A 45-year-old injection drug user presents with fever, bacteremia, and new regurgitant murmur. Blood cultures grow methicillin-resistant Staphylococcus aureus (MRSA). TTE shows a 1.2 cm vegetation on the tricuspid valve with moderate regurgitation. He has no signs of systemic embolism or heart failure. What is the antibiotic of choice and duration?
- A Vancomycin 4 weeks intravenously
- B Vancomycin 6 weeks with gentamicin for first 2 weeks
- C Daptomycin 6 weeks intravenously ✓
- D Linezolid 6 weeks orally
Explanation
For MRSA right-sided (tricuspid) endocarditis, current AHA 2015 IE guidelines allow daptomycin 6 mg/kg/day for 6 weeks as an effective alternative to vancomycin, with some evidence favoring daptomycin for MRSA endocarditis (higher bactericidal activity, reduced nephrotoxicity). Vancomycin 6 weeks is also acceptable. Right-sided IE has a better prognosis than left-sided, with surgery reserved for persistent sepsis, large vegetations >20 mm, recurrent septic pulmonary emboli, or tricuspid stenosis. Gentamicin addition to vancomycin for Staph. aureus is no longer recommended (increased nephrotoxicity, no added benefit — AHA 2015).
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.