Antibiotics are medications used to treat, and in some cases prevent, bacterial infections.

They can be used to treat relatively mild conditions such as acne as well as potentially life-threatening conditions such as pneumonia.

However, antibiotics often have no benefit for many other types of infection and using them unnecessarily would only increase the risk ofantibiotic resistance, so they are not routinely used.

How do I take antibiotics?

Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist.

Doses of antibiotics can be provided in several ways:

oral antibiotics – tablets, pills and 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 is 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.

However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

If you have to take two doses closer together than normal, there is an increased risk of side effects.


Accidentally taking an extra dose

Accidentally taking one extra dose of your antibiotic is unlikely to cause you any serious harm.

However, 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, or if you are worried or are experiencing severe side effects, speak to your GP or call 111 as soon as possible.


Types of antibiotics

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

  • Penicillins are widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections.

  • Cephalosporins can be used to treat a wide range of infections but are also effective in treating more serious infections such assepticaemia and meningitis.

  • Aminoglycosides tend to be used only to treat very serious illnesses such as septicaemia as they can cause serious side effects, including hearing loss and kidney damage. They break down quickly inside the digestive system so they have to be given by injection. They are also used as drops for some ear or eye infections.

  • Tetracyclines can be used to treat a wide range of infections. They are commonly used to treat moderate to severe acne and a condition called rosacea, which causes flushing of the skin and spots.

  • Macrolides can be particularly useful in treating lung and chest infections. They can also be a useful alternative for people with a penicillin allergy or to treat penicillin-resistant strains of bacteria.

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

Side effects

Antibiotics, as with any medication, can cause side effects. Most antibiotics, if used properly, don't cause problems for people who take them and serious side effects are rare.

The most common side effects of antibiotics include:

  • being sick

  • feeling sick

  • bloating and indigestion

  • diarrhoea

Around one person in 15 has an allergic reaction to antibiotics, especially penicillin and cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis), which is a medical emergency.


Considerations and interactions

Some antibiotics are not suitable for people with certain medical conditions, or for women who are pregnant or breastfeeding. You should only ever take antibiotics that are prescribed to you – never 'borrow' them from a friend of family member.

Some antibiotics can also react unpredictably with other medications, for example, the oral contraceptive pill and alcohol. It is therefore important to read the information leaflet that comes with your medication carefully.


Both and health organisations across the world are trying to reduce the use of antibiotics, especially for conditions that are not serious. This is to try to combat the problem of antibiotic resistance, which is when a strain of bacteria no longer responds to treatment with one or more types of antibiotics.


Strains of bacteria can mutate (change) and, over time, become resistant to a specific antibiotic. The chance of this increases if a person does not finish the course of antibiotics as some bacteria may be left to develop resistance.

Also, antibiotics can destroy many of the harmless strains of bacteria that live in and on the body. This allows resistant bacteria to multiply quickly and replace them.

The overuse of antibiotics in recent years has played a major part in antibiotic resistance. This includes using antibiotics to treat minor conditions that would have got better anyway.


It has led to the emergence of 'superbugs'. These are strains of bacteria that have developed resistance to many different types of antibiotics. They include:

  • meticillin-resistant Staphylococcus aureus (MRSA)

  • Clostridium difficile (C. diff)

  • the bacteria that cause multi-drug-resistant tuberculosis (MDR-TB)

  • CPE (Carbapenemase-producing Enterobacteriaceae)

These types of infections can be serious and challenging to treat, and are becoming an increasing cause of disability and death across the world. For example, the World Health Organization (WHO) estimates that there are around 170,000 deaths due to MDR-TB each year.


The biggest worry is that there may emerge new strains of bacteria that are effectively untreatable by any existing antibiotics.

Carbapenemase-producing Enterobacteriaceae are one such emerging group of bacteria, with several types. These bacteria are widespread in some parts of the world, including parts of Europe.


Uses of antibiotics 

Antibiotics may be used to treat, or in some cases prevent, bacterial infections.

However, your GP will only prescribe antibiotics to treat:

  • conditions that are not especially serious but are unlikely to clear up without the use of antibiotics, such as moderately severe acne

  • conditions that are not especially serious but could spread to other people if not promptly treated, such as the skin infection impetigo or the sexually transmitted infection chlamydia

  • conditions where evidence suggests that antibiotics could significantly speed up recovery, such as a kidney infection

  • conditions that carry a risk of more serious complications, such as cellulitis or pneumonia.


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 risk than average of developing one

  • people with heart failure

  • people who have to take insulin to control their diabetes

  • people with a weakened immune system – either due to an underlying health condition such as HIV or as a side effect of certain treatments such as chemotherapy


Intravenous antibiotics

Antibiotics are usually given as liquids, tablets or capsules. In more serious cases, injections or infusions of antibiotics can be given intravenously (directly into the blood or muscles).

Intravenous antibiotics are usually only required to treat more serious bacterial infections, such as:

  • bacterial meningitis

  • septicaemia (blood poisoning)

  • infection of the outer layer of the heart (endocarditis)

  • some cases of MRSA infection

  • an infection that develops inside a bone (osteomyelitis)


Antibiotics to prevent infection

There are several circumstances in which you may be given antibiotics as a precaution to prevent, rather than treat, an infection. This is known as antibiotic prophylaxis.

For example, antibiotic prophylaxis is normally recommended if you are having surgery on a certain part of the body that is known to carry a high risk of infection or that could lead to devastating effects if it were to become accidentally infected.


For example, it may be used if you are 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


Bites or wounds

Antibiotic prophylaxis may be recommended for a wound that has a high chance of becoming infected.

For example, an animal or human bite, 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, meaning antibiotic prophylaxis is necessary.

For example, people who have had their spleen removed or those with the blood disorder sickle cell anaemia, whose spleen does not work properly, should take antibiotics to prevent some infection. The spleen plays an important role in filtering out harmful bacteria from the blood.

In some cases, antibiotic prophylaxis is prescribed for people who experience a recurring infection that is causing distress or an increased risk of complications. For example:

  • cellulitis

  • a urinary tract infection

  • genital herpes

  • rheumatic fever

  • Considerations


Some important considerations associated with the six main classes of antibiotics are listed below.


Do not take penicillins if you have had a previous allergic reaction to them. People with a history of allergies, such as asthma, eczema orhay fever, are at higher risk of developing a serious allergic reaction (anaphylaxis) to penicillins. However, such reactions are rare.


Patients who are allergic to one type of penicillin will be allergic to all (the allergy is related to the basic penicillin structure).

Penicillin may not be suitable if you:

  • Pregnancy and breastfeeding

  • Most penicillins can be used during pregnancy and breastfeeding in the usual doses.

  • Tell your healthcare professional if you are pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you.



If you have had a previous allergic reaction to penicillin you may also be allergic to cephalosporins.

Cephalosporins may not be suitable if you have kidney disease. If the professional in charge of your care does decide to prescribe cephalosporins it will probably be at a lower dose.

You should never take a cephalosporin if you have acute porphyria, a genetic condition that can cause skin and nerve problems.

Cephalosporins are thought to be safe to take during pregnancy but, as a precaution, they are only ever used if the benefits of treatment are thought to outweigh potential risks.

Cephalosporins are not recommended for women who are breastfeeding.



Aminoglycosides are normally only used to treat life-threatening conditions such as septicaemia, as they can cause kidney damage in people with pre-existing kidney disease. They are only used during pregnancy if your doctor believes they are essential.



The use of tetracyclines is not usually recommended (unless absolutely necessary) in the following groups:


You should not take macrolides if:

You should not take a type of macrolide called telithromycin if you havemyasthenia gravis, which is an uncommon condition that causes muscle weakness.

If you are pregnant or are breastfeeding, the only type of macrolide you can take is erythromycin (Erymax, Erythrocin, Erythroped or Erythroped A). Erythromycin can be used at the usual doses throughout your pregnancy and while you are breastfeeding.


Side effects of antibiotics  

The most common side effects of antibiotics affect the digestive system. These occur in around one in 10 people.

Side effects of antibiotics that affect the digestive system include:

  • being sick

  • feeling sick

  • diarrhoea

  • bloating and 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 additional side effects other than those listed above you should contact your GP or the doctor in charge of your care for advice.


Antibiotic allergic reactions

Around one person in 15 has an allergic reaction to antibiotics, especially penicillin and cephalosporins. In most cases the allergic reaction is mild to moderate and can take the form of:

  • a raised itchy skin rash (urticaria or ‘hives’)

  • coughing

  • wheezing

  • tightness of the throat, which can cause breathing difficulties


These mild to moderate allergic reactions can usually be successfully treated by taking a medication known as antihistamines.

However, if you are concerned or your symptoms fail to respond to treatment then you should call your GP for advice. If you can't contact your GP, call 111.

In rare cases (estimated to be somewhere between one and five in 10,000) an antibiotic can cause a severe and potentially life-threatening allergic reaction known as anaphylaxis. Initial symptoms of anaphylaxisare often the same as above and can lead to:

  • a rapid heartbeat

  • increasing breathing difficulties due to swelling and tightening of the neck

  • a sudden intense feeling of apprehension and fear

  • a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused

  • unconsciousness


Anaphylaxis is a medical emergency and, without prompt treatment, can be life-threatening. Dial 999 immediately and ask for an ambulance if you think that you or someone you know is experiencing anaphylaxis.

Tetracyclines and sensitivity to light 

Tetracyclines can make your skin sensitive to sunlight as well as artificial sources of light such as sun lamps and sunbeds. You should avoid prolonged exposure to bright light while taking tetracyclines.


Reporting side effects

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine that you are taking.

It is run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA). See the Yellow Card Scheme website for more information.


Interactions with other medicines 

Antibiotics can sometimes interact with other medicines or other substances. This means that the effects of one of the medicines can be altered by the other.

Some of the more common interactions are listed below. However, this is not a complete list.

If you want to check that your medicines are safe to take with your antibiotics, ask your GP or local pharmacist. You should also always carefully read the patient information leaflet that comes with your medicine.


Combined oral contraceptives

Some antibiotics, such as rifampicin and rifabutin (which can be used to treat tuberculosis and other infections) can reduce the effectiveness of the combined oral contraceptive pill. Other antibiotics do not have this effect.

If you are prescribed rifampicin or rifabutin, you may need to use additional contraception, such as condoms, while taking antibiotics. Speak to your GP or nurse for advice.



Some of the medications you may need to avoid, or seek advice on, while taking a specific class of antibiotic are outlined below.



It is usually recommended that you avoid taking penicillin at the same time as a medication called methotrexate, which is used to treat some types of cancers and severe autoimmune conditions such as the skin condition psoriasis. This is because combining the two medications can cause a range of unpleasant and sometimes serious side effects. You may experience a skin rash if you take penicillin and a medication called allopurinol, which is used to treat gout.



Cephalosporins may not be suitable to take if you are also taking blood-thinning medications (anticoagulants) such as heparin andwarfarin.

If you need treatment with cephalosporins, you may temporarily have to stop taking the blood-thinning medication.



The risk of damage to your kidneys and hearing is increased if you are taking one or more of the following medications:

  • antifungals – used to treat fungal infections

  • cyclosporin – used to treat autoimmune conditions such as Crohn’s disease and given to people who have had an organ transplant

  • diuretics – used to remove water from the body

  • muscle relaxants

However, the risk of kidney and hearing damage has to be balanced against the benefits of using aminoglycosides to treat life-threatening conditions such as septicaemia. In hospital, blood levels are carefully monitored to ensure that the antibiotic is only present in the blood in safe amounts. If aminoglycosides are used properly in topical preparations, such as ear drops, these side effects do not occur.



You should check with your GP or pharmacist before taking a tetracycline if you are currently taking any of the following medications:

  • vitamin A supplements

  • retinoids such as acitretin, isotretinoin and tretinoin used to treat severe acne

  • blood-thinning medication

  • diuretics

  • kaolin-pectin and bismuth subsalicylate used to treat diarrhoea

  • medicines to treat diabetes such as insulin

  • atovaquone used to treat pneumonia

  • antacids used to treat indigestion and heartburn

  • sucralfate used to treat ulcers

  • lithium used to treat bipolar disorder and severe depression

  • digoxin to treat heart rhythm disorders

  • methotrexate

  • strontium ranelate used to treat osteoporosis

  • colestipol or colestyramine used to treat high cholesterol

  • ergotamine and methysergide used to treat migraines



It is highly recommended that you do not combine a macrolide with any of the following medications (unless directly instructed to by your GP), as the combination could cause heart problems:

  • terfenadine, astemizole and mizolastine – which are all antihistamines used to treat allergic conditions such as hay fever

  • amisulpride – used to treat episodes of psychosis

  • tolterodine – used to treat urinary incontinence

  • statins – used to treat high cholesterol



You should check with your GP or pharmacist before taking a fluoroquinolone if you are currently taking any of the following medications:

  • theophylline, which is used to treat asthma and also found in some cough and cold medicines

  • the non-steroidal anti-inflammatory drug (NSAID) painkillers such as ibuprofen

  • ciclosporin

  • probenecid used to treat gout

  • clozapine used to treat schizophrenia

  • ropinirole used to treat Parkinson's disease

  • tizanadine used to treat muscle spasms

  • glibenclamide used to treat diabetes

  • cisapride used to treat indigestion, heartburn, vomiting or nausea

  • tricyclic antidepressants, such as amitriptyline, steroid medications (corticosteroids)


Some fluoroquinolones can intensify the effects of caffeine (a stimulant found in coffee, tea and cola), which could make you feel irritable, restless and cause problems falling asleep (insomnia).

Finally, you may need to avoid taking medication that contains high levels of minerals or iron as this can block the beneficial effects of fluoroquinolones. This includes:

  • antacids

  • zinc supplements

  • some types of multivitamin supplements

  • Interactions with food


Some antibiotics need to be taken with food while others need to be taken on an empty stomach.

Make sure you read the information leaflet that comes with your medication carefully to find out whether this is the case.


Can I drink alcohol if I'm on antibiotics?

If you are taking the antibiotics metronidazole or tinidazole, you should completely avoid alcohol as this can cause very unpleasant side effects such as:

  • feeling and being sick

  • stomach pain

  • hot flushes

  • headaches


It is recommended that you avoid alcohol with all antibiotics as drinking could make your infection last longer. But provided you drink in moderation, alcohol is unlikely to interact significantly with your medication.


Frequently asked questions 

Why should antibiotics not be used to treat coughs and colds?

All colds and most coughs and sore throats are caused by viruses. Antibiotics do not work against viral infections.

How should I treat my cold?

The best way to treat most colds, coughs or sore throats is to rest and drink plenty of fluids.

Colds can last about two weeks and may end with a cough that brings up phlegm. There are many over-the-counter remedies to ease the symptoms,such as paracetamol. Ask your pharmacist for advice. If the cold lasts more than three weeks, or you become breathless or have chest pains, or if you already have a chest complaint, see your GP.

But what about my children? They’re always getting coughs and colds.

It is common for children to get coughs and colds, especially when they go to school and mix with other children. Ask your pharmacist for advice. If the symptoms persist and you are concerned, see your GP, but do not expect to be prescribed antibiotics.


What is antibiotic resistance?

Bacteria can adapt and find ways to survive the effects of an antibiotic. They become antibiotic resistant, which means that the antibiotic no longer kills the bacteria.

The more we use an antibiotic, the more likely it is that bacteria will become resistant to it. Some bacteria that cause infections in hospitals, such as MRSA, are resistant to several antibiotics.


Why can’t other antibiotics be used instead?

Other antibiotics can be used, but they may not be as effective and they may have more side effects. Eventually, the bacteria will become resistant to them too.

Only two new types of antibiotics have been found in the past 30 years and there is no guarantee that new ones will be discovered.


How can antibiotic resistance be avoided?

By using antibiotics carefully, we can slow down the development of resistance. It is not possible to stop it completely, but slowing it down stops resistance spreading and buys some time to develop new types of antibiotics.


What can I do about antibiotic resistance?

You should only use antibiotics when it is appropriate to do so. We now know that most coughs and colds get better just as quickly without antibiotics.

When antibiotics are prescribed, the complete course should be taken to get rid of the bacteria completely. If the course is not completed, some bacteria may be left to develop resistance.


So when will I be prescribed antibiotics?

Your doctor will only prescribe antibiotics when you need them, for example, for a kidney infection or pneumonia. Antibiotics may be life-saving for infections such as meningitis. By using them only when necessary, they are more likely to work when we need them in future.

  • have severe kidney disease

  • have liver disease

  • 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

  • you have porphyria – a rare, inherited blood disorder

  • you have a heart rhythm disorder or you're at risk of developing one – such as atrial fibrillation, where the heart beats abnormally fast