A 35-year-old IV drug user presents with 2 weeks of high-grade fever, chills, and pleuritic chest pain. Blood cultures grow Staphylococcus aureus (MSSA). Echo shows a 1.2 cm mobile vegetation on the tricuspid valve with moderate tricuspid regurgitation, and small septic pulmonary emboli on CT. Which antibiotic regimen is most appropriate?
- A Oral amoxicillin-clavulanate for 4 weeks
- B IV nafcillin (or oxacillin) for 6 weeks ✓
- C IV vancomycin for 2 weeks
- D IV penicillin G for 4 weeks
Correct answer: B. IV nafcillin (or oxacillin) for 6 weeks
Explanation
Right-sided native valve endocarditis due to MSSA in an IV drug user is best treated with IV nafcillin or oxacillin (anti-staphylococcal penicillin) for 4–6 weeks; some studies support 2-week short-course therapy for uncomplicated right-sided MSSA endocarditis. Vancomycin is inferior to beta-lactams for MSSA and is reserved for MRSA or penicillin-allergic patients. Oral therapy may be considered in select stable patients per recent POET trial data for streptococcal or enterococcal endocarditis, but not for MSSA.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.