1. Study design: endoscopist-blinded, prospective, randomized controlled trial
2. Subjects
1. Entry criteria: Male or female patients, aged between18 and 80 years undergoing elective outpatient colonoscopy were eligible for the study.
2. Exclusion criteria:
patients who had chronic kidney disease, severe heart failure(New York Heart Association \[NYHA\] class III or IV), uncontrolled hypertension (systolic pressure ≥170 mm Hg, diastolic pressure ≥100 mm Hg), severe constipation, any bowel resection, significant gastroparesis, or suspected bowel obstruction or perforation.
3. Sampling design: Consecutive recruitment of consenting patients
4. Variables Predictor
1. group 1 (SPMC 2) received one sachet of SPMC at 7 p.m the evening before colonoscopy and another sachet of SPMC at 5 hours before procedure
2. group 2 (PEG-Asc) received 1 L solution of PEG-Asc at 7 p.m the evening before colonoscopy and another 1 L solution of PEG-Asc at 5 hours before procedure;
5. Primary Outcome: Quality of bowel preparation (Boston Bowel Preparation Scale, Aronchick scale, bubble score)
6. Secondary Outcome: Tolerability, palatability
