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Abstract
Probiotics may benefit irritable bowel syndrome (IBS) symptoms, but randomised controlled
trials (RCTs) have been conflicting; therefore a systematic review was conducted.
MEDLINE (1966 to May 2008), EMBASE (1988 to May 2008) and the Cochrane Controlled
Trials Register (2008) electronic databases were searched, as were abstracts from
DDW (Digestive Diseases Week) and UEGW (United European Gastroenterology Week), and
authors were contacted for extra information. Only parallel group RCTs with at least
1 week of treatment comparing probiotics with placebo or no treatment in adults with
IBS according to any acceptable definition were included. Studies had to provide improvement
in abdominal pain or global IBS symptoms as an outcome. Eligibility assessment and
data extraction were performed by two independent researchers. Data were synthesised
using relative risk (RR) of symptoms not improving for dichotomous data and standardised
mean difference (SMD) for continuous data using random effects models.
19 RCTs (18 papers) in 1650 patients with IBS were identified. Trial quality was generally
good, with nine reporting adequate methods of randomisation and six a method of concealment
of allocation. There were 10 RCTs involving 918 patients providing outcomes as a dichotomous
variable. Probiotics were statistically significantly better than placebo (RR of IBS
not improving=0.71; 95% CI 0.57 to 0.88) with a number needed to treat (NNT)=4 (95%
CI 3 to 12.5). There was significant heterogeneity (chi(2)=28.3, p=0.001, I(2)=68%)
and possible funnel plot asymmetry. Fifteen trials assessing 1351 patients reported
on improvement in IBS score as a continuous outcome (SMD=-0.34; 95% CI -0.60 to -0.07).
There was statistically significant heterogeneity (chi(2)=67.04, p<0.001, I(2)=79%),
but this was explained by one outlying trial.
Probiotics appear to be efficacious in IBS, but the magnitude of benefit and the most
effective species and strain are uncertain.