Treatment of Right-Sided Endocarditis
For uncomplicated right-sided endocarditis caused by methicillin-susceptible Staphylococcus aureus (MSSA), a 2-week course of parenteral β-lactam therapy (such as nafcillin or oxacillin) without gentamicin is the recommended treatment approach. 1
Antimicrobial Therapy Based on Causative Organism
Staphylococcus aureus (most common cause)
MSSA (Methicillin-Susceptible S. aureus):
- For uncomplicated right-sided IE: Nafcillin or oxacillin 12g/24h IV in 4-6 divided doses for 2 weeks 1
- For complicated right-sided IE (renal failure, extrapulmonary infections, aortic/mitral valve involvement, meningitis): Extend treatment to 6 weeks 1
- Addition of gentamicin is NOT recommended for right-sided staphylococcal native valve endocarditis 1
- A 2-week monotherapy regimen with cloxacillin has been shown to be equivalent to cloxacillin plus gentamicin 1
MRSA (Methicillin-Resistant S. aureus):
- Vancomycin 30 mg/kg/24h IV in 2 equally divided doses for 6 weeks 1
- Daptomycin 6 mg/kg IV once daily is FDA-approved for S. aureus bacteremia, including right-sided infective endocarditis 2
- Glycopeptide therapy (vancomycin) often requires more prolonged treatment regimens compared to β-lactams for right-sided IE 1
Alternative Regimens:
- For penicillin-allergic patients (non-anaphylactoid): Cefazolin 6g/24h IV in 3 equally divided doses for 6 weeks 1
- For penicillin-allergic patients (anaphylactoid): Vancomycin 30 mg/kg/24h IV in 2 equally divided doses for 6 weeks 1
- For non-compliant patients: Oral therapy with ciprofloxacin plus rifampin for 4 weeks has shown 90% cure rates in studies of IDUs with uncomplicated right-sided S. aureus endocarditis 1
Special Considerations
Duration of Therapy:
- Uncomplicated right-sided IE caused by MSSA: 2 weeks 1
- Complicated right-sided IE: 4-6 weeks 1
- MRSA infections: Generally require 6 weeks of therapy 1
Criteria for Short-Course (2-week) Therapy:
- MSSA infection 1
- Good response to treatment 1
- Absence of metastatic sites of infection or empyema 1
- No evidence of left-sided involvement 1
- No evidence of renal failure 1
- No evidence of meningitis 1
Surgical Indications:
Surgery should be considered in the following scenarios:
- Right heart failure secondary to severe tricuspid regurgitation with poor response to diuretic therapy 1
- Persistent bacteremia for >7 days despite adequate antimicrobial therapy 1
- Persistent tricuspid valve vegetations >20mm after recurrent pulmonary emboli 1
- Infections caused by difficult-to-eradicate organisms (e.g., persistent fungi, P. aeruginosa) 1
Monitoring and Follow-up
- Blood cultures should be repeated to confirm clearance of bacteremia 1
- For persisting or relapsing S. aureus bacteremia/endocarditis, repeat blood cultures and MIC susceptibility testing should be performed 2
- Consider diagnostic evaluation for sequestered foci of infection in cases of poor clinical response 2
- Monitor for complications such as septic pulmonary emboli, which may manifest as chest pain, cough, or hemoptysis 1
Common Pitfalls and Caveats
- Gentamicin should not be used for treatment of right-sided staphylococcal native valve endocarditis due to increased nephrotoxicity risk without improved outcomes 1
- Glycopeptides (vancomycin) may be less effective for right-sided S. aureus IE due to limited bactericidal activity, poor penetration into vegetations, and increased drug clearance in IDUs 1
- Daptomycin is not indicated for the treatment of left-sided infective endocarditis due to S. aureus, as outcomes in these patients were poor in clinical trials 2
- In cases of brain abscess complicating MSSA IE, nafcillin is preferred over cefazolin due to better blood-brain barrier penetration 1