Metronidazole

In Aotearoa New Zealand, metronidazole is available as tablets (200 mg or 400 mg), liquid (200 mg in 5 mL), suppositories (500 mg) and can be given as an injection in the hospital. 

• The dose of metronidazole will be different for different people, depending on the type of infection and your age.
• The usual dose in adults is 200 mg to 400 mg taken 2 or 3 times a day. Your dose may be more or less than this.
• Your healthcare provider will tell you how long to take metronidazole for (usually 3 to 14 days).
• For some infections, metronidazole can be given as a single, larger dose of five 400 mg tablets (2g) to take at once.
• The dose for children will depend on their body weight. It's usually given 3 times a day.
• Always take your metronidazole exactly as your healthcare provider has told you. The pharmacy label on your medicine will tell you how much metronidazole to take, how often to take it, and any special instructions.

• Timing: Take metronidazole at the same times each day. Space your metronidazole doses evenly throughout the day. For example, if you're taking it 3 times a day, take your doses first thing in the morning, early afternoon and at bedtime.
• Tablets: Take the tablets with food. Swallow the tablets with a glass of water.
• Liquid: If possible, it's best to take the liquid on an empty stomach, 1 hour before or 2 hours after food. Shake the medicine well. Measure the right amount using an oral syringe or medicine spoon. You can get these from your pharmacy. Don't use a kitchen spoon, as it won't give you the right amount.
  Read more tips on how to give medicines to babies and children.
• Missed dose: If you forget to take your dose, take it as soon as you remember. But, if it’s nearly time for your next dose, just take the next dose at the right time. Don’t take double the dose.
• Finish the course: It’s best to take the whole course of antibiotics for the number of days your healthcare provider has told you to. Don’t stop taking it, even if you feel your infection has cleared up – talk to your healthcare provider first.

Here are some things to know when you're taking metronidazole. Other things may be important as well, so ask your healthcare provider what you should know about.

Drinking alcohol

Don't drink alcohol while you are taking metronidazole and for at least one day (24 hours) after finishing treatment. Drinking alcohol with metronidazole may make you feel nauseous (feel sick), vomit (be sick), or have stomach cramps, headaches and flushing.

Other things to know:

• Driving: Metronidazole can make you feel tired or dizzy. Be careful when driving or using tools until you know how this medicine affects you.
• Other medicines: Metronidazole interacts with some medicines, herbal supplements and rongoā Māori, so check with your healthcare provider before starting metronidazole and before starting any new products.
• If you’re sick: If you’re sick (vomit) less than 30 minutes after having a dose of metronidazole, take the same dose again. But, if you’re sick (vomit) and it’s more than 30 minutes after having a dose of metronidazole, you don’t need to take another dose. Wait until the next usual dose.
• If you're taking the contraceptive pill: You don't usually need to use additional contraception if you're taking metronidazole. But if you have diarrhoea (runny poo/hamuti) or vomiting (being sick) lasting more than 24 hours, absorption of the contraceptive pill may be affected. If this happens, ask your healthcare provider or pharmacist for advice about contraception over the following few days.
• Storage: Store your metronidazole tablets and liquid in a cool, dry place, away from direct heat and light. It doesn’t need to be kept in the fridge.
• Pregnancy or breastfeeding: Talk to your healthcare provider if you're pregnant, planning a pregnancy or want to breastfeed.

Like all medicines, metronidazole can cause side effects, although not everyone gets them. If you're concerned about any symptoms you think might be related to your medicine, talk to your healthcare provider. The following information offers some guidance but doesn't include all possible side effects.

Common side effects

Tell your healthcare provider if these side effects bother you.

• Your urine (pee) might change colour: While you’re taking metronidazole your urine may look a darker colour than normal. On its own, this is nothing to worry about. However, if you also get stomach (tummy) pain, or if you have nausea (feel sick) or feel generally unwell, you should let your healthcare provider know.
• Nausea (feeling sick) or vomiting (being sick): Take metronidazole with food.
• Diarrhoea or sore tummy.
• Not feeling hungry, a metallic taste in your mouth or food tastes different.
• Headache.
• Dry mouth.
• Feeling dizzy or confused: Be careful when driving or using tools until you know how this medicine affects you. Don’t drink alcohol.
• Small white patches in your mouth or a white furry tongue (oral thrush): Ask your healthcare provider for advice.
• Vaginal itching, soreness or discharge (vaginal thrush): Ask your healthcare provider for advice. 

Tell your healthcare provider immediately or phone Healthline free on 0800 611 116 if these occur

• Seizures.
• Changes in vision such as blurred vision.
• Signs of problems with your liver such as yellowing of the skin or eyes, dark urine, pain in the tummy.
   

Phone 111 for an ambulance or go to your nearest accident and emergency (A&E) clinic if these occur

• Signs of an allergic reaction such as itchy skin, and rash, swollen lips or tongue, problems breathing, like a tight chest or shortness of breath.

Read more about medicines and side effects and reporting a reaction you think might be a side effect.