PEG-Asc Vs. SPMC for Bowel Preparation in Capsule-based Procedures

Capsule colonoscopy (CC) and pan-intestinal capsule endoscopy ("panendoscopy") are increasingly used diagnostic modalities in clinical practice. Capsule colonoscopy is most often indicated when a complete conventional colonoscopy cannot be achieved due to technical difficulties (looping, sharp angulation), patient intolerance, or contraindications to sedation. Panendoscopy allows simultaneous visualization of the small bowel and colon and is especially relevant in the diagnostic work-up of Crohn's disease and obscure gastrointestinal bleeding.

A key limitation of capsule-based procedures is the inability to wash or aspirate debris. Consequently, bowel preparation quality has a direct and critical impact on diagnostic yield. Residual stool, bubbles, or opaque fluid can obscure mucosal visualization, leading to missed lesions or inconclusive examinations. Meta-analyses of capsule endoscopy studies highlight substantial variability in preparation protocols, with pooled adequate cleansing rates around 70%. However, no standardized regimen has been established, and current practice often relies on multi-step protocols combining dietary restrictions, stimulant laxatives, split-dose purgatives, prokinetics, and booster solutions.

Traditional polyethylene glycol (PEG)-based regimens are effective but often require ingestion of large fluid volumes (2-4 liters), which reduces tolerability and adherence. Recently, ultra-low-volume regimens (≤1 L) have been developed, aiming to improve patient acceptance while maintaining cleansing efficacy. Among these, 1 L PEG plus ascorbic acid (PEG-Asc) and sodium picosulfate with magnesium citrate (SPMC) are widely used in conventional colonoscopy, where multiple randomized controlled trials and meta-analyses have shown them to be non-inferior to higher-volume preparations, with superior tolerability profiles. However, their performance in capsule-based procedures has not previously been tested.

The primary aim of this study was to compare the bowel cleansing efficacy of PEG-Asc and SPMC in patients undergoing capsule colonoscopy or panendoscopy. Secondary aims were to evaluate tolerability, adverse events, completion rates, and the prevalence of clinically relevant findings (polyps, diverticula, inflammatory changes, angioectasias).

This was a prospective, single-center, randomized, researcher-blinded clinical trial. Between January 2024 and June 2025, consecutive adult outpatients referred for CC or panendoscopy were enrolled and randomized in a 1:1 ratio to receive either PEG-Asc or SPMC. Randomization was performed using block allocation. Patients provided written informed consent prior to participation.

All patients discontinued iron supplementation one week before the procedure and followed a low-fiber diet two days before capsule ingestion. Oral senna 12 mg was administered twice daily for two days prior. After 2:00 PM on the day before the procedure, patients transitioned to a clear liquid diet.

PEG-Asc group: In the evening (8:00 PM), patients ingested 1 L solution consisting of 500 mL PEG-Asc taken over one hour, followed by 500 mL of clear fluids. The second dose was repeated at 6:00 AM on the day of the procedure.

SPMC group: In the evening, patients dissolved one sachet of SPMC in 150 mL water, ingested it, and followed with 1.5-2 L of clear fluids over 1-2 hours. The second sachet was taken at 6:00 AM in the same manner.

Patients received 10 mg domperidone 30 minutes before capsule ingestion. A PillCam™ COLON 2 or PillCam™ CROHN'S capsule was swallowed. Real-time viewer checks ensured small-bowel entry; if delayed, domperidone was repeated or endoscopic delivery was performed. Booster doses of sodium phosphate solution were administered to facilitate capsule propulsion (30 mL + 1 L water after small-bowel entry; 15 mL + 1 L water 3 hours later). Bisacodyl suppository was administered if the capsule had not been expelled after the scheduled meal.

Primary outcomes: Adequate bowel cleansing (assessed using the validated CC-CLEAR scale) and procedure completion rate (visualization of hemorrhoidal plexus or documented expulsion).

Secondary outcomes: Patient-reported tolerability (questionnaire), adverse events, compliance, and detection of clinically relevant findings (polyps, diverticula, inflammation, angioectasias).

Capsule videos were reviewed independently by two experienced readers blinded to allocation, using twin-head mode on RAPID® software. The colon was divided into right, transverse, and left segments, scored according to the percentage of mucosa visualized. Adequate cleansing was defined as all segments scoring ≥2 and an overall CC-CLEAR score ≥6. If any segment scored ≤1, the preparation was considered inadequate.

Continuous variables were tested for normality (Shapiro-Wilk). Normally distributed data were compared with Student's t-test; non-normal data with the Mann-Whitney U test. Categorical variables were analyzed using chi-square or Fisher's exact test. Significance was set at p<0.05 (two-tailed). Analyses were conducted using SPSS v28.

This trial addresses a critical gap in evidence regarding ultra-low-volume bowel preparation regimens for capsule endoscopy. Because capsule procedures cannot compensate for residual stool or fluid, optimal preparation is essential to ensure diagnostic accuracy and clinical utility. By comparing PEG-Asc and SPMC directly in this context, the study will provide much-needed data to inform best practices. Findings are expected to guide selection of bowel regimens in clinical practice, improve patient outcomes by optimizing mucosal visualization, and support the broader adoption of capsule-based diagnostics.