Comparison of 1 L, 2 L, and 4 L polyethylene glycol solutions for colonoscopy preparation in hospitalised patients: a multicentre, randomised controlled trial

Aims Adequate bowel preparation is essential for high-quality colonoscopy, yet remains particularly challenging among hospitalised patients, who frequently present multiple risk factors for poor cleansing. Current European guidelines provide no specific recommendations, while US guidelines favour high-volume (4 L) polyethylene glycol (PEG) regimens despite low-quality evidence. We conducted a multicentre, randomised, endoscopist-blinded trial to compare the efficacy, safety, tolerability, and patient acceptability of 1 L PEG–ascorbate, 2 L PEG–ascorbate, and 4 L PEG in inpatients. We tested the hypothesis that 1 L PEG–ascorbate would be non-inferior to higher volumes in achieving adequate bowel cleansing [ 1 ] [ 2 ] [ 3 ]. Methods This investigator-initiated phase IV trial was conducted in seven Italian hospitals (June 2021–January 2025). Hospitalised adults scheduled for elective colonoscopy were randomised (1:1:1) to receive 1 L PEG–ascorbate (PLENVU), 2 L PEG–ascorbate (MOVIPREP), or 4 L PEG (SELG-ESSE), all in split-dose regimen. Endoscopists were blinded to allocation. The primary endpoint was adequate cleansing, defined as Boston Bowel Preparation Scale (BBPS)≥6 with all segments≥2. Secondary outcomes included high-quality cleansing (BBPS 8–9), right-colon cleansing, tolerability, willingness to repeat, adverse events, and compliance (≥75% intake). Analyses were performed on the modified full analysis set (mFAS), excluding incomplete colonoscopies due to strictures, previous colectomy, or therapeutic procedures. Non-inferiority was concluded if the lower bound of the two-sided 95% CI for 1 L versus comparator was above –10%. Missing data were conservatively imputed as failures. Results Overall, 665 patients were randomised (1 L=228; 2 L=218; 4 L=219); 624 constituted the mFAS (1 L=210; 2 L=204; 4 L=210). Baseline characteristics were balanced across arms. Adequate cleansing was achieved in 84.8% with 1 L PEG–ascorbate, 79.5% with 2 L PEG–ascorbate, and 79.1% with 4 L PEG. The absolute difference versus 2 L PEG–ascorbate was+5.3% (95% CI –2.2 to+12.8) and versus 4 L PEG+5.7% (95% CI –1.7 to+13.1), meeting non-inferiority criteria. High-quality cleansing (BBPS 8–9) was superior with 1 L (50.0%) compared with 2 L (36.6%) and 4 L (39.1%): absolute difference+13.4% (95% CI+3.9 to+22.7) and+10.9% (95% CI+1.4 to+20.3), respectively. Right-colon high-quality cleansing (BBPS=3) was achieved in 41.9%, 28.8%, and 31.9% (p<0.05), translating to numbers-needed-to-treat of 7.6 (1 L vs 2 L) and 10 (1 L vs 4 L). Compliance (≥75% intake) was 95.6%, 94.5%, and 93.6% across groups (p=0.643). Despite more vomiting (14.9% vs 7.3% vs 11.4%) and thirst (27.6% vs 14.2% vs 14.2%), willingness to repeat was highest with 1 L (84.2%) versus 2 L (82.1%) and 4 L (68.0%; p<0.001). Serious adverse events were rare: one bowel perforation (in 1 L group) and one hypertensive crisis (4 L), both judged unrelated to treatment. No clinically relevant electrolyte disturbances or renal impairment were observed. Conclusions Among hospitalised patients, 1 L PEG–ascorbate achieved non-inferior adequate cleansing and superior high-quality and right-colon cleansing compared with 2 L and 4 L PEG regimens. Despite higher transient symptoms (i.e., vomiting, thirst), patient acceptability was significantly greater, suggesting easier intake and reduced procedural burden. These findings support the use of a low-volume regimen as an effective, safe, and patient-centred alternative for inpatient bowel preparation. Adoption of 1 L PEG–ascorbate in real-world practice may streamline preparation, improve adherence, and reduce the need for repeated colonoscopies—challenging current US guideline assumptions, and addressing a gap in European recommendations. Publication History Article published online: 05 June 2026 © 2026. European Society of Gastrointestinal Endoscopy. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany