The Ins and Outs (and Outs and Outs and Outs) of Colonoscopy Preparation
Preparing for a colonoscopy is generally worse than the procedure itself (at least for 78% of patients ). For most, the procedure is performed under sedation* in the United States. In Europe and Asia, sedation-free colonoscopies are the standard (and are an option in the US).(2) Because of the sedation, most US-based patients don’t remember a thing about the scope itself, and the only residuals (aside from the sedative effect) are a bit of bloating and a little gas release. For those with IBD, the prep itself is what is most dreaded.
The prep involves some form of fasting, coupled with a bowel cleansing routine that involves frequent and urgent trips to the bathroom. Depending on the timing of the procedure itself, it lasts for anywhere between 12 and 18 hours. Of the various bowel cleansing methods, none are pleasant but there is some variability in how well they are tolerated and how well they work at cleansing.
The most common preparation put forth is Polyethylene Glycol (or PEG). PEG is used in everything from paintballs to electronics manufacturing, and has been the drug of choice for colon prep for a couple of decades. Originally, PEG preps contained sulfate compounds (that were not well tolerated), and required large volumes (4 Liters) of liquid be consumed the night before the procedure. The taste and volume led to nausea and non-compliance with the prep, but advancements have been made in the past few years to address these concerns.*
The original PEG preparations (GoLYTLELY™, CoLyte™) were fairly poor tasting. The first enhancement to PEG was to remove the sodium sulfate. This resulted in high volumes of slightly less salty (and therefore less pleasant) preparation material. The new versions, called PEG-SF, included NuLYTELY™ and TriLyte™), had similar performance to PEG and largely replaced the original formulations (though they are still used where electrolyte imbalances are a high risk).
The next generation PEG formulations were low-volume PEG. These halved the amount of liquid that needed to be taken to 2 Liters, generally through the use of Bisacodyl and/or Magnesium Citrate or Ascorbic Acid (Moviprep™ and MiraLax™). The taste wasn’t any better, but there was less of the prep to consume. Research showed no clinical difference between the low volume and high volume PEG preps.
Following the introduction of low volume PEG, another enhancement was split-dosage preparation. Split dosing involved taking half of the dose the night before, and the second half closer to the time of the procedure. Originally frowned upon because risks associated with anesthesia and non-evacuated gastric contents, these have now been accepted and show higher patient compliance with equal or better prep quality. (3,4)
For a few years, it appeared that pill-based preps, based on Sodium Phosphate, would overtake the PEG-based preparations. They involved swallowing many large pills with water (Visicol™, OsmoPrep™), but had good tolerance due to the lack of needing to consume liters of salty muck. Sodium Phophate had been previously used in over-the-counter prep Fleet PhoshoSoda, a drinkable prep. Unfortunately, in 2008 the FDA gave them the kiss-of-death black box labeling due to potential kidney damage, and they are now very limited in their use.(5)
A new version of low-volume PEG, PEG-CS (polyethylene glycol-citrate-simethicone) with bisacodyl, that is sulfate free has shown promise in clinical trials as being even better prep than standard low volume prep, but has yet to make a major market impact.(6)
Clear liquid diets are still the standard prior to prep. There have been some low-residue diets like NutraPrep that have been proposed as adjuncts to the clear liquid. Ultimately, the clear liquid diets help keep dyes that would affect contrast out of the colon and are a necessary part of the early preparation process. Unfortunately, they are not an effective substitute for the cleansing PEG.
Hopefully, the bar will continue to be lowered in terms of the volume needed to be consumed for prep, and the flavors will improve. Remember, a good prep not only provides the best diagnostic result, but avoids retesting and potentially hazardous situations.
· Low-volume PEG are the best tolerated and current standard preps
· Sodium Phosphate pill-based preps are contraindicated
* The original guidance told patients to try mixing the PEG with Gatorade or similar drinks to cut the flavor. The practical impact was similar to using cologne in lieu of a shower – it didn’t so much cover up the unpleasantness as mix it with something palatable.
(1) Nicholson, Fiona B., and Melvyn G. Korman. "Acceptance of flexible sigmoidoscopy and colonoscopy for screening and surveillance in colorectal cancer prevention." Journal of medical screening. 2005.
(3) Kilgore, Todd W., et al. "Bowel preparation with split-dose polyethylene glycol before colonoscopy: a meta-analysis of randomized controlled trials."Gastrointestinal endoscopy 2011.
(4) Wexner, Steven D., et al. "A consensus document on bowel preparation before colonoscopy: prepared by a task force from the American Society of Colon and Rectal Surgeons (ASCRS), the American Society for Gastrointestinal Endoscopy (ASGE), and the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES)." Diseases of the colon & rectum 2006.
(6) Friedman, L. S., Commentary: low-volume bowel preparation for colonoscopy. Alimentary Pharmacology & Therapeutics, 2012.