Maximum Dose of Nitrofurantoin for Uncomplicated UTI
The maximum recommended dose of nitrofurantoin for uncomplicated UTI in adults with normal renal function is 100 mg four times daily (400 mg total daily dose), though the standard dosing is 100 mg twice daily for most patients. 1
Standard Dosing Regimens
The typical dosing varies by formulation and clinical context:
Nitrofurantoin monohydrate/macrocrystals (Macrobid): 100 mg twice daily for 5-7 days is the preferred first-line regimen recommended by the Infectious Diseases Society of America and European Association of Urology for uncomplicated UTI in women 1, 2
Nitrofurantoin macrocrystals: 50-100 mg four times daily for 5 days is an alternative formulation 1
For VRE (Vancomycin-resistant Enterococci) UTIs: The maximum dose of 100 mg four times daily (400 mg/day total) is specifically recommended 1
Gender-Specific Dosing Differences
Women: 100 mg twice daily for 5 days achieves clinical cure rates of 88-93% 1, 2
Men: 100 mg every 6 hours (four times daily) for 7-14 days is recommended by European Urology, with 14 days preferred when prostatitis cannot be excluded 3. Note that nitrofurantoin has substantially lower efficacy in males (25% failure rate versus 10-16% in females) 3
Critical Contraindications
Renal function is the most important limiting factor: Nitrofurantoin is contraindicated when creatinine clearance is <60 mL/min due to inadequate urinary drug concentrations and increased toxicity risk, including peripheral neuropathy 3, 2. This is the most common and dangerous prescribing error to avoid 2
However, some evidence suggests nitrofurantoin may be used cautiously in patients with CrCl 30-60 mL/min for susceptible organisms, though this contradicts current guideline recommendations 4, 5
When NOT to Use Nitrofurantoin
Do not prescribe nitrofurantoin for:
- Suspected pyelonephritis or upper tract infections (inadequate renal tissue concentrations) 1, 2
- Complicated UTIs with structural/functional abnormalities 1
- Men with suspected prostatitis (poor prostatic tissue penetration) 1
- Perinephric abscess 1
Common Pitfalls
Always check renal function before prescribing—this is the single most critical safety measure 2. Nausea and headache occur in 5.6-34% of patients and are the most common side effects 1, 2. Ensure adequate hydration during treatment to prevent crystal formation 1.