Split dose bowel cleansing is recommended method for colonoscopy. For afternoon colonoscopy, same-day dose of bowel cleansing is alternative option. Recently, same-day bowel cleansing for morning colonoscopy was validated. To date, there was no study which compared the bowel cleansing efficacy between same-day dose and split dose regardless of colonoscopy time. The aim of current study is to compare the bowel cleansing efficacy, adverse events, and patient's tolerability between the two group.

Subjects who underwent colonoscopy for various reasons were included. After agreeing to participate in the study, study participants were randomly assigned to split dose or same day dose group. Bowel cleansing is done using polyethylene glycol (PEG). All colonoscopy was done between 10 AM to 6 PM. Study participants were instructed to ingest 500ml PEG every 15 minutes. Subjects who were assigned to split dose group ingested 2L PEG from 9PM 1 day before colonoscopy. Remaining 2L PEG was ingested 3-5 hours before colonoscopy. In the same-day dose group, bowel cleansing was started from 5AM for subjects who were scheduled to receive colonoscopy in the morning. Afternoon colonoscopy group in the same-day dose group ingested 2L PEG from 5AM. Remaining 2L PEG was finished 3-5 hours before colonoscopy.

Bowel cleansing efficacy was assessed using Boston bowel preparation scale. Vital signs and laboratory tests were checked before colonoscopy. Study participants completed questionnaire which contained patient's satisfaction, tolerability, and adverse event during bowel cleansing. Bowel cleansing efficacy, patient's tolerability, and safety profile were compared between the two groups. Successful bowel cleansing was estimated 85% for split dose group.

The investigators set 10% for inferior margin. Considering 10% drop out, a total of 352 subjects will be recruited.

Randomization and blinding:

Randomization will be done using computer generated randomization list. A specialized nurse will explain the method of bowel cleansing. Investigators (endoscopists) are blinded to bowel cleansing method.

Endpoint:

Primary end point is successful bowel cleansing rated by Boston bowel preparation (BBPS) scale. Successful bowel cleansing is defined as all segment is 2 or 3 points. Endoscopists will assess BBPS when colonoscopy withdrawal.

Secondary end point was patient's tolerability and safety profile including adverse events. Patient's satisfaction to the different bowel cleansing method and adverse events (nausea, vomiting, dizziness, fatigue) will be investigated by questionnaire before colonoscopy. Blood test will be done before colonoscopy.

Statistical analysis:

Bowel cleansing success, patient's tolerability and safety profile will be compared between the two groups. Student t test for continuous variables and the chi-square test or Fisher exact test for categorical variables.

Sample size:

This study is non-inferioty study. Assuming bowel cleansing success rate 85% in the split-dose group, the significant difference between the two groups were hypothesized at 10%. Considering 80% power and 10% drop rate, a total of 352 participants is needed.

Inclusion Criteria:

• all subjects who undergo colonoscopy for various reasons.

Exclusion Criteria:

• hemodynamic instability
• ileus or bowel obstruction
• active inflammatory bowel disease
• advanced colon cancer

Participants who ingested bowel cleansing agent according to protocol

Adverse events were collected between enrollment and 4 weeks of procedure