Oral Antibiotic Treatment for Enterococcus faecalis
For most Enterococcus faecalis infections requiring oral therapy, high-dose amoxicillin 1000 mg orally three times daily is the gold standard first-line treatment, achieving MICs two to four times lower than penicillin G against enterococci. 1, 2
First-Line Oral Therapy
Amoxicillin is the preferred oral agent for E. faecalis infections when susceptibility is confirmed (MIC ≤8 mg/L), as it is FDA-approved for genitourinary tract infections, skin and skin structure infections, and upper respiratory tract infections caused by β-lactamase-negative E. faecalis. 3, 1
Dosing Regimens by Infection Site:
- Uncomplicated cystitis: Amoxicillin 500 mg orally every 8 hours for 7-14 days 4, 1, 2
- Chronic bacterial prostatitis: High-dose amoxicillin 1000 mg orally three times daily for 4-6 weeks, targeting trough concentrations of 40-80 mg/L to overcome the blood-prostate barrier 1, 2
- Less severe infections (general): High-dose amoxicillin 1000 mg orally three times daily 1, 2
Alternative Oral Agents for Specific Scenarios
For Vancomycin-Resistant E. faecalis (VRE):
Linezolid 600 mg orally every 12 hours is the preferred agent for VRE infections, with proven clinical efficacy (86.4% microbiological cure rate and 81.4% clinical cure rate) and excellent tissue penetration. 4, 1 Treatment duration depends on the site of infection and clinical response, with a minimum of 8 weeks for serious infections. 1
For Uncomplicated UTI Due to VRE:
- Nitrofurantoin 100 mg orally every 6 hours is recommended for uncomplicated urinary tract infections due to VRE 4
- Single-dose fosfomycin 3 g orally is an alternative for uncomplicated cystitis due to VRE 4
- High-dose amoxicillin 500 mg orally every 8 hours can be used if the VRE strain retains ampicillin susceptibility (only 3% of E. faecalis are multidrug-resistant, and most retain ampicillin susceptibility) 4, 1
For Penicillin Allergy:
Vancomycin is not available orally for systemic infections and should only be reserved for true severe penicillin allergy in the intravenous setting. 1, 2 For oral therapy in penicillin-allergic patients with VRE, linezolid 600 mg orally every 12 hours is the appropriate choice. 1
Critical Pitfalls to Avoid
- Never use cephalosporins alone for enterococcal coverage—they have no intrinsic activity against enterococci despite in vitro synergy when combined with ampicillin. 1, 2
- Do not prescribe vancomycin empirically for E. faecalis when ampicillin/amoxicillin is superior unless there is documented beta-lactam allergy or confirmed resistance. 1
- Avoid fluoroquinolones as monotherapy for E. faecalis, as they are not guideline-recommended first-line agents and resistance is common. 5
- Ensure adequate treatment duration: Continue therapy for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication. 3
Special Considerations for Chronic Prostatitis
For E. faecalis chronic prostatitis specifically, linezolid 600 mg orally every 12 hours can be used as pulse therapy (2 weeks on, 1 week off) to minimize myelosuppression and peripheral neuropathy risk, particularly for resistant strains. 6 Consider 2-3 cycles of pulse therapy if symptoms persist but are improving with each cycle. 6
When Oral Therapy Is Insufficient
Serious infections requiring bactericidal activity (endocarditis, osteomyelitis, prosthetic joint infections) typically require intravenous combination therapy with ampicillin plus gentamicin or ampicillin plus ceftriaxone, not oral monotherapy. 4, 5, 7 Sequential oral treatment with amoxicillin may be considered after initial IV therapy once clinical stability is achieved. 5, 7