A 60-year-old man who underwent prosthetic aortic valve replacement 3 months ago develops fever, chills, and a new systolic murmur. Blood cultures grow *Staphylococcus aureus*. What is the most appropriate initial empiric antibiotic regimen for presumed prosthetic valve endocarditis?

The correct answer to the question "A 60-year-old man who underwent prosthetic aortic valve replacement 3 months ago develops fever, chills, and a new systolic murmur. Blood cultures grow *Staphylococcus aureus*. What is the most appropriate initial empiric antibiotic regimen for presumed prosthetic valve endocarditis?" is Option C: Vancomycin, gentamicin, and rifampin.

The other options — A) Vancomycin monotherapy, B) Penicillin G and gentamicin, D) Ceftriaxone and azithromycin — are incorrect for this USMLE Exam Prep question. As explained above: Early prosthetic valve endocarditis (within 1 year of surgery) is often caused by *Staphylococcus* species. The recommended empiric regimen is a combination of antibiotics, typically vancomycin (for …