Nitrofurantoin Dosing for Uncomplicated UTI
For adults with uncomplicated urinary tract infection and normal renal function, nitrofurantoin should be administered 100 mg orally twice daily (every 12 hours) for 5 days. 1
Standard Dosing Regimen
The Infectious Diseases Society of America (IDSA) and European Society for Microbiology and Infectious Diseases (ESCMID) recommend nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days as first-line therapy for uncomplicated cystitis in women. 1, 2
This 5-day regimen achieves clinical cure rates of 88-93% and bacteriological cure rates of 81-92%, making it highly effective for uncomplicated lower urinary tract infections. 1, 2
The twice-daily dosing (rather than four times daily) improves adherence while maintaining excellent efficacy, and extending therapy beyond 5-7 days provides no additional benefit but increases adverse event risk. 1, 2
Alternative Dosing Schedules
A 7-day course of 100 mg twice daily is acceptable and shows equivalent efficacy (89-93% clinical cure), though the 5-day regimen is preferred to minimize antibiotic exposure. 2
Avoid the older four-times-daily regimen (100 mg every 6 hours), as it has lower efficacy (88% clinical cure, 74% bacterial cure) compared to twice-daily dosing and is more burdensome for patients. 2
The macrocrystals formulation at 50-100 mg four times daily for 5 days is an alternative mentioned in European guidelines, but twice-daily dosing with monohydrate/macrocrystals is strongly preferred. 1
Critical Contraindications
Do not prescribe nitrofurantoin if pyelonephritis is suspected (fever >38°C, flank pain, costovertebral angle tenderness, nausea/vomiting), as the drug does not achieve adequate renal tissue concentrations for upper tract infections. 1, 2
Nitrofurantoin is contraindicated when creatinine clearance is <30 mL/min due to reduced efficacy and increased risk of peripheral neuropathy. 1, 2
For creatinine clearance 30-60 mL/min, guidelines vary: some recommend avoidance 2, though recent evidence suggests efficacy may be preserved in this range 3, 4. Exercise caution and consider alternatives if CrCl <60 mL/min.
Special Populations
For men with uncomplicated UTI, the European Urology guidelines recommend 100 mg every 6 hours (four times daily) for 7-14 days, with 14 days preferred when prostatitis cannot be excluded. 5
However, nitrofurantoin has substantially lower efficacy in males (25% failure rate versus 10-16% in females), so consider alternative agents like trimethoprim-sulfamethoxazole or fluoroquinolones for men. 5
For children ≥12 years, use the adult dose of 100 mg twice daily; for children <12 years, use 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days. 1, 2
Common Pitfalls to Avoid
Never use nitrofurantoin for "borderline" upper tract symptoms—any flank pain or low-grade fever warrants a fluoroquinolone or cephalosporin instead. 1
Do not prescribe for complicated UTIs (structural abnormalities, obstruction, instrumentation, pregnancy) or suspected prostatitis, as nitrofurantoin does not penetrate prostatic or renal tissue adequately. 1
Always verify renal function before prescribing; efficacy drops markedly when creatinine clearance falls below 30 mL/min. 1, 2
Routine post-treatment urine cultures are unnecessary for asymptomatic patients; obtain cultures only if symptoms persist after therapy or recur within 2 weeks. 1
Expected Adverse Effects
Nausea and headache are the most common side effects, occurring in 5.6-34% of patients depending on the study, with rates comparable to trimethoprim-sulfamethoxazole. 1, 2
Serious pulmonary and hepatic toxicity are extremely rare (0.001% and 0.0003% respectively). 1
Patients should ensure adequate hydration during treatment to prevent crystal formation. 1