Question

A $64$-year-old man is admitted to the hospital with a $2$-week history of progressively worsening mid-back pain and low-grade fevers. He has a history of poorly controlled type 2 diabetes mellitus. His temperature is $38.2^\circ\text{C}$ ($100.8^\circ\text{F}$), blood pressure is $128/78\text{ mmHg}$, and pulse is $92\text{/min}$. Physical examination reveals point tenderness over the $T10-T11$ spinous processes. Neurologic examination of the lower extremities is completely normal. Laboratory studies show an erythrocyte sedimentation rate (ESR) of $85\text{ mm/h}$ and a C-reactive protein (CRP) level of $112\text{ mg/L}$. Magnetic resonance imaging (MRI) of the thoracic spine demonstrates abnormal marrow signal and enhancement of the $T10$ and $T11$ vertebral bodies with a small adjacent fluid collection, diagnostic of vertebral osteomyelitis. Two sets of blood cultures are obtained, and the patient is started on empiric intravenous vancomycin and piperacillin-tazobactam. On hospital day $3$, the patient's temperature is $37.4^\circ\text{C}$ ($99.3^\circ\text{F}$). Both sets of blood cultures are positive for Staphylococcus aureus that is susceptible to oxacillin, cefazolin, and vancomycin, but resistant to penicillin. Which of the following is the most appropriate next step in the pharmacologic management of this patient?