Overview-Antibiotics
Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything.
Many mild bacterial infections get better on their own without using antibiotics.
Antibiotics do not work for viral infections such as colds and flu, and most coughs and sore throats.
Antibiotics are no longer routinely used to treat:
- chest infections
- ear infections in children
- sore throats
When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future.
When antibiotics are needed
Antibiotics may be used to treat bacterial infections that:
- are unlikely to clear up without antibiotics
- could infect others
- 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.
How to 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.
Antibiotics can come as:
- tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body
- creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections
- injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections
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. Do not take a double dose to make up for a missed one.
Accidentally taking an extra dose
There's an increased risk of side effects if you take 2 doses closer together than recommended.
Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm.
But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick.
If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible.
Side effects of antibiotics
As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare.
The 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.
Considerations and interactions
Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding. Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member.
Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol.
Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP.
Types of antibiotics
There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups.
- 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 acne and a skin condition called rosacea
- Macrolides (such as erythromycin and clarithromycin) – can be particularly useful for treating lung and chest infections, or as an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria
- Fluoroquinolones (such as ciprofloxacin and levofloxacin) – are broad-spectrum antibiotics that were once used to treat a wide range of infections, especially respiratory and urinary tract infections. These antibiotics are no longer used routinely because of the risk of serious side effects
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Uses-Antibiotics
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
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
Considerations-Antibiotics
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.
Side effects-Antibiotics
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).
interactions-Antibiotics
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.
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
Antibiotic resistance-Antibiotics
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.