Antibiotics are a type of medication used to treat bacterial infections. Read on to find out what antibiotics are, how they work, and what kind of infections they are used to treat.
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Claudia Jackson (RN)
Dr Adam Abbs
Next Review: Dec 1, 2025
What are antibiotics?
Antibiotics are used to treat or prevent some infections caused by bacteria.
There are many classes of antibiotics and different antibiotics are used to treat different types of infections. Antibiotics come in several forms including:
- capsules and tablets
- creams, sprays, or ointments that you apply to the skin
- eye or ear drops
- intravenous medications that are injected into the blood stream
What do antibiotics do?
Antibiotics treat some types of bacterial infections in humans and animals. They either work by killing bacteria (germs) in the body or by preventing the bacteria from reproducing and spreading, which gives your body the time and opportunity to kill the bacteria.
Antibiotics can also be used to prevent infections from developing, such as when given with surgery or after an animal bite.
How do antibiotics work?
Antibiotics are either:
- bactericidal —work by killing bacteria
- bacteriostatic — work by reducing the bacteria’s ability to grow and spread in the body
They work in one of 3 ways by:
- attacking the outer coating of the bacteria
- blocking the production of proteins the bacteria need to survive
- stopping the bacteria from reproducing
What are antibiotics used for?
Antibiotics are used to treat some types of bacterial infections. They do not work against infections caused by viruses or fungi such as:
- influenza (flu)
- yeast infections
- athlete’s foot
Your immune system can often deal with mild bacterial infections and antibiotics are not usually necessary. Antibiotics are no longer routinely prescribed to treat:
- most chest infections
- most ear infections in children
- most sore throats
When are antibiotics prescribed?
Antibiotics are prescribed for bacterial infections:
- that are unlikely to clear up without antibiotics, such as acne
- that could spread to others if left untreated like chlamydia
- where antibiotics have been shown to significantly speed up recovery such as kidney infections
- where there is a risk of developing serious complications like pneumonia
Antibiotics may also be prescribed to people at high risk of complications if they get a bacterial infection. This includes:
- newborn babies (under 3 days old) with a bacterial infection, or who are at risk of developing one
- people over 75 years of age
- people with diabetes
- people with heart failure
- people with a weakened immune system such as people with HIV, or those taking medicines that suppress the immune system like some rheumatoid arthritis medication and chemotherapy
Antibiotics are also used to prevent infections where a bacterial infection is likely to develop. This is called antibiotic prophylaxis.
Antibiotics may be prescribed to prevent infection if you:
- have an operation or dental procedure
- are bitten by an animal
- have a deep wound that could become infected
- have a medical condition that puts you at high risk of developing an infection like sickle cell anaemia
- are having chemotherapy treatment for cancer
- have had your spleen removed
Antibiotics may also be prescribed if you have infections that keep coming back, or have a high chance of complications such as:
- urinary tract infections (UTIs)
- rheumatic fever
How long do antibiotics take to work?
Antibiotics start working as soon as you start taking them, but you may not feel better for about 2 to 3 days. Most antibiotics are prescribed for 7 to 10 days. Always take your antibiotics exactly as your doctor tells you to, and don’t stop your treatment early even if you feel better. Not finishing your prescribed course of antibiotics may mean your infection isn’t properly treated and it may come back and be harder to treat next time. Read the patient information leaflet that comes with your medication carefully and ask your doctor or pharmacist if you have any questions.
How to get antibiotics
Most antibiotics need to be prescribed by a doctor. Some antibiotic creams and ointments are available over the counter without a prescription.
If you have an infection that you think needs treatment with antibiotics, make an appointment with your GP. Your doctor will decide with you whether you will benefit from antibiotics and if so which antibiotic is the most appropriate treatment. Never take antibiotics belonging to someone else, even if you have the same symptoms. This could be dangerous and can cause antibiotic resistance and allergic reactions.
Which antibiotics become toxic after expiration?
The expiration date is the date past which your medication may no longer be safe or effective. You can find the expiration date on the packaging of your medication. Most medications become less effective after they expire, meaning they may not work as well. In the case of antibiotics, this may mean your infection isn’t fully treated and may come back and be harder to treat next time.
Most antibiotics are unlikely to cause you harm if you take them after their expiry date, but there is still a risk, so we would recommend you never take any medication after its expiry date. In particular, a group of antibiotics called tetracyclines have been linked to irreversible kidney damage if taken past their expiry date. If you think you have taken expired antibiotics, speak to your doctor or pharmacist.
What happens if you take antibiotics when you don’t have a bacterial infection?
Taking antibiotics when you don’t have a bacterial infection can put you at unnecessary risk of side effects such as nausea, diarrhoea, or allergic reaction. It also contributes to antibiotic resistance. Antibiotic resistance is a global problem that has been caused by people misusing antibiotics.
Antibiotic misuse includes:
- taking antibiotics when you don’t need to, such as when you don’t have an infection, or you have an infection caused by a virus or fungi (antibiotics don’t work against these types of infections).
- not taking your antibiotics as directed by your doctor
- stopping your antibiotic treatment early
- taking the wrong antibiotic for the infection you have
- taking expired antibiotics
When people misuse antibiotics, the bacteria they treat may develop resistance, meaning they are no longer affected by the antibiotic. Antibiotic-resistant infections are very difficult to treat and may lead to sepsis, serious illness and death.
What happens if I take antibiotics too often?
Antibiotics are normally prescribed in short courses of 5 to 10 days, but there are some conditions such as acne or recurrent urinary infections where they may be prescribed long-term. Your doctor will weigh up the risks and benefits of prescribing long-term antibiotics and will only do so if the risk of not taking antibiotics is greater than the risk of taking them. Long-term or frequent use of antibiotics can cause:
- antibiotic resistance —when your antibiotics no longer work properly to treat infections
- side effects —common side effects include headaches, nausea, and diarrhoea, but more serious side effects like liver damage, secondary infections and adverse reactions may also occur
- imbalance of healthy gut bacteria —antibiotics can disrupt the balance of bacteria in the gut, lead to the growth of antibiotic-resistant bacteria and cause other infections of the bowel or long term, or recurrent diarrhoea
Are there natural substances that have antibiotic-type properties?
Certain foods, herbs, and spices have been used for centuries as “natural antibiotics”, and recent scientific research suggests that some of them may have some antibiotic action.
A recent study found that fresh garlic may have properties that work against some antibiotic-resistant bacteria, but more research is needed.
Some natural products that may have antibiotic-type properties include:
Remember that just because something is natural, it doesn’t mean it is safe or that it won’t cause side effects. Talk to your doctor before taking any kind of natural antibiotic. Don’t use natural products as a substitute for antibiotics prescribed by your doctor. Please complete any prescription that your doctor thinks you need. If you have an infection please seek medical attention and discuss the options with your doctor.
What happens if you double-dose antibiotics?
If you take double the dose of your antibiotic it is unlikely to harm you, but it may increase your risk of side effects, and every antibiotic is different, so please seek medical attention if you make a mistake with your dosing. Using things like pill boxes and medication-reminder apps can help to remind you to take your medication on time.
What happens if you miss a day of antibiotics?
If you miss a dose of your antibiotic, take it as soon as you remember and discuss this with a doctor or pharmacist as soon as possible.
Can you drink whilst taking antibiotics?
As a rule, it’s best to avoid alcohol if you are unwell to give your body the best chance of recovery.
Drinking alcohol can make the side effects of some antibiotics worse, or stop them from working. Some antibiotics may interact with alcohol and cause unpleasant side effects such as:
- feeling sick
- fast or irregular heartbeat
- stomach pain
- hot flushes
Avoid alcohol completely if you are taking:
- metronidazole —avoid alcohol while you are taking this antibiotic and for 48 hours afterwards
- tinidazole — avoid alcohol while you are taking this antibiotic and for 72 hours afterwards
Do antibiotics make you tired?
It’s common to feel tired and low in energy while taking antibiotics. This is more likely to be due to your body fighting the infection, but may also be a side effect of your antibiotics.
Some antibiotics that may cause tiredness include:
- amoxicillin (Amoxil, Moxatag)
- azithromycin (Z-Pak, Zithromax, and Zmax)
- ciprofloxacin (Cipro, Proquin)
What to do if antibiotics make you tired
If you feel tired, weak, or low in energy while taking antibiotics:
- talk to your GP about switching to a different medication or altering your dose
- avoid taking other medications that can cause drowsiness
- avoid activities where you need to be alert like driving, or operating machinery
- avoid alcohol
- ensure you get a good night’s sleep by implementing healthy sleep habits and good sleep hygiene
Can a pharmacist prescribe antibiotics?
Most pharmacists cannot prescribe antibiotics, but if they have a pharmacist independent prescriber (PIP) qualification, they can prescribe certain medications.
If you have signs of an infection, like fever, or feeling generally unwell, the best course of action is to make an appointment with your GP. Your GP can assess your symptoms, run any necessary tests, and prescribe the correct treatment which may include antibiotics.
How long do antibiotics stay in your system?
The amount of time antibiotics stay in your system varies according to the antibiotic. Some antibiotics like amoxicillin and ciprofloxacin take around 24 hours from the last dose to be eliminated from your body, while others such as azithromycin take around 15 days.
If you have kidney problems it may slow the excretion of some medications including antibiotics, meaning the drugs are in your system for longer. Ask your doctor or pharmacist for specific information about the antibiotics you are taking.
Can you take antibiotics while pregnant?
Some antibiotics are safe to take while pregnant or breastfeeding, while others may cause harm to your baby. If you need treatment with antibiotics during pregnancy, your doctor will prescribe one that is safe for you to take. Always tell your doctor if you are, or maybe, pregnant or become pregnant when taking any medication.
How much is a private prescription for antibiotics in the UK?
In the UK the cost of a private prescription varies according to the medication you are being prescribed and the service you are using.
At Medicspot, our NHS-trained GPs can offer advice, guidance, and support and issue private prescriptions to treat a range of conditions.
Consultations are by video link, from your phone wherever you are.
Making an appointment with an online doctor is quick and easy at Medicspot. Simply click the link and arrange an appointment at a time that is convenient for you. If you have any questions about antibiotics and would like to speak to a doctor, make an appointment today.
Antibiotics are a highly effective treatment when used correctly, but misuse of antibiotics has led to antibiotic resistance which is a growing problem around the world. Antibiotic resistance is when antibiotics no longer work properly in treating infections.
If you have symptoms of an infection and think you need to take antibiotics, make an appointment with your GP.
MedlinePlus: Antibiotics January 14th 2022 (Accessed October 29th 2022)
NHS: Antibiotics May 23rd 2019 (Accessed October 29th 2022)
NHS Inform: Antibiotics October 24th 2022 (Accessed October 29th 2022)
PubMed: Antibiotic resistance July-August 2017 (Accessed October 29th 2022)
PubMed: Antibiotics, past, present, and future October 2019 (Accessed October 29th 2022)
Centers for Disease Control and Prevention: Antibiotic Use Questions and Answers October 6th 2021 (Accessed October 29th 2022)
PubMed: Drug expiry debate: the myth and the reality September 2019 (Accessed October 30th 2022)
Nursing 2022: Can medications become harmful after the expiration date? August 2019 (Accessed October 30th 2022)
Centers for Disease Control and Prevention: How Antimicrobial Resistance Happens October 5th 2022 (Accessed October 30th 2022)
PubMed: Antibiotics as Major Disruptors of Gut Microbiota November 24th 2020 (Accessed October 30th 2022)
Medical News Today: Top seven safe, effective natural antibiotics January 1st 2020 (Accessed October 30th 2022)
NHS: Antibiotics May 23rd 2019 (Accessed October 30th 2022)
Healthline: Do antibiotics make you tired? March 26th 2020 (Accessed October 30th 2022)
Drugwatch: Taking antibiotics safely August 10th 2022 (Accessed October 30th 2022)
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