Failed bowel preparation for colonoscopy occurs commonly, but the optimal regimen for the subsequent attempt is unknown. High-volume preparations are often employed but are not well studied. The objective of this study was to compare the efficacy, tolerability, and safety of two regimens for use after failed bowel preparation.
A multi-center, endoscopist-blinded randomized controlled trial was conducted in patients who previously failed bowel preparation despite adequate compliance. Patients were randomized to one of two split polyethylene glycol (PEG) regimens, preceded by 15 mg of bisacodyl: PEG 2 liters the evening before and 2 liters the day of colonoscopy (PEG 2+2L+bisacodyl), or 4 liters and 2 liters (PEG 4+2L+bisacodyl). All patients followed a low fiber diet 3 and 2 days before the procedure followed by a clear fluid diet the day before and the morning of the colonoscopy. The primary outcome was adequate bowel preparation, defined as a Boston Bowel Preparation Scale (BBPS) total score ≥ 6 with all segment scores ≥ 2. Secondary outcomes included adenoma detection (ADR), advanced adenoma detection (aADR), sessile serrated lesion detection (SSLDR), cecal intubation rate (CIR), tolerability, and adverse events.
A total of 196 subjects were randomized at four academic centers in Canada (mean (SD) age 60.7 (11.4), 87 (44.9% female)). There were no significant differences between the PEG 2+2L+bisacodyl and the PEG 4+2L+bisacodyl groups in achieving adequate bowel preparation (91.2% vs. 87.6%, p=0.44). There were no significant differences with regards to mean ADR (37.4% vs. 31.5%, p=0.41), aADR (18.7% vs. 11.2%, p=0.16), SSLDR (8.8% vs. 5.6%, p=0.41) and CIR (96.7% vs. 92.1%, p=0.19). The 2 regimens were similarly well tolerated, but PEG 2+2L+bisacodyl was associated with higher willingness to repeat bowel preparation (91.2% vs. 66.2%, p<0.001).
Split-dose 4L-PEG with 15 mg of bisacodyl, along with dietary restrictions, has similar efficacy as a higher-volume preparation, and should be considered for patients who previously failed bowel preparation.

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