Twenty eight studies were included in the review (n=approximately 2,000, range 14 to 220): 21 RCTs (n=approximately 1,700); one CCT (n=79); and six crossover studies (n=approximately 200). Ten were high quality (scored at least six points). Overall methodological quality was poor. Mean overall quality score was 4.8 points (range one to 10). The most common limitations were lack of allocation concealment, unblinded outcome assessment, lack of intention-to-treat analysis and prognostic differences between groups.
One high quality RCT provided moderate evidence that polyethylene glycol was significantly more effective than placebo at increasing defaecation frequency (WMD 1.64 bowel movements per week, 95% CI 0.99 to 2.28); faecal incontinence rates did not differ significantly.
Polyethylene glycol was significantly more likely than other laxatives to achieve treatment success (RR 1.47, 95% CI 1.23 to 1.76, NNT=4, 95% CI 2.9 to 6; seven studies, two high quality). There was significant heterogeneity (p<0.0001) for this analysis.
Polyethylene glycol was significantly associated with treatment success (or soft/normal stools) when compared with lactulose only (RR 1.63, 1.40 to 1.90, NNT=3.3, 95% CI 2.6 to 4.5; four studies, two high quality). There was significant heterogeneity (p<0.0001) for this analysis.
Overall, there was conflicting evidence on the effectiveness of lactulose (eight studies, three high quality), senna (three low-quality studies) and mineral oil (three low-quality studies) versus comparators. Two studies (one high quality) that compared fibre versus placebo found no significant difference for defaecation frequency. There was moderate evidence (one high-quality study) that infant formula with sn-2 palmitic acid did not differ significantly from standard infant formula for defaecation frequency.
Other results were reported in the review.