A urinary (UTI) antibiotic
Nitrofurantoin
A first-line antibiotic for lower urinary tract infections that works in the bladder and urine — not for kidney infections, and avoided in significant kidney impairment.
What is Nitrofurantoin?
Nitrofurantoin is a first-line antibiotic for lower urinary tract infections (UTIs) — the common 'water infection' affecting the bladder. It becomes concentrated in the urine, where it acts directly on the bacteria causing the infection.
Education and reference only. This is a plain-language guide to Nitrofurantoin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Nitrofurantoin is a first-line antibiotic for lower urinary tract infections (UTIs) — the common "water infection" affecting the bladder. It is concentrated in the urine, where it reaches the bacteria causing the infection. It is taken as a short course. Because it acts in the bladder and urine rather than throughout the body, it is used for lower UTIs but not for kidney infections or infections elsewhere.
How it works
After it is swallowed, nitrofurantoin is absorbed and then concentrated in the urine as the kidneys filter it out. In the urine it damages several vital parts of the bacterial cell at once, which kills the bacteria causing the bladder infection. This focus on the urinary tract is also its limitation: it does not build up to useful levels in the bloodstream or kidney tissue, so it cannot treat a kidney infection (pyelonephritis) or infections in other parts of the body. It needs reasonably working kidneys to reach the urine in the first place.
Company & origin
Originated / developed by: Eaton Laboratories (Norwich Pharmacal, USA; now defunct).
Nitrofurantoin is a synthetic urinary antibacterial patented in 1952 by Eaton Laboratories of Norwich, New York (part of the Norwich Pharmacal company), entering clinical use around 1953 under the brand Furadantin. It is now sold generically and as Macrobid and Macrodantin.
Practical use
How to take Nitrofurantoin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it with food or a meal to improve absorption and reduce stomach upset.
- Complete the full course as prescribed, even once symptoms settle, to clear the infection.
- Space the doses evenly through the day as directed.
- Do not be alarmed if it turns your urine a darker, yellow-brown colour, which is harmless.
- If you miss a dose, take it when you remember unless the next is nearly due; do not double up.
- Report any new cough, breathlessness, numbness or tingling, especially with longer use, and seek advice.
Weighing it up
Advantages & disadvantages of Nitrofurantoin
Advantages
- A reliable first-choice treatment for uncomplicated bladder infections.
- Concentrates in the urine, targeting the infection where it is needed.
- Resistance remains relatively low for common UTI bacteria.
- Usually a short course taken by mouth at home.
Disadvantages
- Does not work well if the kidneys are not functioning adequately, as it cannot reach effective levels in the urine.
- Generally avoided near the end of pregnancy because of a risk to the baby.
- Avoided in people with G6PD deficiency, and in the final weeks of pregnancy, because it can cause breakdown of red blood cells.
- Can cause nausea and, rarely with longer use, lung or nerve problems.
- Only suitable for lower UTIs, not for kidney infections or those that have spread.
Practical use
Good to know
Nitrofurantoin is one of the recommended first choices for an uncomplicated lower UTI. A harmless but surprising effect is that it can turn the urine a brown or dark yellow colour — this is normal and not a cause for concern. It needs reasonably good kidney function to work, so it is avoided when the kidneys are significantly impaired, and it is avoided towards the end of pregnancy (near the due date) because of a risk to the newborn. Taking it with food helps absorption and reduces stomach upset. It is taken exactly as prescribed and finished as advised, in keeping with using antibiotics responsibly. Long-term or repeated use can, rarely, affect the lungs, liver or nerves, so prolonged courses are monitored.
Who should not take it / use with caution
- People with significantly reduced kidney function — it may not reach the urine well enough to work and side effects become more likely.
- Women at the very end of pregnancy (around the time of delivery) and babies in the first few weeks of life, because of a risk of a blood problem in the newborn.
- People with the inherited condition G6PD deficiency, and used with care in long-term use because of rare lung, liver and nerve effects.
Monitoring
- Whether the UTI symptoms are settling
- Kidney function (to confirm it is suitable)
- For breathing, liver or nerve symptoms with longer or repeated courses
Side effects
- Brown or dark-coloured urine — harmless and expected.
- Feeling sick, loss of appetite or stomach upset, which is eased by taking it with food.
- Rarely, and mainly with long-term use, effects on the lungs (cough, breathlessness), the liver, or the nerves (tingling or numbness in the hands and feet) — report these; and, rarely, a serious allergic reaction (call 999 for swelling of the face or throat, wheeze or collapse).
Key interactions
- Certain antacids containing magnesium can reduce its absorption.
- Some medicines used for gout (probenecid) can affect how it is handled by the body.
- Generally few major interactions compared with some antibiotics, but always tell your pharmacist what else you take.
Available as: Capsules and tablets, including modified-release capsules, and an oral suspension (liquid) for those who cannot swallow capsules.
Answers
Nitrofurantoin: frequently asked questions
Why has my urine turned brown?
Nitrofurantoin commonly colours the urine brown or dark yellow as it is removed by the kidneys. This is completely harmless and expected, and it goes back to normal once you finish the course. It is not a sign that anything is wrong.
Can nitrofurantoin treat a kidney infection?
No. Nitrofurantoin works by concentrating in the bladder and urine, so it treats lower urinary tract (bladder) infections but does not reach the kidney tissue or bloodstream in useful amounts. A kidney infection needs a different antibiotic, so tell your prescriber if you have back or flank pain, a high temperature or feel generally very unwell.
Why is it not suitable if my kidneys are not working well?
Nitrofurantoin relies on healthy kidneys to filter it into the urine, where it does its job. If kidney function is significantly reduced, not enough reaches the urine to clear the infection, and side effects become more likely — so a different antibiotic is chosen instead.
Is it safe in pregnancy?
It can often be used during much of pregnancy, but it is avoided right at the end (near your due date) because of a small risk of a blood problem in the newborn. Always tell your prescriber if you are pregnant or might be, so the timing and choice of antibiotic can be made safely.
What is the difference between nitrofurantoin, Macrobid and Macrodantin?
They all contain the same active ingredient, nitrofurantoin — Macrobid and Macrodantin are brand names (Macrobid is a modified-release form). Generic nitrofurantoin contains the identical active ingredient.
The wider class
About UTI antibiotics
Nitrofurantoin belongs to the uti antibiotics class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Nitrofurantoin.
- electronic Medicines Compendium (SmPC): Nitrofurantoin (Macrobid, Macrodantin).
- NICE CKS: Nitrofurantoin.
- NICE: Urinary tract infection (lower) — antimicrobial prescribing.
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