Q. A 32-year-old woman with a history of recurrent urinary tract infections presents to the emergency department with complaints of fever, chills, and abdominal pain. She reports having a history of similar episodes, but the symptoms are more severe this time. Physical examination reveals costovertebral angle tenderness, temperature of 102°F, and tachycardia. Urinalysis shows pyuria and bacteriuria, and a subsequent urine culture confirms the presence of Escherichia coli. A diagnosis of pyelonephritis is made, and the patient is admitted to the hospital for further management. What is the most appropriate initial antibiotic therapy for the patient?