Effective Antibiotics for Enterococcus faecalis Infections

First-Line Treatment Options

• The American Heart Association recommends ampicillin as the drug of choice for enterococcal infections, including E. faecalis, when the organism is susceptible 1, 2
• High-dose ampicillin (18-30g IV daily) or amoxicillin (500mg PO/IV every 8h) is recommended to achieve sufficient therapeutic concentrations 1, 2
• For serious infections like endocarditis, ampicillin 2g IV every 4 hours is the standard dosing regimen 3, 4

Alternative Options for Resistant Strains

• Vancomycin is effective against E. faecalis and shows low resistance rates 1, 3, 4
• The Infectious Diseases Society of America recommends vancomycin 30 mg/kg per 24h IV in 2 equally divided doses 3, 4
• Linezolid shows excellent activity against E. faecalis, including vancomycin-resistant strains 1
• Daptomycin is preferred for serious vancomycin-resistant E. faecalis infections at dosing of at least 8 mg/kg and up to 10-12 mg/kg 1, 2

Site-Specific Considerations

• For E. faecalis endocarditis, treatment duration should be 4-6 weeks 3, 4
• Double beta-lactam therapy (ampicillin plus ceftriaxone) has comparable efficacy to ampicillin-gentamicin with less nephrotoxicity 5

Clinical Pearls and Pitfalls

• Always differentiate colonization from true infection before initiating anti-enterococcal therapy 1, 2
• E. faecalis and E. faecium have different resistance patterns; E. faecalis is generally more susceptible to ampicillin and less likely to be multidrug-resistant 1, 3
• Only about 3% of E. faecalis strains are multidrug-resistant, compared to up to 95% of E. faecium strains 3
• Ceftaroline and most cephalosporins have poor activity against enterococci and should not be used as monotherapy 1, 2

Emerging Options

• Eravacycline has in vitro activity against vancomycin-resistant enterococci but clinical evidence for its use is limited 1, 2

Nitrofurantoin for E. faecalis UTI with MIC ≤16 mg/L

Treatment Recommendation

• The American College of Cardiology is not mentioned, however, the Journal of Microbiology, Immunology and Infection recommends nitrofurantoin 100 mg orally every 6 hours for uncomplicated lower urinary tract infections caused by E. faecalis with an MIC ≤16 mg/L, as this organism demonstrates excellent in vitro susceptibility to nitrofurantoin and the drug achieves high urinary concentrations 6
• Nitrofurantoin was approved by the U.S. FDA in the 1950s specifically for treatment of lower urinary tract infections and has good in vitro activity against enterococci 7

Alternative First-Line Options

• Ampicillin remains the drug of choice for E. faecalis infections when the organism is susceptible (penicillin MIC ≤8 mg/L) 8, 9
• High-dose ampicillin (18-30g IV daily in divided doses) or amoxicillin (500 mg PO/IV every 8 hours) can be used for uncomplicated UTIs, as high urinary concentrations may overcome resistance 7, 6
• Fosfomycin 3g PO single dose is FDA-approved for UTI caused by E. faecalis and recommended for uncomplicated VRE UTIs 7, 6

Important Clinical Considerations

• Nitrofurantoin should NOT be used for pyelonephritis, complicated UTIs, or systemic enterococcal infections due to inadequate tissue penetration 7
• Avoid nitrofurantoin in patients with creatinine clearance <30-50 mL/min due to reduced urinary drug concentrations 10
• Typically 5-7 days for uncomplicated cystitis in women 6

For Complicated or Systemic E. faecalis Infections

• Ampicillin 2g IV every 4 hours combined with gentamicin (if aminoglycoside-susceptible) for 4-6 weeks for endocarditis 8, 11, 10, 9
• Double beta-lactam therapy (ampicillin plus ceftriaxone) offers comparable efficacy with less nephrotoxicity for gentamicin-resistant strains 11
• Daptomycin 8-12 mg/kg/day for vancomycin-resistant E. faecalis bacteremia 7, 6

First‑Line and Adjunctive Therapy for Enterococcus faecalis Pyelonephritis

First‑Line Beta‑Lactam Regimen

• Ampicillin 2 g intravenously every 4–6 hours for a total of 10–14 days is the recommended initial treatment for adult patients with pyelonephritis caused by Enterococcus faecalis who have no beta‑lactam allergy. This high‑dose schedule ensures adequate renal tissue concentrations and is supported by clinical data. 12

Importance of Susceptibility Confirmation

• Routine susceptibility testing should be performed to verify ampicillin susceptibility before finalizing therapy, allowing targeted treatment and avoiding unnecessary broad‑spectrum agents. 12

Adjunctive Aminoglycoside for Severe Disease

• In patients with severe pyelonephritis requiring hospitalization or when bacteremia is suspected, adding an aminoglycoside (e.g., gentamicin) to ampicillin can provide synergistic bactericidal activity, especially when the isolate remains aminoglycoside‑susceptible. 12

Monitoring for Nephrotoxicity

• When an aminoglycoside is combined with ampicillin, renal function must be closely monitored because approximately 23 % of such patients develop nephrotoxicity. 13

Recommended Treatment Duration

• Beta‑lactam–based regimens for E. faecalis pyelonephritis should be continued for 10–14 days, which is longer than the 5–7‑day courses typically used for fluoroquinolone therapy. 12