Efficacy and Safety of 1‐L Polyethylene Glycol With Low Ascorbic Acid for Bowel Preparation: A Randomized Clinical Trial

BACKGROUND AND AIMS: Ultra-low-volume polyethylene glycol (PEG) with ascorbic acid (Asc) improves tolerability, but Asc-related gastrointestinal and metabolic adverse events remain a concern. Whether reducing the Asc dose preserves cleansing efficacy without compromising safety is unclear. We compared a modified 1-L PEG regimen with reduced Asc (1-L PEG + low Asc) with standard 1-L PEG + Asc and 2-L PEG + Asc formulations. METHODS: In this multicenter, randomized, investigator-blinded, three-arm noninferiority trial across five hospitals, low-risk adults undergoing colonoscopy were allocated (1:1:1) to 1-L PEG + low Asc, 1-L PEG + Asc, or 2-L PEG + Asc. The primary endpoint was successful bowel cleansing by the Harefield Cleansing Scale (HCS). Secondary endpoints included Boston Bowel Preparation Scale (BBPS), endoscopic outcomes, gastric residual volume quantified by esophagogastroduodenoscopy, patient-reported tolerability, and adverse events. RESULTS: Among 242 per-protocol participants, HCS-defined successful cleansing was achieved in 92.7% with 1-L PEG + low Asc, 100.0% with 1-L PEG + Asc, and 98.7% with 2-L PEG + Asc (p = 0.01). The low-Asc regimen met noninferiority criteria versus both comparators (risk difference vs. 1-L PEG + Asc, -7.3%; 97.5% CI, -13.0 to -1.6). BBPS-defined success, adenoma detection rate (31.7%, 18.1%, and 20.8%), gastric fluid volume (27.4, 28.2, and 25.2 mL), and willingness to repeat the regimen (78.0%, 73.5%, and 71.4%) were similar across groups. Adverse-event rates were comparable, with no electrolyte disturbances or renal events observed. CONCLUSIONS: A modified 1-L PEG regimen with reduced Asc provides bowel cleansing efficacy noninferior to both standard 1-L and 2-L PEG + Asc preparations, with comparable tolerability and safety.