A phase III RCT was published showing this approach is effective

We seek to evaluate whether a same day, reduced liquid volume (2liters) polyethylene glycol (PEG-ELS) bowel preparation can achieve adequate colon cleansing in patients scheduled for afternoon colonoscopies. The primary outcome will be adequacy of the bowel preparation. Secondary outcomes will include Boston Bowel Preparation Scale score, patient compliance with completing the preparation, tolerability of the preparation, willingness to repeat the preparation, side effects, duration of procedure (endoscope insertion and withdrawal times), and polyp detection.

The diagnostic accuracy of colonoscopy depends on the quality of the preparation. The adequacy of the preparation determines whether complete visualization of the mucosa and identification of pathologic lesions is achieved. For reasons that are not entirely clear, colonoscopies scheduled in the afternoon have been identified as a risk factor for having an inadequate preparation. Standard bowel preparation regimens at BMC include polyethylene glycol- electrolyte solutions (PEG-ELS) in full (four liters) and reduced (two liters) forms. These laxatives are typically administered either the evening prior to the colonoscopy or in "split dose" (a portion the evening before and a portion the morning of the colonoscopy). The percent of failed colonoscopies due to a fair/poor preparation in our endoscopy unit is 17-20%. Our trial seeks to establish the efficacy and safety of a reduced volume PEG-ELS laxative given on the day of the colonoscopy.

Inclusion Criteria:

• English speaking patients referred for colonoscopy.

Exclusion Criteria:

• Age < 18,
• Pregnancy,
• History of bowel resection,
• Allergy to PEG-ELS, and
• Inability to provide informed consent.