Always follow your doctor or pharmacist's advice, and the instructions that come with your medicine.
Dosage
The dose of nitrofurantoin you take depends on whether it's to treat or prevent a urinary tract infection, your age, and how bad the infection is.
Nitrofurantoin tablets and capsules come as 50mg or 100mg strengths. The slow release capsules are 100mg. The liquid comes as 25mg in 5ml.
The usual adult dose of nitrofurantoin is:
- to treat a urinary tract infection – either 100mg taken as slow release capsules, twice a day, or 50mg taken as standard tablets or capsules, 4 times a day. Severe infections may need a higher dose of 100mg taken as standard tablets or capsules, 4 times a day
- to prevent a urinary tract infection – 50mg to 100mg taken as standard tablets or capsules, once a day at night
Doses are usually lower for children. Your child's doctor will work out the correct dose based on your child's weight or age.
Try to space your doses evenly throughout the day. If you're taking nitrofurantoin twice a day, leave 12 hours between each dose – for example, take it at 8am and 8pm.
If you're taking it 4 times a day, this will usually be first thing in the morning, at about midday, late in the afternoon, and at bedtime.
Important: Finishing your course of nitrofurantoin
Carry on taking this medicine until you finish the course, even if you feel better. If you stop your treatment early, your problem could come back.
How to take it
Swallow nitrofurantoin tablets or capsules whole with a drink of water. Do not chew or break them.
Nitrofurantoin also comes as a liquid for younger children or people who find it difficult to swallow tablets.
If you're taking nitrofurantoin as a liquid, the medicine will come with a syringe or spoon to help you take the right amount. If you do not have a syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not measure the right amount.
Take nitrofurantoin with or after a meal or snack. This helps your body absorb the medicine, as well as helping to prevent stomach upset.
How long to take it for
If you're taking nitrofurantoin to:
- treat a urinary tract infection, you usually need to take it for 3 to 7 days
- stop urinary tract infections coming back, you may need to take it for several months
- prevent an infection when having surgery, you'll usually need to take it on the day of the operation and for the next 3 days
If you forget to take it
If you forget to take a dose of nitrofurantoin, 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 at the usual time.
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 help you remember to take your medicine.
If you take too much
Taking an extra dose of nitrofurantoin is unlikely to harm you.
Urgent advice: Contact 111 for advice now if:
You've taken more than your prescribed dose of nitrofurantoin and:
- you're worried or get severe side effects
- you've taken more than 1 extra dose
Go to 111.nhs.uk or call 111
Call 111 if you're asking about a child under the age of 5 years.
If you go to A&E, take the nitrofurantoin box or leaflet inside the packet plus any remaining medicine with you.