Review Question - QID 214855

A 12-year-old girl presents with worsening left buttock pain, lower back pain, and a limp for approximately 1 week. She denies any inciting events. On physical examination, the left hip has full range of motion without significant pain. However, severe posterior pain is elicited with FABER testing. She is febrile with a temperature of 102° F (38.8 C), blood pressure of 125/83 mm Hg, and heart rate of 74 beats per minute. Labs are remarkable for WBC count of 14,000 cells/mm^3 (reference <11,000 cells/mm^3) with a significant left-shift. Blood cultures demonstrate gram-positive cocci on gram stain. Final cultures are pending. Current imaging is shown in figures A-C. What is the best initial treatment option for this patient?