Oral Treatment for Ampicillin-Susceptible Enterococcal UTI
Yes, oral amoxicillin 500 mg every 8 hours for 7 days is the recommended oral treatment for uncomplicated urinary tract infections caused by ampicillin-susceptible Enterococcus species. 1
First-Line Oral Regimen
Amoxicillin 500 mg orally every 8 hours for 7 days is the preferred oral option, achieving clinical cure rates of 88.1% and microbiological eradication rates of 86% for susceptible Enterococcus faecalis UTIs. 1
Equivalent Alternative
- Ampicillin 500 mg orally every 8 hours for 7 days provides similar efficacy and is an acceptable alternative to amoxicillin. 1, 2
When to Extend Duration Beyond 7 Days
For complicated UTIs or pyelonephritis, treatment duration may need to extend beyond the standard 7 days, though specific duration should be guided by clinical response. 1
For uncomplicated UTI with associated bacteremia (such as catheter-related bloodstream infection), a 7-14 day course is recommended. 1
Patients with signs of endocarditis, persistent bacteremia >72 hours, or metastatic infection require extended IV therapy and infectious disease consultation rather than oral treatment. 1
Critical Pre-Treatment Considerations
Always confirm ampicillin susceptibility before initiating oral aminopenicillin therapy, as approximately 23% of Enterococcus species demonstrate ampicillin resistance, and 60% of E. faecium are vancomycin-resistant with variable ampicillin susceptibility. 1, 3
Alternative Oral Agents for Resistant Strains
If the isolate proves ampicillin-resistant or vancomycin-resistant:
Fosfomycin 3 g as a single oral dose is effective for uncomplicated VRE UTI. 1, 4
Nitrofurantoin 100 mg orally every 6 hours for 7 days is another option for VRE with uncomplicated UTI. 1, 4
Fluoroquinolones should be avoided due to high resistance rates (46-47%) among enterococci. 1
Important Clinical Nuance: Treating "Resistant" Isolates
Aminopenicillins may still be effective for lower UTIs even when the isolate tests as ampicillin-resistant in vitro, because urinary concentrations of ampicillin far exceed serum levels and can overcome resistance at the MIC breakpoint. 5, 6 A retrospective study showed aminopenicillins achieved 83.9% clinical cure rates for vancomycin-resistant enterococcal UTI regardless of ampicillin susceptibility status, compared to 73.3% for non-β-lactam antibiotics. 6
Common Pitfalls to Avoid
Do not extend treatment beyond 7 days for uncomplicated UTI without clear indication, as this increases antibiotic resistance risk without proven benefit. 1
Do not use oral therapy for complicated infections requiring IV treatment, such as pyelonephritis with systemic symptoms, bacteremia, or prosthetic material involvement—these require IV ampicillin 2 g every 4 hours. 1
Do not assume all enterococci are ampicillin-susceptible—E. faecium has significantly higher resistance rates than E. faecalis, making culture confirmation essential. 1, 3