Bacterial vaginosis is a common infection in women who have reached reproductive age, and its presence has been associated with an increased risk of human immunodeficiency virus (HIV) transmission, pelvic inflammatory disease (PID), and other sexually transmitted infections. Women who are pregnant may be at risk of preterm labor or premature rupture of membranes. Oral or topical antibiotic treatment provides short-term cure rates for more than 80 percent of women, but many still have recurrences. The authors evaluated suppressive intravaginal metronidazole (MetroGel) and its effect on recurrent episodes of bacterial vaginosis.

Women who had two or more episodes of bacterial vaginosis and still had symptoms were eligible for the multicenter study. Participants also were required to have three or more of the Amsel criteria for bacterial vaginosis: homogenous vaginal discharge, amine odor, vaginal pH greater than 4.5, and clue cells. The women who met the criteria were treated with 0.75% metronidazole gel (5 g) intravaginally at bedtime for 10 days, and they were reassessed three to five days after the treatment regimen was completed. The infection was considered cured if they met two or fewer of the Amsel criteria. They then were randomly assigned to receive 0.75% metronidazole gel (5 g) or placebo twice a week for 16 weeks. After the initial phase, the participants underwent 12 weeks without therapy, but they were evaluated for recurrence of bacterial vaginosis every four weeks.

There were 157 women who participated in the trial, and 88.2 percent responded to initial therapy. During the 16-week maintenance phase, 13 women who received intra-vaginal metronidazole had a recurrence of bacterial vaginosis compared with 26 women in the placebo group (P = .001); however, at the end of the study, 26 of the women who were given metronidazole had recurrences compared with 33 women in the placebo group (P = .02). At 16 weeks, the probability of maintaining a cure was 39 percent for placebo and 70 percent for metronidazole. This dropped to 18 and 34 percent, respectively, at the end of the study. There were few adverse effects, but participants who were treated with metronidazole did have a higher incidence of vaginal candidiasis.

The authors conclude that suppressive therapy with twice-weekly intravaginal metronidazole gel does reduce the recurrence of bacterial vaginosis and is a well-tolerated therapy, but that vaginal candidiasis is a common complication.