A 28-year-old woman from Delhi presents to the emergency department with acute onset dysuria, frequency, and suprapubic pain for 2 days. She denies fever, flank pain, or vaginal discharge. Urinalysis shows pyuria (>5 WBC/hpf), bacteriuria, and nitrites. Urine culture is pending. Blood pressure is 110/70 mmHg, temperature 37.2°C. She has no known drug allergies. Which of the following is the most appropriate empiric antibiotic choice for uncomplicated acute cystitis in this patient?