Low Volume Bowel Prep Best for Hospitalized Colonoscopy Patients, Study Finds

Among hospitalized adults undergoing elective colonoscopy, bowel prep with very low volume polyethylene glycol (PEG)-ascorbate achieved noninferior cleansing results compared to higher volume PEG, with higher rates of high-quality cleansing, in a multicenter, randomized trial, published in Annals of Internal Medicine.

High-quality cleansing was achieved in close to 47% of patients receiving the 1 liter PEG regimen during bowel prep, compared to 35% and 37%, respectively, in those receiving 2 and 4 liters of the prep solution, and very low volume PEG prep was associated with higher willingness to repeat the procedure.

Researchers noted that the benefit of low-volume prep was shown mostly in the right colon, "where inadequate preparation increases the risk for missed proximal lesions."

"The number needed to treat to achieve 1 additional high-quality cleansing was approximately 8 to 10, suggesting a clinically meaningful advantage in routine practice," wrote researcher Lorenzo Fuccio, MD, of the University of Bologna, Italy, and colleagues.

"These findings have direct implications for inpatient colonoscopy. Inadequate cleansing often leads to repeated procedures and prolonged hospitalization. A low-volume regimen may improve completion rates and reduce resource use while preserving cleansing quality."

Fuccio and colleagues noted that suboptimal bowel prep is common among hospitalized patients undergoing colonoscopy due to the frequency of comorbid conditions, as well as immobility and the common use of medications which promote constipation.

Guidelines generally recommend high-volume (4-liter) polyethylene glycol for use in hospitalized patients, but the researchers further noted that this recommendation is based on low-quality evidence from outpatient studies.

Their aim in conducting the multicenter, randomized INTERPRET study was to compare the "efficacy, tolerability and safety" of very-low volume (1 liter), low-volume (2-liter) and high-volume (4-liter) PEG regimens in patients receiving colonoscopies while hospitalized.

The study’s primary endpoint was adequate bowel cleaning, assessed as Boston Bowel Preparation Scale [BBPS] score of ≥6 with all segments ≥2. Secondary endpoints included high-quality cleansing (BBPS score, 8 to 9), high-quality right-colon cleansing (BBPS score, 3), and willingness to repeat.

A total of 665 patients were randomized for the study, including 228 receiving PEG 1 L, 218 receiving PEG 2L, and 219 receiving PEG 4L.

Among the main findings in the PEG 1L, PEG 2L, and PEG 4L respectively, the study authors reported:

• "Adequate overall cleansing occurred in 82.0%, 78.0%, and 78.5% (absolute difference between the 1L and 2L groups [Δ1L–2L], 4.0 percentage points [95% CI, -3.4 to 11.4 percentage points]; absolute difference between the 1L and 4L groups [Δ1L–4L], 3.5 percentage points [CI, -3.9 to 10.9 percentage points]).
• "High-quality overall cleansing occurred in 46.9%, 35.3%, and 37.4% (Δ1L–2L, 11.6 percentage points [CI, 2.5 to 20.5 percentage points]; Δ1L–4L, 9.5 percentage points [CI, 0.3 to 18.5 percentage points]). High-quality right-colon cleansing occurred in 40.6%, 29.5%, and 31.6% (Δ1L–2L, 11.2 percentage points [CI, 2.1 to 20.0 percentage points]; Δ1L–4L, 9.0 percentage points [CI, 0.0 to 17.9 percentage points]).
• "Tolerability was good across regimens,with the highest willingness torepeat in the 1L group (84.2%), despite more frequent vomiting and thirst"

The researchers noted that there are key mechanisms which could explain why lower volume PEG would yield higher quality results than higher volume PEG prep.

"Unlike isosmotic high-volume PEG solutions that rely mainly on large fluid volumes, 1L PEG-ascorbate regimens include a higher concentration of osmotic agents (notably ascorbate), which can promote intraluminal water retention and catharsis despite lower volume," they wrote. "In the inpatient setting, where reduced mobility, constipation, and concomitant medications commonly impair preparation performance, a regimen combining lower volume with a stronger osmotic load may facilitate more homogeneous cleansing."

Fuccio and colleagues cautioned, however, that since the study did not address mechanistic endpoints, "this interpretation should be viewed as hypothesis generating rather than causal."

A key study limitation cited by the researchers was the exclusion of patients requiring urgent colonoscopy for active gastrointestinal bleeding from the study cohort, along with those having severe comorbid conditions.

Despite these and other limitations, the researchers concluded that the findings "support adopting a low-volume regimen as a practical, patient-centered approach to inpatient bowel preparation."

The primary funding source for this study was Norgine Srl. Fuccio reported no relevant disclosures.

Frazzoni L, et al "Low-volume polyethylene glycol for bowel preparation in hospitalized adults: a multicenter randomized trial" Ann Intern Med 2026; DOI: 10.7326/ANNALS-25-05005.