Background Several studies have demonstrated the importance of intestinal bacterial flora in the pathogenesis of inflammatory bowel disease. It has therefore been suggested that modifying the bacterial flora with probiotics will attenuate the inflammatory process and prevent relapses in ulcerative colitis (UC).

Aim To evaluate the available evidence on the use of probiotics for the maintenance of remission in UC and to assess the occurrence of adverse events associated with the use of probiotics.

Design Systematic review and meta-analysis of randomised controlled trials (RCTs) published between 1966 and October 2009.

Methods Data sources were MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Inflammatory Bowel Disease Specialised Register, and reference lists of retrieved articles. We aimed to include trials which compared probiotics with either placebo or other interventions. Data extraction and assessment of methodological quality were performed independently by two reviewers.

Results Three RCTs met the inclusion criteria. All three trials compared probiotics with mesalazine and no placebo-controlled studies were identified. Meta-analysis of the results of the three RCTs, which involved 555 patients, showed no statistically significant difference in relapse rates between patients who received probiotics and those who received mesalazine (pooled odds ratio 1.45, 95% CI 0.99 to 2.13). The incidence of adverse events was not statistically significantly different between the probiotic and mesalazine groups (pooled odds ratio 1.21, 95% CI 0.80 to 1.84).

Conclusion The available evidence does not demonstrate a statistically significant difference between probiotics and mesalazine for the maintenance of remission in UC. However, two of the included studies had relatively small sample sizes and there is insufficient evidence to make any definite conclusions about the efficacy of probiotics for induction of remission in UC. Further well-designed randomised controlled trials including those that compare probiotics with placebo are needed to investigate whether probiotics are effective for the maintenance of remission in UC.