A 35-year-old intravenous drug user presents with fever, chills, and a new murmur of tricuspid regurgitation. Three sets of blood cultures grow Staphylococcus aureus (MSSA). Echocardiogram confirms a 1.5 cm vegetation on the tricuspid valve. Which antibiotic regimen is recommended?
- A Nafcillin or oxacillin for 6 weeks ✓
- B Vancomycin for 2 weeks
- C Ceftriaxone plus gentamicin for 4 weeks
- D Daptomycin for 4 weeks
Correct answer: A. Nafcillin or oxacillin for 6 weeks
Explanation
Right-sided MSSA endocarditis on native tricuspid valve in an IVDU without metastatic complications can be treated with antistaphylococcal penicillin (nafcillin or oxacillin) for 6 weeks. Some guidelines permit a 2-week course of nafcillin plus gentamicin in uncomplicated right-sided MSSA endocarditis without pulmonary complications. Vancomycin is used for MRSA; it is inferior to beta-lactams for MSSA. Daptomycin is an alternative for MSSA or MRSA right-sided endocarditis but is not the first-line choice for MSSA when a beta-lactam is available.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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