Is blinding the endoscopists to bowel preparations in randomized-controlled trials a reality?

A number of studies compared the quality, efficacy and tolerability of oral sodium phosphate (NaP) and polyethylene glycol (PEG)-based solutions in preparation for colonoscopy. The primary aim of this study was to explore whether endoscopists can be effectively blinded to the type of bowel preparation.

We recruited 3 experienced endoscopists and 57 outpatients (18-65 years old) undergoing colonoscopy. We randomized eligible patients to receive one of the two bowel preparations. Endoscopists who performed the tests were blinded to the type of preparation, and made their best judgment on the type and quality of the bowel preparation.

Forty-five patients completed the study. The overall correct estimation of the type of bowel preparation was 60.0% (95% CI; 45.5%, 73.0%). The cleansing quality did not differ between the two preparations. Patients found oral NaP solution much easier to take (81.8% versus 36.4%; P = 0.005) and the PEG-based group tended to have more nausea or vomiting. 47.6% of patients in the PEG group indicated they would prefer to try another bowel preparation in the future compared to 4.5% in the oral NaP group (P = 0.002). We stopped the study after an interim analysis indicating that more than 600 patients would be required to detect statistically significant differences in the primary aim.

Our findings suggest that blinding of endoscopists in clinical trials comparing oral NaP to PEG had a relatively low likelihood of bias. The study also suggests that oral NaP is easier to take and more tolerable than PEG without impairing cleansing quality.