The invention relates to a pharmaceutical vaginal composition for treating or preventing vaginal infections. The composition includes a synergistic mix of a bioadhesive, extended release formulation that decreases the pH and that contains a peroxide in an amount sufficient to increase oxygen concentration without sterilizing the vagina or substantially killing the normally-desired local vaginal flora. The invention also relates to a method of treating or preventing vaginal infections in a patient comprising inserting vaginally an amount of the pharmaceutical vaginal composition in an amount sufficient to decrease the pH and increase oxygen concentration without sterilizing the vagina or substantially killing the normally-desired local vaginal flora.