What is the recommended amoxicillin regimen for Enterococcus faecalis (E. faecalis) urinary tract infections (UTIs)?

Amoxicillin Regimen for Enterococcus faecalis UTI

For Enterococcus faecalis urinary tract infections, amoxicillin at a dose of 500-875 mg three times daily for 7 days is the recommended first-line treatment when susceptibility is confirmed. 1

Treatment Selection Algorithm

First-Line Options:

1. Amoxicillin: 500-875 mg orally three times daily for 7 days

   • Preferred for susceptible E. faecalis strains
   • High urinary concentrations make it effective even for some isolates with higher MICs 2

2. Amoxicillin-clavulanic acid: 500/125 mg orally three times daily for 7 days

   • Alternative first-line option per WHO guidelines 3
   • Note: The addition of clavulanic acid provides no additional benefit for E. faecalis (which rarely produces beta-lactamases) 4

Alternative Options (if amoxicillin resistance confirmed):

1. Nitrofurantoin: 100 mg orally twice daily for 5-7 days

   • Effective for lower UTIs only (not for pyelonephritis)
   • Good activity against E. faecalis 1, 5

2. Fosfomycin: 3 g single oral dose

   • Convenient single-dose therapy
   • Active against many resistant enterococci 1, 5

Special Considerations

Severity-Based Approach:

• Uncomplicated lower UTI: Oral amoxicillin is appropriate
• Complicated UTI/Pyelonephritis: Consider parenteral therapy initially
  • Ampicillin 2 g IV every 6 hours 3
  • Switch to oral therapy when clinically improved

Resistance Patterns:

• E. faecalis generally remains susceptible to ampicillin/amoxicillin (unlike E. faecium) 6
• For ampicillin-resistant strains, consider:
  • Vancomycin (if susceptible)
  • Linezolid or daptomycin for severe infections 7, 5

Important Caveats:

• Do not use fluoroquinolones as empiric therapy for E. faecalis UTIs due to high resistance rates (47% resistance to ciprofloxacin reported) 6
• Avoid cephalosporins as enterococci are intrinsically resistant
• Distinguish colonization from infection before initiating therapy, especially in catheterized patients 5
• Remove indwelling catheters whenever possible to improve treatment outcomes 7

Monitoring and Follow-up

• Clinical response should be assessed within 48-72 hours
• Repeat urine culture only if symptoms persist after appropriate therapy
• Consider infectious disease consultation for vancomycin-resistant enterococci (VRE) 1

Duration of Therapy

• Uncomplicated lower UTI: 5-7 days
• Complicated UTI or pyelonephritis: 10-14 days

The high urinary concentrations of amoxicillin (exceeding serum levels by 10-100 times) make it particularly effective for treating E. faecalis UTIs, even when in vitro susceptibility testing suggests resistance based on serum breakpoints 2.