Bowel preparation for Colonoscopy

Colonoscopy is a modality to diagnose and treat luminal disease. This makes adequate visualization of the mucosa paramount. Preparing patients for these procedures requires an understanding of the various options. There is no obvious superior agent or regimen in the literature. Clinician should use some judgment as to what is most appropriate for the individual patient. All regimens have a failure rate and to some degree this is determined by compliance, slow gut transit medication and co morbidities (Diabetes, Mobility etc). Patient education hence becomes a significant factor in determining the views obtained during endoscopy.

Bowel preparation for colonoscopy

Poor bowel preparation is a significant problem facing colonoscopist throughout the world. A prospective study by Bowels et al in 2004 showed that poor bowel prep accounted for 19.6% of failed procedures. In addition there is evidence that polyp detection rate is determined by the quality of bowel prep. It is inherent that poor preparation would make colonoscopy more hazardous. The existing regimens have been tabulated below.

Polyethylene glycol (PEG) Osmotic Laxatives Stimulant laxative
Klean Prep and Moviprep (low volume preparation) are non-absorbable macrogol polymer with an electrolyte mixture. Phospho soda (Fleet), Magnesium citrate, Mannitol Sodium picosulphate-SPS (Picolax, Citrafleet are mixtures of SPS and magnesium salts) Bisacodyl
PEG results in osmotic retention of electrolytes in the lumen which acts as a cleanser. The action of saline laxatives results from the hyperosmotic effect of poorly absorbed magnesium or phosphate ions within the small intestine and from the retention of water that indirectly stimulates stretch receptors and increases peristalsis. SPS regimens stimulate bowel peristalsis and promote fluid sequestration in the gut.

  • Cause minimal osmotic fluid shifts into the gut lumen.
  • It is hence preferred in high risk group patients eg CCF, Renal impairment, Liver insufficiency.

  • Low volume preparation
  • More palatable than PEG solutions especially if used with Fleets Dilution Solution

  • Low volume preparation
  • Causes less fluid and electrolyte shifts than phospho soda
  • Disadvantages

    • Large volume of fluid (4 L) to drink. The addition of low dose stimulant laxatives allows the volume to be halved. Moviprep is a newer low volume low volume preparation.
    • Unpalatable salty taste.
    • Dilutional Hyponatremia can be a problem due to absorption of some of the ingested fluid.

    • Causes significant fluid shifts, precipitating intravascular volume depletion. As a result, it should not be used in patients with CCF, CRF, decompensated cirrhosis, or electrolyte abnormalities.
    • Acute Phosphate nephropathy may occur in up to 1:1000 patients receiving the drug.
    • Apthous ulceration and petechial haemorrhages are common although the exact mechanism is unclear. This may result in an inappropriate diagnosis of IBD.

    • Can cause fluid shifts and electrolyte disturbance
    • Complications include syncope and convulsions
    • Co administration with ORS may help prevent dehydration

    Divided-dose PEG regimens (2–3 litres given the night before the colonoscopy and 1–2 litres on the morning of procedure) are usually used. Patients find this more tolerable.


    For afternoon procedure (1 dose in the evening the day before the procedure and the 2nd dose on the morning of the procedure. For morning procedure the doses should be taken on the morning and evening of the day before the procedure.


    Two doses are taken having been mixed with 250mls of water. For morning procedures they are taken at 2Pm and 6am the next day. For afternoon procedure at 4pm and 8am the next day.

    Dietary modification

    Dietary modification can be a useful adjunct to bowel preparation regimens. We recommend a 48 hr low residue and 24 hr liquid diet prior to the colonoscopy.

    Absolute contraindications

    • Gastrointestinal obstruction or perforation, ileus, or gastric retention
    • Acute intestinal or gastric ulceration
    • Severe acute inflammatory bowel disease or toxic megacolon
    • Reduced levels of consciousness
    • Hypersensitivity to any of the ingredients
    • Difficulty swallowing due to nausea (a nasogastric tube may help)
    • Ileostomy

    Drug Modifications

    Oral iron should be stopped 5 days before and appropriate advice is given for patients with diabetes. In addition patients on OCP need to be informed reduced bioavailability with bowel preparation agents and need for temporary alternative methods of contraception. Consider stopping ACE inhibitors, NSAIDs and diuretics as this may increase the risk of renal dysfunction and hypovolemia.

    Failed Bowel preparation

    In patients in whom preparation has failed clarify the factors that may have contributed.

    • Unpalatability, lack of understanding/ failure to recognise the importance of following the regimen may be significant factors in compliance.
    • Patients on opiods may need to temporarily use alternative agents.
    • Diabetic / Constipated patients have slow gut transit and may need prolonged regimens.
    • Adding a stimulant such as Senna or Bisacodyl may help.
    • Combining preparations such as PEG and SPS agents may be successful.


    ASGE Guidance

    BSG Guidance

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