How the dose is calculated
Nitrofurantoin is dosed in mg/kg/day. Treatment of an active uncomplicated UTI uses a higher dose split four times a day; long-term prophylaxis against recurrent UTI uses a much lower once-nightly dose.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| UTI treatment | 6 mg/kg/day | every 6h (4×/day) | 400 mg/day |
| UTI prophylaxis | 1.5 mg/kg once nightly | once nightly | 100 mg/day |
Nitrofurantoin only achieves effective concentrations in the urine, not in blood or tissue — it treats uncomplicated lower urinary tract infection only, and is not appropriate for pyelonephritis or suspected systemic infection. It is also contraindicated in infants under 1 month and avoided near term in pregnancy, and requires caution in significant renal impairment (reduced efficacy and increased toxicity risk).
Clinical use
- Nitrofurantoin is a first-line option for uncomplicated cystitis because of low resistance rates and minimal impact on gut flora compared to broader-spectrum agents.
- Not suitable for suspected pyelonephritis or any infection beyond the bladder — it doesn't reach adequate tissue/blood concentrations outside the urinary tract.
- Low-dose once-nightly prophylaxis is used for recurrent UTI in selected patients, typically as a time-limited course reviewed periodically.
- Reduced efficacy and increased toxicity risk occur with significant renal impairment (reduced urinary concentration) — avoid or use with specialist input in this setting.
Frequently asked questions
What is nitrofurantoin used for?
Nitrofurantoin treats uncomplicated urinary tract infections (cystitis) and is also used at a lower dose for long-term prevention of recurrent UTIs — it is not used for kidney infections or infections outside the urinary tract.
Why can't nitrofurantoin be used for a kidney infection?
Nitrofurantoin only reaches effective concentrations in the urine, not in blood or kidney tissue, so it can't adequately treat pyelonephritis or any infection beyond the bladder.
Is nitrofurantoin safe for newborns?
No — it's contraindicated in infants under 1 month of age because of a risk of haemolytic anaemia related to immature enzyme systems.
Can nitrofurantoin be used in kidney disease?
It's generally avoided or used with caution in significant renal impairment, since reduced kidney function lowers the urinary drug concentration (reducing effectiveness) while increasing systemic toxicity risk.
References
- Gupta K, et al. International Clinical Practice Guidelines for Uncomplicated Cystitis (IDSA/ESCMID). Clin Infect Dis. 2011.
- British National Formulary for Children (BNFc) — Nitrofurantoin.
- American Academy of Pediatrics Red Book — Urinary Tract Infection.