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Getting to the bottom of colonoscopy prep

March 24, 2016 | UCI Health
Man holding glassful of colonoscopy prep liquid

Even if you've never had a colonoscopy, you've surely heard the stories. The colonoscopy procedure itself? No problem. You won't feel or remember much, if anything.

It's the day prior to the procedure — the so-called prep day — that makes many colonoscopies unforgettable. For all the miracles of modern medicine, it seems, no one has figured out a pleasant way to cleanse the colon.

First, one must forego solid food for a day. Then comes the glassful unpleasant-tasting colon-cleansing liquid — glassful after glassful of it — that compels the patient to trot to the toilet

But new studies promise to make the day-before ritual less hunger-filled and more comfortable.

Why is an empty colon so important?

Since it's quite clear that colonoscopies save lives, colonoscopy prep is a big deal. An empty colon is necessary for the doctor to thoroughly examine the digestive tract for signs of cancer, including detecting harder-to-see flat polyps, says Dr. Jason Samarasena, a UCI Health gastroenterologist with the H. H. Chao Comprehensive Digestive Disease Center (CDDC).

"Bowel prep quality is really the most important aspect of the colonoscopy," he says, adding that it's even more important than who performs the exam.

However, emptying the bowel completely is not a simple matter. There is a risk that the body’s electrolytes can get out of whack after excessive diarrhea. Electrolytes are minerals in the blood and other body fluids that carry an electric charge, and they affect the amount of water in your body, your muscle function, and other important processes. For patients with health problems, the fasting and cleansing carry special considerations.

So many preps to choose from

Gastroenterologists can choose among several products when they prescribe bowel preps, and different doctors apparently have their favorites.

Dr. C. Gregory Albers, a UCI Health gastroenterologist with the CDDC, prefers to use FDA-approved regimens in a split dose method, if possible. Many FDA-approved agents are lower volume (SuPrep, Prepopik, and MoviPrep), requiring the patient to drink less prep liquid, and can be the right fit for many healthy patients, he says. 

Not interested in gulping down questionable-tasting liquid? Another bowel preparation requires the patient to take 32 capsules, but it carries risks of kidney insufficiency and electrolyte problems and thus it is generally not used unless the patient is very healthy and specifically requests it, says Albers.

Commonly, the larger-volume preparations like GoLytely, TriLytely, NuLytely, and generic versions of these four-liter “jug preparations” are given to many patients. They are better suited for people who have risk factors for less-than-ideal bowel preparation, he says. These include people on narcotics and similar medications that slow down the bowel, those with prior poor preparations, and very tall or very obese patients, research has shown.

Safety for patients with medical conditions

These prescription four-liter bowel preps also are generally felt to be safest for patients who have other diseases, such as diabetes or kidney, heart and liver disease because they limit fluid shifts and electrolyte disturbances.

"GoLytely, or a variant of it, is considered the gold standard in preps," Albers says.

However, the somewhat-ironically named GoLytely is not many patients' top choice. "It tastes like sea water with a bit of a bad odor," notes Samarasena, who says he has tested colonoscopy preps himself to better understand his patients' complaints.

Splitting the dose

The good news is that doctors now recommend splitting the laxative dose; drinking half of the solution the day before and the other half about five hours before the colonoscopy.

"I think splitting the dose was a breakthrough in cleansing," Samarasena says. "It made it easier for patients to drink it. And, in terms of the quality of the prep, it has led to a 40 percent improvement."

Another popular prep is over-the-counter MiraLAX mixed with Gatorade. But, says Albers: "That prep is not approved by the Food and Drug Administration. It has been shown in many studies to be an inferior prep compared to the GoLytely prep. There have been some recently reported issues with the MiraLAX prep because it's hyperosmotic (meaning it draws water out of bowel tissues). Very infrequently, it can lead to low sodium levels. There are some risks in theory, but the tolerance seems to be better, and if patients want it, I'll certainly give it to them." But it is not Albers’ first choice.

In a study published in 2012, Samarasena compared the MiraLAX-Gatorade prep with GoLytely in healthy patients and found that when both were consumed in split doses, they were comparable in safety and efficacy. And it was preferred by patients: 96.8 percent of the MiraLAX-Gatorade participants said they would be willing repeat the same prep, compared to only 75 percent of the GoLytely group.

No more fasting?

In addition to consuming the icky drinks, patients are typically placed on a clear-liquids-only diet the day before the procedure. Hunger and diarrhea, too? Ugh.

However, there's reason for optimism. Samarasena is studying whether people can eat certain foods on prep day without compromising the success of the colonoscopy. Foods such as scrambled eggs, milk, white bread with butter, chicken nuggets, pasta and ice cream are called "low residue," meaning they are easy to digest. These foods don't contain much fiber that ends up undigested in the stool.

In a study of a clear-liquids-only diet compared to a low-residue diet, Samarasena found that people on the low-residue diet were less fatigued and weak, tolerated the prep better and were more satisfied with the experience.

"You don't feel like you're starving yourself all day before you attempt to drink two to four liters of something you don't want to drink in the first place," Samarasena says.

Most significantly, the study showed that the low-residue diet participants turned up with cleaner colons on colonoscopy day. It makes sense, says Samarsena, who will present his study in May at Digestive Disease Week, a major international medical meeting. When you don't eat, your bowels get sluggish. Eating food during the day triggers more bowel movements and better empties the colon.

A preventable cancer

Here's something else that might make prep day less traumatic: Colorectal cancer — the second-leading cause of cancer deaths among men and women combined — is almost completely preventable if people get their recommended screenings, Albers says.

March is Colorectal Cancer Awareness month, and UCI Health doctors are aiming to make Orange County a "colon cancer-free zone" by encouraging regular screenings. Insurance covers recommended colonoscopies, which are usually performed every 10 years beginning at age 50.

“No one ‘loves’ bowel preparation,” Albers says. “But given the significant importance of excellent bowel cleansing, the end justifies the means.”

Learn more about our colorectal disease services ›

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