A 28-year-old IV drug user presents with fever (39.8°C), new regurgitant murmur, and septic pulmonary emboli. Blood cultures grow Staphylococcus aureus (MSSA). Duke criteria confirm infective endocarditis. What is the MOST appropriate antibiotic regimen?

• A IV vancomycin for 4–6 weeks
• B IV nafcillin (or cloxacillin) for 6 weeks ✓
• C IV ceftriaxone 2 g daily for 4 weeks
• D Oral amoxicillin-clavulanate after initial IV induction

Explanation

For MSSA endocarditis, anti-staphylococcal penicillin (nafcillin, oxacillin, or cloxacillin) is bactericidal and superior to vancomycin — clinical outcomes are significantly better with beta-lactams than with vancomycin for MSSA (lower mortality, lower relapse). AHA and ESC guidelines recommend anti-staphylococcal penicillin for 6 weeks for native valve MSSA endocarditis. Vancomycin is reserved for MRSA or penicillin allergy. Ceftriaxone is appropriate for streptococcal endocarditis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.