Nitrofurantoin (Furadantin)
Urinary antibiotic for the treatment and prevention of urinary tract infections
Nitrofurantoin is a prescription antibiotic used specifically to treat and prevent urinary tract infections (UTIs). It belongs to the nitrofuran class of antibiotics and works by damaging bacterial DNA and other cellular processes, making it effective against most bacteria that cause bladder infections. Nitrofurantoin is one of the most commonly prescribed antibiotics for uncomplicated lower UTIs worldwide and is listed on the WHO Model List of Essential Medicines. It should always be taken with food to improve absorption and reduce side effects.
Quick Facts
Key Takeaways
- Nitrofurantoin is a first-line antibiotic specifically designed for uncomplicated lower urinary tract infections (bladder infections) and is not effective for kidney infections.
- Always take nitrofurantoin with food or milk to improve absorption by up to 40% and significantly reduce nausea.
- A typical adult course is 50–100 mg three to four times daily for 5–7 days; complete the full course even if symptoms improve.
- Do not use in patients with severe kidney impairment (eGFR <30 mL/min), neonates under 1 month, or those with G6PD deficiency.
- Seek immediate medical attention if you develop breathing difficulties, persistent cough, yellowing of the skin, or tingling in the hands and feet.
What Is Nitrofurantoin and What Is It Used For?
Nitrofurantoin is a synthetic antibacterial agent belonging to the nitrofuran class of antimicrobials. It has been used clinically since the 1950s and remains one of the most widely prescribed medications for uncomplicated urinary tract infections worldwide. The World Health Organization includes nitrofurantoin on its Model List of Essential Medicines, recognising it as one of the most important medications needed in a basic health system.
Unlike many other antibiotics, nitrofurantoin achieves its therapeutic effect exclusively in the urinary tract. After oral administration, it is rapidly absorbed from the gastrointestinal tract and concentrated in the urine by the kidneys, reaching bactericidal concentrations in the bladder. Because serum and tissue concentrations remain low, nitrofurantoin is not suitable for treating systemic infections, kidney infections (pyelonephritis), or infections outside the urinary tract.
The drug works through a unique multi-target mechanism of action. Bacterial enzymes called nitroreductases reduce nitrofurantoin to highly reactive intermediates that attack multiple sites within the bacterial cell, including ribosomal proteins, DNA, RNA, and cell wall components. This multi-target approach explains why bacterial resistance to nitrofurantoin remains remarkably low even after decades of clinical use — a significant advantage in an era of increasing antimicrobial resistance.
Nitrofurantoin is effective against the majority of common urinary tract pathogens, including Escherichia coli (which causes approximately 80% of uncomplicated UTIs), Staphylococcus saprophyticus, Enterococcus faecalis, and many strains of Klebsiella and Enterobacter species. It is generally not active against Proteus, Serratia, or Pseudomonas species.
Primary Uses
Nitrofurantoin has two principal clinical applications in the management of urinary tract infections:
- Acute treatment of uncomplicated lower UTIs – A standard 5–7 day course effectively clears most bladder infections in women and men. International guidelines from the Infectious Diseases Society of America (IDSA) and the European Association of Urology (EAU) recommend nitrofurantoin as a first-line agent for uncomplicated cystitis.
- Long-term prophylaxis of recurrent UTIs – For patients who experience frequent recurrences (typically defined as three or more infections per year), low-dose nitrofurantoin taken once daily at bedtime can significantly reduce the frequency of infections. Prophylactic courses may extend for several months or even years under medical supervision.
Nitrofurantoin is effective only for lower urinary tract infections (cystitis / bladder infections). It should not be used for upper urinary tract infections (pyelonephritis / kidney infections), as it does not achieve adequate concentrations in renal tissue or the bloodstream. If you have symptoms of a kidney infection such as high fever, flank pain, or chills, seek prompt medical attention — a different antibiotic will be needed.
What Should You Know Before Taking Nitrofurantoin?
Before starting nitrofurantoin, it is essential to discuss your complete medical history with your prescribing physician. Certain conditions can increase the risk of serious side effects or render the medication ineffective. Your doctor needs a clear picture of your health to determine whether nitrofurantoin is the safest and most appropriate choice for your infection.
Contraindications
Nitrofurantoin must not be used in the following situations:
- Severe renal impairment – Patients with an estimated glomerular filtration rate (eGFR) below 30 mL/min should not receive nitrofurantoin. Inadequate kidney function means the drug cannot be sufficiently concentrated in the urine to be effective, and the risk of systemic toxicity increases.
- Neonates and infants under 1 month of age – Due to the immature enzyme systems in very young infants, nitrofurantoin carries a risk of haemolytic anaemia (destruction of red blood cells) in this age group.
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency – Patients with this inherited enzyme disorder are at significantly elevated risk of haemolytic anaemia when exposed to nitrofurantoin. G6PD deficiency is relatively common in populations of African, Mediterranean, Middle Eastern, and Southeast Asian descent.
- Known allergy – Do not take nitrofurantoin if you have previously experienced a hypersensitivity reaction to nitrofurantoin or any of the excipients in the formulation.
Warnings and Precautions
Inform your doctor before starting nitrofurantoin if you have any of the following conditions, as they may require closer monitoring or dosage adjustments:
- Diabetes mellitus – Patients with diabetes may be at increased risk of peripheral neuropathy (nerve damage in the hands and feet) when taking nitrofurantoin.
- Anaemia or vitamin B deficiency – These conditions may also predispose patients to peripheral neuropathy during treatment.
- Moderate renal impairment – Patients with an eGFR between 30–44 mL/min should only use nitrofurantoin for acute, uncomplicated UTIs when no safer alternative is available. Long-term prophylactic use is not recommended in this group.
- Liver disease – Nitrofurantoin has been associated with hepatotoxicity (liver damage), including both acute and chronic hepatitis. Patients with pre-existing liver conditions should be monitored closely.
- Lung disease – Pulmonary reactions, ranging from acute hypersensitivity pneumonitis to chronic interstitial fibrosis, have been reported with nitrofurantoin use, particularly during long-term therapy.
- Electrolyte imbalances – Conditions that disturb acid-base balance may increase the risk of peripheral neuropathy.
Stop taking nitrofurantoin and contact your doctor immediately if you experience any of the following symptoms of angioedema: swelling of the face, tongue, or throat; difficulty swallowing; hives combined with breathing difficulties. These may indicate a severe allergic reaction requiring urgent treatment.
Contact your doctor promptly if you notice fatigue, yellowing of the skin or eyes (jaundice), itching, skin rash, joint pain, abdominal discomfort, nausea, vomiting, loss of appetite, dark urine, or pale/grey-coloured stools. These symptoms may indicate a hepatic (liver) reaction that requires immediate assessment.
Pregnancy and Breastfeeding
Nitrofurantoin requires careful consideration during pregnancy and breastfeeding. The risks and benefits must be weighed individually by a healthcare professional:
- Pregnancy – Nitrofurantoin may be used during the second trimester of pregnancy when the benefit clearly outweighs the risk. However, it should be avoided at term (from 38 weeks of gestation) and during labour and delivery because of the theoretical risk of haemolytic anaemia in the newborn, whose red blood cell enzyme systems are immature. First-trimester use has also been associated with a small increase in birth defect risk in some epidemiological studies, though the absolute risk remains low.
- Breastfeeding – Nitrofurantoin passes into breast milk in small quantities. It should not be used during breastfeeding if the infant is under 1 month of age or has known or suspected G6PD deficiency. For older infants without G6PD deficiency, nitrofurantoin is generally considered compatible with breastfeeding.
Always consult your doctor or midwife before taking any medication during pregnancy or while breastfeeding.
Driving and Operating Machinery
Nitrofurantoin has no known clinically significant effects on the ability to drive or operate machinery. However, dizziness and drowsiness have been reported as rare side effects. If you experience these symptoms, avoid driving or operating heavy machinery until you know how the medication affects you.
Lactose Content
Some formulations of nitrofurantoin tablets (including the Furadantin brand) contain lactose monohydrate as an excipient. Patients with rare hereditary problems of galactose intolerance, total lactase deficiency, or glucose-galactose malabsorption should consult their doctor before taking these formulations.
How Does Nitrofurantoin Interact with Other Drugs?
Drug interactions can reduce the effectiveness of nitrofurantoin or increase the risk of adverse effects. It is critical to inform your prescribing physician and pharmacist about all medications you currently take, including prescription drugs, over-the-counter products, vitamins, and herbal supplements. The following interactions are clinically important:
Major Interactions
| Interacting Drug | Effect | Clinical Significance |
|---|---|---|
| Magnesium trisilicate antacids | Reduces absorption of nitrofurantoin by binding the drug in the gastrointestinal tract | Significantly decreased efficacy; avoid concurrent use or separate doses by at least 2 hours |
| Probenecid | Inhibits renal tubular secretion of nitrofurantoin, reducing urinary concentrations and increasing serum levels | Reduced therapeutic effect in urine and increased risk of systemic toxicity; avoid combination |
| Sulfinpyrazone | Same mechanism as probenecid — inhibits tubular secretion of nitrofurantoin | Reduced urinary concentration and increased systemic exposure; avoid combination |
| Quinolone antibiotics (e.g. nalidixic acid, norfloxacin) | Mutual antagonism — nitrofurantoin may reduce the effectiveness of quinolones and vice versa | Do not use concurrently; choose one agent |
Minor Interactions and Considerations
- Urine alkalinising agents (e.g. sodium bicarbonate, potassium citrate) – Alkalinisation of the urine can reduce the antibacterial activity of nitrofurantoin, as the drug is most effective in acidic urine (pH ≤5.5). Patients should be aware that cranberry juice or vitamin C supplements that acidify urine may theoretically enhance nitrofurantoin activity, though clinical evidence is limited.
- Oral typhoid vaccine (Ty21a) – Antibiotics including nitrofurantoin may reduce the effectiveness of live bacterial vaccines. The oral typhoid vaccine should ideally be completed before starting nitrofurantoin therapy.
- Other hepatotoxic drugs – Concurrent use of medications known to affect the liver (e.g. paracetamol in high doses, statins, methotrexate) may increase the cumulative risk of hepatotoxicity. Your doctor may need to monitor liver function more frequently.
- Oral contraceptives – Unlike some other antibiotics, nitrofurantoin does not reduce the effectiveness of combined oral contraceptives. No additional contraceptive measures are needed during treatment.
Nitrofurantoin may cause false-positive results for urine glucose when using copper-reduction methods (such as Benedict's reagent or Clinitest). Glucose oxidase-based tests (such as Clinistix or Diastix) are not affected. Additionally, nitrofurantoin commonly turns urine a dark yellow or brown colour, which is harmless but may interfere with certain urinalysis readings.
What Is the Correct Dosage of Nitrofurantoin?
The dosage of nitrofurantoin is determined by your doctor based on the type of infection, its severity, the specific formulation being used, and individual patient factors such as kidney function and body weight. Always take nitrofurantoin exactly as prescribed. Do not adjust your dose or stop treatment early without consulting your healthcare provider.
Adults
| Indication | Dose | Frequency | Duration |
|---|---|---|---|
| Acute UTI (microcrystalline) | 50–100 mg | 3–4 times daily | 5–7 days |
| Acute UTI (macrocrystalline/MR) | 100 mg | Twice daily | 5–7 days |
| Prophylaxis (recurrent UTIs) | 50–100 mg | Once daily at bedtime | Months to years (under medical supervision) |
Nitrofurantoin should always be taken with food or milk. Taking it with a meal serves two important purposes: it significantly reduces gastrointestinal side effects (particularly nausea), and it increases drug absorption by approximately 40%, improving the concentration of active drug reaching the urine.
Children
Nitrofurantoin may be prescribed for children aged 1 month and older. The standard paediatric dose is 3 mg per kg of body weight per day, divided into at least two doses, typically given for 7 days. Tablets may be crushed and mixed with a small amount of liquid or food to aid administration in young children. The exact dose and duration will be determined by the prescribing physician based on the child's weight and clinical situation.
Paediatric Dosing Example
A child weighing 20 kg would typically receive a total daily dose of 60 mg (3 mg/kg × 20 kg), divided into two doses of 30 mg, or three doses of 20 mg, depending on physician preference.
Contraindication: Nitrofurantoin must not be given to neonates under 1 month of age due to the risk of haemolytic anaemia related to immature enzyme systems.
Elderly Patients
Elderly patients may use nitrofurantoin for acute UTIs, but kidney function must be assessed before prescribing. Age-related decline in renal function is common, and many elderly patients have an eGFR below 45 mL/min even without diagnosed kidney disease. Long-term prophylactic use of nitrofurantoin in the elderly requires particular caution due to the increased risk of pulmonary and hepatic side effects with prolonged therapy. Regular monitoring of lung and liver function is recommended for courses exceeding 6 months.
Missed Dose
If you forget to take a dose, take it as soon as you remember, provided it is not almost time for your next scheduled dose. If it is nearly time for the next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose to compensate for a missed one. If you miss multiple doses, contact your doctor for advice, as this may affect the treatment outcome.
Overdose
If you or someone else has taken more nitrofurantoin than prescribed, contact your local poison control centre or seek emergency medical attention immediately. Symptoms of overdose may include severe nausea, vomiting, and diarrhoea. There is no specific antidote for nitrofurantoin overdose; treatment is supportive. Maintaining high fluid intake can help promote urinary excretion of the drug. Haemodialysis is effective at removing nitrofurantoin from the blood in severe cases.
What Are the Side Effects of Nitrofurantoin?
Like all medicines, nitrofurantoin can cause side effects, although not everyone will experience them. Most side effects are mild and resolve after completing the course of treatment. However, some rare side effects can be serious and require immediate medical attention. Understanding what to watch for allows you to seek appropriate help promptly.
Uncommon Side Effects
Affects fewer than 1 in 100 patients
- Nausea and vomiting (especially at higher doses or on an empty stomach)
- Loss of appetite
- Diarrhoea
- Abdominal discomfort
- Headache and dizziness
- Drowsiness
Hypersensitivity Reactions
Uncommon – may affect up to 1 in 100 patients
- Shortness of breath and acute pulmonary hypersensitivity (fever, cough, chest tightness)
- Skin rash, itching, and urticaria (hives)
- Drug-induced fever
- Muscle and joint pain
- Asthma-like symptoms
- Dry mouth
Rare Side Effects
Affects fewer than 1 in 1,000 patients
- Peripheral neuropathy (tingling, numbness, or burning in hands and feet) — risk increases with renal impairment, diabetes, anaemia, or vitamin B deficiency
- Difficulty focusing the eyes (nystagmus)
- Hair loss (usually reversible)
- Benign intracranial hypertension (raised pressure inside the skull causing headache and visual disturbances)
- Parotitis (inflammation of the salivary glands)
- Chronic pulmonary fibrosis (with long-term use) — gradual onset of cough and breathing difficulties
- Angioedema (swelling of the face, lips, tongue, or throat with potential breathing or swallowing difficulty)
Reported (Frequency Unknown)
Reported in post-marketing surveillance
- Anaphylactic reactions (severe allergic reaction with fever, rash, swelling, and potential cardiovascular collapse)
- Hepatitis (both acute and chronic autoimmune-type liver inflammation)
- Cholestatic jaundice
- Blood disorders including haemolytic anaemia (especially in G6PD-deficient patients), agranulocytosis, leucopenia, and thrombocytopenia
- Vasculitis (inflammation of small blood vessel walls causing skin manifestations)
- Tubulointerstitial nephritis (kidney inflammation causing renal impairment)
- Lupus-like syndrome
Discontinue nitrofurantoin and seek immediate medical advice if you develop:
- Breathing difficulties, persistent cough, or chest pain (possible pulmonary reaction)
- Yellowing of the skin or eyes, dark urine, or pale stools (possible liver damage)
- Tingling, numbness, or weakness in the hands or feet (peripheral neuropathy)
- Swelling of the face, tongue, or throat with difficulty breathing (angioedema)
- Severe skin reactions such as widespread rash with blistering
Harmless Effects
Nitrofurantoin commonly causes the urine to turn a dark yellow or rust-brown colour. This is a completely harmless effect of the drug's metabolism and does not indicate a medical problem. The discolouration resolves promptly after stopping the medication. It is important not to confuse this normal effect with the dark urine associated with liver problems, which would typically be accompanied by other symptoms such as jaundice or abdominal pain.
Long-Term Use Monitoring
Patients receiving nitrofurantoin for prophylaxis of recurrent UTIs require regular monitoring. Guidelines recommend checking liver function tests and pulmonary function at baseline and at least every 6 months during prolonged therapy. Any new onset of cough, breathlessness, abnormal fatigue, or abnormal blood results should prompt immediate discontinuation and medical evaluation. The risk of chronic pulmonary fibrosis and hepatotoxicity increases with the duration of therapy.
How Should You Store Nitrofurantoin?
Proper storage of medications is essential to maintain their effectiveness and safety. Follow these guidelines for storing nitrofurantoin:
- Temperature – 5 mg tablets should be stored at or below 25°C (77°F). 50 mg and 100 mg tablets have no special temperature requirements but should be kept at room temperature. Avoid exposure to excessive heat or direct sunlight.
- Moisture – Keep the tablets in their original container or blister packaging to protect them from moisture. Do not store in the bathroom or near a sink.
- Keep out of reach of children – Store all medications in a location that is not accessible to children. Consider using child-resistant containers.
- Expiry date – Check the expiry date (marked "EXP" on the packaging) and do not use the medication after this date. Expired antibiotics may be less effective and should be disposed of properly.
- Disposal – Do not dispose of unused or expired nitrofurantoin by flushing it down the toilet or throwing it in household rubbish. Return unwanted medication to your pharmacy for safe disposal to protect the environment.
What Does Nitrofurantoin Contain?
Understanding the composition of your medication helps identify potential allergens or intolerances. Below is the detailed breakdown of nitrofurantoin tablet formulations:
Active Ingredient
Each tablet contains nitrofurantoin as the active pharmaceutical ingredient. Nitrofurantoin is a synthetic nitrofuran derivative with the chemical formula C8H6N4O5 and a molecular weight of 238.16 g/mol. It is a yellow crystalline powder with limited water solubility.
Inactive Ingredients (Excipients)
The following excipients are present in common nitrofurantoin tablet formulations (e.g. Furadantin):
- Lactose monohydrate (132.5–177.5 mg per tablet depending on strength) – a filler/binder; relevant for patients with lactose intolerance
- Potato starch – a disintegrant that helps the tablet break down in the stomach
- Methylcellulose – a binding agent
- Colloidal anhydrous silicon dioxide – a glidant that improves powder flow during manufacturing
- Magnesium stearate – a lubricant that prevents the tablet from sticking to manufacturing equipment
Appearance and Packaging
Nitrofurantoin tablets are typically yellow, round, and biconvex with a scored line (cross-score) for dose splitting. Tablet sizes and packaging vary by manufacturer and strength:
- 5 mg tablets – typically supplied in plastic containers of 50 tablets
- 50 mg tablets – available in blister packs of 15 or 25 tablets, or plastic containers of 100 tablets
- 100 mg modified-release capsules (Macrobid) – available in various pack sizes depending on the manufacturer
Not all strengths, formulations, or pack sizes may be available in every market. Your pharmacist can advise on the specific products available in your region.
Frequently Asked Questions About Nitrofurantoin
Nitrofurantoin is a prescription antibiotic used specifically to treat and prevent urinary tract infections (UTIs), also known as bladder infections or cystitis. It works by killing the bacteria that commonly cause these infections, including E. coli, Enterococcus, and Staphylococcus saprophyticus. It is not effective for kidney infections (pyelonephritis) or infections outside the urinary tract because it only reaches therapeutic concentrations in the urine. Nitrofurantoin is recommended as a first-line treatment for uncomplicated UTIs by international guidelines including those from the IDSA and EAU.
Most patients begin to notice improvement in urinary symptoms within 24 to 48 hours of starting nitrofurantoin. However, it is essential to complete the full prescribed course of treatment (usually 5 to 7 days for an acute infection) even if symptoms improve earlier. Stopping antibiotic treatment prematurely increases the risk of treatment failure, recurrent infection, and the development of antibiotic-resistant bacteria. If your symptoms do not improve within 48 hours or worsen at any point, contact your doctor.
Nitrofurantoin may be prescribed during pregnancy when the potential benefit justifies the potential risk, particularly during the second trimester. It should be avoided at term (from 38 weeks of gestation) and during labour and delivery because of the theoretical risk of haemolytic anaemia in the newborn. Some studies have suggested a small increase in birth defect risk with first-trimester use, though the absolute risk is low. It should also be avoided during breastfeeding if the infant is under 1 month old or has G6PD deficiency. Always discuss the risks and benefits with your doctor or midwife before taking any medication during pregnancy.
Nitrofurantoin and its metabolites are excreted in the urine and have a natural dark yellow to rust-brown colour. This discolouration is completely harmless and is not a sign of blood in the urine, kidney damage, or any other medical problem. It occurs in most patients taking nitrofurantoin and resolves promptly once the medication is stopped. However, if you notice dark urine accompanied by other symptoms such as yellowing of the skin or eyes, abdominal pain, or fatigue, you should contact your doctor, as this could indicate a liver problem rather than the normal drug effect.
No, nitrofurantoin should not be used to treat kidney infections (pyelonephritis). The drug achieves therapeutic concentrations only in the urine and the lower urinary tract, not in the bloodstream or kidney tissue. Kidney infections require antibiotics that reach adequate levels in the blood and renal parenchyma, such as trimethoprim-sulfamethoxazole, ciprofloxacin, or intravenous beta-lactams. If you have symptoms suggestive of a kidney infection — such as high fever, severe flank pain, rigors, or vomiting — seek urgent medical attention.
If you forget to take a dose of nitrofurantoin, take it as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose and continue with your regular dosing schedule. Never take a double dose to make up for a missed one. Missing occasional single doses is unlikely to significantly affect treatment outcome, but consistently missing doses increases the risk of treatment failure and development of antibiotic resistance. If you find it difficult to remember your doses, consider setting phone reminders or using a pill organiser.
References
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List, 2023. Geneva: WHO; 2023.
- Gupta K, Hooton TM, Naber KG, et al. International Clinical Practice Guidelines for the Treatment of Acute Uncomplicated Cystitis and Pyelonephritis in Women: A 2010 Update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases. Clin Infect Dis. 2011;52(5):e103–e120.
- European Association of Urology (EAU). EAU Guidelines on Urological Infections 2024. Arnhem: EAU; 2024.
- National Institute for Health and Care Excellence (NICE). Urinary tract infection (lower): antimicrobial prescribing. NICE guideline [NG109]. London: NICE; 2018 (updated 2024).
- British National Formulary (BNF). Nitrofurantoin. London: BMJ Group and Pharmaceutical Press; 2025.
- European Medicines Agency (EMA). Nitrofurantoin – Summary of Product Characteristics. Amsterdam: EMA.
- US Food and Drug Administration (FDA). Macrodantin (Nitrofurantoin Macrocrystals) Prescribing Information. Silver Spring, MD: FDA.
- Huttner A, Kowalczyk A, Turjeman A, et al. Effect of 5-Day Nitrofurantoin vs Single-Dose Fosfomycin on Clinical Resolution of Uncomplicated Lower Urinary Tract Infection in Women: A Randomized Clinical Trial. JAMA. 2018;319(17):1781–1789.
- McKinnell JA, Stollenwerk NS, Jung CW, Miller LG. Nitrofurantoin compares favorably to recommended agents as empirical treatment of uncomplicated urinary tract infections in a decision and cost analysis. Mayo Clin Proc. 2011;86(6):480–488.
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- Gardiner BJ, Stewardson AJ, Abbott IJ, Peleg AY. Nitrofurantoin and fosfomycin for resistant urinary tract infections: old drugs for emerging problems. Aust Prescr. 2019;42(1):14–19.
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This article was written and reviewed by iMedic's medical editorial team, consisting of licensed physicians and pharmacists specialising in clinical pharmacology, infectious disease, and antimicrobial therapy.
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