Oral Antibiotic Treatment for Enterococcus Species in Urine Culture
Amoxicillin 500 mg orally every 8 hours for 7 days is the first-line oral antibiotic for Enterococcus urinary tract infections when the organism is ampicillin-susceptible. 1, 2
Initial Management Approach
Distinguish Infection from Colonization
- Do not treat asymptomatic bacteriuria with Enterococcus species - this represents colonization rather than true infection and does not require antibiotics 2, 3
- Only treat when urinary symptoms are present (dysuria, frequency, urgency, suprapubic pain) or signs of systemic infection exist 3
Obtain Susceptibility Testing
- Always obtain antibiotic susceptibility testing before finalizing therapy, even for strains initially reported as "pansensitive," as resistance patterns vary significantly by institution 2
- High urinary concentrations of ampicillin can overcome elevated MICs in some ampicillin-resistant strains, making it effective even when in vitro testing suggests resistance 2
First-Line Oral Treatment Options
For Ampicillin-Susceptible Enterococcus (Including Most E. faecalis)
- Amoxicillin 500 mg orally every 8 hours for 7 days achieves clinical eradication rates of 88.1% and microbiological eradication of 86% 2
- Ampicillin 500 mg orally every 8 hours for 7 days is an equivalent alternative with similar efficacy 2
Alternative Oral Agents for Uncomplicated Cystitis
- Nitrofurantoin 100 mg orally four times daily for 7 days has good activity against E. faecalis with resistance rates below 6%, though emerging resistance has been observed in some centers 1, 2, 4
- Fosfomycin 3 g orally as a single dose is FDA-approved specifically for E. faecalis UTI and recommended for uncomplicated infections 1, 2
Critical Limitations and Contraindications
When NOT to Use Nitrofurantoin
- Never use nitrofurantoin for complicated UTIs, pyelonephritis, or any systemic enterococcal infection (bacteremia, endocarditis, intra-abdominal infections) as it achieves poor tissue and serum concentrations 2
- Contraindicated when creatinine clearance <60 mL/min as urinary concentrations become inadequate 2
Antibiotics to Avoid
- Do not use cephalosporins - Enterococcus species have natural resistance to all cephalosporins 2
- Avoid fluoroquinolones (ciprofloxacin, levofloxacin) due to high resistance rates of 46-47% and unfavorable risk-benefit ratio for uncomplicated UTIs 2
Treatment for Vancomycin-Resistant Enterococcus (VRE)
Uncomplicated VRE Cystitis
- Nitrofurantoin 100 mg orally four times daily for 3-7 days remains appropriate despite vancomycin resistance 1, 3
- Fosfomycin 3 g orally every other day for 3 doses is an alternative option 1
- Ampicillin 18-30 g/day IV in divided doses can be used even for some ampicillin-resistant VRE due to high urinary concentrations 1, 2
Complicated VRE UTI or Upper Tract Infection
- Linezolid 600 mg orally every 12 hours for 5-7 days is first-line for complicated VRE UTI, with clinical cure rates of 81.4% and microbiological cure of 86.4% 1, 5, 6
- Daptomycin 6-12 mg/kg IV daily for 5-7 days is an alternative for severe VRE UTI 1
- Reserve linezolid and daptomycin for confirmed or suspected upper tract/bacteremic VRE UTIs among ampicillin-resistant strains 2, 3
Special Clinical Scenarios
If Bacteremia is Present
- Escalate to IV therapy immediately - oral antibiotics are insufficient for enterococcal bacteremia 5
- Use high-dose daptomycin 10-12 mg/kg/day IV plus ampicillin (if susceptible) for 2-4 weeks 5
- Perform transesophageal echocardiography if bacteremia persists >4 days to evaluate for endocarditis 7
Penicillin Allergy
- Nitrofurantoin 100 mg orally four times daily for 7 days is the appropriate alternative for patients with penicillin allergy 2
- Linezolid 600 mg orally every 12 hours is an option for VRE in penicillin-allergic patients 1
Monitoring Requirements
For Linezolid Therapy >2 Weeks
- Obtain weekly complete blood counts due to myelosuppression risk, particularly thrombocytopenia 5
For High-Dose Daptomycin
- Monitor weekly CPK levels throughout therapy due to significant myopathy risk 5
- Discontinue immediately if CPK rises significantly or muscle pain/weakness develops 5
When to Consult Infectious Disease
- Obtain ID consultation for VRE infections, relapsed enterococcal infections, bacteremic urosepsis, multidrug-resistant strains, or treatment failures 5