Treatment of Native Valve Staphylococcal Endocarditis
For native valve Staphylococcus endocarditis, the recommended treatment is a semisynthetic, β-lactamase-resistant penicillin (nafcillin or oxacillin) given intravenously for 4-6 weeks for methicillin-susceptible strains, or vancomycin for 6 weeks for methicillin-resistant strains. 1
Treatment Algorithm Based on Methicillin Susceptibility
For Methicillin-Susceptible Staphylococcus aureus (MSSA):
- First-line therapy: Nafcillin or oxacillin 12 g/day IV in 4-6 divided doses for 4-6 weeks 1
- Alternative for non-anaphylactic penicillin allergy: Cefazolin (first-generation cephalosporin) for 4-6 weeks 1
- Optional addition: Gentamicin for the first 3-5 days may accelerate bacterial killing, but this is based on experimental models and increases risk of renal toxicity 1
For Methicillin-Resistant Staphylococcus aureus (MRSA):
- First-line therapy: Vancomycin 30 mg/kg/day IV in 2 divided doses for a minimum of 6 weeks 1, 2
- Alternative for vancomycin intolerance or failure: Daptomycin (where available) in combination with another antistaphylococcal agent 1, 3
Special Considerations
Monitoring During Treatment
- Daily clinical assessment
- Serial blood cultures until sterilization is confirmed
- Regular echocardiographic follow-up
- Monitoring of renal function
- Drug level monitoring for vancomycin (target trough levels 10-15 μg/mL) 4
Surgical Evaluation
- All patients with S. aureus endocarditis should be cared for in a medical facility with cardiothoracic surgery capabilities and infectious diseases consultation 1
- Surgical intervention should be considered for:
- Heart failure due to valve dysfunction
- Uncontrolled infection despite appropriate antibiotics
- Large mobile vegetations (>10mm) with embolic risk
- Perivalvular abscess or fistula formation 4
Treatment Failures
- For persisting or relapsing S. aureus bacteremia/endocarditis:
- Repeat blood cultures
- Perform MIC susceptibility testing
- Rule out sequestered foci of infection
- Consider surgical intervention (debridement, removal of prosthetic devices)
- Consider change in antibiotic regimen 3
Important Caveats
- The addition of gentamicin in staphylococcal native valve IE is no longer routinely recommended as it increases renal toxicity without clear mortality benefit 1
- Vancomycin is inferior to beta-lactams for MSSA and should only be used for MRSA or in cases of true beta-lactam allergy 1
- Patients with high vancomycin MIC (≥1.5 mg/L) may have higher mortality even with susceptible strains 1
- For S. lugdunensis (a coagulase-negative staphylococcus), treat similarly to S. aureus despite being coagulase-negative 1, 5
Outpatient Therapy Considerations
Decisions about outpatient therapy may be individualized based on:
- Clinical improvement and symptomatic recovery
- Cardiovascular stability
- Ability to follow prescribed treatment
- Availability of infrastructure for outpatient monitoring 1
Remember that staphylococcal endocarditis, particularly S. aureus, is an aggressive infection with significant mortality risk. Early and appropriate antibiotic therapy, combined with timely surgical intervention when indicated, is essential for optimal outcomes.