Sixteen RCTs (n=1,342) met the inclusion criteria. Studies scored between 5 and 12 points on the Rome II methodology scale. Eleven studies were considered to be of suboptimal design (precise definition of suboptimal was not clear).
Two of the appropriately-designed RCTs evaluated Bifidobacterium infantis 35624 and reported statistically significant improvements in abdominal pain/discomfort, bloating/distension and/or bowel movement relative to placebo (p<0.05). In these two trials B. infantis 35624 was given daily for four or eight weeks as 1x1010 live cells in malted milk drink or 1x106, 1x108 or 1x1010 colony forming units per millilitre in capsule form. None of the other studies described as appropriately designed showed significant improvements in IBS symptoms.
No studies reported quantifiable data on relative tolerability or adverse events.