Maximum Dose of Nitrofurantoin
The maximum recommended dose of nitrofurantoin for adults with normal renal function is 100 mg four times daily (400 mg/day total), though the standard dosing for uncomplicated UTIs is 100 mg twice daily.
Standard Dosing for Uncomplicated UTI
For uncomplicated urinary tract infections, nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg twice daily for 5 days is the recommended first-line regimen, with clinical cure rates of 88-93% and bacterial cure rates of 81-92% 1, 2.
The twice-daily dosing (200 mg total daily dose) represents the standard therapeutic approach endorsed by the Infectious Diseases Society of America and European Association of Urology 1, 2.
Higher Dosing Regimens
For specific infections such as vancomycin-resistant Enterococci (VRE) UTIs, the dose can be increased to 100 mg four times daily (400 mg/day), representing the maximum recommended daily dose 2.
Nitrofurantoin macrocrystals can be dosed at 50-100 mg four times daily for 5 days according to European Urology guidelines 2.
In research settings, nitrofurantoin has been studied at 100 mg four times daily for three days with demonstrated efficacy 3.
Critical Renal Function Contraindication
Nitrofurantoin is absolutely contraindicated in patients with creatinine clearance <60 mL/min due to inadequate urinary drug concentrations and substantially increased risk of peripheral neuropathy and other serious toxicities 1.
This contraindication should not be used in older adults with reduced renal function, as expert consensus strongly recommends avoiding nitrofurantoin when creatinine clearance falls below 30 mL/min 4.
Duration Considerations
The optimal treatment duration is 5-7 days for uncomplicated UTIs, with 5 days being the most commonly recommended duration that balances efficacy with minimizing antibiotic exposure 2.
Three-day courses at 100 mg twice daily have been studied but lack robust supporting evidence compared to 5-day regimens 5.