UTI Antibiotics UK: Nitrofurantoin vs Trimethoprim, and Which Is Used When
The antibiotics used for cystitis and urine infections in the UK: how nitrofurantoin and trimethoprim compare, other options, how long courses last, and what helps alongside them.
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 is not suitable in these situations.
Key fact: UK guidance (NICE NG109) recommends two first-choice antibiotics for cystitis in women who aren’t pregnant: nitrofurantoin, if your kidneys work well enough, and trimethoprim, if the risk of resistance is low. Both are usually taken for 3 days, and both are prescription-only.
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.
The quick answer
Most urine infections in women are cystitis: a bladder infection, usually caused by E. coli bacteria from the gut. For women who aren’t pregnant, NICE recommends one of two antibiotics:
- Nitrofurantoin 100mg modified-release, twice a day with food for 3 days, if your kidney function is good enough (an eGFR of 45 or more).
- Trimethoprim 200mg, twice a day for 3 days, if the risk of resistance is low: for example, you haven’t taken it in the last 3 months.
Neither is “better” for everyone. Nitrofurantoin is often preferred because bacteria are less often resistant to it, but trimethoprim is a good choice when nitrofurantoin doesn’t suit you. The prescriber decides, based on your kidney health, recent antibiotics, other medicines and allergies.
Nitrofurantoin (Macrobid)
Nitrofurantoin is used almost only for the urinary tract. Your kidneys concentrate it in the urine, right where a bladder infection is, and it damages several targets inside bacteria at once, so resistance to it has stayed uncommon. Because so little reaches the blood, it isn’t used for kidney infections or infections elsewhere in the body.
- One 100mg modified-release capsule twice a day, with or just after food, usually for 3 days.
- Often turns urine dark yellow or brown. This is harmless and stops after the course.
- Not suitable if your kidney function is reduced (eGFR below 45), or if you have G6PD deficiency or acute porphyria.
- Don’t take it with cystitis sachets such as CanesOasis, which make it work less well.
- Also sold as Macrobid. Macrodantin is an older, immediate-release form.
Our nitrofurantoin guide covers the dose, side effects and who should avoid it.
Trimethoprim
Trimethoprim blocks an enzyme bacteria need to make folate, so they can’t multiply. It was once the usual first choice for UTIs in the UK. Heavy use over decades means bacteria are now more often resistant to it, so NICE recommends it when the risk of resistance is low, rather than for everyone.
- One 200mg tablet twice a day, with or without food, usually for 3 days.
- Usually avoided if you’ve taken it in the last 3 months, because resistance is more likely.
- Must not be used in the first 3 months of pregnancy, because it affects folate.
- Interacts with methotrexate, warfarin and medicines that raise potassium, such as some blood pressure tablets.
Our trimethoprim guide covers how it’s taken and how quickly it works, and trimethoprim side effects covers what to expect.
Nitrofurantoin vs trimethoprim: side by side
| Nitrofurantoin | Trimethoprim | |
|---|---|---|
| NICE NG109 | First choice if eGFR is 45 or more | First choice if resistance risk is low |
| How it works | Damages bacterial DNA and proteins (several targets) | Blocks folate production (one target) |
| Usual dose | 100mg modified-release twice a day | 200mg twice a day |
| Usual course for cystitis | 3 days | 3 days |
| Food | Take with food | With or without food |
| Resistance | Uncommon | More common, especially after recent use |
| Avoid if | Reduced kidney function; G6PD deficiency; at the end of pregnancy | Used in the last 3 months; early pregnancy; methotrexate |
| Worth knowing | Turns urine dark (harmless); don’t use with cystitis sachets | Can raise potassium; interacts with warfarin |
| Penicillin allergy | Not a penicillin | Not a penicillin |
How the choice is made
Most cystitis is treated before a urine culture result is available, so the first antibiotic is chosen on what’s most likely to work and be safe for you. The prescriber weighs up:
- Your kidney function, which decides whether nitrofurantoin can work.
- Antibiotics in the last 3 months, especially trimethoprim, and whether they worked.
- Allergies and previous reactions to either medicine.
- Pregnancy and breastfeeding, which change both the choice and where you should be treated.
- Your other medicines, particularly methotrexate, warfarin and medicines that raise potassium.
- Any urine culture result, which shows exactly which antibiotics the bacteria respond to.
Check it’s cystitis first. Burning and needing to pee often can also be caused by thrush, an STI such as chlamydia, vaginal dryness after the menopause or bladder pain syndrome. If you have unusual discharge or itching, or you’ve had a new sexual partner, an antibiotic for cystitis may not help.
Other antibiotics, pregnancy and men
Nitrofurantoin and trimethoprim cover most cystitis in women. A GP may use other antibiotics in some situations, often after a urine culture:
| Situation | What usually happens (NICE NG109) |
|---|---|
| No better after 48 hours, or the first choice isn’t suitable | A urine culture, then a second-choice antibiotic such as pivmecillinam or fosfomycin, or nitrofurantoin if it wasn’t used first |
| Pregnancy | A urine culture and a 7-day course, usually nitrofurantoin (not near the end of pregnancy). Trimethoprim isn’t recommended. See your GP or midwife the same day. |
| Men | A 7-day course of trimethoprim or nitrofurantoin, after a GP assessment and urine culture |
| Signs of a kidney infection | Different antibiotics, assessed in person the same day. Nitrofurantoin doesn’t work for kidney infections. |
How long UTI antibiotics take to work
With the right antibiotic, most women notice their symptoms starting to ease within 24 to 48 hours, and they usually settle by the end of the course. Mild discomfort can take a few more days to go completely.
If your symptoms haven’t started to improve within 48 hours, or they get worse, contact your GP or NHS 111. No improvement usually means the bacteria are resistant, and a urine culture shows which antibiotic will work. Don’t start a second course of the same antibiotic, or leftover tablets, without advice.
Taking your antibiotic properly
1
Take it at regular times
Both antibiotics are taken twice a day, about 12 hours apart, usually morning and evening.
2
Food
Take nitrofurantoin with food. Trimethoprim can be taken with or without food.
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.
4
Finish the course
Keep going even if you feel better after a day or two, so the infection doesn’t come back.
Contraception: neither antibiotic reduces the effect of the combined pill, the mini pill or other hormonal contraception. If you’re sick or have severe diarrhoea, follow the missed-pill advice in your pill’s leaflet.
Alcohol: neither has a direct interaction, but alcohol can irritate the bladder and make sickness worse, so keep it to a minimum until you’ve finished.
Antibiotic resistance and why it matters
Every time an antibiotic is used, the bacteria that survive it are more likely to be resistant next time. UK surveillance (UKHSA ESPAUR) has tracked rising trimethoprim resistance in urine infections over many years, which is why UK guidance changed. Nitrofurantoin resistance has stayed uncommon, partly because it attacks bacteria in several ways at once.
You can help keep these antibiotics working:
- Only take an antibiotic when a prescriber thinks you need one. Mild cystitis often settles by itself within a few days.
- Take the course exactly as prescribed, and finish it.
- Never use leftover antibiotics for a new infection: the bacteria may be different, or resistant.
- Never share antibiotics, even with someone who has the same symptoms.
- Return unused tablets or capsules to a pharmacy.
Over-the-counter options
There are no over-the-counter antibiotics for cystitis in the UK. These can help with symptoms, but they don’t clear an infection:
- Paracetamol, or ibuprofen if it’s suitable for you, to ease pain while the infection clears.
- Cystitis sachets such as CanesOasis (sodium citrate) make urine less acidic and may ease burning. NICE found no good evidence that they treat cystitis. They’re for women only, aren’t suitable for everyone (for example in pregnancy, or with heart disease, high blood pressure, diabetes or kidney disease), and mustn’t be used with nitrofurantoin.
- Cranberry products: NICE found no good evidence that they treat cystitis.
Our guide to how to treat cystitis covers self-care in more detail.
Getting UTI antibiotics in the UK
Nitrofurantoin and trimethoprim are prescription-only, but you don’t always need a GP appointment:
- NHS Pharmacy First (England): many pharmacies assess and treat uncomplicated cystitis in women aged 16 to 64 for free. Scotland and Wales have similar pharmacy schemes.
- Your GP or NHS 111, especially if you’re pregnant, a man, 65 or over, keep getting UTIs, or have signs of a kidney infection.
- Online: if you’re a woman aged 18 to 64 with typical symptoms, our cystitis treatment online service lets a GPhC-registered pharmacist independent prescriber choose the right antibiotic for you.
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 symptoms, causes and when to get help, see our cystitis guide.
Frequently Asked Questions
What is the best antibiotic for a UTI in the UK?
For cystitis in women who aren’t pregnant, NICE recommends two first choices: nitrofurantoin, if your kidneys work well enough, and trimethoprim, if the risk of resistance is low. Nitrofurantoin is often preferred because resistance to it is less common. The best choice for you depends on your kidney health, recent antibiotics, other medicines and allergies.
What is the NICE first-line antibiotic for cystitis?
NICE NG109 lists two first-choice antibiotics for cystitis in women who aren’t pregnant: nitrofurantoin 100mg modified-release twice a day for 3 days, if eGFR is 45 or more, and trimethoprim 200mg twice a day for 3 days, if the risk of resistance is low. Pivmecillinam and fosfomycin are second choices.
Is trimethoprim better than nitrofurantoin?
Not usually. Both are first-choice antibiotics for cystitis and work well when the bacteria are sensitive. Bacteria are more often resistant to trimethoprim, so nitrofurantoin is often chosen first. Trimethoprim is a good option if you haven’t taken it in the last 3 months, or if nitrofurantoin isn’t suitable, for example because your kidney function is reduced.
How long is a course of UTI antibiotics?
For cystitis in women who aren’t pregnant, NICE recommends 3 days of either nitrofurantoin or trimethoprim. Pregnant women and men usually need 7 days, after a urine test. Your prescriber may give a longer course in some situations, and you should always finish the course you’re given.
How quickly do UTI antibiotics work?
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, as the bacteria may be resistant and you may need a urine test and a different antibiotic.
Can I buy UTI antibiotics over the counter in the UK?
No. Nitrofurantoin and trimethoprim are prescription-only. In England, many pharmacies can treat uncomplicated cystitis in women aged 16 to 64 for free through Pharmacy First. You can also see your GP, or use a regulated online service. Cystitis sachets and painkillers are sold over the counter, but they don’t treat the infection.
Can I take nitrofurantoin and trimethoprim together?
No. They aren’t taken together for cystitis. If the first antibiotic doesn’t work, a prescriber may switch you to another one, ideally guided by a urine culture. Never add a second antibiotic to a course without a prescriber’s advice.
Do UTI antibiotics affect the contraceptive pill?
No. Nitrofurantoin and trimethoprim don’t reduce the effect of hormonal contraception. If you’re sick or have severe diarrhoea, the pill may not be absorbed properly, so follow the missed-pill advice in your pill’s leaflet.
Which UTI antibiotics are used in pregnancy?
A UTI in pregnancy needs same-day advice from your GP or midwife, a urine culture and usually a 7-day course. Nitrofurantoin is usually the first choice, but not near the end of pregnancy. Trimethoprim isn’t recommended. Our online service doesn’t treat anyone who is pregnant.
Can cystitis sachets be used with antibiotics?
Not with nitrofurantoin, because sachets such as CanesOasis make urine less acidic and reduce how well it works. NICE also found no good evidence that sachets help cystitis. Paracetamol, or ibuprofen if it’s suitable for you, is a better way to ease the pain.
References
- NICE. Urinary tract infection (lower): antimicrobial prescribing (NG109). nice.org.uk
- NICE Clinical Knowledge Summaries. Urinary tract infection (lower) – women. cks.nice.org.uk
- Electronic Medicines Compendium. Nitrofurantoin 100mg prolonged-release capsules: Summary of Product Characteristics. medicines.org.uk
- Electronic Medicines Compendium. Trimethoprim: Summary of Product Characteristics (50mg/5ml oral suspension; same active ingredient as the 200mg tablets). medicines.org.uk
- UK Health Security Agency. English Surveillance Programme for Antimicrobial Utilisation and Resistance (ESPAUR) report. gov.uk
- NICE. Urinary tract infection (recurrent): antimicrobial prescribing (NG112). nice.org.uk
- NHS. Cystitis. nhs.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.