A 32-year-old woman presents to the emergency department with a 2-day history of fever, chills, and right flank pain. She has a history of recurrent urinary tract infections. On examination, she is febrile with a temperature of 38.5°C, her heart rate is 110 bpm, and her blood pressure is 110/70 mmHg. There is tenderness on palpation of the right costovertebral angle. Urinalysis shows pyuria and bacteriuria. What is the most appropriate initial management for this patient?