Research progress on bowel preparation regimens before colonoscopy: a narrative review

Adequate bowel preparation is the single most important determinant of colonoscopy quality, yet suboptimal preparation affects up to one-quarter of colonoscopies, leading to repeat procedures, increased health-system costs, and health disparities. This narrative review synthesizes the current evidence on bowel preparation regimens through a public health lens, organized around four interconnected dimensions: cleansing efficacy, safety, tolerability, and population-specific applicability. We define and classify preparation regimens by volume (high-volume ≥4 L, low-volume 2-<4 L, ultra-low-volume <2 L) and administration schedule (split-dose, same-day). Low-volume, split-dose formulations achieve non-inferior cleansing efficacy to high-volume 4L polyethylene glycol (PEG) regimens, with improved patient tolerability and compliance. The Boston Bowel Preparation Scale (BBPS) is the most widely adopted assessment instrument; commonly used adequate preparation is defined as total BBPS ≥6 with each segment ≥2, although definitions vary across studies. PEG-based preparations maintain the most favorable safety profile, particularly in patients with renal or cardiovascular comorbidities, while sodium phosphate carries a small but clinically significant risk of acute phosphate nephropathy. Special populations-including older adults with frailty and polypharmacy, patients with inflammatory bowel disease, and those with diabetes-require tailored preparation strategies. Emerging evidence on glucagon-like peptide-1 receptor agonists (GLP-1 RAs), linaclotide, simethicone, dietary optimization, and artificial intelligence (AI)-based bowel preparation assessment is critically evaluated. Health system implications, including the impact of inadequate preparation on resource utilization, adherence barriers linked to health literacy, and equity considerations, are examined. The review concludes that no single regimen is universally optimal; personalized preparation strategies integrating risk stratification, AI-assisted quality assessment, and evidence-based adjunctive protocols represent the most promising path toward improving colonoscopy outcomes at the population level.