What oral antibiotic is effective against Enterococcus (E.) faecalis urinary tract infections (UTIs)?

Oral Antibiotic Options for Enterococcus Faecalis UTI

For uncomplicated urinary tract infections caused by Enterococcus faecalis, nitrofurantoin 100 mg PO every 6 hours is recommended as first-line oral therapy. 1

First-Line Oral Options (in order of preference)

1. Nitrofurantoin

   • Dosage: 100 mg PO every 6 hours
   • Duration: 5-7 days for uncomplicated UTI
   • Evidence quality: Very low quality evidence, but strong recommendation 1
   • Advantages: Good in vitro activity against E. faecalis, including vancomycin-resistant strains

2. Fosfomycin

   • Dosage: Single 3 g PO dose
   • Evidence quality: Very low quality evidence 1
   • Particularly useful for patients who need single-dose therapy
   • FDA approved for E. faecalis UTIs

3. Amoxicillin

   • Dosage: 500 mg PO every 8 hours
   • Evidence quality: Very low quality evidence 1
   • Use only if susceptibility is confirmed
   • For ampicillin-resistant strains, high-dose therapy may overcome resistance in the urinary tract due to high urinary concentrations

Alternative Options (for resistant strains)

• Linezolid
  • Dosage: 600 mg PO every 12 hours
  • Duration: Based on clinical response 1
  • Reserve for multidrug-resistant strains
  • Caution: Monitor for hematological toxicity with prolonged use

Clinical Decision Algorithm

1. Assess UTI severity:

   • Uncomplicated (lower UTI/cystitis): Use oral therapy
   • Complicated/pyelonephritis: Consider initial parenteral therapy

2. Check local resistance patterns:

   • If local E. faecalis has high resistance to nitrofurantoin, consider fosfomycin or amoxicillin

3. Consider patient factors:

   • Renal function: Avoid nitrofurantoin if CrCl <30 ml/min
   • Compliance: Consider fosfomycin for single-dose advantage
   • Prior antibiotic exposure: May influence resistance patterns

Important Clinical Considerations

• Differentiate colonization from infection before initiating therapy, particularly in catheterized patients 1
• Remove indwelling catheters when possible to improve treatment outcomes
• Obtain urine culture and susceptibility testing to guide definitive therapy
• Vancomycin-resistant E. faecalis (VRE) UTIs can often still be treated with nitrofurantoin or fosfomycin

Common Pitfalls to Avoid

• Treating asymptomatic bacteriuria with E. faecalis is not recommended unless in specific populations (pregnancy, pre-urologic procedures)
• Using agents with poor urinary concentrations (e.g., tigecycline) for UTI treatment
• Overusing broad-spectrum agents (e.g., linezolid) for uncomplicated UTIs
• Failing to adjust therapy based on culture and susceptibility results

Recent evidence from a 2024 multicentre study demonstrated high efficacy (97.5% success rate) of linezolid for enterococcal UTIs, supporting its use as a reserve option for resistant cases 2. However, nitrofurantoin and fosfomycin should be preferred for uncomplicated infections to preserve more broad-spectrum agents.