What are the best antibiotics to treat vancomycin-sensitive Enterococcus faecalis (formerly known as Enterococcus vocalis is not a valid species, assuming it's a typo) bacteremia in a 76-year-old male with normal renal function?

Best Antibiotics for Vancomycin-Sensitive Enterococcus faecalis Bacteremia in a 76-Year-Old Male with Normal Renal Function

Ampicillin plus gentamicin is the first-line treatment for vancomycin-sensitive Enterococcus faecalis bacteremia in a 76-year-old male with normal renal function. 1, 2

First-Line Treatment Options

Preferred Regimen:

• Ampicillin: 2g IV every 4 hours 1, 2
• Plus Gentamicin: 3 mg/kg/day IV in 3 divided doses 1, 2

This combination provides synergistic bactericidal activity against E. faecalis, which is critical for treating bloodstream infections. The American Heart Association recommends this combination as first-line therapy for enterococcal infections 2.

Alternative Regimens

For Gentamicin-Resistant Strains:

• Ampicillin: 2g IV every 4 hours
• Plus Ceftriaxone: 2g IV every 12 hours 1

This double β-lactam combination is particularly valuable for patients with normal or impaired renal function, or those with abnormal cranial nerve VIII function 1.

For Gentamicin-Resistant but Streptomycin-Susceptible Strains:

• Ampicillin: 2g IV every 4 hours
• Plus Streptomycin: 15 mg/kg/day IV/IM in 2 divided doses 1

Streptomycin should be adjusted to achieve serum peak concentrations of 20-35 μg/mL and trough concentrations <10 μg/mL 1.

For Penicillin-Allergic Patients:

• Vancomycin: 30 mg/kg/day IV in 2 divided doses
• Plus Gentamicin: 3 mg/kg/day IV in 3 divided doses 1, 2

This combination is recommended only for patients unable to tolerate penicillin or ampicillin, as the vancomycin-gentamicin combination has increased risk of ototoxicity and nephrotoxicity compared to penicillin-gentamicin combinations 1.

Treatment Duration

For bloodstream infections:

• Uncomplicated bacteremia: 10-14 days 2
• If endocarditis is suspected or confirmed:
  • Native valve with symptoms <3 months: 4 weeks
  • Native valve with symptoms >3 months: 6 weeks
  • Prosthetic valve: minimum 6 weeks 1, 2

Monitoring

• Weekly renal function tests with aminoglycoside therapy
• Follow-up blood cultures to ensure clearance of bacteremia
• Consider transesophageal echocardiogram (TEE) if there is:
  • Persistent fever or bacteremia beyond 72 hours of appropriate therapy
  • New murmur or embolic phenomena
  • Presence of prosthetic valves or other endovascular devices 2

Important Considerations

1. Avoid cephalosporin monotherapy: E. faecalis is intrinsically resistant to cephalosporins when used alone 2

2. Aminoglycoside dosing: Adjust based on renal function and therapeutic drug monitoring

3. Vancomycin caution: While the organism is vancomycin-sensitive, vancomycin should not be used alone for enterococcal endocarditis or serious infections; it must be combined with an aminoglycoside 3

4. For vancomycin-tolerant strains: Consider high-dose daptomycin (8-12 mg/kg/day) if the patient fails to respond to standard therapy despite in vitro susceptibility 4

5. Infectious disease consultation: Strongly recommended for serious enterococcal infections, especially if bacteremia persists despite appropriate therapy 2

The combination of ampicillin plus gentamicin remains the cornerstone of treatment for vancomycin-sensitive E. faecalis bacteremia in patients with normal renal function, providing optimal bactericidal activity and clinical outcomes.