What antibiotic is recommended for treating an adult urinary tract infection caused by Enterococcus faecalis?

Antibiotic for E. faecalis in Urine

For uncomplicated urinary tract infections caused by E. faecalis, use nitrofurantoin 100 mg PO every 6 hours for 5 days, or fosfomycin 3 g PO as a single dose. For complicated UTIs or pyelonephritis, ampicillin (high-dose: 18-30 g IV daily in divided doses) or amoxicillin 500 mg PO/IV every 8 hours is the preferred treatment, even when in vitro resistance is reported 1, 2.

Treatment Algorithm Based on Clinical Scenario

Uncomplicated Cystitis (Lower UTI)

• First-line options:
  • Nitrofurantoin 100 mg PO every 6 hours for 5 days 1
  • Fosfomycin 3 g PO single dose 1
  • High-dose ampicillin (18-30 g IV daily) or amoxicillin 500 mg PO/IV every 8 hours 1

Key point: Nitrofurantoin demonstrates 88% susceptibility against enterococci in clinical studies 3, making it highly effective for lower UTIs. Fosfomycin is FDA-approved specifically for E. faecalis UTIs 1.

Complicated UTI or Pyelonephritis

• Preferred treatment: Ampicillin or amoxicillin at high doses
  • Ampicillin: 18-30 g IV daily in divided doses 1
  • Amoxicillin: 500 mg PO/IV every 8 hours 1
  • Duration: 7-14 days depending on severity 4

Critical caveat: High urinary concentrations of ampicillin can overcome in vitro resistance in E. faecalis UTIs. Clinical cure rates of 88.1% and microbiological eradication of 86% have been documented even with ampicillin-resistant strains 2. This is because urinary drug concentrations far exceed serum levels, achieving bactericidal activity despite reported resistance 1, 5.

Vancomycin-Resistant E. faecalis (VRE)

If the isolate is vancomycin-resistant but ampicillin-susceptible:

• First choice: High-dose ampicillin (18-30 g IV daily) or amoxicillin 500 mg every 8 hours 1
• Alternative oral options for uncomplicated cystitis:
  • Nitrofurantoin 100 mg PO every 6 hours 1
  • Fosfomycin 3 g PO single dose 1

If ampicillin-resistant VRE:

• For uncomplicated cystitis: Nitrofurantoin or fosfomycin (as above)
• For complicated/systemic infection: Linezolid 600 mg IV or PO every 12 hours 1 (strong recommendation for enterococcal infections)

Penicillin Allergy

• Preferred: Linezolid 600 mg IV or PO every 12 hours 4
• Alternative: Fluoroquinolones (levofloxacin) if susceptible, though 37% of experts consider this inappropriate due to resistance concerns 4
• Duration: 14 days for most cases 4

Important Clinical Considerations

Do not treat asymptomatic bacteriuria: Differentiate true infection from colonization, especially in catheterized patients. Consider therapeutic abstention in:

• Catheterized patients without systemic symptoms (51% of experts support this) 4
• Polymicrobial cultures suggesting contamination (50% support abstention) 4
• Leukocyturia <10⁴/mL without symptoms (64% support abstention) 4

Catheter management: In catheter-associated UTIs, remove or exchange the catheter when possible. Cure rates are similar whether catheters are exchanged/removed (90.5%) or retained (87.5%), but removal is preferred 2.

Risk factors for treatment failure:

• Immunocompromised status: Lower cure rates (78.1% vs 94.2%) 2
• Underlying urinary tract abnormalities: Lower cure rates (71.4% vs 93.7%) 2
• These patients may require longer treatment courses (21 days vs 14 days) 4

Species-Specific Resistance Patterns

E. faecalis typically shows:

• 88% susceptibility to nitrofurantoin 3
• 72% susceptibility to ampicillin 6
• 51% resistance to fluoroquinolones 6
• Very low vancomycin resistance (1.3%) 1

Avoid fluoroquinolones as empiric therapy due to high resistance rates (>50%) in E. faecalis 6, 7.

Duration of Therapy

• Uncomplicated cystitis: 5 days (nitrofurantoin) or single dose (fosfomycin)
• Complicated UTI/pyelonephritis: 7-14 days, with 14 days being most common practice 4
• Immunocompromised or structural abnormalities: Consider 21 days 4