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Antibiotics are medicines used to treat infections caused by bacteria. They are used for many things from a sore throat to serious infections like pneumonia. You can only get certain products (antibiotic tablets, capsules or syrup) on prescription from a doctor, nurse prescriber or dentist. But you can buy eye drops from a pharmacy.

It's important to take antibiotics correctly as this will help to prevent the increasing problem of antibacterial resistance. This is when antibiotics are no longer effective against bacteria.

Your doctor may prescribe you antibiotics to treat an infection that’s caused by bacteria. Common bacterial infections include those affecting your ear, throat, urinary system and skin and some types of food poisoning, such as salmonella. Some sexually transmitted infections (STIs), for example gonorrhoea, can also be caused by bacteria.

Many infectious illnesses are actually caused by viruses and not bacteria. These include flu, mumps, hepatitis and some types of illnesses where you have vomiting and diarrhoea, such as food poisoning. Antibiotics don’t work against viruses, so your doctor won’t prescribe them to treat these. See our FAQs for more information.

If you’re having an operation, you may be given antibiotics to prevent an infection.

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  • Types What are the main types of antibiotics?

    There are lots of different types of antibiotics that work in different ways. These include penicillins, tetracyclines, macrolides and cephalosporins. See Common names below for more examples.

    Antibiotics may be broad-spectrum, which means they can treat infections caused by a wide range of different bacteria. Examples of these include amoxicillin and erythromycin. Other antibiotics only work against specific types of bacteria and are known as narrow-spectrum antibiotics. Examples of these include vancomycin and teicoplanin.

  • How they work How do antibiotics work?

    Some antibiotics work by killing bacteria. They usually do this by destroying the cell walls of bacteria. Penicillin is an example of an antibiotic that works in this way. Other antibiotics work by stopping bacteria from growing and multiplying. Most bacteria don’t live long, so the infecting bacteria will eventually die out once you start taking these medicines. Chloramphenicol is an example of this type of antibiotic.

  • Taking the medicine How to take antibiotics

    You’ll need to take antibiotics for a set period of time. This can be a short course of several days or a longer course of some weeks. It depends on the type of infection you have. Take your antibiotics at regular, specified time intervals, such as three times a day. This will ensure that there is always a steady level of the medicine in your body. Make sure you follow the advice of your doctor, nurse prescriber or dentist and read the patient information leaflet that comes with your medicine.

    You may have to follow specific instructions about exactly when to take your antibiotics. For example, you may need to take your antibiotics on an empty stomach, usually an hour before meals, or two hours afterwards. There are other types of antibiotics that you need to take when you eat a meal.

    Check if you need to cut out certain foods or drinks if you’re taking antibiotics. Alcohol can cause a reaction with some antibiotics, particularly one called metronidazole that’s used to treat dental infections among other things. Alcohol, dairy products and fruit juice can all affect how your body absorbs antibiotics. Follow the instructions on the medicine label or patient information leaflet, and if you have any questions, ask your doctor or pharmacist for advice.

    It’s important to take your antibiotics according to the instructions and to finish the whole course. This will help to prevent the bacteria developing resistance to the medicine. Always take your antibiotics as directed and don’t stop taking them early, even if you start to get better. See our FAQs for more information.

    Antibiotics usually come as tablets or capsules (or syrup for children or if you have difficulty swallowing). Others come as an injection, or you can apply some directly to the affected part of your body as drops, lotions or ointments.

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  • Special care Special care

    If you have problems with your liver or kidneys, tell your doctor, nurse prescriber or dentist before they prescribe you antibiotics. It’s also important to tell your health professional if you’re pregnant or breastfeeding.

  • Side-effects Side-effects of antibiotics

    Side-effects are the unwanted effects of taking a medicine. The most common side-effects of antibiotics include diarrhoea and feeling sick or vomiting but you may not necessarily have any of these.

    It’s possible that you may get a fungal infection such as thrush after you take broad-spectrum antibiotics. This is because as well as killing the harmful bacteria that are causing your infection, antibiotics may also destroy your body’s protective bacteria. These normally stop micro-organisms such as fungi growing out of control. If you develop a fungal infection, you may need to take an antifungal medicine to treat it.

    More serious side-effects of antibiotics include kidney problems, blood disorders and increased sensitivity to the sun. However, most of these are rare and often specific to the type of antibiotic you’re taking.

    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.

  • Complications Allergies

    Some people are allergic to antibiotics, particularly penicillin and cephalosporins. If you’re allergic to an antibiotic, you may get an itchy rash. If you have a severe allergic reaction, this is called anaphylaxis. The symptoms of anaphylaxis include a swollen face, throat and tongue and difficulty breathing. Your blood pressure may fall and you may lose consciousness. It’s important to be aware that anaphylaxis can be serious, or even fatal. Seek immediate medical attention if you think you’re having these symptoms after taking antibiotics or any other medicines.

    Always tell your doctor, nurse prescriber or dentist if you think you have had an allergic reaction to an antibiotic before. As an alternative to penicillin, you may be prescribed erythromycin, which works against similar types of bacteria.

  • Interactions Interactions of antibiotics with other medicines

    Certain antibiotics, for example rifampicin, can stop the contraceptive pill from working. If you get side-effects from taking antibiotics, such as diarrhoea and vomiting, they may stop your contraceptive pill from being absorbed into your body too. If you’re taking antibiotics that affect the contraceptive pill, or have vomited or had diarrhoea, it’s important to use extra contraception, such as a condom.

    Antibiotics can interact with a number of other medicines and herbal remedies. Before you take anything else at the same time as antibiotics, check with your doctor or health professional who prescribed them.

  • Common names Names of common antibiotics

    Examples of common antibiotics are shown in the table below. The antibiotics are grouped by class.

    You may have noticed that your medicine has two or more names. All medicines have a generic name. Many medicines also have one or more brand names. Generic names are in lower case, whereas brand names start with a capital letter.


    Generic name Example of common brand names
    amoxicillin Amoxil
    ampicillin Penbritin
    benzylpenicillin (penicillin G) Crystapen
    co-amoxiclav Augmentin
    flucloxacillin Floxapen,Fluclomix, Ladropen
    phenoxymethylpenicillin (Penicillin V)  
    clarithromycin Klaricid
    erythromycin Erymax, Erythrocin, Erythroped
    cefaclor Distaclor
    cefalexin Ceporex, Keflex
    doxycycline Vibramycin-D
    oxytetracycline Oxymycin
    gentamicin Cidomycin, Genticin
    neomycin Nivemycin
    ciprofloxacin Ciloxan, Ciproxin
    chloramphenicol Kemicetine, Minims


    metronidazole Flagyl, Metrolyl, Metrosa
    rifampicin Rifadin, Rimactane
    trimethoprim Trimopan
    vancomycin Vancocin
  • Resistance Resistance

    Some infections are resistant to certain antibiotics. This means that the antibiotic is no longer any good at getting rid of the infection. For example, if you get infected with meticillin-resistant Staphylococcus aureus (MRSA), it won’t be possible to treat you with standard antibiotics.

    Resistance can start if the bacteria that have caused an infection aren't completely killed off by an antibiotic. Some bacteria survive because they have a genetic mutation that helps them to resist the treatment. The few bacteria that survive can then reproduce, causing an infection that’s resistant to that particular antibiotic. It’s really important to complete a course of antibiotics, even if you feel better. This is the best way to prevent any bacteria from surviving.

    If you complete a course of antibiotics and don’t get better, it could be because the bacteria causing your infection are resistant. If this happens, your doctor, nurse prescriber or dentist will usually prescribe a different antibiotic for you to take.

  • FAQs FAQs

    How does my doctor choose an antibiotic to treat my infection?


    Your doctor (or nurse prescriber or dentist) will prescribe you an antibiotic based on your symptoms and your medical history. This will take into account whether you’re allergic to any antibiotics, if you’re pregnant and how bad your infection is. Some bacterial infections will get better on their own so your doctor may not prescribe any antibiotics.


    Before your doctor chooses an antibiotic, they will ask you about your symptoms and examine you. Your doctor may also ask if you have any problems with your immune system or allergies to any antibiotics.

    Your doctor may take a sample of your urine, mucus or blood, or a swab from your throat or skin. These samples will be tested in a laboratory to see which bacteria are causing your infection, so you can be prescribed the appropriate antibiotic.

    Your doctor may prescribe you a broad-spectrum antibiotic to take until the results of your tests come back. He or she may also prescribe this antibiotic if your infection may be caused by more than one type of bacteria. Broad-spectrum antibiotics act on infections caused by a wide range of bacteria. They aren’t always the best solution, as using them can cause bacteria to become resistant. However, if you have a potentially serious infection, you will usually be given these. This is so your treatment isn’t delayed, which could lead to your illness getting worse.

    If your doctor thinks a specific bacteria or type of bacteria is causing your infection, they may prescribe a narrow-spectrum antibiotic. This type of antibiotic only works against specific bacteria.

    If you need penicillin antibiotics but are allergic to them, your doctor will prescribe a different type for you.

    Always read the patient information leaflet that comes with your medicine. If you have any questions, ask your pharmacist or doctor for advice.

    If I feel better after a few days, can I stop taking my antibiotics?


    Always finish your entire course of antibiotics, even if you feel better after a few days.


    To clear your infection completely you will need to continue taking your antibiotics for the full course of treatment. It’s important to do this even if you begin to feel better after a few days. If you stop taking your antibiotics too soon, your symptoms may return.

    Finishing your course of antibiotics will also reduce the risk of antibiotic resistance developing. If the bacteria aren’t completely killed off, they can change in a way that makes them more difficult to cure with antibiotics. Some bacteria aren’t killed because they have a genetic mutation that allows them to survive and multiply. This can cause your infection to continue. If the bacteria become resistant, your doctor will need to prescribe you a different antibiotic.

    You may be prescribed antibiotics for a period of several days, or a longer course that you will need to take for some weeks. You will usually need to take them at regular intervals throughout the day. It’s very important that you take your antibiotics as prescribed and follow the directions on the medicine label. This will ensure you have the right amount of medicine in your body to kill off the bacteria.

    If you miss a dose, follow the advice in the patient information leaflet that comes with your medicine. If your antibiotics make you feel ill or you want to stop taking them for some reason, contact your doctor as soon as possible. Always ask your doctor for advice and read the patient information leaflet that comes with your medicine.

    Why won't my doctor give me antibiotics for cold or flu symptoms?


    Antibiotics only work against infections caused by bacteria. Flu and colds are caused by viruses, so antibiotics won’t work and shouldn’t be used for these infections.


    You may be prescribed antibiotics to help your immune system fight bacterial infections but they don’t work against viral infections such as colds or flu.

    Your body may be weakened after fighting a cold or flu infection. This can make you vulnerable to picking up a secondary infection caused by bacteria, such as pneumonia. Your body may find it difficult to fight this off so your doctor may have to prescribe antibiotics to help.

    If you have flu, it can take a week or two to recover completely. The best treatment is usually bed rest, drinking enough fluids and taking over-the-counter painkillers. However, contact your GP if you’re concerned about your symptoms, particularly if they get worse. If you’re at risk of developing complications of flu, it’s a good idea to have the flu vaccine each year to help prevent getting it. You’re more at risk if you’re over 65 or have a lung disease such as asthma or chronic obstructive pulmonary disease (COPD), or heart disease. Contact your GP for more information.

  • Resources Resources

    Further information


    • Using antibiotics correctly and avoiding resistance. Institute for Quality and Efficiency in Healthcare., accessed 7 January 2015
    • Overview of antibacterial drugs. The Merck Manuals., published July 2009
    • Sore throat. PatientPlus., published 20 November 2013
    • Amendments to the misuse of drugs regulations 2001 (the 2001 regulations), to implement key elements of the action programme published in safer management of controlled drugs (December 2004). GOV.UK., published 17 July 2006
    • Antimicrobial eye preparations. PatientPlus., published 13 August 2013
    • Antimicrobial resistance: global report on surveillance. World Health Organization., published June 2014
    • Antimicrobial resistance. World Health Organization., published April 2014
    • Antibiotics. Microbiology online., accessed 1 April 2015
    • Hepatitis. World Health Organization., accessed 7 January 2015
    • Measles. World Health Organization., accessed 7 January 2015
    • Mumps. World Health Organization. accessed 7 January 2015
    • Viral gastroenteritis. BMJ Best Practice., published 4 February 2015
    • Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 12 February 2015
    • Blind treatment of bacterial infection. PatientPlus., reviewed February 2013
    • Chloramphenicol 0.5% w/v eye drops. Electronic Medicines compendium., published 3 September 2012
    • Children and medications: getting the dose right. Institute for Quality and Efficiency in Healthcare., accessed 7 January 2015
    • Tetracycline. DermNet NZ., published 1 February 2015
    • Anaphylaxis and its treatment. PatientPlus., reviewed March 2015
    • Anaphylaxis clinical presentation. Medscape., published 15 December 2014
    • Drug interactions with hormonal contraception. Faculty of Sexual and Reproductive Healthcare clinical guidelines., published January 2012
    • Merrily AK. Herbal remedies: drug-herb interactions. Crit Care Nurse 2002; 22(2): 22–32.
    • Combating antibiotic resistance. US Food and Drug Administration (FDA)., published 14 October 2014
    • Joseph C, Togawa Y, Shindoc N. Bacterial and viral infections associated with influenza. Influenza and Other Respiratory Viruses 2013; 7(Suppl 2):105–13. doi: 10.1111/irv.12089
    • Influenza – seasonal. NICE Clinical Knowledge Summaries., published December 2014
    • Influenza: the green book, chapter 19. GOV.UK., published 10 December 2014
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