Is Macrobid (nitrofurantoin) effective for treating Enterococcus infections, particularly in urinary tract infections?

Nitrofurantoin for Enterococcus faecalis Treatment

Nitrofurantoin 100 mg orally every 6 hours for 5-7 days is an effective alternative treatment for uncomplicated urinary tract infections caused by Enterococcus faecalis, but ampicillin/amoxicillin remains the preferred first-line therapy. 1, 2

First-Line Treatment Hierarchy

Ampicillin or amoxicillin is the drug of choice for enterococcal UTIs, with amoxicillin 500 mg orally every 8 hours for 7 days achieving clinical cure rates of 88.1% and microbiological eradication rates of 86%. 1, 2 High urinary concentrations of ampicillin can overcome high MICs even in ampicillin-resistant strains, making it effective when in vitro testing suggests resistance. 1, 2

For hospitalized patients requiring IV therapy, use high-dose ampicillin 18-30 g IV daily in divided doses or amoxicillin 500 mg IV every 8 hours. 1, 2

Nitrofurantoin as Alternative Therapy

Nitrofurantoin is recommended as an alternative specifically for uncomplicated UTIs due to E. faecalis when ampicillin cannot be used. 1, 2 The recommended dosing is:

• 100 mg orally every 6 hours (four times daily) for 5-7 days 1, 2
• Alternative dosing: 50-100 mg four times daily for 5 days or 100 mg twice daily for 5 days 1

Nitrofurantoin demonstrates excellent in vitro activity against E. faecalis with resistance rates below 6%. 2 Research confirms 80.76% of vancomycin-resistant enterococci remain susceptible to nitrofurantoin, including both E. faecalis and E. faecium. 3, 4

Critical Limitations and Contraindications

Do not use nitrofurantoin for:

• Complicated UTIs or pyelonephritis - achieves poor tissue and serum concentrations 2
• Systemic enterococcal infections (bacteremia, endocarditis, intra-abdominal infections) - inadequate serum levels 1, 2
• Patients with creatinine clearance <60 mL/min - urinary concentrations become inadequate 2

Clinical Decision-Making Algorithm

1. Differentiate colonization from true infection - asymptomatic bacteriuria with E. faecalis does not require treatment 1, 2

2. Obtain urine culture and susceptibility testing before initiating therapy, even for "pansensitive" strains, as resistance patterns vary significantly by institution 1, 2

3. For uncomplicated UTI in symptomatic patients:

   • First choice: Amoxicillin 500 mg PO every 8 hours for 7 days 1, 2
   • Alternative: Nitrofurantoin 100 mg PO every 6 hours for 5-7 days 1, 2
   • Alternative: Fosfomycin 3 g PO single dose (FDA-approved for E. faecalis UTI) 1, 2

4. For penicillin allergy: Nitrofurantoin 100 mg orally every 6 hours for 7 days 2

Common Pitfalls to Avoid

• Avoid fluoroquinolones - high resistance rates (46-47% for ciprofloxacin/levofloxacin) and unfavorable risk-benefit ratios for uncomplicated UTIs 1
• Do not perform routine post-treatment urine cultures in asymptomatic patients 1
• For symptoms that do not resolve or recur within 2-4 weeks, obtain repeat culture and assume the organism is not susceptible to the original agent 1
• Be aware that nitrofurantoin exposure may increase virulence properties in enterococci, though clinical significance in acute treatment remains unclear 5

Evidence Quality Considerations

The recommendation for nitrofurantoin is based on high-quality guideline evidence from the European Urology Association and American College of Physicians. 1, 2 Multiple research studies confirm maintained susceptibility despite widespread use, with efficacy ratios ≥8 observed in 76.5% of MDR E. faecalis isolates. 6 Even vancomycin-resistant strains show 80% susceptibility to nitrofurantoin. 3, 4