Proper bowel cleansing prior is an essential requirement for the conduct of colonoscopy. However, due to the nature of cleansing process, the ideal bowel cleansing preparation remains elusive.

The objective of this study is to compare the efficacy, safety and tolerability of oral polyethylene glycol lavage given either as a single dose or split dose. The study will be a randomized controlled single blind two group study. The primary study outcomes will be the previously validated Ottawa bowel preparation score.

All patients between the age of 50 and 75 years referred to the Forzani & MacPhail Colorectal Cancer Screening Centre in Calgary, Alberta, Canada for colonoscopy will be considered for inclusion. During pre-assessments at the clinic, patients will be asked to participate in the study by a nurse clinician. If they agree - final consent will be obtained by a gastroenterologist along with consent for the colonoscopy. Those not interested in participating will simply receive their physicians standard bowel preparation protocol. There will be no coercion of any sort.

Patients with acute coronary syndrome, congestive heart failure, unstable angina, known or suspected renal failure, ascites, megacolon, known or suspected bowel obstruction, or other comorbidities that may prevent colonoscopy will be excluded. Patients will also be excluded if they previously had partial or subtotal colectomy or if the colonoscopy is warranted for the evaluation of diarrhea.

Enrollment of participants will be performed with block randomizations of 8 stratified by AM versus PM procedure time using a computer-generated table, with allocation concealment maintained through the use of consecutively numbered sealed envelopes. Colonoscopists and investigators will be blinded to allocation groups. Patients will be allocated to one of two groups: (1) 4L PEG day prior to procedure; (2) 4L of PEG split in two 2L doses

A study assistant will assign patients to their group and instruct them on the proper use of their assigned bowel preparation method. Patients will be given a tolerability questionnaire, that was modified from a previously reported questionnaire, to be completed once their bowel preparation is finished and before coming to the hospital for the colonoscopy. Patient concerns or questions regarding the preparation will be directed toward the assistant as opposed to their gastroenterologist, so as to avoid unblinding the gastroenterologist.

Outcomes

The previously validated Ottawa bowel preparation scale80 will be used to assess the quality of bowel cleanliness. Each of the right, mid and rectosigmoid colon is rated on a 5-point scale (0-4). In addition, a complete 3-point rating for overall colonic fluid is assessed resulting in an overall score range of 0 to 14. An excellent preparation with little fluid would score 0 to 1; a good preparation, 2 to 4; while scores higher than 4 would indicate progressively worsening bowel preparations. A completely unprepared colon would score 11 to 14, depending on the amount of colonic fluid.

Colonoscopy will be performed in a standard fashion and endoscopists will rate the bowel-preparation quality during the procedure and record the result on a separate standardized form.

Secondary outcomes will include a previously validated tolerability questionnaire and patient and investigator reported adverse events.

Inclusion Criteria:

• All patients between the age of 50 and 75 years referred to the Forzani & MacPhail Colorectal Cancer Screening Centre in Calgary, Alberta, Canada for colonoscopy will be considered for inclusion.

Exclusion Criteria:

• patients with acute coronary syndrome,
• congestive heart failure,
• unstable angina,
• known or suspected renal failure,
• ascites,
• megacolon,
• known or suspected bowel obstruction, or
• other comorbidities that may prevent colonoscopy will be excluded. Patients will also be excluded if they previously had partial or subtotal colectomy or if the colonoscopy is warranted for the evaluation of diarrhea.