Whorwell PJ et al. (2006) Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome. Am J Gastroenterol 101: 1581–1590

Previous research indicates that the bacterial flora of the gut could have a role in irritable bowel syndrome (IBS). A pilot study by O'Mahony et al. demonstrated that a specific strain of probiotic bacteria, Bifidobacterium infantis 35624, might be a promising treatment for IBS. The same team have now confirmed its efficacy in a randomized, double-blind, placebo-controlled, dose-ranging study.

In total, 362 women with IBS received either active treatment at one of three doses (1 × 106, 1 ×108, or 1 × 1010 live bacteria) in capsule form, taken daily for 4 weeks, or placebo. Patients were followed up for a further 2 weeks. Intention-to-treat analysis revealed that, compared to placebo, only the 1 × 108 dose resulted in a significant improvement from baseline for the primary endpoint of improved abdominal pain and discomfort (P = 0.023). The 1 × 108 dose was also the only dose to result in improvements in any of the secondary endpoints (all P ≤0.05). The 1 × 108 dose seemed to be equally effective across IBS subtypes; however, there was a trend towards greater efficacy in those with diarrhea-predominant IBS.

Given that the 1 × 1010 dose had shown efficacy in the pilot study, Whorwell et al. were surprised at its lack of efficacy in this trial. Post hoc experiments showed that this dose 'coagulated' into a firm mass that probably inhibited the organism's growth. While this study shows that B. infantis 35624 (in capsule form) can effectively treat IBS, it also emphasises the need for clinical trials of the final formulations of all probiotic products.