Background: Colonoscopy is common procedure performed for diagnostic or therapeutic colorectal diseases. Good quality mechanical bowel preparation is important for good visualized colonic mucosa. Sodium phosphate solution ingestion is a common mechanical bowel preparation, with low side effects and less tolerability.

Objective: The present study was conducted to compare the efficacy and tolerability of mechanical bowel preparation using the split 45 ml x2 doses and 30 ml x3 doses of sodium phosphate solution in patient undergoing colonoscopy.

Material and Method: The present study was conducted in Ramathibodi Hospital, Thailand between November 2015 and December 2016. Eighty eligible patients who underwent colonoscopy at our unit were randomized assigned to study group (sodium phosphate 30 ml x3 doses) and control group (sodium phosphate 45 ml x2 doses). The quality of bowel preparation was evaluated by endoscopist and tolerability was recorded from patient’s questionnaire.

Results: Eighty participants were included in this study; 65 participants were analyzed about quality of bowel preparation and 34 participants were analyzed about tolerability of bowel preparation. There was no statistical difference in patient characteristic, quality of bowel preparation (p = 0.68), nausea (p = 0.73), vomiting (p = 1.00), pain (p = 0.25), difficult to eat this solution (p = 0.07), amount of feces (p = 0.20), time from last dose to last defecation (p = 0.72), and frequency of defecation (p = 0.76) between the two bowel preparation regimens.

Conclusions: The present study demonstrated no difference in quality and tolerability between the 45 ml x2 doses and 30 ml x3 doses of sodium phosphate solution for mechanical bowel preparation in patient undergoing colonoscopy.

Keywords: Bowel preparation, Sodium phosphate solution, Colonoscopy