In a well-designed and well-executed randomised, controlled trial in five Italian centres, Repici and colleagues[1] showed that 2 L of a new iso-osmotic sulphate-free bowel preparation of polyethylene glycol-citrate-simethicone (PEG-CS), in combination with 10–20 mg of bisacodyl, was slightly more effective than 2 L of PEG-ascorbate (PEG-ASC) plus 1 L of additional water. Two litres of PEG-ASC (plus 1 L of water) has been shown to be as effective as standard 4-L PEG regimens. The preparations were taken the evening before outpatient colonoscopy the following morning, and were comparable in tolerability and compliance. Adenoma detection rates were not reported.

The authors did not use a split regimen (half the evening before and half the morning of colonoscopy), which is clearly superior to evening-before administration with standard 4-L PEG preparations.[2] They note that split regimens generally are not recommended with low-volume PEG preparations and are recommended for high-volume PEG preparations primarily to enhance patient tolerability.

In fact, recent randomised, controlled trials have shown that the tolerability of low-volume preparations is also improved by split dosing,[3, 4] with slightly more frequent preparations of excellent quality for PEG-sulphate than for PEG-ascorbate. Moreover, as the authors note, split-dose PEG-ASC has resulted in better cleansing than single-dose 2-L PEG plus bisacodyl, at least for afternoon colonoscopies.[5] And in inpatients undergoing morning colonoscopies, split-dose PEG-ASC was as effective as and better tolerated than split-dose 4-L PEG with electrolytes.[6]

Arguments against split-dosing of low-volume preparations include potential interference with American Society of Anaesthesiology fasting guidelines, the possible need for a bathroom stop during the trip from home to the endoscopy centre, and potentially reduced compliance with the second dose so early in the morning; none of these concerns seems insurmountable.[7] The authors also note concern about ischaemic colitis with regimens that include bisacodyl.[8]

Clearly, PEG-CS is another option for colonoscopy preparation, but more comparative studies are needed, not only of the agents used in various regimens but also of the timing of their administration.


  1. Top of page
  2. Acknowledgements
  3. References

Declaration of personal interests: L. S. Friedman has received royalties from Elsevier, McGraw-Hill and UpToDate, and honoraria from Digestive Disease Week Council and American Society for Gastrointestinal Endoscopy. Declaration of funding interests: None.


  1. Top of page
  2. Acknowledgements
  3. References
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    Repici A, Cestari R, Annese V, et al. Randomised clinical trial: low-volume bowel preparation for colonoscopy - a comparison between two different PEG-based formulations. Aliment Pharmacol Ther 2012; 36: 71724.
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    Weber FH Jr. Optimizing colonic preparation: the solution is becoming clearer and clearer. Clin Gastroenterol Hepatol 2011; 9: 2869.
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    Di Palma JA, Rodriguez R, McGowan J, Cleveland MB. A randomized clinical study evaluating the safety and efficacy of a new, reduced-volume, oral sulfate colon-cleansing preparation for colonoscopy. Am J Gastroenterol 2009; 104: 227584.
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    Rex DK, Johnson DA, Anderson JC, Schoenfeld PS, Burke CA, Inadomi JM. American College of Gastroenterology. American College of Gastroenterology guidelines for colorectal cancer screening 2009 [corrected]. Am J Gastroenterol 2009; 104: 73950.
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    Cohen LB, Sanyal SM, Von Althann C, et al. Clinical trial: 2-L polyethylene glycol-based lavage solutions for colonoscopy preparation–a randomized, single-blind study of two formulations. Aliment Pharmacol Ther 2010; 32: 63744.
  • 6
    Ell C, Fischbach W, Bronisch HJ, et al. Randomized trial of low-volume PEG solution versus standard PEG + electrolytes for bowel cleansing before colonoscopy. Am J Gastroenterol 2008; 103: 88393.
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    Cohen LB. Split dosing of bowel preparations for colonoscopy: an analysis of its efficacy, safety, and tolerability. Gastrointest Endosc 2010; 72: 40612.
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    Baudet JS, Castro V, Redondo I. Recurrent ischemic colitis induced by colonoscopy bowel lavage. Am J Gastroenterol 2010; 105: 7001.