"Friendly" bacteria (probiotics) are widely used and recommended for general health and specifically for vaginal problems.
But new research, published on bmj.com today, shows that probiotics do not prevent inflammation of the vaginal area (vulvovaginitis) that often develops after antibiotic treatment and is usually caused by the bacteria Candida albicans.
The study involved 235 non-pregnant women aged 18-50 years who required a short course of oral antibiotics for a non-gynaecological infection.
Women took probiotic (containing lactobacillus bacteria) or placebo preparations orally or vaginally until four days after completion of their antibiotic course. They recorded any symptoms and provided vaginal swabs for analysis.
Overall, 23% of women developed vulvovaginitis after antibiotics. Compared with placebo, probiotic treatments were ineffective in preventing vulvovaginitis. In fact, the trial was stopped early because it was considered unethical to continue with no potential benefit.
The role of lactobacillus in post-antibiotic vulvovaginitis is an example of a treatment that has widespread use despite lack of a biologically plausible basis or evidence of effectiveness, say the authors.
"Our results should prompt health professionals to inform women that lactobacillus is unlikely to prevent post-antibiotic vulvovaginitis and that they should consider using proved antifungal treatment if symptoms develop," they conclude.