One-Liter PEG-Ascorbate Improves High-Quality Inpatient Bowel Cleansing

Optimizing Inpatient Colonoscopy Preparation

Achieving adequate bowel cleansing is a prerequisite for high-quality colonoscopy, yet it remains a significant clinical hurdle in the inpatient setting where patient factors often impede preparation success. While 4-liter polyethylene glycol (a high-volume osmotic laxative) has long been a standard, its high volume frequently leads to poor compliance and patient discomfort [1, 2, 3]. Recent shifts in outpatient care have favored low-volume alternatives and split-dose regimens, which involve dividing the laxative dose between the evening before and the morning of the procedure to improve tolerability and mucosal visualization [4, 5]. However, data specifically addressing the unique needs of hospitalized adults have been limited, leaving clinicians to balance the necessity of thorough cleansing against the practical challenges of volume intolerance [6, 7]. A multicenter randomized trial now provides evidence regarding the efficacy and tolerability of very low-volume polyethylene glycol regimens in the inpatient population, offering a potential strategy to improve diagnostic yield without compromising patient comfort.

Trial Design and Volume Comparisons

The researchers conducted a multicenter, randomized controlled, endoscopist-blinded trial across several community and academic hospitals in Italy to evaluate bowel preparation efficacy. The study enrolled 658 hospitalized adults scheduled for elective colonoscopy, a population often prone to suboptimal preparation due to reduced mobility and comorbid conditions. These participants were randomly assigned in a 1:1:1 ratio to one of three treatment arms: 217 patients received a very low-volume 1-liter (1L) polyethylene glycol (PEG)-ascorbate regimen, 222 patients received a low-volume 2-liter (2L) PEG-ascorbate regimen, and 219 patients received a high-volume 4-liter (4L) PEG regimen. All three groups followed a split-dose administration protocol, which involves consuming half of the preparation the evening before the procedure and the remaining half on the morning of the colonoscopy.

To assess the quality of the preparation, the authors utilized the Boston Bowel Preparation Scale (BBPS), a validated clinical tool that assigns a score from 0 to 3 to each of the three segments of the colon (right, transverse, and left) based on the degree of mucosal visualization after suctioning and washing. The primary end point was defined as adequate bowel cleansing, which required a total BBPS score of 6 or higher with no individual segment scoring below a 2. Secondary end points focused on more stringent measures of clarity, including high-quality overall cleansing (a total BBPS score of 8 to 9) and high-quality right-colon cleansing (a segment-specific BBPS score of 3). Additionally, the trial evaluated patient-centered outcomes by measuring the willingness to repeat the same preparation regimen in the future, providing insight into the trade-off between volume reduction and clinical efficacy.

Superior Mucosal Visualization with Lower Volume

The trial results demonstrated that the very low-volume regimen achieved clinical parity with higher-volume preparations regarding the primary end point of adequate bowel cleansing. Adequate overall cleansing occurred in 82.0% of the 1-liter group, 78.0% of the 2-liter group, and 78.5% of the 4-liter group. When comparing the 1-liter and 2-liter cohorts, the absolute difference in adequate cleansing was 4.0 percentage points (95% CI, -3.4 to 11.4 percentage points). Similarly, the absolute difference between the 1-liter and 4-liter groups was 3.5 percentage points (95% CI, -3.9 to 10.9 percentage points). These findings indicate that reducing the volume of polyethylene glycol to a single liter does not compromise the baseline requirement for a successful inpatient colonoscopy.

Beyond basic adequacy, the 1-liter polyethylene glycol-ascorbate regimen provided superior mucosal visualization across more stringent secondary measures. High-quality overall cleansing, defined as a Boston Bowel Preparation Scale score of 8 to 9, occurred in 46.9% of the 1-liter group, compared to 35.3% of the 2-liter group and 37.4% of the 4-liter group. The absolute difference in high-quality cleansing between the 1-liter and 2-liter groups was 11.6 percentage points (95% CI, 2.5 to 20.5 percentage points), while the difference between the 1-liter and 4-liter groups was 9.5 percentage points (95% CI, 0.3 to 18.5 percentage points). These data suggest that the very low-volume preparation may facilitate more thorough inspection of the colonic mucosa in a hospital population where preparation quality is often suboptimal.

The researchers also observed significant improvements in visualization within the right colon, a region where flat or sessile serrated lesions are frequently difficult to detect and easily obscured by residual stool. High-quality right-colon cleansing, indicated by a segment-specific Boston Bowel Preparation Scale score of 3, was achieved in 40.6% of the 1-liter group, 29.5% of the 2-liter group, and 31.6% of the 4-liter group. For this specific metric, the absolute difference between the 1-liter and 2-liter groups was 11.2 percentage points (95% CI, 2.1 to 20.0 percentage points). The absolute difference between the 1-liter and 4-liter groups was 9.0 percentage points (95% CI, 0.0 to 17.9 percentage points). For practicing gastroenterologists, these results suggest that the 1-liter polyethylene glycol-ascorbate regimen may enhance the detection of proximal pathology by providing a cleaner mucosal surface in the right colon compared to traditional 2-liter or 4-liter alternatives.

Patient Tolerability and Clinical Limitations

The researchers assessed how well hospitalized patients managed the different preparation volumes, noting that tolerability was good across all three regimens. However, the very low-volume preparation was associated with a specific side-effect profile. Patients in the 1-liter group reported more frequent vomiting and thirst compared to those receiving the 2-liter or 4-liter doses. Despite these symptoms, the reduced volume appeared to be a significant factor in patient preference. The 1-liter group demonstrated the highest willingness to repeat the procedure at 84.2%, suggesting that the burden of consuming larger volumes of liquid may be more detrimental to the patient experience than a transient increase in thirst or nausea.

When applying these findings to clinical practice, physicians must consider the specific population enrolled in this trial. The study focused on elective inpatient procedures and maintained strict safety protocols that limited its generalizability to certain high-acuity scenarios. Specifically, patients requiring urgent colonoscopy for active gastrointestinal bleeding were excluded, as were patients with severe or unstable comorbid conditions. Consequently, the efficacy and safety of the 1-liter polyethylene glycol-ascorbate regimen remain unverified for the most critically ill patients or those requiring emergency intervention for acute hemorrhage. Ultimately, this multicenter study, supported by Norgine Srl, provides a practical basis for utilizing very low-volume preparations to improve inpatient bowel cleansing, offering clinicians a viable option to enhance mucosal visualization while maintaining high patient acceptability.

References

1. Tian X, Shi B, Chen H, et al. Comparative Efficacy of 2 L Polyethylene Glycol Alone or With Ascorbic Acid vs. 4 L Polyethylene Glycol for Colonoscopy: A Systematic Review and Network Meta-Analysis of 12 Randomized Controlled Trials.. Frontiers in medicine. 2019. doi:10.3389/fmed.2019.00182

2. Yi L, Tian X, Shi B, et al. Low-Volume Polyethylene Glycol Improved Patient Attendance in Bowel Preparation Before Colonoscopy: A Meta-Analysis With Trial Sequential Analysis.. Frontiers in medicine. 2019. doi:10.3389/fmed.2019.00092

3. Ma G, Fang X. The safety and effects of high- and low-volume polyethylene glycol bowel preparation methods before colonoscopy on bowel cleanliness: a systematic review and meta-analysis.. Journal of gastrointestinal oncology. 2023. doi:10.21037/jgo-23-581

4. Kilgore TW, Abdinoor AA, Szary NM, et al. Bowel preparation with split-dose polyethylene glycol before colonoscopy: a meta-analysis of randomized controlled trials.. Gastrointestinal endoscopy. 2011. doi:10.1016/j.gie.2011.02.007

5. Spadaccini M, Frazzoni L, Vanella G, et al. Efficacy and Tolerability of High- vs Low-Volume Split-Dose Bowel Cleansing Regimens for Colonoscopy: A Systematic Review and Meta-analysis.. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association. 2020. doi:10.1016/j.cgh.2019.10.044

6. Xiao K, Khan F, Link R, et al. Efficacy and Safety of Low Volume Bowel Preparation for Colonoscopy in Hospitalized Patients: A Randomized Noninferiority Trial.. Journal of clinical gastroenterology. 2025. doi:10.1097/MCG.0000000000002269

7. Vassallo R, Maida M, Zullo A, et al. Efficacy of 1 L polyethylene glycol plus ascorbate versus 4 L polyethylene glycol in split-dose for colonoscopy cleansing in out and inpatient: A multicentre, randomized trial (OVER 2019).. Digestive and liver disease : official journal of the Italian Society of Gastroenterology and the Italian Association for the Study of the Liver. 2024. doi:10.1016/j.dld.2023.07.032