Nitrofurantoin
Is It Right for You?
A complete guide to Nitrofurantoin — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Nitrofurantoin?
Nitrofurantoin is an antibiotic used almost exclusively to treat and prevent urinary tract infections (UTIs). It belongs to a class of antibiotics known as nitrofuran derivatives and works by damaging the genetic material and metabolic processes of bacteria within the urinary tract, preventing them from surviving and reproducing.
First introduced in the 1950s, nitrofurantoin remains one of the most commonly prescribed antibiotics for uncomplicated lower UTIs in the UK. It is available in two main formulations: immediate-release capsules (Macrodantin) and modified-release capsules (Macrobid), the latter being taken twice daily rather than four times, making it more convenient for patients. It is not suitable for treating upper urinary tract infections such as kidney infections (pyelonephritis).
Nitrofurantoin is a prescription-only medication in the UK. A licensed clinician must assess your symptoms and medical history before it can be prescribed – which can now be done quickly and conveniently through a telehealth consultation.
What Conditions Is Nitrofurantoin Used For?
Nitrofurantoin is prescribed specifically for infections within the urinary tract:
The most common indication; treats bacterial cystitis in adults, including women and men.
Low-dose nitrofurantoin is sometimes used as long-term prophylaxis (prevention) in patients who suffer from frequent UTIs.
Bacteria detected in the urine during pregnancy without symptoms may require treatment to prevent complications; nitrofurantoin is one of the preferred options in early-to-mid pregnancy.
A single dose taken after sexual intercourse may be prescribed for those whose UTIs are triggered by sexual activity.
Nitrofurantoin concentrates almost entirely in the urine and is not effective for infections elsewhere in the body, including kidney infections, bloodstream infections, or respiratory infections. If you have symptoms of a kidney infection – such as high fever, back or flank pain, or rigors – you must seek urgent medical assessment.
How Does Nitrofurantoin Work?
Nitrofurantoin is a prodrug, meaning it is converted into an active form after being absorbed. Bacteria within the urinary tract reduce nitrofurantoin using their own enzymes, generating highly reactive compounds that simultaneously attack multiple bacterial targets – including DNA, ribosomes, and the enzymes responsible for bacterial metabolism and cell wall synthesis.
Because nitrofurantoin attacks bacteria through several mechanisms at once, bacterial resistance to it is relatively rare compared to many other antibiotics. This multi-target approach makes it difficult for bacteria to develop resistance through a single genetic mutation.
Nitrofurantoin achieves very high concentrations in the urine – far higher than in the blood or other tissues – which is why it is effective specifically for urinary tract infections and not for infections elsewhere in the body. It is active against most strains of Escherichia coli (the most common cause of UTIs), Enterococcus faecalis, Staphylococcus saprophyticus, and Klebsiella species.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Always take nitrofurantoin with food or milk. Taking it with food significantly improves absorption and reduces the risk of nausea and stomach upset, which are the most common side effects.
Swallow capsules whole – do not crush or chew them.
Drink plenty of fluids during treatment to help flush bacteria from the urinary tract. Your urine may turn yellow or brown during treatment – this is harmless and expected.
Always complete the full prescribed course even if symptoms resolve within the first day or two. Stopping early allows surviving bacteria to return and may contribute to antibiotic resistance.
Side Effects of Nitrofurantoin
Most side effects are mild and resolve once treatment is complete. Serious side effects are uncommon but require prompt medical attention.
- Nausea or upset stomach (less common when taken with food)
- Vomiting
- Diarrhoea
- Loss of appetite
- Headache
- Dizziness or drowsiness
- Discolouration of urine (yellow to brown) – harmless
- both short-term and long-term use)
- Hepatotoxicity (liver damage) – jaundice, dark urine, severe fatigue, upper abdominal pain
- Peripheral neuropathy – numbness, tingling, or pain in the hands or feet (more likely with prolonged use or kidney impairment)
- Severe allergic reaction – hives, facial swelling, difficulty breathing
- Haemolytic anaemia – particularly in patients with G6PD deficiency
- Stevens-Johnson Syndrome – rare but serious skin reaction
Nitrofurantoin must not be used in patients with significantly reduced kidney function (eGFR below 45 mL/min). In these patients, the drug does not reach adequate concentrations in the urine to be effective, and toxic levels may accumulate in the blood, increasing the risk of serious side effects including peripheral neuropathy and pulmonary toxicity.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting nitrofurantoin.
Significantly reduce the absorption of nitrofurantoin from the gut, potentially rendering the antibiotic ineffective. Avoid concurrent use.
These gout medications reduce the kidney excretion of nitrofurantoin, increasing blood levels and reducing urinary concentrations – decreasing effectiveness while raising the risk of toxicity. Concurrent use should be avoided.
Antagonistic interaction – these antibiotics may reduce the effectiveness of nitrofurantoin. Do not co-prescribe for UTI treatment.
Some antacids can interfere with nitrofurantoin absorption. Space doses apart where possible and inform your clinician of any antacid use.
As with other antibiotics, there is a theoretical possibility that nitrofurantoin may reduce the efficacy of hormonal contraception, though evidence is limited. Using a backup contraceptive method during treatment is advisable.
Concurrent use of other medications that carry a risk of peripheral neuropathy may increase that risk when combined with nitrofurantoin. Inform your clinician of your full medication list.
Important Warnings
Acute pulmonary reactions (lung inflammation) can occur, typically within the first week of treatment. Symptoms include sudden onset shortness of breath, cough, and fever. Chronic pulmonary reactions are rarer but can occur with prolonged use and may present with gradual breathlessness. Stop taking nitrofurantoin and seek immediate medical attention if you develop any breathing difficulties during treatment.
Serious liver reactions, including hepatitis and cholestatic jaundice, have been reported. Risk is higher with long-term use. Stop treatment and contact a clinician immediately if you develop jaundice (yellowing of the skin or eyes), dark urine, or severe fatigue.
Long-term use of nitrofurantoin, particularly in patients with kidney impairment, diabetes, anaemia, electrolyte imbalances, or vitamin B deficiency, increases the risk of peripheral neuropathy. Report any numbness, tingling, or weakness in the limbs to your clinician promptly.
Nitrofurantoin should be used with extreme caution – or avoided entirely – in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, as it can cause haemolytic anaemia in these individuals. Always disclose any known G6PD deficiency before starting treatment.
Nitrofurantoin is generally considered safe during the first and second trimesters of pregnancy. It should be avoided at term (38–42 weeks) and during labour, as it may cause haemolytic anaemia in the newborn. It passes into breast milk in small amounts; use with caution if breastfeeding, particularly if the infant has known G6PD deficiency or is premature.
Older patients are at higher risk of adverse effects, including pulmonary and hepatic reactions. Kidney function should be assessed before prescribing nitrofurantoin to elderly patients, as reduced eGFR is common in this group and may contraindicate use.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Nitrofurantoin FAQs
Yes. A licensed clinician can evaluate your symptoms via a telehealth consultation and prescribe nitrofurantoin if it is clinically appropriate. Prescriptions are typically sent to your preferred pharmacy the same day, often within minutes of your consultation.
Most patients notice an improvement in UTI symptoms – such as reduced burning, urgency, and frequency – within 24 to 48 hours of starting treatment. It is important to complete the full course even if symptoms resolve quickly, to ensure the infection is fully cleared.
No. Nitrofurantoin is only suitable for lower urinary tract infections (cystitis). It does not reach effective concentrations in kidney tissue and must not be used for pyelonephritis (kidney infection). Symptoms of a kidney infection – including high fever, back pain, and rigors – require urgent medical assessment and a different antibiotic.
This is a harmless and expected side effect caused by the drug itself and its metabolites being excreted in the urine. It does not indicate anything is wrong. Your urine will return to its normal colour once you finish the course.
Yes. Taking nitrofurantoin with food or milk significantly improves how well it is absorbed and reduces the likelihood of nausea. It should always be taken with a meal or snack.
Nitrofurantoin is generally considered safe during the first and second trimesters of pregnancy and is commonly prescribed for UTIs during this period. However, it should be avoided in the final weeks of pregnancy (from 38 weeks onwards) due to the risk of haemolytic anaemia in the newborn. Always consult your clinician before starting any medication during pregnancy.
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and resume your regular schedule. Do not take a double dose to make up for a missed one.
There is no known dangerous interaction between alcohol and nitrofurantoin. However, alcohol can irritate the bladder and potentially worsen UTI symptoms. It is generally advisable to avoid alcohol while you are recovering from an infection.
Both contain nitrofurantoin but in different formulations. Macrodantin is immediate-release and is taken four times daily for 7 days. Macrobid is a modified-release formulation taken twice daily for 5 days, which many patients find more convenient. Your clinician will prescribe whichever is most appropriate for your circumstances.
Yes. While UTIs are far more common in women, men can also develop lower urinary tract infections and may be prescribed nitrofurantoin. However, UTIs in men may be more likely to have an underlying cause (such as prostate enlargement), so a clinician will typically investigate further.