Metronidazole

1. About metronidazole

Metronidazole is an antibiotic.

It's used to treat skin infections, rosacea and mouth infections (including infected gums and dental abscesses). It's used in the treatment of conditions such as bacterial vaginosis and pelvic inflammatory disease. It's also used to treat infected insect bites, skin ulcers, bed sores and wounds, and to treat and prevent bacterial and parasitic infections.

Metronidazole is only available on prescription.

It comes as a tablet, a liquid you drink, a suppository (a small plug of medicine you push gently into your back passage), gel or cream. It's also given by injection, but this is usually only done in hospital.

2. Key facts

  • The most common side effects of metronidazole tablets, liquid, suppositories or vaginal gel are feeling sick, vomiting and diarrhoea, and a slight metallic taste in your mouth.
  • Do not drink alcohol while taking a course of metronidazole tablets, liquid, suppositories or vaginal gel, or for 2 days after finishing treatment. Alcohol can cause side effects such as feeling sick, vomiting, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache.
  • For most infections, you'll start to feel better in a few days but for some it may take longer. When treating rosacea, you may only notice a difference after several weeks.
  • Metronidazole tablets or suppositories are called by the brand name Flagyl.
  • Metronidazole cream is called by the brand names Rosiced or Rozex. The gel is called by the brand names Acea, Anabact, Metrogel, Metrosa, Rozex or Zyomet.

3. Who can and can't take metronidazole

Metronidazole can be taken by most adults and children.

Metronidazole isn't suitable for some people.

To make sure the tablets, liquid or suppositories are safe for you, tell your doctor if you:

  • have had an allergic reaction to metronidazole or any other medicines in the past
  • are pregnant or breastfeeding
  • have liver problems
  • are having dialysis
  • feel you won't be able to stop drinking alcohol while using metronidazole

To make sure the external cream or gel is safe for you, tell your doctor if you:

  • have had an allergic reaction to metronidazole or any other medicines (including any creams or ointments) in the past
  • are pregnant or breastfeeding

To make sure the vaginal gel is safe for you, tell your doctor if you:

  • have had an allergic reaction to metronidazole or any other medicines in the past
  • are pregnant or breastfeeding
  • have liver problems
  • feel you won't be able to stop drinking alcohol while using metronidazole
  • think you may have vaginal thrush

4. Tablets, liquid or suppositories

Metronidazole tablets, liquid and suppositories are prescribed for a number of infections, including pelvic inflammatory disease. The form your doctor prescribes, the dose and how long you'll need to take the medicine for depends on the type of infection and how serious it is.

Some infections can be treated with a single dose, while others may need a 2-week course. Children's doses are lower and depend on the age or weight of your child. Follow the instructions from your doctor or pharmacist.

Metronidazole tablets should be swallowed whole with a drink of water, after you have eaten some food.

Metronidazole liquid does not need to be taken after food. This medicine comes with a plastic syringe or spoon to help you measure out the right dose. If you don't have one, ask your pharmacist for one.

Your doctor may prescribe metronidazole suppositories if you have difficulty swallowing medicines. Metronidazole suppositories are usually used 3 times a day. Follow the instructions that come in the packaging with your medicine.

If you need to take several doses of metronidazole a day, try to space them evenly. For example, if you take your medicine 3 times a day, this could be first thing in the morning, mid-afternoon, and at bedtime.

How long should I take it for?

It's very important to keep taking metronidazole for as long as your doctor has prescribed it.

Important

Carry on taking this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it's nearly time for your next dose. In this case, just leave out the missed dose and take your next dose as normal.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to remember your medicines.

What if I take too much?

Accidentally taking an extra dose of metronidazole is unlikely to harm you or your child.

Speak to your pharmacist or doctor if you're worried or you take more than 1 extra dose.

5. Cream or gel

When metronidazole cream or gel is prescribed for rosacea, you'll normally use it twice a day for about 2 months. Treatment can sometimes last longer. Follow the instructions from your doctor or pharmacist.

If you're using the cream or gel for a skin infection, or infected ulcers or wounds, it's usual to put it on once or twice a day. Follow your doctor or pharmacist's instructions, and continue treatment until your infection has healed.

How to put it on

Put a thin layer of cream or gel onto the area you're treating and rub it in very gently. Try to avoid getting it into your eyes, as it can sting. If you do get some in your eye, wash it out immediately with cold water.

How long should I use it for?

It's very important to keep using metronidazole cream or gel for as long as your doctor has prescribed it.

Important

Carry on using this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to use it?

If you forget to use metronidazole cream or gel, put it on as soon as you remember. Then continue to use the cream or gel at the usual time.

What if I use too much?

If you put on too much cream or gel - or if you get some in your mouth - it's unlikely to harm you.

Talk to your pharmacist or doctor if you're worried, or if you or your child accidentally swallow a lot of it.

6. Vaginal gel

For treating bacterial vaginosis, you'll use an applicator to put the metronidazole gel into your vagina. The usual dose is 1 applicator full, every night for 5 nights. It's recommended that you don't use the gel while having your period.

How to use it

Follow the instructions that come in the packaging along with your medicine. These will tell you how to fill the applicator with gel and put it into your vagina. Do not have sex while using the vaginal gel.

How long should I use it for?

It's very important to keep using metronidazole vaginal gel for as long as your doctor has prescribed it.

Important

Carry on using this medicine until you have finished the course, even if you feel better. If you stop your treatment early, the infection could come back.

What if I forget to use it?

If you forget to use metronidazole vaginal gel, use it as soon as you remember. Then continue to use the gel at the usual time.

What if I use too much?

If you accidentally use too much gel it's unlikely to harm you.

Talk to your pharmacist or doctor if you're worried.

7. Side effects

It's unusual to have side effects when using metronidazole cream or gel. However, there can be some common side effects with the tablets, suppositories or vaginal gel.

Do not drink alcohol while taking the tablets, liquid or suppositories, or using the vaginal gel. It can give you severe side effects such as feeling sick, vomiting, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache. After finishing your treatment, wait for 2 days before drinking alcohol again. This allows the metronidazole to leave your body.

Common side effects of tablets, liquid, suppositories or vaginal gel

Keep taking the medicine, but talk to your doctor or pharmacist if these side effects bother you or don't go away:

  • feeling sick
  • diarrhoea or vomiting
  • metallic taste in your mouth or a furry tongue

Serious side effects of tablets, liquid, suppositories or vaginal gel

Serious side effects are rare and happen in less than 1 in 1,000 people.

Call a doctor straight away if:

  • your skin and the whites of your eyes turn yellow - these can be warning signs of liver or gallbladder problems
  • you get unexpected infections, mouth ulcers, bruising, bleeding gums, or extreme tiredness - these can be caused by a blood problem
  • you have bad stomach pains which may reach through to your back - this can be a sign of pancreatitis
  • you have blurred or double vision
  • you have a fever (38C and above) and stiff neck, you're seeing or hearing things that aren't there (hallucinating), feeling confused, unable to cope with bright light or having difficulty speaking - these can be warning signs of meningitis, or that metronidazole is affecting your brain

If you suspect that you or someone else are showing signs of meningitis, or other problems related to the brain, speak to a doctor or go to your nearest accident and emergency (A&E) department straight away.

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to metronidazole.

Contact a doctor straight away if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

These are warning signs of a serious allergic reaction. A serious allergic reaction is an emergency.

These are not all the side effects of metronidazole tablets, cream, gel, suppositories or vaginal gel. For a full list see the leaflet inside your medicines packet.

Information:

You can report any suspected side effect to the UK safety scheme.

8. How to cope with side effects

What to do about:

  • feeling sick - stick to simple meals and don't eat rich or spicy food. You should always try to take your metronidazole after a meal or snack.
  • diarrhoea or vomiting - drink plenty of water or other fluids if you have diarrhoea or vomiting. Speak to a pharmacist if you have signs of dehydration, such as peeing less than usual or having dark, strong-smelling pee. If diarrhoea or vomiting continues for more than 24 hours contact your doctor for advice. Don't take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
  • metallic taste in your mouth or a furry tongue - drink plenty of water and eat plain foods that you usually enjoy. If your tongue is very furry, this could be a sign of thrush - ask your doctor or pharmacist for advice.

9. Pregnancy and breastfeeding

It's generally safe to use metronidazole while you're pregnant or breastfeeding.

If you're breastfeeding, take care when using metronidazole cream or gel and make sure you don't accidentally get it on your breasts. If this happens, wash off any cream or gel from your breasts before feeding your baby.

Important

For safety, tell your doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

10. Cautions with other medicines

Metronidazole cream or gel isn't known to cause any problems with other medicines. However, there are some medicines that don't mix well with the tablets, suppositories, liquid or vaginal gel.

Tell your doctor if you're taking these medicines before you start taking metronidazole tablets, suppositories, liquid or vaginal gel:

  • a blood thinner called warfarin
  • lithium (used to treat some types of mental health problem)
  • disulfiram (used to help people stay off alcohol)
  • phenytoin or phenobarbitone (used to treat epilepsy)
  • ciclosporin (used to dampen the immune system)
  • fluorouracil or busulfan (used to treat some types of cancer)
  • any medicines that you take as a liquid, in case these contain alcohol

Mixing metronidazole with herbal remedies and supplements

There are no known problems with taking herbal remedies and supplements alongside metronidazole. However, some remedies and supplements that come as liquids that you drink may also contain alcohol. Check the list of ingredients or ask the supplier or manufacturer.

Important

For safety, tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

11. Common questions

How does metronidazole work?

Metronidazole is an antibiotic. It works by stopping the growth of the bacteria (or parasites) causing the infection.

How long does it take to work?

For most infections, you should feel better within a few days. With serious swelling (including dental infections), the medicine will start working within a few days but it may take longer before your symptoms start to get better.

For some of the infections that metronidazole is used for, you may only begin to notice an improvement after a week.

When using the cream or gel to treat rosacea, you may have to wait a few weeks before you see any improvement.

It's very important that you keep taking metronidazole until the course is finished. Do this even if you feel better. It will help stop the infection coming back.

What if I don't get better?

Tell your doctor if you still don't feel better 2 or 3 days after finishing your course of metronidazole. Also tell them if, at any time, you start to feel worse.

Will it stop my contraception working?

Metronidazole doesn't stop contraceptive pills working.

However, if metronidazole makes you vomit or have severe diarrhoea (6 to 8 watery poos in 24 hours) for more than 24 hours, your contraceptive pills may not protect you from pregnancy. Look on the pill packet to find out what to do.

Read more about what to do if you're on the pill and you're vomiting or have diarrhoea.

Will it give me thrush?

Some people get a fungal infection called thrush after taking a course of antibiotics like metronidazole. This is more common if you're using the vaginal gel. It happens because antibiotics kill the normal harmless bacteria that help to protect you against thrush.

Ask your doctor or pharmacist for advice if this happens to you.

Will it reduce my fertility?

Metronidazole won't affect male or female fertility. However, speak to a pharmacist or your doctor before taking it if you're trying to get pregnant.

Can I drive or ride a bike?

Metronidazole doesn't usually affect you being able to drive or cycle.

However, very rarely, some people suffer from drowsiness or blurred vision. Do not drive or ride a bike until you stop feeling drowsy and your vision is clear.

Can I drink alcohol with it?

Don't drink alcohol while you're taking metronidazole, including for 2 days afterwards. This gives the medicine time to leave your body.

This is important because metronidazole can react with alcohol to cause a number of side effects. These include feeling sick, vomiting, stomach pain, hot flushes, a pounding heartbeat (palpitations) and a headache.

Is there any food or drink I need to avoid?

You must not have any alcohol (in either your food or drink) while taking metronidazole - and for 2 days afterwards.

Otherwise you can eat and drink normally.

Page last reviewed: 21/02/2018
Next review due: 21/02/2021