Metronidazole suppositories should not be inserted into the vagina during menstruation: 1. When menstruation occurs, menstrual blood will be discharged from the vagina. This may cause a large number of bacteria to multiply and cause vaginal inflammation, or bacteria may enter the uterine cavity in retrograde infection and cause endometrial inflammation or even pelvic inflammation, so the pills should not be inserted into the vagina for treatment during menstruation. If you have vaginal inflammation and have symptoms during menstruation, you can take oral medication for treatment.