What antibiotic is effective against Enterococcus faecium, particularly vancomycin-resistant strains?

Antibiotic Treatment for Enterococcus faecium Infections

For Enterococcus faecium infections, linezolid is the most effective treatment option for vancomycin-resistant strains, while ampicillin remains the drug of choice for ampicillin-susceptible strains. 1, 2

First-Line Treatment Algorithm

Step 1: Determine Susceptibility Pattern

• For ampicillin-susceptible E. faecium: Use ampicillin as first-line therapy 1
• For vancomycin-susceptible but ampicillin-resistant E. faecium: Use vancomycin 2
• For vancomycin-resistant E. faecium (VRE): Use linezolid 600 mg IV/PO every 12 hours 2, 3

Step 2: Alternative Options for VRE

• Daptomycin 8-12 mg/kg/day IV is recommended as an alternative for VRE bacteremia 2, 4
• Quinupristin-dalfopristin (Synercid) inhibits growth only in E. faecium (not E. faecalis) 2, 5
• Tigecycline 100 mg IV loading dose followed by 50 mg IV every 12 hours for intra-abdominal infections 2

Clinical Considerations

Antimicrobial Resistance Patterns

• E. faecium is more likely to be resistant to multiple antibiotics compared to E. faecalis 1, 6
• Five phenotypes of vancomycin resistance (vanA through E) exist in enterococci, with vanA and vanB genes found primarily in E. faecium 2
• Vancomycin-resistant E. faecium is often multidrug-resistant, creating significant treatment challenges 2, 7

Combination Therapy for Severe Infections

• For severe VRE infections, consider combination therapy with daptomycin plus ampicillin or ceftaroline for potential synergistic effects 1, 8
• Double β-lactam combinations (imipenem and ampicillin or cephalosporins plus ampicillin) have shown synergistic bactericidal activity against some E. faecalis strains 2

Special Situations

Urinary Tract Infections

• For uncomplicated VRE urinary tract infections, consider:
  • Fosfomycin 3 g PO single dose 2
  • Nitrofurantoin 100 mg PO every 6 hours 2
  • High-dose ampicillin (18-30 g IV daily in divided doses) or amoxicillin 500 mg PO/IV every 8 hours if susceptible 2

Endocarditis

• For endocarditis caused by vancomycin-resistant E. faecium, linezolid therapy resulted in cure of 77% of cases 2
• Daptomycin at higher doses (10-12 mg/kg/day) may be more effective for serious infections like endocarditis 1, 4

Common Pitfalls and Monitoring

• Linezolid resistance can emerge during therapy, particularly with prolonged use (>14 days) 9, 10
• Monitor for bone marrow suppression and neuropathy with prolonged linezolid use 1
• Enterococci are intrinsically resistant to cephalosporins when used as monotherapy 1
• Daptomycin monotherapy may lead to treatment failure in severe infections; consider combination therapy for better outcomes 1, 8
• The FDA has approved linezolid specifically for the treatment of vancomycin-resistant Enterococcus faecium infections, including cases with concurrent bacteremia 3

Duration of Therapy

• For uncomplicated infections: 7-14 days 1
• For bacteremia or endocarditis: 14-28 days 3
• For complicated infections: Duration should be based on clinical response 2