Timing of bowel preparation for colonoscopy in adults

Oral lavage solutions usually act within a few hours, and the effects may last for 6 to 12 hours; however, warn patients that this timing can be unpredictable.

The bowel preparation must be scheduled to allow for the laxative to take effect before the patient leaves for the colonoscopy centre or hospital. The period of fasting before anaesthesia (at least 2 hours) must also be considered.

A ‘split prep’, where the lavage solution is taken in 2 doses separated by several hours, is generally preferred. The second dose should be taken approximately 4 to 6 hours before the procedure is scheduledASGE Standards of Practice Committee, 2015.

A ‘split prep’ may be impractical if the colonoscopy is scheduled for early morning (before 10 am). In these cases, the entire bowel preparation can be consumed the night before.

A ‘split prep’ should be used if the colonoscopy is scheduled for mid to late morning. Approximately half of the lavage solution should be taken the night before the colonoscopy and the other half taken early on the morning of the colonoscopy.

If the colonoscopy is scheduled for the afternoon, the bowel preparation may be given as a ‘split prep’ or alternatively the entire bowel preparation can be consumed on the morning of the procedure.