What is the best antibiotic for a patient with a urinary tract infection caused by Enterococcus faecalis?

Best Antibiotic for Enterococcus faecalis UTI

Amoxicillin 500 mg orally every 8 hours for 7 days is the first-line treatment for uncomplicated E. faecalis urinary tract infections, achieving 88.1% clinical and 86% microbiological eradication rates. 1

First-Line Oral Treatment

• Ampicillin/Amoxicillin remains the drug of choice for enterococcal UTIs, with ampicillin 500 mg orally every 8 hours being equivalent to amoxicillin 1, 2

• High urinary concentrations of ampicillin can overcome elevated MICs even in strains that appear resistant on in vitro testing, making it effective when susceptibility testing suggests resistance 1

• For beta-lactamase producing strains, substitute amoxicillin-clavulanate at the same dosing schedule 1

Alternative Oral Agents

• Nitrofurantoin 100 mg orally every 6 hours for 7 days is an effective alternative with >94% susceptibility rates for E. faecalis and low resistance (<6%) 1, 2, 3

• Fosfomycin 3 g orally as a single dose is FDA-approved specifically for E. faecalis UTI and provides convenient single-dose therapy for uncomplicated infections 1, 2

Critical Treatment Considerations

• Always obtain susceptibility testing before initiating therapy, even for strains described as "pansensitive," as resistance patterns vary significantly by institution 1, 2

• Avoid fluoroquinolones due to high resistance rates (46-47% for ciprofloxacin/levofloxacin in E. faecalis) and unfavorable risk-benefit ratios for uncomplicated UTIs 1, 4, 3

• Differentiate colonization from true infection before prescribing antibiotics, as asymptomatic bacteriuria with E. faecalis does not routinely require treatment 1, 5

Treatment Algorithm

1. Start with amoxicillin 500 mg every 8 hours for 7 days if no penicillin allergy and uncomplicated UTI 1, 2

2. Switch to nitrofurantoin 100 mg every 6 hours for 7 days if penicillin allergy exists 1, 2

3. Consider fosfomycin 3 g single dose for uncomplicated cystitis when adherence is a concern 1, 2

4. For complicated UTI or pyelonephritis, longer treatment durations may be necessary, though specific evidence for E. faecalis is limited 1

Important Caveats

• Remove indwelling urinary catheters when present, as this alone may resolve bacteriuria 5

• For vancomycin-resistant E. faecalis (rare), ampicillin and nitrofurantoin remain >90% effective 6

• Resistance rates to tetracycline (72-96%) and erythromycin (92%) are extremely high and these agents should be avoided 4, 3