Antibiotics are used to treat or prevent some types of bacterial infections. They are not effective against viral infections, such as the common cold or flu.

Antibiotics should only be prescribed to treat health problems:

• that are not serious but are unlikely to clear up without antibiotics – such as acne
• that are not 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

Learn why antibiotics are no longer routinely used to treat infections.

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 who have a bacterial infection, or a higher than average risk of developing one
• people with heart failure
• people who have to take insulin for diabetes
• people with a weakened immune system – either because of an underlying health condition such as HIV 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 called antibiotic prophylaxis. Situations where antibiotics are given as a preventive treatment include:

• if you're having an operation
• after a bite or wound that could get infected
• if you have a health problem that means you're at higher risk of infection such as if you've had your spleen removed or you're having chemotherapy treatment

If you're having an operation

Antibiotics are normally recommended if you're having a type of surgery that carries a high risk of infection.

For example, you may be prescribed antibiotics 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 antibiotics.

Bites or wounds

Antibiotics 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

Some people are particularly vulnerable to infection, making antibiotics necessary. They include:

• people who have had their spleen removed
• people having chemotherapy for cancer
• people with sickle cell anaemia

In some cases, antibiotics are prescribed for people who have an infection that keeps coming back or that's causing distress or an increased risk of complications, such as: 

• cellulitis
• a urinary tract infection
• genital herpes
• rheumatic fever

There are some important things to consider before taking antibiotics.

Penicillin

Do not 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:

• severe kidney disease
• liver disease

Pregnancy and breastfeeding

You can take most penicillins 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 a rare inherited blood disorder called acute porphyria – check with your doctor, midwife or pharmacist before taking cephalosporins.

Aminoglycosides

Aminoglycosides are normally only used in hospital to treat life-threatening health 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

Tetracyclines are not usually recommended unless absolutely necessary in:

• people with kidney disease – except doxycycline, which can be used
• people with liver disease
• people with the autoimmune illness called lupus – which can cause skin problems, joint pain and swelling, and fatigue
• children under the age of 12
• pregnant or breastfeeding women

Macrolides

Do not 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 (also called by the brand names Erymax, Erythrocin, Erythroped or Erythroped A) unless a different antibiotic is recommended by your doctor.

You can take erythromycin at the usual doses throughout your pregnancy and while you're breastfeeding.

Other macrolides should not be used during pregnancy, unless advised by a specialist.

Fluoroquinolones

Fluoroquinolones are not normally suitable for women who are pregnant or breastfeeding.

The most common side effects of antibiotics affect the digestive system. These happen in around 1 in 10 people.

Side effects of antibiotics that affect the digestive system include: 

• vomiting
• nausea (feeling like you may vomit) 
• 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 get any additional side effects, contact your GP or the doctor in charge of your care for advice.

Antibiotic allergic reactions

Around 1 in 15 people have 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 antihistamines.

But if you're concerned, or your symptoms don't get better with treatment, call your GP for advice. If you cannot contact your GP, call NHS 111.

In rare cases, an antibiotic can cause a severe and potentially life-threatening allergic reaction known as anaphylaxis.

Initial symptoms of anaphylaxis are often the same as a mild allergic reaction. They include:

• feeling lightheaded or faint 
• breathing difficulties – such as fast, shallow breathing
• wheezing
• a fast heartbeat
• clammy skin
• confusion and anxiety
• collapsing or losing consciousness

There may be other allergy symptoms, including an itchy, raised rash (hives), feeling or being sick, swelling (angioedema), or stomach pain.

Anaphylaxis is a medical emergency and can be life-threatening. Dial 999 immediately and ask for an ambulance if you think you or someone around you is experiencing anaphylaxis.

Tetracyclines and sensitivity to light 

Tetracyclines can make your skin sensitive to sunlight and artificial sources of light, such as sun lamps and sunbeds.

Avoid prolonged exposure to bright light while taking these medicines.

Fluoroquinolones and severe aches and pains

In very rare cases, fluoroquinolone antibiotics can cause disabling, long-lasting or permanent side effects affecting the joints, muscles and nervous system.

Stop taking fluoroquinolone treatment straight away and see your GP if you get a serious side effect including:

• tendon, muscle or joint pain – usually in the knee, elbow or shoulder
• tingling, numbness or pins and needles

Reporting side effects

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

It's run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA).

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

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

Some antibiotics need to be taken with food, while others need to be taken on an empty stomach. Always read the patient information leaflet that comes with your medicine.

Alcohol

It's best to completely avoid alcohol while taking metronidazole or tinidazole, and for 48 hours afterwards, as this combination can cause very unpleasant side effects, such as:

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

It's recommended that you do not drink alcohol while taking antibiotics in general. However, as long as you drink in moderation, alcohol is unlikely to interact significantly with your medicine.

Read more about drinking alcohol while taking antibiotics.

The contraceptive pill

Some antibiotics, such as rifampicin and rifabutin, can reduce the effectiveness of the contraceptive pill.

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

Mixing medicines

Some of the medicines you may need to avoid, or seek advice on, while taking an antibiotic include:

Penicillins

It's usually recommended that you avoid taking penicillin at the same time as methotrexate, which is used to treat psoriasis, rheumatoid arthritis and some forms of cancer. This is because combining the 2 medications can cause a range of unpleasant and sometimes serious side effects.

However, some forms of penicillin, such as amoxicillin, can be used in combination with methotrexate.

You may experience a skin rash if you take penicillin and allopurinol, which is used to treat gout.

Cephalosporins

Cephalosporins may increase the chance of bleeding if you're taking blood-thinning medications (anticoagulants) such as heparin and warfarin.

If you need treatment with cephalosporins, you may need to have your dose of anticoagulants changed or additional blood monitoring.

Aminoglycosides

The risk of damage to your kidneys and hearing is increased if you're taking 1 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

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 there's a safe amount of the antibiotic in the blood.

These side effects do not happen with aminoglycoside creams and eardrops if they're used properly.

Tetracyclines

Check with your GP or pharmacist before taking a tetracycline if you're currently taking:

• vitamin A supplements
• retinoids – such as acitretin, isotretinoin and tretinoin, which are 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 – used 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

Macrolides

Do not take a macrolide antibiotic with any of the following medications unless directly instructed to by your GP, as the combination could cause heart problems:

• terfenadine, astemizole and mizolastine – these 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

Fluoroquinolones

Check with your GP or pharmacist before taking a fluoroquinolone if you're currently taking:

• theophylline – used to treat asthma; also found in some cough and cold medicines
• 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
• steroids (corticosteroids) – such as prednisolone)

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

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

Antibiotics are no longer routinely used to treat infections because:

• many infections are caused by viruses, so antibiotics are not 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

Both the NHS and health organisations across the world are trying to reduce the use of antibiotics, especially for health problems that are not serious.

For example, antibiotics are no longer routinely used to treat:

• chest infections
• ear infections in children
• sore throats

Antibiotic resistance and 'superbugs'

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:

• MRSA (methicillin-resistant Staphylococcus aureus)
• Clostridium difficile (C. diff)
• the bacteria that cause multi-drug-resistant tuberculosis

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 cannot be treated by any existing antibiotics.