A 32-year-old IV drug user presents with fever, bacteremia, and tricuspid regurgitation on echo with vegetations. Blood cultures grow methicillin-sensitive Staphylococcus aureus (MSSA). What is the antibiotic of choice and minimum treatment duration?
- A Vancomycin for 6 weeks
- B Daptomycin for 4 weeks
- C Nafcillin or oxacillin for 2 weeks (right-sided MSSA IE) ✓
- D Ceftriaxone for 4 weeks
Correct answer: C. Nafcillin or oxacillin for 2 weeks (right-sided MSSA IE)
Explanation
Right-sided MSSA infective endocarditis (tricuspid valve) in IV drug users can be treated with anti-staphylococcal penicillin (nafcillin/oxacillin) for a shorter 2-week course — validated in the 'short-course' regimens for uncomplicated right-sided IE without metastatic infection, emboli, or severe TR. This is the exception to the general 4–6 week rule. Vancomycin is inferior to beta-lactams for MSSA and should be reserved for MRSA or PCN allergy. Daptomycin is deactivated by pulmonary surfactant and should not be used for right-sided IE with pulmonary involvement.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.