What is the recommended dosage of Nitrofurantoin (macrocrystals) for treating urinary tract infections (UTIs)?

Nitrofurantoin Macrocrystals Dosage for UTI

For uncomplicated urinary tract infections, prescribe nitrofurantoin macrocrystals 100 mg orally twice daily for 5 days. 1, 2

Standard Dosing Regimen

• The IDSA and European Society for Microbiology and Infectious Diseases recommend 100 mg twice daily for 5 days as the optimal regimen for uncomplicated UTIs in women. 1, 2
• This 5-day regimen achieves clinical cure rates of 84-90% and bacterial cure rates of 92% at early follow-up (5-9 days post-treatment). 2
• At 30-day follow-up, clinical cure rates remain robust at 84%, demonstrating sustained efficacy. 2

Alternative Duration Options

• A 7-day course (100 mg twice daily) is acceptable if you prefer a longer duration, with clinical cure rates of 89-93% and bacterial cure rates of 86%. 2
• The 7-day regimen shows equivalent efficacy to ciprofloxacin and trimethoprim-sulfamethoxazole when comparing similar duration courses. 2
• Avoid 3-day regimens (100 mg four times daily) due to inferior efficacy—only 88% clinical cure and 74% bacterial cure rates. 2 This contradicts some UK guidance that promotes 3-day courses without strong supporting evidence. 3

Special Populations and Situations

Vancomycin-Resistant Enterococcus (VRE) UTIs

• For VRE uncomplicated UTIs specifically, increase the dose to 100 mg four times daily (every 6 hours). 1, 4
• Continue treatment for 7-10 days until clinical resolution for enterococcal UTIs. 4

Pediatric Dosing

• For children ≥12 years: use the adult dose of 100 mg twice daily. 2
• For children <12 years: use 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days. 1, 2

Critical Contraindications

• Do not use nitrofurantoin if creatinine clearance is <60 mL/min—inadequate urinary drug concentrations prevent bactericidal activity and increase toxicity risk. 2, 4
• Avoid nitrofurantoin if early pyelonephritis is suspected—it does not achieve adequate tissue concentrations for upper tract infections. 1, 2

When to Switch to Alternative Agents

• If renal impairment (CrCl <60 mL/min): switch to trimethoprim-sulfamethoxazole or fosfomycin. 2, 4
• If local E. coli resistance to trimethoprim-sulfamethoxazole is <20% and no sulfa allergy exists: trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days is equivalent. 2
• Fosfomycin 3 g single dose is an alternative first-line option with slightly lower efficacy (90% vs 95% clinical cure for nitrofurantoin). 2

Expected Adverse Effects

• Nausea and headache are the most common side effects, occurring in 5.6-34% of patients. 1, 2
• These rates are comparable to trimethoprim-sulfamethoxazole (31-38% adverse events). 2
• Mild headache occurs in approximately 10.8% of patients, and rash may occasionally require discontinuation. 5

Follow-Up Recommendations

• Do not perform routine post-treatment urinalysis or urine cultures in asymptomatic patients. 1, 4
• If symptoms do not resolve by end of treatment or recur within 2 weeks: obtain urine culture with susceptibility testing and consider retreatment with a 7-day regimen using another agent. 1, 4