Comparison of a Split Dose Bowel Preparation With 2-L Polyethylene Glycol Plus Ascorbic Acid and 1-L Polyethylene Glycol Plus Ascorbic Acid and Bisacodyl Prior to Colonoscopy

• Study design A single center, randomized, comparative observer-blinded study was performed from May 2015 to September 2015 at the Department of Gastroenterology and Digestive Endoscopy at Korea University Anam Hospital (Seoul, Korea).

In total, 200 outpatients received lower volume 1-L PEG with ascorbic acid plus bisacodyl (1L-PEG/AB) or low volume 2-L PEG with ascorbic acid (2L-PEG/A) in a 1:1 ratio.

At the time of registration, subjects were randomly allocated to either group. They were randomized by a computer-generated list and were provided with written instructions. All patients provided written informed consent.

• Patients All patients between the ages of 20 and 75 years. Patients were excluded from the analysis if they had known or suspected gastrointestinal obstruction, Ileus, severe heart failure, uncontrolled hypertension (systolic pressure > 170 mmHg, diastolic pressure > 100 mmHg), severe constipation, clinically significant electrolyte abnormalities, any prior bowel resection, or significant gastroparesis.
• Bowel preparation In the 2L-PEG/A group, 1 L of PEG containing ascorbic acid was taken at 8:00 pm on the day before the colonoscopy, followed by an extra 500 mL of water. The second 1-L of PEG containing ascorbic acid was taken 4 h before the colonoscopy examination, with an additional 500 mL of water. Each liter of preparation and the extra 500 mL water had to be consumed within 2 h of the procedure.

The 1L-PEG/AB group received 10 mg bisacodyl at 9:00 pm on the day before the colonoscopy. Four hours before the colonoscopy examination, 1 L of PEG containing ascorbic acid was taken, followed by an additional 1 L of water. The preparation was completed 2 h before the examination. All colonoscopies were performed between 9 am and 1 pm.