Study design
This study was a prospective, multi-center, randomized controlled trial conducted at Kosin University Gospel Hospital and Inje University Haeundae Paik Hospital in Korea between August 2020 and February 2021. The study protocol was approved by the institutional review board of both participating hospitals. This trial is registered with the International Clinical Trials Registry Platform, number KCT0005451.
Patients
Patients older than 19 years undergoing colonoscopy for screening or post-polypectomy surveillance at the endoscopy centers of Kosin University Gospel Hospital and Inje University Haeundae Paik Hospital in Korea were enrolled. Patients with a history of chronic kidney disease, heart failure, ascites, ileus or intestinal obstruction, gastrointestinal bleeding, and allergy to bowel preparation regimen and those who were pregnant were excluded. Patients who had taken laxatives, metoclopramide, tegaserod, or erythromycin within one month prior to colonoscopy were also excluded. A study investigator of each hospital explained the aim and contents of the study in detail, and all participants provided written informed consent before enrollment. Clinical information including age, sex, height, weight, body mass index, previous colonoscopy experience, and the reason for a colonoscopy were collected using a questionnaire. All patients were provided education with a brochure for bowel preparation and colonoscopy, which included the diet schedule (low-fiber diet for three days and soft diet for dinner the day before the colonoscopy), methods for taking OST or PEG, the colonoscopy process, and potential adverse events during bowel preparation or colonoscopy. Patients were randomized to either the OST group (Orafang, Pharmbio Korea Co. Ltd., Seoul, Korea) or the PEG group (Coolprep, TaeJoon Pharmaceuticals, Seoul, Korea) using the table of random numbers. Orafang is 28 tablets which consist of sodium sulfate, potassium sulfate, magnesium sulfate, and simethicone and Coolprep consists of 2 L PEG and ascorbic acid.
Data collection
On the day of colonoscopy, all patients were interviewed and filled out a questionnaire, which consisted of questions on compliance, satisfaction, difficulty, taste, willing to switch to another preparation on next examination, total water intake and adverse events during bowel preparation. Compliance was checked as two factors, one based on the total dose that was taken (<25%, 25–50%, 50–75%, 75–99%, or 100%) and another based on a total taking time (per a split dose; <30 min, 30 min to 1 h, 1–2 h, 2–3 h, or >3 h) for bowel preparation. Satisfaction was assessed by visual analogue scale (VAS; 0: very bad, 10: excellent). Difficulty of eating was evaluated by a four-point rating scale (1: ease, 2: relative ease, 3: a little difficult, 4: quite difficult). Taste was also evaluated by a four-point rating scale (1: good, 2: no taste, 3: not good, but edible, 4: bad). Total water intake was based on the amount of total water intake (<500 mL, 500–1000 mL, >1000 mL). Adverse events during bowel preparation including abdominal distension, abdominal pain, nausea and vomiting were assessed as none, mild, moderate, and severe.
Colonoscopic examinations were performed by two experienced endoscopists who were blinded to the group information. During the examination, bowel preparation scale, bubble score, and polyp detection were recorded. The bowel preparation scale was assessed according to the Boston bowel preparation scale (BBPS) [14], and the bubble score was checked using a numeric rating scale (3: excellent, 2: good, 1: poor, 0: inadequate) [15]. After examination, an endoscopist evaluated the own satisfaction during colonoscopy using VAS.
Endpoints
The primary endpoint in this study was the comparison of efficacy and safety between the OST and PEG groups according to age. Secondary endpoints included the comparison of compliance, satisfaction, difficulty of eating, taste, willingness to switch to another preparation, polyp detection rate, and adenoma detection rate between the OST and PEG groups according to age.
Statistical analysis
The number of patients in each group was calculated based on expected successful cleansing rates of 85% for both groups, a non-inferiority margin of 15% with a power of 0.8, and one-sided significance level of 0.025. Considering a dropout rate of 10%, at least 98 subjects in each group were needed for the study. Continuous data with normal distributions are expressed as mean ± standard deviation, and categorical data are presented as the number of subjects (%). Student’s t-test and the chi-square test were performed for continuous and categorical variables, as appropriate. P values less than 0.05 were considered statistically significant. Statistical analyses were performed using SPSS version 23.0 (IBM Co., Armonk, NY, USA).