A 26-yeаr-оld nоnpregnаnt wоmаn presents with dysuria, urinary frequency, and urgency. She is afebrile and denies flank pain, nausea, or vomiting. She has no significant medical history, has not received antibiotics within the previous six months, and has no known medication allergies. Acute uncomplicated cystitis is diagnosed. Which antibiotic is an appropriate first-line pharmacologic treatment?