Metronidazole For Bacterial Infection (Flagyl)
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- Medicine information
- Infection treatment medicine
- Metronidazole for bacterial infection
Flagyl
Peer reviewed by Dr Colin Tidy, MRCGPLast updated by Michael Stewart, MRPharmSLast updated 26 Mar 2023
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Swallow metronidazole tablets with plenty of water. Take them with a meal or a snack.
Do not drink alcohol while you are taking metronidazole, and for 48 hours after finishing your course of treatment.
Space your doses evenly throughout the day, and keep taking the medicine until the course is finished.
The most common side effects of metronidazone are feeling sick (nausea) and being sick (vomiting).
In this article:
Video picks for Infection treatment medicine
Continue reading below
About metronidazole
Type of medicine | Antimicrobial agent (antibiotic) |
Used for | To treat or prevent infection |
Also called | Flagyl® |
Available as | Tablets, oral liquid medicine, suppositories, and injection |
What is metronidazole used for?
Back to contentsMetronidazole is an antibiotic used to treat a wide variety of bacterial infections caused by anaerobic bacteria and types of micro-organisms called protozoa.
These types of organisms often cause infections in areas of the body such as the gums, pelvic cavity and tummy (stomach or intestines) because they do not need oxygen to grow and multiply.
Metronidazole is commonly prescribed to treat bacterial vaginosis, and, is also prescribed before gynaecological surgery and surgery on the intestines, to prevent infection from developing.
Metronidazole is also used, alongside other medicines, to get rid of Helicobacter pylori, a bacterial infection often associated with stomach ulcers.
It can safely be taken by people who are allergic to penicillin.
Metronidazole is available as a skin preparation also. This leaflet does not give information about metronidazole when it is used for skin conditions, but there is more information available in a separate leaflet called Metronidazole skin gel and cream.
Continue reading below
Side effects of Metronidazole
Back to contentsCommon side effects of metronidazole are:
Feeling sick.
Being sick.
Changes in how things taste.
Furred tongue
Sore mouth.
Lack of appetite.
You will find a full list in the manufacturer's information leaflet supplied with your medicine.
The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.
How to manage metronidazole side effects
Back to contentsMetronidazole side effects | What can I do if I experience this? |
Feeling sick or being sick | Stick to simple foods. Make sure you take your doses after a meal or a snack |
Changes in the way things taste, furred tongue, sore mouth | Ask your pharmacist to recommend a suitable mouthwash |
Lack of appetite | This should soon pass, but in the meantime choose food that you usually enjoy |
If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.
Continue reading below
Who should not take metronidazole
Back to contentsSome medicines aren’t suitable for certain health conditions or may require extra care. Before taking metronidazole, it is important to let your doctor know:
If you are pregnant or breastfeeding.
If you feel you will be unable to stop drinking alcohol for the duration of your treatment.
If you have any problems with the way your liver works.
If you have a rare inherited blood disorder called porphyria.
If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
If you have ever had an allergic reaction to a medicine.
How to take metronidazole
Back to contentsRead the information leaflet in your pack before starting. It explains metronidazole and lists possible side effects.
Take the tablets or liquid exactly as your doctor or dentist tells you. Your dose depends on the type and severity of your infection.
Adults often take 400 mg two or three times a day, but your dose may be different. Children’s doses depend on age and weight. You're doctor will tell you what dose to take.
Space your doses evenly throughout the day and finish the full course unless your doctor tells you to stop. Stopping early can make the infection come back.
Most courses of metronidazole last about seven days, but some can last anywhere from 3-14 days. For certain infections, you may be given one large dose, usually five 400 mg tablets (2 g),to take at once.
Take each of your doses with a snack or just after eating a meal. Swallow the tablets whole (that is, without chewing or crushing them) with a full glass of water.
If you forget to take a dose, take it as soon as you remember and try to space your remaining doses evenly throughout the rest of the day. Do not take two doses together to make up for a forgotten dose.
If you have been given metronidazole suppositories
Remove the suppository from its wrapping.
Using your finger, gently push the suppository into your back passage (rectum) as far as is comfortable. Many people find that inserting a suppository is easier if they squat or bend forward.
Remain still for a few moments to help you to hold the suppository in place.
Wash your hands.
Getting the most from your treatment
Back to contentsMetronidazole can make your urine look darker. This is usually harmless, but if you also get stomach pain, feel sick, or feel unwell, tell your doctor.
Check with a pharmacist before buying any other medicines. Some cold and cough products contain alcohol and shouldn’t be taken with metronidazole.
If you need to take metronidazole for more than 10 days, your doctor may arrange tests. Be sure to attend any appointments.
Important: do not drink alcohol while you are on metronidazole and for 48 hours after finishing your course of treatment. This is because drinking alcohol with metronidazole is likely to make you feel very sick (nauseated) and cause other unpleasant effects, such as the sensation of having a 'thumping heart' (palpitations), hot flushes, and headache.
How to store metronidazole
Back to contentsKeep all medicines out of the reach and sight of children.
Store in a cool, dry place, away from direct heat and light.
Important information about all medicines
Back to contentsImportant information about all medicines
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.
If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
Never keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
If you have any questions about this medicine ask your pharmacist.
CloseReport side effects to a medicine or vaccine
If you experience side effects, you can report them online through the Yellow Card website.
Frequently asked questions
Back to contentsHow long does it take for metronidazole to work?
Metronidazole usually starts to work within 1-2 days, with most people noticing an improvement in their symptoms after 48 hours. Always finish your course of treatment even if you are feeling better.
Is it safe to take metronidazole during pregnancy?
Yes, it is usually safe to take metronidazole during pregnancy if it is prescribed to you. However, always let your doctor know that you are pregnant before taking metronidazole.
Can you drink alcohol when taking metronidazole?
No, you should not drink alcohol if you are taking metronidazole as it can cause a strong reaction, including nausea, vomiting, flushing, headaches, and a fast heartbeat. You should wait until 2 days after your last dose before having alcohol.
How long does metronidazole stay in your system for?
Metronidazole stays in your system for about 2-3 days after your last dose. It has a half-life of around 8 hours, which means it takes about 8 hours for the amount of the drug in your bloodstream to reduce by half.
Unsure about mixing medicines?
Check for possible interactions between medicines, supplements and foods before taking them together.
Check safetyFurther reading and references
- Manufacturer's PIL, Flagyl® 200 mg and 400 mg Tablets; Sanofi, The electronic Medicines Compendium. Dated December 2021.
Continue reading below
Article history
The information on this page is written and peer reviewed by qualified clinicians.
Next review due: 25 Mar 2026
26 Mar 2023 | Latest version
Last updated by
Michael Stewart, MRPharmSPeer reviewed by
Dr Colin Tidy, MRCGP
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