What is the appropriate antibiotic choice for Enterococcus infections?

Antibiotic Choice for Enterococcus Infections

For Enterococcus infections, ampicillin is the drug of choice for ampicillin-susceptible strains, with vancomycin recommended for ampicillin-resistant strains. 1

First-line Treatment Options Based on Susceptibility

• For ampicillin-susceptible Enterococcus (particularly E. faecalis):

  • Ampicillin is the preferred first-line agent 1, 2
  • Penicillin G or ampicillin combined with gentamicin for 4-6 weeks is recommended for native valve infective endocarditis (IE) caused by susceptible strains 1
  • Piperacillin-tazobactam is an effective alternative, particularly in polymicrobial infections 2, 3

• For ampicillin-resistant Enterococcus:

  • Vancomycin is the recommended alternative when the pathogen is resistant to ampicillin 1, 3
  • For vancomycin-resistant enterococci (VRE), linezolid or daptomycin should be used based on susceptibility testing 1, 4

Special Treatment Considerations

Infective Endocarditis

• For enterococcal IE, combination therapy is critical:
  • Native valve IE: Penicillin G or ampicillin plus gentamicin for 4-6 weeks 1
  • For aminoglycoside-resistant strains: Ampicillin plus ceftriaxone is recommended 1
  • For prosthetic valve IE: Extended therapy duration of at least 6 weeks is recommended 1

Catheter-Related Bloodstream Infections

• For enterococcal catheter-related bloodstream infections (CRBSI):
  • Remove infected short-term intravascular catheters 1
  • For long-term catheters, removal is indicated for insertion site/pocket infection, suppurative thrombophlebitis, sepsis, endocarditis, persistent bacteremia, or metastatic infection 1
  • 7-14 days of therapy is recommended for uncomplicated enterococcal CRBSI 1

Vancomycin-Resistant Enterococcus (VRE)

• For VRE infections:
  • Linezolid (600 mg every 12 hours) has demonstrated efficacy with cure rates of 67% across various infection sites 4, 5
  • Daptomycin is effective against VRE and can be used based on susceptibility results 1, 6
  • For ampicillin and vancomycin-resistant enterococci, linezolid or daptomycin are the recommended options 1

Combination Therapy Considerations

• For enterococcal IE, combination therapy is standard:
  • The combination of ampicillin plus ceftriaxone is effective for aminoglycoside-nonsusceptible E. faecalis strains 1
  • For non-endocarditis infections, the role of combination therapy remains unresolved 1
  • In patients with normal renal function, aminoglycosides should be divided into 2-3 doses daily rather than given as a single daily dose when used for enterococcal infections 1

Duration of Therapy

• For uncomplicated enterococcal infections: 7-10 days is typically sufficient 3
• For complicated skin infections: 10-14 days is recommended 3
• For enterococcal IE: 4-6 weeks of therapy is recommended, with longer duration (6 weeks) for prosthetic valve IE 1
• For CRBSI: 7-14 days for uncomplicated infections 1

Common Pitfalls and Caveats

• Enterococci are intrinsically resistant to cephalosporins, and these drugs used alone are not an option for treatment of enterococcal infections 1
• High-level aminoglycoside resistance eliminates the expected bactericidal synergistic effect with cell wall-active agents 7
• Management of patients with enterococcal IE should always involve infectious disease consultation as the standard of care 1
• Failure to obtain appropriate cultures before initiating antibiotics can lead to inadequate treatment 3
• Resistance to newer agents like linezolid has been reported, emphasizing the need for susceptibility testing 1

Algorithm for Antibiotic Selection for Enterococcus Infections

1. Identify the Enterococcus species and obtain susceptibility testing
2. For susceptible strains:
   • Use ampicillin or penicillin G as first-line therapy
3. For ampicillin-resistant strains:
   • Use vancomycin
4. For vancomycin-resistant strains:
   • Use linezolid or daptomycin based on susceptibility
5. For endocarditis or severe infections:
   • Add synergistic agent (gentamicin) or use ampicillin-ceftriaxone combination
6. Adjust therapy based on clinical response and follow-up cultures