- Antibiotics can only treat infections caused by bacteria.
- Antibiotics can interfere with some other medicines, including the contraceptive pill, making them less effective.
- Always finish your course of antibiotics, even if you feel better.
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
Your doctor will prescribe antibiotics to treat an infection that’s caused by bacteria. Common bacterial infections include those affecting your ear, chest, urinary system and skin. Some sexually transmitted infections (STIs), for example chlamydia, is also caused by bacteria.
Some bacterial infections clear up by themselves, so your doctor may want to wait before prescribing antibiotics you may not need. They’ll advise you on other treatment and self-management that could help.
Many infectious illnesses are caused by viruses, not bacteria. These include influenza (flu), measles, mumps and hepatitis. Antibiotics don’t work against viruses, so your doctor won’t normally prescribe them to treat these illnesses.
Your medical history and an examination can help your doctor decide whether your infection is caused by a virus or bacteria. They may want to take samples of your blood, urine, faeces or mucus, or a swab (from your throat or skin, for example). Laboratory tests on these will help show what’s causing your infection. If it’s bacteria, the results will help your doctor pick the most effective antibiotic to treat you.
Sometimes, a viral infection leads to what’s called a secondary bacterial infection, such as pneumonia. In circumstances like this, your doctor may prescribe antibiotics to treat the secondary bacterial infection.
You may be given antibiotics to prevent an infection after certain types of surgery or if you’re at particular risk of certain infections.
Some bacterial infections don’t respond to antibiotics alone. For instance, if you have an abscess, you may also need to have it drained.
Your doctor will try to find the antibiotic that suits you best. There are at least 70 different types that work in different ways. Classes of antibiotics include penicillins, tetracyclines, macrolides and cephalosporins.
A broad-spectrum antibiotic can treat infections caused by a wide range of different bacteria. Penicillins are generally this type.
Your doctor may prescribe you a broad-spectrum antibiotic until the results of any tests come back. They may also prescribe this type of antibiotic if your infection is caused by more than one type of bacteria. Broad-spectrum antibiotics aren’t always the best solution, because using them may 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 necessary, your doctor will order tests to see exactly what bacteria is causing your infection and choose a narrow-spectrum antibiotic to target it. But if they want to start your treatment immediately, without waiting for test results, they’ll usually prescribe a broad-spectrum antibiotic.
Always read the patient information leaflet that comes with your medicine. If you have any questions, ask your pharmacist or doctor for advice.
Some antibiotics work by killing bacteria. They usually do this by interrupting the chemical processes that the bacteria use to make their cell walls. 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 have started treatment with these medicines. Chloramphenicol is an example of this type of antibiotic.
Antibiotics come in different forms including:
- tablets or capsules (most commonly)
- liquids (if you have difficulty swallowing or when giving to children)
- ear and eye drops (eg for conjunctivitis)
- creams (for skin conditions like eczema and broken skin which gets infected)
- injections (for serious infections – these are usually given in hospital)
How long do I take them for?
You’ll need to take antibiotics for a set period of time, which could be days or weeks. Your prescription should say how long you should take your medicine for, or when your treatment will be reviewed.
The length of your course of antibiotics depends on the type of infection you have. For instance, a three-day course may clear up cystitis and other urinary tract infections (UTIs) that need antibiotics. But if you have a serious infection such as osteomyelitis, you could have to take antibiotics for weeks or months to clear it up.
It’s important to finish the whole course, even if you start to feel better. This will make sure all the bacteria are gone and stop them from becoming resistant to the medicine.
Your doctor may want to check if your infection has completely cleared up with tests and an examination.
Make sure you follow the advice your doctor gives you and read the patient information leaflet that comes with your medicine.
When should I take them?
You may have to follow specific instructions about exactly when to take your antibiotics. Taking your antibiotics at regular intervals – your doctor will tell you how often – means there’s a steady level of the medicine in your body.
Some antibiotics should be taken before, with or after a meal as well as taking them at specific times. For example, you might need to take your medicine four times a day on an empty stomach, so you’ll need to factor this in when timing your meals. Ask your doctor if you have any questions. It’s usually best to take antibiotics in tablet form with water.
It’s important not to misuse antibiotics by:
- taking someone else’s
- sharing yours with another person
- taking them ‘just in case’ (when you’re travelling abroad, for instance) unless your doctor has advised you to because you’re at particular risk of infection
- not finishing your prescribed course and keeping any left over to use another time or flushing them down the toilet or sink
Follow the instructions on the medicine label or patient information leaflet. This will tell you what to do if you miss a dose or think you’ve taken too much. If you have any questions, ask your doctor or pharmacist for advice.
Liver and kidney problems
If you have problems with your liver or kidneys, tell your doctor, nurse prescriber or dentist before they prescribe you antibiotics
Pregnant or breastfeeding
It’s also important to tell your health professional if you’re pregnant or might be, if you’re planning to get pregnant or are breastfeeding. Some antibiotics are safe to use in pregnancy, but others aren’t. There is a risk that they get into your breast milk and affect your baby.
You’ll need strong antibiotics urgently if your doctor suspects your infection has developed into sepsis. This is a very serious condition when your body responds to infection and the response results in serious damage to tissues and vital organs. To start with, you’ll have an injection of broad-spectrum antibiotics within an hour, as well as other supportive measures such as oxygen. Results from blood and other tests can help show exactly where and what the infection is. This helps your doctors decide whether your antibiotic should then be switched to one with a narrower spectrum.
Side-effects are the unwanted effects of taking a medicine. The most common side-effects of antibiotics are diarrhoea, feeling sick and vomiting but you may not have any obvious side-effects.
Antibiotic eye drops can sting and blur your vision when you put them in. Ear drops may make the inside of your ear inflamed and affect your hearing.
It’s possible that you may get a fungal infection such as thrush after treatment with broad-spectrum antibiotics. This is because as well as killing the harmful bacteria causing your infection, antibiotics may also destroy your body's harmless bacteria that stop micro-organisms such as fungi growing out of control. This side-effect is more common if you have been taking antibiotics for an extended period of time. If you develop a fungal infection, you may then need to take an antifungal medicine to treat it.
You may also develop bowel problems if antibiotics affect a type of bacteria called Clostridium difficile found in your intestine. This can increase the levels of toxins normal bacteria produce and lead to more serious infection. Older people and those with a weakened immune system are most at risk.
More serious side-effects of antibiotics include kidney problems, blood disorders, increased sensitivity to the sun and deafness. However, these are rare and often specific to the type of antibiotic you’re taking.
If your antibiotics make you feel ill or you want to stop taking them for any reason, contact your doctor as soon as possible. Depending on your infection, he or she may be able to offer you an alternative antibiotic, although this won’t always be possible.
A more serious side-effect of taking antibiotics is having an allergic reaction. However, true allergy to antibiotics is quite rare. About one in 10 people think they have an allergy to penicillin, but fewer that one in 10 of those people have a true allergy. The reason people think they have an allergy when they perhaps don’t is because they got a rash when taking penicillin as a child. But if the rash was minor or only appeared after three days of taking penicillin, then it’s likely not to be an allergy. If this is what happened to you and you get a serious infection, your doctor may suggest you take penicillin because it’s the best medicine to treat your illness. They will consider this carefully though because a severe reaction to penicillin is potentially fatal.
If you’ve had an allergic reaction in the past, be sure to tell your doctor. If you’re at risk of having a severe reaction, you won’t be able to have that particular type of antibiotic so your doctor will prescribe a different one for you.
If you’re allergic to an antibiotic, typical symptoms include:
- an itchy rash
- sore eyes
- a blocked or runny nose
- swelling in any part of your body but especially your face, throat and tongue
- difficulty breathing
- a faster heartbeat
- feeling or being sick
- feeling faint
These reactions usually happen very quickly after taking antibiotics.
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.
It’s possible you might get a referral to a specialist allergy clinic to find out exactly what you’re allergic to so you can avoid it in future.
Certain antibiotics (for example rifampicin) can stop the contraceptive pill from working. If you’re taking antibiotics that interfere with the contraceptive pill or have vomiting or diarrhoea when you're taking antibiotics, it’s important that you use additional, barrier contraception such as a condom. Doctors recommend doing this while you’re taking the antibiotics and for seven days after you’ve finished the course.
Antibiotics can interact with a number of other medicines and herbal remedies. It's important to check with whoever prescribes your antibiotics before you take anything else at the same time.
You should also check if it’s OK to have certain foods or drinks if you’re taking antibiotics. For example, dairy products (including milk) and fruit juice can affect how your body absorbs some antibiotics. So does alcohol, which can also cause a reaction with some antibiotics, particularly one called metronidazole. Metronidazole is used to treat a number of infections including dental infections. Dietary supplements containing minerals like calcium may make your antibiotic less effective.
Some bacteria are resistant to certain antibiotics. This means that the antibiotic is no longer any good at getting rid of infection caused by these bacteria. For example, if you get infected with meticillin-resistant Staphylococcus aureus (MRSA), it won’t be possible to treat you with standard antibiotics.
Health professionals are trying to slow down the development of resistance, which is caused by the over-use and misuse of antibiotics. Your doctor or pharmacist may advise how you can manage an infection without antibiotics. They can also suggest ways to avoid infection, like handwashing and food hygiene.
Resistance can start if the bacteria that have caused an infection aren't completely killed off by an antibiotic. There’s more risk the infection will come back and the bacteria that survive may adapt so they’re resistant to that particular antibiotic. Bacteria may also pass on resistance when they multiply. This is why it’s really important to complete a course of antibiotics, even if you feel better. It’s the best way to prevent any bacteria from surviving.
Using antibiotics when you don’t really need them, especially broad-spectrum ones, means there’s more risk a wide variety of bacteria will become resistant. Some multi-resistant bacteria are resistant to several antibiotics at the same time.
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.
1. How does my doctor choose the right 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 the severity of your infection. Some bacterial infections will get better on their own so your doctor may not prescribe any antibiotics.
Before choosing an antibiotic, your doctor will ask you about your symptoms and examine you. If relevant, he or she may ask if you have travelled abroad recently or if you have any problems with your immune system. If you’re vomiting or have diarrhoea, your doctor may ask you to provide a sample of faeces (also called a stool sample). These samples will be tested in a laboratory to see which bacteria are causing your infection, so you can be prescribed the correct antibiotic.
Your doctor may prescribe you a broad-spectrum antibiotic to take until he or she gets the results of your tests, or if he or she is unsure of the specific bacteria causing your infection. This type of antibiotic gets rid of infections caused by a wide range of bacteria. Broad-spectrum antibiotics 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 so that your treatment isn’t delayed as this could lead to your illness getting worse.
If your doctor is confident which bacteria or type of bacteria is causing your infection, he or she may prescribe a narrow-spectrum antibiotic. This type of antibiotic only works against specific bacteria.
As well as considering which bacteria are most likely to be causing your infection, your doctor will consider your medical history and how severe your infection is to guide his or her choice of antibiotics. This may include whether you have any allergies to specific antibiotics, if you have any problems with your kidneys or liver and whether you're pregnant or breastfeeding. You may need to take more than one type of antibiotic at the same time.
If you need penicillin antibiotics but are allergic to them, your doctor will prescribe a different type for you.
Always ask your doctor or pharmacist for advice and read the patient information leaflet that comes with your medicine.
2. Why won't my GP give me antibiotics for my flu?
Antibiotics are only effective against infections caused by bacteria. Flu (influenza) is caused by a virus, so antibiotics won’t work and shouldn't be used for this type of infection. Antibiotics may sometimes be helpful if you develop a secondary bacterial infection when you have flu or are recovering from it.
You may be prescribed antibiotics to help your immune system fight bacterial infections but they don’t work against viral infections such as flu.
Your body may be weakened after fighting a flu infection, which makes it possible that you will pick up a secondary infection caused by bacteria, such as pneumonia. Your body may find it difficult to fight off this secondary infection so your doctor may have to prescribe antibiotics to help. Secondary infections can affect your chest, ears, nose or throat.
If you have flu, it can take up to two weeks 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 any of your symptoms, particularly if they don’t go away. If you’re particularly at risk of developing complications of flu, for example you’re over 65 or have a serious medical condition such as chronic obstructive pulmonary disease (COPD), having the flu vaccine each year can help prevent you from getting it. Speak to your GP for more information.
3. Can ginkgo biloba help improve my memory?
You should always finish your entire course of antibiotics even if you feel better after a few days. This is because the bacteria causing your infection may still be in your body and could flare up to cause another infection. If you stop antibiotics too early, you increase the risk of the bacteria becoming resistant to the antibiotic and this may make the infection more difficult to treat in the future. It also means that the infection may come back soon after.
To clear your infection completely you will need to continue taking your antibiotics for the full course of treatment, as directed by your doctor, nurse prescriber or dentist. You should 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 causing your infection 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 causing the infection you're being treated for become resistant, your doctor will need to prescribe you a different antibiotic.
You’re likely to be prescribed antibiotics for a period of two to four or seven to 10 days, and 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 that you have the correct amount of medicine in your body to kill off the bacteria causing your infection.
If you miss a dose of antibiotic, take it as soon as possible and then return to your usual dosing schedule. If it’s nearly time to take your next dose, don’t take the one you forgot and stick to your usual schedule. Don't double up on doses. 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.
3. Can I stop taking my antibiotics once I feel better?
Always finish your entire course of antibiotics, even if you feel better after a few days, to clear your infection completely. 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 kill 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.
This information was published by Bupa Group's Health Content Team and has been reviewed by appropriate medical or clinical professionals. To the best of their knowledge the information is current and based on reputable sources of medical evidence, however Bupa (Asia) Limited makes no representation or warranty as to the completeness or accuracy of the Content.
The information on this page, and any information on third party websites referred to on this page, is provided as a guide only. It should not be relied upon as a substitute for professional medical advice, nor is it intended to be used for medical diagnosis or treatment. Bupa (Asia) Limited is not liable for any loss or damage you suffer arising out of the use of, or reliance on, the information.
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