What is the recommended dose of Nitrofurantoin (antibiotic) for a typical adult patient with a urinary tract infection (UTI)?

Nitrofurantoin Dosing for Adults with UTI

For uncomplicated urinary tract infections in adults, prescribe nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg twice daily for 5 days. 1, 2

Standard Dosing Regimens

Women with Uncomplicated UTI

• Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days is the preferred first-line regimen recommended by the Infectious Diseases Society of America, European Association of Urology, and European Society for Microbiology and Infectious Diseases 1, 2
• This regimen achieves clinical cure rates of 88-93% and bacterial cure rates of 81-92% 1, 2
• Alternative formulations include nitrofurantoin macrocrystals 50-100 mg four times daily for 5 days 1

Men with Uncomplicated UTI

• 100 mg twice daily for 7 days (longer duration than women due to limited data in men) 2
• The 7-day course is based on observational data and accounts for potential prostatic involvement 2

Special Clinical Scenarios

• VRE (Vancomycin-resistant Enterococci) UTIs: 100 mg four times daily 1
• Prophylaxis for recurrent UTI: 50-100 mg once daily (continuous) or once postcoitus (postcoital prophylaxis) 3

Critical Contraindications

Renal Function Requirements

• Do NOT prescribe if creatinine clearance <60 mL/min - this is the most common and dangerous prescribing error 2, 4
• Below this threshold, urinary drug concentrations become inadequate and toxicity risk (particularly peripheral neuropathy) increases significantly 2, 4
• For patients with CrCl <60 mL/min, use trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days or fosfomycin trometamol 3 g single dose instead 2, 4

Clinical Situations Where Nitrofurantoin Should NOT Be Used

• Suspected pyelonephritis or upper tract infection - nitrofurantoin does not achieve adequate renal tissue concentrations 1
• Suspected prostatitis in men - inadequate prostatic tissue penetration 1
• Complicated UTIs (structural/functional abnormalities, obstruction, instrumentation) 1
• Perinephric abscess 1

Treatment Duration Considerations

The 5-day regimen represents a consensus across major guideline societies and balances efficacy with minimizing antibiotic exposure 1, 2. This is notably different from some international guidance:

• UK guidelines recommend 3 days, but a 2023 review found little direct evidence supporting this shorter duration 5
• The 5-day regimen has been shown equivalent to trimethoprim-sulfamethoxazole 3-day regimens in clinical and microbiological cure rates 1
• Do not extend beyond 7 days unless symptoms persist, as shorter courses minimize adverse effects while maintaining efficacy 1

Follow-Up and Retreatment

When Follow-Up Is NOT Needed

• Routine post-treatment cultures are NOT indicated for asymptomatic patients 2

When Follow-Up IS Required

• If symptoms do not resolve by end of treatment or recur within 2 weeks: perform urine culture with susceptibility testing 1, 2
• For retreatment: assume the organism is not susceptible to nitrofurantoin and use a different antibiotic for 7 days 2

Adverse Effects

• Most common: nausea and headache (occurring in 5.6-34% of patients) 1, 2
• Serious toxicities are rare: pulmonary toxicity (0.001%) and hepatic toxicity (0.0003%) 1
• Patients should maintain adequate hydration during treatment to prevent crystal formation 1

Pediatric Dosing (≥12 years)

• Children ≥12 years: 100 mg twice daily for 7 days 1, 2
• Children <12 years: 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days 1, 2