Evidence on the efficacy of vaginal acidification with lactic acid or acetic acid is conflicting. Studies are generally small and of poor quality. There is insufficient evidence to make a recommendation on the use of vaginal acidification for the treatment of bacterial vaginosis (BV).

Vaginal acidification compared with placebo:

CKS identified one randomized controlled trial (RCT) comparing intravaginal acetic acid gel with placebo.

• A total of 44 women with confirmed symptomatic BV were randomized to receive 5 mL acetic acid gel (Aci-Jel^®) or placebo gel intravaginally twice a day for 7 days [Holley et al, 2004].
• At follow up (14 days after the start of treatment) there was no evidence of a significant difference between the two groups in terms of symptoms or signs of BV.

Vaginal acidification compared with antibiotic:

CKS identified two RCTs comparing intravaginal lactic acid with standard antibiotic treatment and one small pilot study comparing an acid-buffering gel with standard antibiotic treatment for symptomatic BV.

• In one blinded RCT, 125 women with a diagnosis of BV were randomized to receive oral metronidazole 500 mg twice a day for 7 days plus placebo pessary, 100 mg lactic acid pessary at night for 7 days plus placebo tablets, or placebo tablets and placebo pessary [Boeke et al, 1993].
• Symptoms improved significantly faster in the metronidazole group compared with the lactic acid group (p = 0.0002) or the placebo group (p = 0.0005). There was no evidence of a significant difference between the lactic acid and placebo groups (p = 0.65).
• The median duration until absence of symptoms was 21 days for metronidazole and 80 days for placebo. Disappearance of symptoms did not occur in 50% of women in the lactic acid group in 90 days of follow up.
• After 2 weeks, the cure rates (cure defined as less than three of four clinical criteria present) were 83% with metronidazole, 49% with lactic acid, and 47% with placebo. After three months the proportion of women who remained cured were 78%, 38%, and 34%.
• No differences in adverse events were found between the three groups.
• In one open-label RCT, 90 women with symptomatic BV were randomized to treatment with 5 g lactic acid vaginal gel (Lactacyd^®) at bedtime for 7 days, oral metronidazole 500 mg twice a day for 7 days, or both treatments [Decena et al, 2006].
• The lactobacilli count significantly increased over time in all three groups. At day 14, growth of lactobacilli was significantly higher among women in the lactic acid gel and combination treatment arms than the metronidazole-only arm.
• Significant reduction of vaginal discharge and lower recurrence of BV were noted in the combination treatment group.
• In a small pilot study, 30 women with confirmed symptomatic BV were randomized to receive 5 g ACIDFORM^® gel (an acid-buffering gel) or 10% metronidazole intravaginal gel once a day for 5 days [Simoes et al, 2006].
• After 7–12 days, 15 of the 17 women in the metronidazole group (88%) were cured compared with 3 of the 13 women (23%) in the ACIDFORM^® group (p < 0.001).