What is the recommended treatment for Enterococcal (a type of bacteria) prosthetic endocarditis (infection of the heart valve)?

Treatment of Enterococcal Prosthetic Valve Endocarditis

For enterococcal prosthetic valve endocarditis with susceptible strains, treat with ampicillin (or penicillin G) plus gentamicin for a minimum of 6 weeks. 1

First-Line Therapy for Susceptible Strains

The preferred regimen combines a cell wall-active agent with an aminoglycoside for the entire treatment duration:

Antibiotic Selection and Dosing

Primary regimen (for penicillin-susceptible enterococci):

• Ampicillin 12 g/24 hours IV divided into 6 equal doses for minimum 6 weeks 1
  • Alternative: Penicillin G 18-30 million units/24 hours IV continuously or in 6 divided doses for minimum 6 weeks 1
• PLUS Gentamicin 3 mg/kg/24 hours IV/IM divided into 3 equal doses for the entire 6-week course 1
  • Target gentamicin peak: 3-4 μg/mL and trough <1 μg/mL 1
  • Administer in multiple divided doses (every 8 hours), NOT once daily 1

For penicillin-allergic patients:

• Vancomycin 30 mg/kg/24 hours IV in 2 divided doses for minimum 6 weeks 1
• PLUS Gentamicin 3 mg/kg/24 hours IV/IM in 3 divided doses for the entire 6-week course 1

Critical Treatment Principles

Duration is non-negotiable for prosthetic valves:

• Minimum 6 weeks of therapy required for all prosthetic valve enterococcal endocarditis 1, 2
• This applies regardless of symptom duration before diagnosis 1
• Unlike native valve disease where 4 weeks may suffice for short symptom duration, prosthetic material mandates the full 6-week course 1

Aminoglycoside administration differs from other endocarditis types:

• Gentamicin must be continued for the entire treatment duration (all 6 weeks), not just the first 2 weeks 1
• This contrasts with streptococcal endocarditis where aminoglycosides are typically limited to 2 weeks 1
• Must use multiple daily divided doses (every 8 hours), not once-daily dosing 1

Antibiotic Preference Hierarchy

Ampicillin/penicillin + gentamicin is superior to vancomycin + gentamicin:

• Penicillin-aminoglycoside combinations show greater in vitro activity and better outcomes in animal models 1
• Vancomycin-gentamicin carries higher risk of nephrotoxicity and ototoxicity 1
• Reserve vancomycin only for documented penicillin allergy 1
• Vancomycin has decreased intrinsic activity against enterococci, necessitating the full 6-week duration 1

Monitoring Requirements

Renal function and drug levels:

• Monitor gentamicin peak and trough levels to maintain therapeutic targets 1
• Weekly renal function tests and drug level monitoring recommended due to nephrotoxicity risk 1, 2
• For creatinine clearance 20-50 mL/min: adjust gentamicin dosing and monitor levels closely 1
• For creatinine clearance <20 mL/min: consult infectious disease specialist 1

Treatment response:

• Repeat blood cultures until sterile to confirm treatment adequacy 2
• Monitor for clinical improvement and complications requiring surgical intervention 3

Special Situations and Resistance Patterns

High-level aminoglycoside resistance:

• If enterococci demonstrate high-level gentamicin resistance, consider ampicillin plus ceftriaxone combination for 6 weeks 1
• This regimen effective for aminoglycoside-nonsusceptible Enterococcus faecalis strains 1
• Note: Enterococci are intrinsically resistant to cephalosporins; ceftriaxone works only in combination with ampicillin through synergy 1

Vancomycin-resistant enterococci (VRE):

• Limited data available for optimal treatment 1
• Linezolid and daptomycin show in vitro activity and some clinical success in adults 1
• Mandatory infectious disease consultation for VRE prosthetic valve endocarditis 1

Infectious Disease Consultation

Mandatory consultation recommended:

• American Heart Association guidelines state that infectious disease consultation should be standard of care for all enterococcal endocarditis 1
• Particularly critical for prosthetic valve cases given complexity and high stakes 1

Common Pitfalls to Avoid

Duration errors:

• Do not shorten therapy to 4 weeks for prosthetic valves, even if patient improves rapidly 1, 2
• Do not stop gentamicin early (e.g., at 2-3 weeks) as done in streptococcal endocarditis 1

Dosing errors:

• Do not use once-daily gentamicin dosing; enterococcal endocarditis requires traditional divided dosing 1
• Do not use ceftriaxone or other cephalosporins as monotherapy; they are ineffective alone 1

Drug selection errors:

• Do not use vancomycin as first-line if patient can tolerate beta-lactams 1
• Do not use monotherapy; combination therapy is essential for bactericidal effect 2

Surgical Considerations

When to consider valve replacement:

• Prosthetic valve enterococcal endocarditis can often be cured with antibiotics alone (69% success rate in one series) 3
• However, maintain low threshold for surgical consultation if clinical deterioration, persistent bacteremia, or hemodynamic compromise occurs 3
• Aortic valve involvement associated with higher complication rates 3