Q. A 21-year-old woman comes to her gynecologist for severe vaginal itching and vaginal discharge for the past 2 weeks. She says that the discharge is foul-smelling and has a greenish hue. She denies recent fever, back pain, hematuria, or vaginal bleeding. She has been sexually active with multiple partners and rarely uses protection. Her last menstrual period was a week ago. Her temperature is 98.4°F (37°C), pulse is 90/min, blood pressure is 110/80 mmHg, and respirations are 14/min. Physical examination shows vulvar erythema and greenish-yellow, frothy, malodorous vaginal discharge. Speculum examination shows punctate hemorrhages on the cervix. Her vaginal pH is 6 and multi-flagellated organisms are seen on wet mount microscopy. Which of the following oral medication is most effective in treating this patient?