Nitrofurantoin 100mg for UTI: Dose, Side Effects and Who Shouldn’t Take It
The UK’s first-choice antibiotic for cystitis explained: how nitrofurantoin works, the usual 100mg course, dark urine and other side effects, and who should avoid it.
Part of our cystitis guide: symptoms, causes and treatment.
Get urgent help first. Call 999 or go to A&E if you feel very unwell, confused or very drowsy, or have a very fast heartbeat or breathing, or cold, blotchy skin: these can be signs of sepsis. Call 999 too for swelling of the face, lips or throat, or difficulty breathing after taking a medicine. Contact your GP or NHS 111 (NHS 24 on 111 in Scotland) the same day if you have pain in your back or side, a high temperature, shivering or vomiting, which can be signs of a kidney infection, or if you can see blood in your urine. Online treatment isn’t suitable in these situations.
Worth knowing up front: nitrofurantoin is a first-choice antibiotic for cystitis in women in UK guidance (NICE NG109), as long as your kidneys work well enough. It concentrates in the urine, resistance to it is uncommon, and the usual course is one 100mg modified-release capsule twice a day with food for 3 days.
Get Cystitis Treatment Online
Access Doctor is a GPhC-registered pharmacy (#9011198). If you’re a woman aged 18 to 64 with cystitis symptoms, a pharmacist independent prescriber reviews your online consultation and prescribes an antibiotic if it’s suitable for you. Dispensed from our UK pharmacy. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start Cystitis Consultation →Who our online service is for. Access Doctor treats cystitis online for women aged 18 to 64 with typical symptoms who aren’t pregnant or breastfeeding. Men, anyone under 18, women aged 65 and over, and anyone who is pregnant or breastfeeding should see a GP, because a urine test and a different plan are usually needed. In England, many pharmacies treat uncomplicated cystitis in women aged 16 to 64 for free through NHS Pharmacy First.
What is nitrofurantoin?
Nitrofurantoin is a prescription-only antibiotic used almost only for the urinary tract. It’s been around for decades, and because it attacks bacteria in several ways at once, resistance to it has stayed uncommon. That’s why NICE guideline NG109 makes it a first-choice treatment for cystitis (a lower urinary tract infection, or UTI) in women who aren’t pregnant, alongside trimethoprim.
Unlike many antibiotics, nitrofurantoin concentrates in the urine rather than spreading through the bloodstream. That makes it good for bladder infections — but not suitable for infections that have reached the kidneys or elsewhere in the body.
How nitrofurantoin works
Once in the urine, nitrofurantoin is taken up by bacteria and turned into reactive compounds. These damage several targets at the same time — bacterial DNA and proteins among them — so the bacteria can’t survive.
Because it hits so many targets, a single genetic change is rarely enough for bacteria to resist it. That’s the main advantage over trimethoprim, which acts on one target and has seen resistance rise as a result.
Why it needs healthy kidneys: your kidneys clear nitrofurantoin into the urine, which is where it works. If your kidney function is reduced (an eGFR below 45), too little reaches the urine to clear the infection, and the medicine can build up in your body instead.
Dosage and how to take it
1
The usual dose
One 100mg modified-release capsule twice a day, morning and evening, usually for 3 days. If your prescriber gives you a 7-day course, take it for the full 7 days.
2
Take it with food
Swallow each capsule whole with water, with or just after a meal. Food helps your body absorb it and makes feeling sick less likely.
3
If you miss a dose
Take it when you remember, unless it’s nearly time for the next one. Never take two doses at once to make up.
4
Finish the course
Keep taking it even if you feel better after a day or two, so the infection doesn’t come back. Don’t keep leftovers.
Most women start to feel better within 24 to 48 hours. If your symptoms haven’t started to improve within 48 hours, or they get worse, contact your GP or NHS 111: the bacteria may be resistant, and a urine test can show which antibiotic will work.
6 or 14 capsules? Our nitrofurantoin 100mg MR capsules come as 6 capsules (a 3-day course) or 14 capsules (a 7-day course). The 3-day course is the usual treatment, and the prescriber supplies the 14-capsule pack only if they decide a longer course is needed.
Check it’s cystitis first. Burning and needing to pee often can also be caused by thrush, an STI, vaginal dryness after the menopause or bladder pain syndrome. Nitrofurantoin only helps when a urine infection is the cause, so never take leftover capsules “just in case”.
Why 3 days?
The product licence for nitrofurantoin modified-release capsules gives a 7-day course. UK guidance (NICE) recommends 3 days for women with uncomplicated cystitis who aren’t pregnant, because a shorter course works just as well with fewer side effects and less pressure on resistance. Prescribing a course that differs from the licence is called “off-label” — standard, accepted practice here, and your prescriber will tell you exactly how long to take it.
Macrobid, Macrodantin and generics
You may see nitrofurantoin under different names. They all contain the same active medicine:
| Name | What it is | How it’s taken |
|---|---|---|
| Nitrofurantoin 100mg MR (generic) | The usual form dispensed in the UK: modified-release (also called prolonged-release) capsules | Twice a day |
| Macrobid | A brand of the modified-release capsule | Twice a day, the same as the generic |
| Macrodantin and other standard capsules | Immediate-release forms | More often each day; your prescriber will explain |
Side effects of nitrofurantoin
Most people take a short course with few or no problems. The side effects people notice most are:
- Feeling sick or losing your appetite: taking each capsule with food helps a lot.
- Headache or dizziness: usually mild and short-lived. Don’t drive if you feel dizzy.
- Dark yellow or brown urine: this is harmless and stops after the course.
- Diarrhoea: usually mild. Get help the same day if it’s severe, watery or bloody.
- Thrush: antibiotics can trigger it. See our guide to thrush after antibiotics.
Serious reactions are rare. A lung reaction can occasionally start within days of the first dose, with a fever, chills, cough, chest pain or breathlessness. Longer-term lung, liver and nerve problems are mostly linked to months of use — for example for prevention — rather than a 3-day course.
Stop taking nitrofurantoin and get help straight away if you develop a new cough, chest pain or breathlessness, yellow skin or eyes, numbness, tingling or weakness in your hands or feet, or signs of a serious allergic reaction such as swelling of the face or throat, difficulty breathing or a widespread rash. Call 999 for difficulty breathing.
Who shouldn’t take nitrofurantoin
- Reduced kidney function (an eGFR below 45). It won’t reach high enough levels in the urine to work, so trimethoprim or another antibiotic is usually chosen instead.
- G6PD deficiency. An inherited condition in which nitrofurantoin can break down red blood cells.
- Acute porphyria, or a previous reaction to nitrofurantoin, including lung or liver problems.
- Late pregnancy. It must not be used at term or during labour, because it can affect the baby’s red blood cells. Any urine infection in pregnancy needs a urine test, so see your GP or midwife the same day.
- Breastfeeding: see your GP or a pharmacist, as nitrofurantoin passes into breast milk in small amounts.
Tell the prescriber if you have lung, liver or nerve problems, diabetes, anaemia or a vitamin B deficiency, as these can raise the risk of side effects. If nitrofurantoin isn’t right for you, trimethoprim is the other first-choice antibiotic: see our trimethoprim guide.
Interactions, CanesOasis and alcohol
| Medicine or product | Why it matters |
|---|---|
| Cystitis sachets that make urine less acidic, such as CanesOasis (sodium citrate) or potassium citrate | They reduce how well nitrofurantoin works. Don’t use them while you’re taking it. |
| Indigestion remedies containing magnesium trisilicate | Can reduce how much nitrofurantoin you absorb |
| Probenecid or sulfinpyrazone (used for gout) | Can stop nitrofurantoin reaching the urine and make side effects more likely |
| Acetazolamide | Makes urine less acidic, which can reduce how well nitrofurantoin works |
Alcohol: there’s no direct interaction, but alcohol can make sickness and dizziness worse and irritate your bladder, which can make cystitis feel worse. Keep it to a minimum until you’ve finished the course.
Contraception: nitrofurantoin doesn’t reduce the effect of hormonal contraception. If you’re sick or have severe diarrhoea, follow the missed-pill advice in your pill’s leaflet.
Nitrofurantoin or trimethoprim?
Both are first-choice antibiotics for cystitis in UK guidance. Nitrofurantoin is often preferred because resistance to it is less common, but it isn’t suitable if your kidneys don’t work well. Trimethoprim is a good choice if you haven’t taken it in the last 3 months and nitrofurantoin doesn’t suit you. The prescriber decides, based on your kidney health, recent antibiotics, other medicines and allergies. Our guide to UTI antibiotics in the UK compares them side by side.
Preventing repeated UTIs
NICE defines recurrent UTIs as 2 or more in 6 months, or 3 or more in 12 months. If that’s you, see your GP rather than ordering treatment again online. They can send a urine sample for culture and look for a cause.
A GP may sometimes prescribe a low dose of nitrofurantoin to prevent infections, either every night or as a single dose after a trigger such as sex. This is only started and reviewed by a GP, because long-term use carries a small risk of lung, liver and nerve problems.
Not something to start yourself: never use leftover nitrofurantoin to prevent infections. Repeated UTIs need a proper review, which may include a urine culture and, for some women, further tests.
Getting nitrofurantoin online
Nitrofurantoin is prescription-only, but you don’t always need a GP appointment. In England, many pharmacies treat uncomplicated cystitis in women aged 16 to 64 for free through NHS Pharmacy First. If you’re a woman aged 18 to 64 and would prefer to order online, our cystitis treatment online service works like this:
1
Complete the consultation
Answer questions about your symptoms, your health, your kidneys, the other medicines you take and any recent antibiotics or urine infections.
2
A prescriber reviews it
A GPhC-registered pharmacist independent prescriber checks that nitrofurantoin is safe and suitable for you, in line with NICE guidance. If it isn’t, they may offer trimethoprim or tell you where to go instead.
3
Dispatch and delivery
Dispensed from our UK pharmacy in plain packaging with a patient information leaflet. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Cystitis treatment from Access Doctor
Both first-choice antibiotics are available after an online consultation. The prescriber decides which one suits you, and the course length.
Antibiotic · Rx · first choice (NICE)
Nitrofurantoin 100mg MR capsules
One capsule twice a day with food, usually for 3 days. Not suitable if your kidneys don’t work well. From £12.99.
View product →Antibiotic · Rx · first choice (NICE) if resistance risk is low
Trimethoprim 200mg tablets
One tablet twice a day, usually for 3 days. Not if you’ve taken it in the last 3 months. From £12.99.
View product →Safety, confidentiality and free NHS options
Nitrofurantoin and trimethoprim are prescription-only medicines in the UK. Before anything is prescribed, a GPhC-registered pharmacist independent prescriber reviews your consultation, including your kidney health, the other medicines you take and any antibiotics you’ve had recently. We only prescribe an antibiotic when it’s appropriate: using antibiotics when they aren’t needed makes them work less well for everyone.
- Read the leaflet in the pack before you start.
- Don’t share antibiotics or keep leftovers for another time. Return unused tablets or capsules to a pharmacy.
- Report side effects to a pharmacist or doctor. You can also report them to the MHRA through the Yellow Card scheme.
Your consultation is confidential, and we only contact your GP if you agree. Access Doctor is a private service, and there are free NHS options:
- England: NHS Pharmacy First at a local pharmacy (women aged 16 to 64), your GP, or NHS 111.
- Scotland: Pharmacy First at a community pharmacy, or NHS 24 on 111.
- Wales: many community pharmacies can treat uncomplicated urine infections; ask your local pharmacy, or call NHS 111 Wales.
- Northern Ireland: your GP, or a community pharmacy for advice.
If you’ve had 2 urine infections in 6 months, or 3 in a year, see your GP rather than ordering again online. A urine culture can show which antibiotic will work, and your GP can look for a cause and talk about prevention.
Start Your Cystitis Consultation
Nitrofurantoin or trimethoprim, chosen by a GPhC-registered pharmacist independent prescriber in line with NICE guidance. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start Cystitis Consultation →For self-care alongside antibiotics, see how to treat cystitis. For symptoms and causes, see our cystitis guide.
Frequently Asked Questions
What is nitrofurantoin used for?
Nitrofurantoin is an antibiotic used mainly to treat cystitis, a lower urinary tract infection, and sometimes by GPs to prevent repeated UTIs. It’s a first-choice treatment for cystitis in women who aren’t pregnant because it concentrates in the urine and resistance to it is uncommon. It isn’t used for kidney infections, because it doesn’t reach effective levels in the blood or kidney tissue.
What is the dose of nitrofurantoin for a UTI?
For cystitis in a woman who isn’t pregnant, the usual dose is one 100mg modified-release capsule twice a day for 3 days, as NICE recommends. The product licence gives 7 days, and your prescriber may give a longer course if it’s needed. Take each dose with food, and finish the course even if you feel better.
Are Macrobid and Macrodantin the same as nitrofurantoin?
Yes. They’re brand names for nitrofurantoin. Macrobid is a modified-release capsule taken twice a day, like the generic 100mg MR capsule most often dispensed in the UK. Macrodantin is an immediate-release form that’s taken more often each day.
Why does nitrofurantoin turn urine dark?
Nitrofurantoin often turns urine dark yellow or brown. This is harmless and expected, and it goes back to normal after you finish the course. Get advice if you see blood in your urine, or if dark urine comes with yellow skin or eyes.
What are the common side effects of nitrofurantoin?
The side effects people notice most are feeling sick, loss of appetite, headache, dizziness, diarrhoea and dark urine. Taking each dose with food helps. Rarely, a lung reaction can start within days, with a fever, cough or breathlessness: stop taking it and get help straight away if this happens.
Who should not take nitrofurantoin?
It isn’t suitable if your kidney function is reduced (an eGFR below 45), because it won’t work well enough. It’s also avoided with G6PD deficiency, acute porphyria, a previous reaction to nitrofurantoin, and at the end of pregnancy. Our online service doesn’t treat anyone who is pregnant or breastfeeding: see your GP or midwife.
Can I take CanesOasis with nitrofurantoin?
No. CanesOasis and other cystitis sachets make urine less acidic, which reduces how well nitrofurantoin works. Don’t use them while you’re taking nitrofurantoin. Paracetamol, or ibuprofen if it’s suitable for you, can ease the pain instead.
How quickly does nitrofurantoin work?
Most women notice their symptoms starting to ease within 24 to 48 hours of the first dose. Finish the course even once you feel better. If your symptoms haven’t improved after 48 hours, or they get worse, contact your GP or NHS 111, as the bacteria may be resistant and you may need a urine test.
Can I drink alcohol while taking nitrofurantoin?
There’s no direct interaction, but alcohol can make sickness and dizziness worse and irritate your bladder, which can make cystitis feel worse. It’s best to avoid it, or keep it to a minimum, until you’ve finished the course and feel better.
Can I get nitrofurantoin online without seeing a GP?
Yes, if you’re a woman aged 18 to 64 with uncomplicated cystitis and you aren’t pregnant or breastfeeding. A GPhC-registered pharmacist independent prescriber reviews your online consultation and prescribes it if it’s suitable. Anyone with a fever, back pain or blood in the urine needs to see a GP or call NHS 111.
References
- NICE. Urinary tract infection (lower): antimicrobial prescribing (NG109). nice.org.uk
- Electronic Medicines Compendium. Nitrofurantoin 100mg prolonged-release capsules: Summary of Product Characteristics. medicines.org.uk
- NICE Clinical Knowledge Summaries. Urinary tract infection (lower) – women. cks.nice.org.uk
- NHS. Nitrofurantoin. nhs.uk
- NICE. Urinary tract infection (recurrent): antimicrobial prescribing (NG112). nice.org.uk
- UK Health Security Agency. English Surveillance Programme for Antimicrobial Utilisation and Resistance (ESPAUR) report. gov.uk
- NHS England. Pharmacy First (uncomplicated UTI in women aged 16 to 64). england.nhs.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.