What are the best antibiotics for an uncomplicated Enterococcus (E.) faecalis urinary tract infection (UTI) in an adult patient?

Best Antibiotics for Enterococcus faecalis UTI

For uncomplicated E. faecalis UTI, amoxicillin 500 mg orally every 8 hours for 7 days is the first-line treatment when susceptibility is confirmed, achieving 88% clinical cure rates. 1

First-Line Treatment Approach

Ampicillin or amoxicillin remains the drug of choice for E. faecalis UTI based on multiple guideline recommendations and proven efficacy. 2, 1 The standard regimen is:

• Amoxicillin 500 mg orally every 8 hours for 7 days 1
• Ampicillin 500 mg orally every 8 hours for 7 days (equivalent alternative) 1

Critical Pre-Treatment Requirement

Always obtain urine culture and susceptibility testing before initiating therapy, as resistance patterns vary significantly. 1 Approximately 2% of E. faecalis strains are vancomycin-resistant, with variable ampicillin susceptibility. 1 This step is non-negotiable for appropriate antibiotic selection.

Alternative Oral Agents for Uncomplicated UTI

When ampicillin/amoxicillin cannot be used or for resistant strains, consider these alternatives:

Nitrofurantoin

• 100 mg orally every 6 hours for 7 days 1, 3
• Maintains excellent activity against E. faecalis with only 1.5% resistance rates 4
• Monitor for pulmonary reactions, hepatic toxicity, and GI disturbances 5
• Do not use for pyelonephritis due to insufficient tissue penetration 6

Fosfomycin

• 3 g as a single oral dose 1, 3
• Demonstrates 0% resistance in E. faecium and excellent activity against vancomycin-resistant enterococci 4
• Particularly useful for uncomplicated cystitis 7, 4

Piperacillin-Tazobactam

• Can be used based on susceptibility testing 2
• Appropriate for both E. faecalis and some resistant strains 2

What NOT to Use

Avoid fluoroquinolones (ciprofloxacin, levofloxacin) for E. faecalis UTI due to:

• High resistance rates (46-47% for ciprofloxacin, 46% for levofloxacin) 8, 4
• Unfavorable risk-benefit profile 1
• FDA advisory against use in uncomplicated UTI 2

Trimethoprim-sulfamethoxazole should not be used as resistance develops rapidly with prolonged treatment, even when initially susceptible. 9 This agent is no longer reliable for enterococcal infections.

Complicated UTI or Pyelonephritis

For more severe infections requiring parenteral therapy:

• Ampicillin 2 g IV every 4 hours 1
• Treatment duration extends to 10-14 days for complicated cases 1
• Consider adding gentamicin for synergy in severe infections (if susceptible to high-level aminoglycosides) 2

Vancomycin-Resistant E. faecalis (VRE)

When dealing with VRE in uncomplicated UTI:

Oral Options

• Fosfomycin 3 g single oral dose 1
• Nitrofurantoin 100 mg orally every 6 hours for 7 days 1

Parenteral Options for Complicated VRE Infections

• Linezolid 600 mg IV or PO every 12 hours for bacteremia or complicated infection 1, 10
• Daptomycin in high doses (though prostatic penetration may be limited) 5
• Linezolid achieved 67% cure rates for vancomycin-resistant enterococcal infections in clinical trials 10

Special Consideration: Chronic Bacterial Prostatitis

For chronic bacterial prostatitis caused by resistant E. faecalis:

• Rifampin combined with nitrofurantoin 100 mg PO every 6 hours is recommended by the American Urological Association 5
• This combination has proven successful for difficult-to-treat enterococcal infections 5
• Complete the full prescribed course to prevent relapse 5

Common Pitfalls to Avoid

1. Do not extend treatment beyond 7 days for uncomplicated UTI without clear indication, as this increases resistance risk without proven benefit 1

2. Do not use empiric therapy without culture confirmation - E. faecalis susceptibility patterns vary significantly by institution and patient population 1

3. Do not treat asymptomatic bacteriuria with multidrug-resistant Enterococcus, as this increases resistance and healthcare costs 2, 3

4. Remove indwelling urinary catheters when possible, as catheterization is associated with enterococcal UTI 3

5. Avoid beta-lactam antibiotics as prolonged prophylaxis due to collateral damage effects and promotion of rapid UTI recurrence 2

Risk Factors for Resistance

Patients at higher risk for ciprofloxacin-resistant E. faecalis include:

• Hospital-acquired infections (18-fold increased risk) 8
• Patients transferred from healthcare centers (7-fold increased risk) 8
• Urological department patients (6-fold increased risk) 8

These patients require culture-directed therapy rather than empiric fluoroquinolone use. 8