Information last reviewed: May 2026 — for educational purposes only.
Nitrofurantoin is a nitrofuran antibiotic used exclusively for the treatment and prevention of lower urinary tract infections (UTIs) caused by susceptible organisms. It is one of the recommended first-line antibiotics for uncomplicated UTIs in adults, particularly in women. Brand names include Macrobid (modified-release 100 mg capsules, twice daily) and Macrodantin (immediate-release 50 mg or 100 mg capsules, four times daily). Nitrofurantoin requires a prescription and is not active against kidney infections (pyelonephritis) or systemic infections.
What Is Nitrofurantoin and How Does It Work?
Nitrofurantoin is reduced to reactive intermediates by bacterial nitroreductase enzymes. These reactive forms attack multiple bacterial targets simultaneously — DNA, ribosomes, and cell wall synthesis — making resistance development difficult. It concentrates almost exclusively in urine and bladder tissue, achieving high local antibacterial concentrations with minimal systemic exposure. This narrow tissue distribution is both its strength (excellent UTI efficacy with low systemic side effects) and its limitation (ineffective for kidney or systemic infections).
It is active against the most common UTI pathogens: Escherichia coli, Enterococcus faecalis, Staphylococcus saprophyticus, and Klebsiella species. It is not effective against Proteus mirabilis or Pseudomonas aeruginosa.
Is Nitrofurantoin Available Over the Counter?
Nitrofurantoin is prescription-only in the US, UK, Canada, EU, and Australia. It is not available over the counter. Patients with UTI symptoms should seek a prescription from a GP, urgent care provider, or qualified telehealth service. In the UK, some community pharmacies can supply nitrofurantoin for uncomplicated UTIs in women under a patient group direction (PGD) or via the NHS pharmacy UTI service in England without a GP appointment.
Capsule Strengths and Formulations
- Macrobid 100 mg modified-release capsules — the most widely prescribed form; each capsule contains 75 mg nitrofurantoin monohydrate and 25 mg nitrofurantoin macrocrystals; taken twice daily for 5 days for uncomplicated UTI treatment
- Macrodantin 50 mg / 100 mg immediate-release capsules — older formulation requiring four times daily dosing; used for treatment and for UTI prophylaxis (long-term low-dose 50 mg or 100 mg at night)
- Oral suspension (25 mg/5 ml) — for patients unable to swallow capsules
Nitrofurantoin should always be taken with food or milk to improve absorption and reduce GI side effects (nausea, vomiting). Urine may turn a harmless dark yellow or brown colour during treatment. This is not a cause for concern.
Price of Generic Nitrofurantoin
Generic nitrofurantoin monohydrate/macrocrystals capsules are widely available. A standard 5-day treatment course costs only a few dollars with a pharmacy discount card in the US. NHS prescriptions in the UK are issued at the standard charge. Brand-name Macrobid commands a premium over generics but contains the same formulation.
Frequently Asked Questions
Can nitrofurantoin treat a kidney infection?
No. Nitrofurantoin does not reach therapeutic concentrations in kidney tissue or blood. It should only be used for lower UTIs (bladder infections). Kidney infections (pyelonephritis) require an antibiotic with systemic tissue penetration such as ciprofloxacin, co-amoxiclav, or cephalexin. Symptoms of kidney infection include fever, back or flank pain, and nausea — a prescriber should be consulted promptly.
Is nitrofurantoin safe during pregnancy?
Nitrofurantoin is generally considered safe during the first and second trimesters of pregnancy for short-term UTI treatment. It should not be used at term (38–42 weeks gestation) or during labour due to a risk of neonatal haemolytic anaemia, and is contraindicated in patients at term or with G6PD deficiency. Prescribers will assess individual risk-benefit.
Why does nitrofurantoin turn urine dark?
Nitrofurantoin is excreted in urine and causes a harmless yellow-brown or rust-coloured discolouration. Patients should be warned of this in advance so they do not become alarmed. The colour resolves once the course is completed.
Disclaimer: This page is for general informational purposes only and does not constitute medical advice. Always consult a licensed healthcare professional before taking any medication. See our full disclaimer.