To investigate the clinical effect of adding erythromycin and metoclopramide to the Polyethylene glycol (PEG) as standard regiment for colonoscopy preparation.

This is a single-center multi-arm randomized clinical trials investigated and compared different regimens for colonoscopy preparation. All patients were randomly divided into five groups of A: high volume PEG (4 liters), B: high volume PEG + 3 tablets of oral metoclopramide C: high volume PEG + 3 tablets of oral erythromycin 400 mg, D: high volume PEG+3 tablets of 10 mg oral metoclopramide + 3 tablets of 400 mg oral erythromycin, E: low volume PEG (2 liters) + 3 tablets of 10 mg oral metoclopramide + 3 tablets of 400 mg oral erythromycin. The primary Outcome was to properly prepare the bowel, determined by a score of 6 or higher on the Boston Bowel Prep Scale with individual segment scores of 2 or higher. The secondary outcome was bowel preparation, polyps observing, and reach the cecum.

A total of 280 patients eligible for colonoscopy were enrolled into the study and randomly divided into five groups. No significant difference between different regimens for time to reaching to cecum. Group A was associated with the highest satisfactory preparation (67.9%), but no significant difference was observed (P-value=0.076). Moreover, group A, B, and D had a similar rate of polyp observation (23.2%) and the lowest proportion was belonging to group E (12.5%). However, reaching to the cecum among different groups was not statistically significant (P-value = 0.523).

Our findings showed that adding metoclopramide or erythromycin to high-volume or low-volume PEG was not significantly different from low-volume or high-volume PEG alone. The study protocol was reviewed and registered at IRCT.ir (IRCT20210719051943N1).