Effect of Adding Simethicone to a Split Regimen of Polyethylene Glycol for Bowel Preparation in a Colorectal Cancer Screening Colonoscopy Setting: an Endoscopist-blinded Randomized Controlled Trial

a. Study type: Endoscopist-blinded randomized controlled trial i. Prospective inclusion of patients scheduled for a colonoscopy by nationwide CRC screening program after a positive faecal immunochemical test.

ii. Randomization by computer generated tables. iii. Allocation concealment by sealed, opaque envelopes. iv. Endoscopist-blinded: endoscopist blinded to the group allocation. v. Patient informed about its bowel cleansing regimen.

b. Selection participant method: i. Inclusion by invitation of patients aged between 50 and 74 years, inclusive, scheduled for colonoscopy by nationwide CRC screening program after a positive faecal immunochemical test. ii. Exclusion criteria for nationwide CRC screening program: previous diagnosis of CRC, presence of known genetic susceptibility syndromes related with CRC, personal history of inflammatory bowel disease, presence of gastrointestinal complaints (significant changes in gastrointestinal transit in the last 6 months or evidence of gastrointestinal bleeding), a normal colonoscopy in the last 10 years and a normal flexible sigmoidoscopy in the last 5 years. Exclusion criteria of this study also include: known or suspected gastrointestinal obstruction or perforation, toxic megacolon, major colonic resection, pregnant or at risk of becoming pregnant and lactating women, known or suspected hypersensitivity to the active or other ingredients.

c. Sample size: i. 412 (2 groups of 206 patients). ii. To improve adequate bowel preparation rate (primary outcome) from 85% (value from the investigator's own database) to 95% (target standard suggested by ESGE) and assuming a normal distribution and a power of 90% (α=0.05), the calculated sample size of each of the 2 groups was 188; allowing for a 10% dropout rate, the sample size is 206 per group (412 patients overall). Adequate bowel preparation is defined as total. Boston Bowel Preparation Scale ≥6 and ≥2 in each segment. The chosen scale is the most systematically validated and appropriate for the clinical setting.

d. Procedures and data collection methods: Form sheets filled by the endoscopist about intraprocedural measures and by the nurse about patient compliance and tolerability to the prescribed cleansing regimen.