A 16-year-old female high school student has been taking ciprofloxacin for the past 10 days for the treatment of a "strep" throat. She visits the school nurse with the complaint of vaginal burning and itching along with a foul-smelling vaginal drainage. The school nurse, who is a family nurse practitioner, prescribes metronidazole (Flagyl) $500 \mathrm{mg}$ every 6 to 8 hours for 7 days.
- What is the action of metronidazole?
- The nurse should provide what patient teaching to the girl?