Oral Ampicillin for E. faecalis UTI
Yes, oral ampicillin is highly effective for treating Enterococcus faecalis urinary tract infections and is the first-line treatment of choice, with recommended dosing of 500 mg orally every 8 hours for 7 days. 1, 2, 3
First-Line Treatment Recommendation
Ampicillin 500 mg orally every 8 hours for 7 days is the preferred first-line therapy for uncomplicated E. faecalis UTIs, achieving clinical eradication rates of 88.1% and microbiological eradication rates of 86%. 1, 2
Amoxicillin 500 mg orally every 8 hours for 7 days is an equivalent alternative with similar efficacy. 1, 3
The FDA specifically approves oral ampicillin for genitourinary tract infections caused by enterococci. 4
Why Ampicillin Works Even When Resistance is Reported
Ampicillin achieves extremely high urinary concentrations that can overcome high minimum inhibitory concentrations (MICs), making it effective even when in vitro susceptibility testing suggests resistance. 1, 5
This pharmacokinetic advantage means ampicillin can successfully treat lower urinary tract infections caused by ampicillin-resistant E. faecalis strains, as the urinary drug levels far exceed typical MIC breakpoints. 1, 6, 5
Recent data demonstrate that aminopenicillins are non-inferior to other antibiotics for enterococcal lower UTIs, with 83.1% clinical success rates at 14 days, even in cases with vancomycin-resistant enterococci (VRE). 6
Alternative Oral Options
Nitrofurantoin 100 mg orally every 6 hours for 7 days is an effective alternative with good in vitro activity against E. faecalis and resistance rates below 6%. 1, 2, 3
Fosfomycin 3 g as a single oral dose is FDA-approved specifically for E. faecalis UTIs and offers convenient single-dose therapy for uncomplicated infections. 1, 2, 3
Critical Pitfalls to Avoid
Do not use fluoroquinolones (ciprofloxacin, levofloxacin) due to high resistance rates of 46-47% in E. faecalis and unfavorable risk-benefit profiles for uncomplicated UTIs. 2, 3, 7
Always differentiate colonization from true infection before prescribing antibiotics, as asymptomatic bacteriuria with E. faecalis does not routinely require treatment. 1, 8
Obtain susceptibility testing before initiating therapy when possible, even for strains described as "pansensitive," as resistance patterns vary by institution. 1, 2, 3
Treatment Algorithm
Confirm symptomatic UTI (dysuria, frequency, urgency, suprapubic pain) versus asymptomatic bacteriuria. 1, 8
For uncomplicated E. faecalis UTI: Start ampicillin 500 mg PO every 8 hours for 7 days. 1, 2, 3
If penicillin allergy: Use nitrofurantoin 100 mg PO every 6 hours for 7 days. 2
For beta-lactamase producing strains: Switch to amoxicillin-clavulanate. 2
For VRE UTI: Use fosfomycin 3 g single dose or nitrofurantoin 100 mg every 6 hours. 3, 8
Special Considerations
For complicated UTIs or pyelonephritis, longer treatment durations may be necessary beyond the standard 7 days. 1, 3
For hospitalized patients requiring IV therapy, use ampicillin 2 g IV every 4 hours. 3
The high urinary concentrations of ampicillin make it effective even against VRE strains when treating lower UTIs, despite in vitro resistance. 1, 6, 5