Although adequate bowel preparation is essential for successful colonoscopy, the 23% of patients had shown inadequate bowel preparation. Inadequate bowel preparation may results in incomplete examination, increased patient's discomfort, decreased polyp detection rates, ultimately leading to repeated colonoscopies. One prior study showed that patients reporting their last rectal effluents as brown color or solid stool had a 54% chance of having fair or poor preparation. Thus, recent consensus guideline suggested consideration of additional oral preparation in patients presenting brown effluents on the day of colonoscopy. However, the data supporting additional oral preparation is still spares. Therefore, the investigators aimed to examine the impact of additional oral preparation on the quality of bowel preparation for colonoscopy in patients showing brown effluents on the day of colonoscopy.

Inclusion Criteria:

• patients who reporting their last rectal effluents as brown color or solid stool on the day colonoscopy

Exclusion Criteria:

• known hypersensitivity to polyethylene glycol
• severe congestive heart failure [New York Heart Association (NYHA) grade III or grade IV]
• severe renal insufficiency (creatinine clearance <30 ml/min)
• hemodynamic instability
• suspected intestinal obstruction or perforation
• compromised swallowing reflex or altered mental status
• pregnancy or lactating woman
• patients who declined to participate