Macrobid (Nitrofurantoin) Dosing for Uncomplicated UTI
Recommended Dosage and Duration
For uncomplicated urinary tract infections in women, prescribe nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days. 1
This 5-day regimen is the evidence-based standard endorsed by both the Infectious Diseases Society of America (IDSA) and the European Society for Microbiology and Infectious Diseases (ESMID), achieving clinical cure rates of 88-93% and bacterial cure rates of 81-92%. 1
Key Dosing Considerations by Patient Population
Women with Uncomplicated Cystitis
- Standard regimen: 100 mg twice daily for 5-7 days 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
- The European Association of Urology specifically endorses the 5-day duration as optimal 1
Men with UTI
- Dosing: 100 mg every 6 hours (four times daily) 2
- Duration: 7-14 days, with 14 days recommended when prostatitis cannot be excluded 2
- Critical caveat: Nitrofurantoin has substantially lower efficacy in males, with a 25% failure rate compared to 10-16% in females 2
- Consider alternative agents like trimethoprim-sulfamethoxazole or fluoroquinolones for male patients given the higher failure rates 2
Special Dosing Situations
- VRE (vancomycin-resistant Enterococci) UTIs: 100 mg four times daily 1
- Pediatric patients ≥12 years: 100 mg twice daily 1
- Pediatric patients <12 years: 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days 1
Critical Contraindications and Precautions
Absolute Contraindications
- Creatinine clearance <60 mL/min due to inadequate urinary drug concentrations and increased risk of peripheral neuropathy 2
- Suspected pyelonephritis or upper tract involvement - nitrofurantoin does not achieve adequate tissue concentrations outside the bladder 1
- Last trimester of pregnancy (final 3 months) 3
Important Clinical Pitfall
While traditional teaching suggests avoiding nitrofurantoin with CrCl <60 mL/min, recent evidence shows it remains effective in patients with CrCl 30-60 mL/min, with failures primarily occurring only when CrCl <30 mL/min. 4 However, current guidelines maintain the CrCl <60 mL/min contraindication, and this should be followed in clinical practice. 2
Treatment Efficacy and Monitoring
Expected Outcomes
- Clinical cure rates: 88-93% 1
- Symptomatic improvement should occur within 3 days 5
- Bacteriological cure by day 3: 81% (21/26 patients in placebo-controlled trial) 5
Follow-Up Recommendations
- No routine post-treatment urinalysis or cultures needed for asymptomatic patients 1
- If symptoms persist or recur within 2 weeks: obtain urine culture with susceptibility testing and consider retreatment with a 7-day course of an alternative agent 1
Common Adverse Effects
- Nausea and headache are most common 1
- Overall adverse event rates: 5.6-34% 1
- Serious long-term risks (pulmonary reactions, polyneuropathy) are primarily associated with prolonged use, not short-term therapy 3
Why Nitrofurantoin Remains First-Line
Nitrofurantoin maintains its position as a first-line agent due to minimal resistance patterns and limited collateral damage to normal flora, particularly important given rising resistance rates to trimethoprim-sulfamethoxazole and fluoroquinolones. 1 It retains excellent activity against E. coli, Staphylococcus saprophyticus, and Enterococcus species despite over 60 years of use. 3