Taking all of the laxatives to prepare for colonoscopy on the day of the procedure is effective in cleaning the colon and lets patients have a better night's rest, less abdominal pain, and less interference with work.

For years colonoscopy prep has been done the day before the procedure.  Recently, splitting the dose between the evening before the test and the next morning has been recommended because viewing of the right colon is better.

But patients often find that they are kept awake with side effects of the laxatives after the evening dose.  In addition, they may lose work time for two days.

Led by David Kastenberg, MD, gastroenterologists  at Jefferson Medical College of Thomas Jefferson University in Philadelphia randomly assigned 116 patients to either split the dose of  laxative solution the night before their exam and the next morning (pm-am) or take the entire dose the morning of the test (am-only).  The preparation was polyethylene glycol electrolyte solution (PEG-ELS).

• Images of the whole colon after both preps were adequate: 92 percent of am-only and 94 percent of pm-am.
• Images of the right colon were also adequate in 93 percent of am-only and 92 percent of pm-am.
• More polyps were found in the am-only group: average of 1.57 polyps per patient compared to .94 per patient in the pm-am group.

While overall side effects didn't differ between the two preparation methods, the am-only group had less abdominal pain, better sleep quality, and less interference with their previous workday.

Kastenberg and his research colleagues concluded,

am-only and pm-am PEG-ELS are clinically equivalent with respect to cleansing efficacy and polyp detection. am-only prep was associated with a lower incidence of abdominal pain, superior sleep quality, and less interference with workday before colonoscopy.

In a news release about the study from Thomas Jefferson University, Dr. Kastenberg said,

Colon cancer is a common and preventable disease, but only half of eligible patients undergo screening,.  Anything we can do that provides additional comfort without affecting results should be considered. If we can make the patient’s experience easier and demonstrate to future patients that the procedure from beginning to end will only last one day, then maybe some of the over 42 million Americans who should be screened, but aren’t, will come forward and we might be able to save some lives.

SOURCE: Kastenberg et al., American Journal of Gastroenterology,advance online publication, April 20, 2010.