Macrobid (Nitrofurantoin) Dosing for Uncomplicated UTI
For uncomplicated urinary tract infections in women, prescribe nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg twice daily for 5 days. 1
Standard Dosing Algorithm
For Women with Uncomplicated Cystitis
- Primary regimen: Nitrofurantoin 100 mg PO twice daily for 5 days 1
- This achieves 88-93% clinical cure rates and 81-92% bacterial cure rates 1
- The 5-day regimen is equivalent to trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days 1, 2
For Men with Uncomplicated UTI
- Extended duration required: Nitrofurantoin 100 mg PO twice daily for 7 days 3
- Men require longer treatment based on observational data showing anatomical differences necessitate extended therapy 3
For Vancomycin-Resistant Enterococcus (VRE) UTI
- Higher frequency dosing: Nitrofurantoin 100 mg PO every 6 hours (four times daily) 1, 4
- Continue for 7-10 days until clinical resolution 4
Critical Contraindications and Precautions
Renal Function Requirements
- Absolute contraindication: Creatinine clearance <60 mL/min per FDA guidelines 3
- Always check renal function before prescribing - this is the most dangerous error to avoid 3
- Inadequate urinary drug concentrations and increased toxicity risk (peripheral neuropathy) occur with impaired renal function 3
- Some emerging data suggests efficacy at CrCl 30-60 mL/min, but follow FDA contraindication in clinical practice 3, 5
Clinical Situations to Avoid Nitrofurantoin
- Do not use if pyelonephritis suspected - nitrofurantoin does not achieve adequate tissue concentrations 1, 3
- Avoid in complicated UTIs or perinephric abscess 1
- Contraindicated in last trimester of pregnancy 6
Alternative Formulations and Dosing
Macrocrystals (Non-Monohydrate Form)
- 50-100 mg PO four times daily for 5 days 1
- Less commonly used than the twice-daily monohydrate/macrocrystal formulation
Pediatric Dosing
- Children ≥12 years: 100 mg PO twice daily for 7 days 1
- Children <12 years: 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days 1
Common Pitfalls to Avoid
Monitoring and Side Effects
- Nausea and headache are most common side effects, with adverse event rates of 5.6-34% 1
- Monitor for peripheral neuropathy, pulmonary reactions, and hepatotoxicity, especially with borderline renal function 3
- Serious side effects (pulmonary reactions, polyneuropathy) mainly occur with long-term use 6
Treatment Failure Management
- Do not order routine post-treatment cultures if asymptomatic 1, 3
- If symptoms persist or recur within 2 weeks, obtain urine culture with susceptibility testing 1, 3
- Retreat with a different antibiotic for 7 days, assuming resistance to nitrofurantoin 3
Why Nitrofurantoin Remains First-Line
- Minimal resistance patterns despite 60+ years of use 1, 6
- Limited collateral damage to normal flora 1
- Fluoroquinolone-sparing option in era of increasing antimicrobial resistance 2
- Recommended by IDSA, European Association of Urology, and European Society for Microbiology and Infectious Diseases as first-line therapy 1