have any problems with most common antibiotics if you drink only moderate amounts of alcohol.

    There are a few important exceptions though. You should avoid alcohol completely if you’re taking:

    • metronidazole
    • tinidazole

    These antibiotics may be used, for example, for infections of the gums and in the pelvis, and to treat stomach ulcers. If you drink alcohol with these medicines, you may get very unpleasant side-effects including abdominal (tummy) cramps, hot flushes, vomiting and a fast heartbeat. Don’t drink any alcohol until two days after taking metronidazole, or three days after taking tinidazole.

    For some antibiotics (eg doxycycline), taking alcohol at the same time might affect how well they work. If so, it’s best to avoid alcohol while you’re taking them too. As always, it’s important to read the patient information leaflet – this will tell you if you should be avoiding alcohol while taking your medicine.

  • Probiotics are foods (often yogurts) or supplements which contain live, so-called ‘friendly’ bacteria which may be beneficial to your health. They can help restore the natural balance of bacteria in the digestive tract for people taking antibiotics.

    Probiotics may be helpful in stopping diarrhoea linked to using antibiotics. To work, they must be started as soon as you start taking the antibiotics, and continued for a week after the end of your course.

    If you’re a generally healthy person and you’re taking antibiotics, taking probiotics as well is probably safe. However, if you have a weakened immune system, you should seek advice from a dietician or your doctor first.


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  • Reviewed by Dr Kristina Routh, Freelance Health Editor, and Alice Windsor, Bupa Health Content Team, October 2019
    Expert reviewer, Dr Adrian Raby, General Practitioner
    Next review due October 2022



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