Effect of Simethicone on Colon Preparation During Water Exchange Colonoscopy

Background: Colonoscopy reduces colorectal cancer mortality by enabling early detection and removal of adenomas. Its effectiveness, however, depends heavily on bowel preparation quality and mucosal visibility. Simethicone, an anti-foaming agent, decreases intraluminal bubbles and improves visualization; studies in conventional air-insufflation colonoscopy generally show benefits for cleanliness and patient comfort, but evidence in water-exchange (WE) colonoscopy remains limited.Objective: To evaluate whether adding oral simethicone to a split-dose polyethylene glycol (PEG) regimen further improves bowel cleanliness and procedural performance in WE colonoscopy.Methods: Adults undergoing outpatient colonoscopy will be randomly assigned (1:1) to a simethicone group or a control group, with a planned enrollment of 180 participants. All procedures will use the WE insertion technique, and endoscopists will be blinded to group allocation. The primary endpoint is the Boston Bowel Preparation Scale (BBPS); adequate preparation is defined as a total score ≥6 with all segment scores ≥2. Secondary endpoints include bubble score and CEBuS, adenoma detection rate (ADR), polyp detection rate (PDR), cecal intubation rate and time, withdrawal time, volume of water used and flushing/irrigation metrics, and patient-reported tolerability and satisfaction.Expected Results: Compared with PEG alone, adding simethicone is expected to (1) increase the proportion of adequate BBPS preparations, (2) reduce bubble coverage, (3) maintain or potentially improve ADR/PDR, and (4) enhance patient tolerability and satisfaction.Conclusion: If effective, this intervention would provide a simple, low-cost strategy to optimize the quality of WE colonoscopy.

Inclusion Criteria: * Consecutive patients undergoing screening, surveillance, or diagnostic colonoscopy. * Procedures performed by participating endoscopists. * Ability to provide written informed consent. Exclusion Criteria: * Colonoscopy performed using air insufflation or water immersion technique. * History of colorectal surgery (e.g., colectomy or colostomy). * Known or suspected colonic obstruction or severe stricture. * Requirement for inpatient bowel preparation. * Known allergy or hypersensitivity to simethicone. * Unable or unwilling to provide informed consent.