Morning-only one-gallon polyethylene glycol improves bowel cleansing for afternoon colonoscopies: a randomized endoscopist-blinded prospective study

Am J Gastroenterol. 2010 Nov;105(11):2368-74. doi: 10.1038/ajg.2010.271. Epub 2010 Jul 6.


Objectives: Inadequate bowel preparation is a known factor associated with increased failure rates of afternoon colonoscopy and lower adenoma detection rates. The aim of our study was to compare the efficacy of bowel cleansing achieved by administering 1-gallon (4 l) polyethylene glycol (PEG) preparation to patients in the morning of an afternoon colonoscopy with that of the traditional evening regimen.

Methods: A prospective endoscopist-blinded study was conducted, in which patients undergoing afternoon colonoscopy were randomized to receive either 1 gallon of PEG the evening before the procedure or the morning of the colonoscopy. 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 prep" interpreted from the Ottawa scale were compared between the two groups.

Results: A total of 136 patients (mean age 51.8 years, 52.2% men) evenly distributed between the two groups formed the study sample. Patients in the morning group had significantly lower Ottawa scale scores and were more likely to have a good preparation for each bowel segment and overall when compared with the evening group (P<0.01). Moreover, patients in the morning group were over 50% less likely to lose sleep or have bloating compared with the evening group (P<0.05). There was no difference in the study groups on overall polyp detection rate, adenomatous polyps, or number of patients with adenomas.

Conclusions: This study shows that the bowel cleansing efficacy of morning-only 1-gallon PEG is superior and better tolerated compared with consumption of 1-gallon PEG in the evening before the day of an afternoon colonoscopy. Thus, administering 1-gallon PEG solution in the morning of an afternoon colonoscopy is a feasible option that can improve the quality of an afternoon colonoscopy.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Administration, Oral
  • Adult
  • Aged
  • Cathartics / administration & dosage
  • Colonoscopy / methods*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Polyethylene Glycols / administration & dosage*
  • Prospective Studies
  • Single-Blind Method
  • Surveys and Questionnaires
  • Time Factors
  • Treatment Outcome


  • Cathartics
  • Polyethylene Glycols