What is the recommended dosage of Nitrofurantoin for an uncomplicated UTI?

Nitrofurantoin 100 mg Dosing for UTI

For uncomplicated UTI in women, use nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days. 1

Standard Dosing for Women

• The recommended regimen is 100 mg orally twice daily for 5 days, as endorsed by the Infectious Diseases Society of America (IDSA) and European Society for Microbiology and Infectious Diseases (ESMID). 1
• This 5-day regimen achieves clinical cure rates of 88-93% and bacterial cure rates of 81-92% for uncomplicated UTIs in women. 1
• The 5-day course is equivalent to trimethoprim-sulfamethoxazole (160/800 mg twice daily for 3 days) in both clinical and microbiological outcomes. 1

Alternative Dosing Regimens

• For macrocrystal formulations, 50-100 mg four times daily for 5 days is an acceptable alternative according to European Urology guidelines. 1
• For VRE (vancomycin-resistant Enterococci) UTIs specifically, increase to 100 mg four times daily. 1

Dosing for Men

• For men with uncomplicated UTI, use 100 mg every 6 hours (four times daily) for 7-14 days, with 14 days recommended when prostatitis cannot be excluded. 2
• Important caveat: Nitrofurantoin has substantially lower efficacy in males, with a 25% failure rate compared to 10-16% in females, making it a less optimal choice for male UTIs. 2
• Consider alternative agents like trimethoprim-sulfamethoxazole or fluoroquinolones for men when possible. 2

Critical Contraindications

• Do not use if pyelonephritis is suspected - nitrofurantoin does not achieve adequate renal tissue concentrations. 1
• Contraindicated when creatinine clearance is <30 mL/min (some sources recommend avoiding below 60 mL/min in older adults due to increased toxicity risk including peripheral neuropathy). 1, 2
• Avoid in men with suspected prostatitis - inadequate prostatic tissue penetration. 1
• Do not use for complicated UTIs with structural/functional abnormalities, obstruction, or instrumentation. 1

Duration Considerations

• 5 days is optimal for women - this represents the shortest effective duration that balances efficacy with minimizing antibiotic exposure. 1
• Do not use 3-day regimens - clinical efficacy drops to only 61-70% with 3-day courses. 3
• 7-day regimens show similar efficacy to ciprofloxacin and trimethoprim-sulfamethoxazole but are unnecessarily long for uncomplicated cases. 1

Common Side Effects

• Nausea and headache are most common, occurring in 5.6-34% of patients. 1
• Gastrointestinal effects (nausea 3%, diarrhea 1%) are generally mild and self-limited. 4
• Serious pulmonary and hepatic toxicity are extremely rare (0.001% and 0.0003% respectively). 1

Clinical Efficacy Data

• A high-quality 2018 randomized trial demonstrated 70% clinical resolution with 5-day nitrofurantoin versus 58% with single-dose fosfomycin (12% absolute difference, P=0.004). 4
• Microbiological resolution was 74% with nitrofurantoin versus 63% with fosfomycin (P=0.04). 4
• Nitrofurantoin maintains excellent activity against E. coli despite 60+ years of use, with minimal resistance development. 1

Follow-up Recommendations

• Routine post-treatment cultures are not indicated for asymptomatic patients. 1
• Obtain urine culture with susceptibility testing if symptoms do not resolve by end of treatment or recur within 2 weeks. 1
• Consider retreatment with a 7-day regimen using another agent if symptoms persist. 1

Key Clinical Pitfall

The most common error is using nitrofurantoin when upper tract involvement (pyelonephritis) is present or suspected - always assess for flank pain, fever, or systemic symptoms before prescribing, as treatment failure is guaranteed in these cases. 1, 2