Colonoscopy is considered the criterion standard for detecting colorectal cancer; adequate preparation is crucial for an effective colonoscopy, but definitive data on the optimal preparation are lacking.

Our aim was to assess the efficacy of split-dose versus non-split–dose preparations, the rate of adequate preparation according to type and dose of laxatives, the role of “runway time” (the interval time between the last drink of purgative and the beginning of colonoscopy), and to evaluate compliance as an additive risk factor for colon cleansing.

A series of meta-analyses of controlled studies.

Randomized clinical trial of split dose regimen versus entire dose taken on the day preceding colonoscopy.

Published trials (1960-2013) comparing split-dose versus non-split–dose preparations in adults undergoing colonoscopy were selected by using MEDLINE, the Cochrane Central Register of Controlled Trials, clinicaltrial.gov, ISI Web of Science, and Scopus.

Colonoscopy.

Rate difference of the degree of colon cleansing between split dose and whole dose was the primary measure of treatment effect.

We included 29 studies. Overall, an adequate preparation was obtained in 85% of patients in the split-dose group and in 63% of the non-split–dose group (rate difference 22%). The heterogeneity was caused by 5 factors: the runway time (the longer, the worse the cleansing), type of diet, male sex, use of polyethylene glycol 4 L, and the Jadad score. Compliance was significantly higher in the split-dose group.

Average quality of the included studies and publication bias.

We provided further evidence of the superiority of a split-dose regimen over a non-split–dose regimen and showed that, regardless of type and dose, the superiority of split-dose regimens remains valid if the “golden 5 hours” rule is preserved.