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.
|Type of medicine||Antimicrobial agent (antibiotic)|
|Used for||To treat or prevent infection|
|Available as||Tablets, oral liquid medicine, suppositories, and injection|
Metronidazole is used to treat a wide variety of infections caused by certain types of germ (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 an infection called bacterial vaginosis. It is also prescribed before gynaecological surgery and surgery on the intestines to prevent infection from developing. It can safely be taken by people who are allergic to penicillin.
Metronidazole is also used, alongside other medicines, to get rid of Helicobacter pylori, a bacterial infection often associated with stomach ulcers.
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.
Before taking metronidazole
Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking metronidazole it is important that your doctor or dentist knows:
- 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
- Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The manufacturer's leaflet will give you more information about metronidazole and a full list of side-effects which you may experience from taking it.
- Take the tablets or liquid medicine exactly as your doctor or dentist tells you to. The dose you are given will depend upon what type of infection you have, and how severe the infection is.
- As a guide, a typical dose for an adult would be 400 mg two or three times a day, but your dose may be more or less than this. Doses for children depend upon the child's age and weight. Your doctor will tell you what dose is right for you (or your child), and this will also be printed on the label of the pack to remind you.
- Space your doses evenly throughout the day, and keep taking the medicine until the course is finished, unless you are told to stop by your doctor. Your symptoms may return if you stop taking metronidazole before the end of the course prescribed for you.
- Most courses of metronidazole last for around seven days, but some may be as short as three days and some as long as 14 days. For certain infections you may be given a single, larger dose of metronidazole, 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
- 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.
- While you are taking metronidazole your urine may look a darker colour than normal. On its own this is nothing to worry about. However, if you also experience tummy (abdominal) pain, or if you feel sick (nausea) or feel generally unwell, you should let your doctor know.
- If you buy any medicines, check with a pharmacist that they are safe to take with metronidazole. Some cough and cold preparations contain alcohol and should not be taken with metronidazole.
- If you need to take metronidazole for longer than ten days, your doctor may want you to have some tests. Make sure you keep any appointments that your doctor gives to you.
Can metronidazole cause problems?
Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the ones associated with metronidazole. 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.
|Metronidazole side-effects||What can I do if I experience this?|
|Feeling sick (nausea) or being sick (vomiting)||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.
How to store metronidazole
- Keep 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
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.
Further reading and references
Manufacturer's PIL, Flagyl® 200 mg and 400 mg Tablets; Sanofi, The electronic Medicines Compendium. Dated July 2019.
British National Formulary, 79th Edition (Mar 2020); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.