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

ABSTRACT 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.