Dr Marie Pirotta, from the University of Melbourne, tested whether supplements of the key probiotic bacterium in yoghurt, Lactobacillus acidophilus, could prevent the yeast infection in women taking antibiotics. Around 50 per cent of women will suffer a bout of thrush after antibiotics at least once in their lifetime.
The results, reported in the 4 September issue of the British Medical Journal (vol 329(7465):548, were so clear cut that the trial was cut short on ethical grounds.
Dr Pirotta and a PhD student gave 235 Melbourne women on a short antibiotics course the probiotic lactobacillus bacteria or placebo orally or vaginally until four days after completion of the therapy. They recorded any symptoms and provided vaginal swabs for analysis.
Lactobacillus treatment was no more effective than placebo, they report. "Compliance with antibiotics and interventions was high. The trial was terminated after the second interim analysis because of lack of effect of the interventions," write the authors.
They concluded that "the use of oral or vaginal forms of lactobacillus to prevent post-antibiotic vulvovaginitis is not supported by these results. Further research on this subject is unlikely to be fruitful, unless new understandings about the pathogenesis of post-antibiotic vulvovaginitis indicate a possible role for lactobacillus."
Currently there are no recommended medicines to prevent thrush, which has a big impact on women's physical and emotional wellbeing, as well as on their relationships. In 1995 the costs associated with diagnosing and treating thrush in the United States were $1.8 billion, according to researchers.
Earlier research by Dr Pirotta found that around 40 per cent of women had used yoghurt or Lactobacillus to try to prevent or treat thrush after antibiotics. These women also reported that they were concerned about getting thrush after antibiotics, and for a small number, the concern was so great that they would choose not to take the antibiotics.
Dr Pirotta said: "It was disappointing to find that this type of Lactobacillus was not effective in this case. But this is a reminder that all medicines, even 'natural' ones, need to be tested, and wherever possible, treatments should be based on evidence."