Researchers at the Cleveland Clinic Florida (Weston, USA) conducted a prospective, randomized, endoscopist-blinded study examining the efficacy of bowel cleansing achieved by administering four liters of PEG preparation to 136 patients (mean age 51.8 years, 52.2% men) in the morning of an afternoon colonoscopy, compared to that of the traditional evening regimen. Patients were randomly assigned to drink the solution between 5-9 PM the evening before colonoscopy, or to drink the solution between 6-10 AM the same day of the procedure; they were allowed to eat breakfast the day before, followed by clear liquids for the rest of the day. Bowel cleansing efficacy was scored by a blinded endoscopist using the Ottawa scale, and each participant filled out a satisfaction survey. Mean scores for each bowel segment, composite mean scores, and rates of good preparation were compared between the two groups.

The results showed that patients in the morning group had significantly lower Ottawa scale scores and were more likely to have a good preparation for each bowel segment separately and overall when compared with the evening group; specifically, the right, middle, and left colon in the morning group were 3, 8, and 3 times more likely, respectively, to have a good preparation than the evening group. Moreover, patients in the morning group were over 50% less likely to lose sleep or have bloating compared with the evening group. There was no difference in the study groups on overall polyp detection rate, adenomatous polyps, or number of patients with adenomas. The study was published online in the July 6, 2010, issue of the American Journal of Gastroenterology.

"One reason why the morning bowel prep results in better cleansing is that as the patient finishes drinking the solution, bile starts to accumulate in the colon, staining the bowel so the colonoscopist can see less,” said lead author Fernando Castro, M.D., of the department of medicine and geriatrics. "The closer the colonoscopy to the time of the prep, the better the visibility is.”

PEG has a low toxicity and is the basis of a number of laxatives, skin creams, and sexual lubricants, frequently combined with glycerin. In whole bowel irrigation, PEG is used in conjunction with added electrolytes for bowel preparation before surgery, colonoscopy, and in treating drug overdoses.

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