BOWEL PREPS: The Good, the Bad and the Ugly


Over the past decade or so, the medical community and patients have become increasingly aware of the advantages of colorectal cancer screening with colonoscopy, and the number of screening colonoscopies for asymptomatic average risk individuals has risen. However, patients have often heard horror stories from family and friends regarding the infamous bowel prep, and healthcare providers are often asked about alternative preparations to the standard polyethylene glycol (PEG) oral gastric lavage. The search for an alternative preparation that is safe, easily tolerated, and effective is ongoing. Several alternatives have been used in the past and more recently. The issue of safety has been brought into the spotlight with newer bowel preps having adverse effects on electrolytes and even kidney function.

Types of Preps

Historically, stimulant and hyperosmotic laxatives were the first agents to be utilized for bowel preparation prior to colonoscopy. Stimulant laxatives such as castor oil, senna and bisacodyl were used; however, they had their own adverse effects — mainly significant gastrointestinal (GI) upset and the potential for metabolic derangements such as metabolic acidosis and hypocalcemia. Consequently, these early agents were often poorly tolerated and gave poor results. Hyperosmotic laxatives (nonabsorbed carbohydrates) such as mannitol and lactulose were also given a try for bowel preparation; however, these had the most dynamic risk of all. There were actual cases of explosion within the colon during electrocautery when bacterial fermentation of the carbohydrate within the colon produced hydrogen gas.1, 2

Today, we have essentially two types of preps to choose from. These include the PEG solutions, for which there are a few variations, and the saline lavages.

PEG solutions such as Golytely, Halflytely and Moviprep can be quite effective and safe. The ingestion of isotonic PEG does not result in changes in electrolytes or other blood chemistries. However, rapid ingestion of the large volumes of fluid required for an effective prep often elicit nausea and vomiting, and many patients relate uncomfortable chills. PEG has been associated with rare adverse events. These include pulmonary aspiration and Mallory-Weiss tear, likely both related to nausea and vomiting sometimes elicited by the prep. Pancreatitis, cardiac arrhythmia, congestive heart failure and SIADH have also been reported with the PEG solution.3,4,5,6

The saline lavages include Fleet’s phosphosoda, Visicol tablets and Fleet prep kits. These preps incorporate laxatives containing magnesium or phosphate, utilizing the hyperosmotic effect of the poorly absorbed ions within the small intestine. Studies have suggested that Fleet’s phosphosoda and Visicol tablets are equally effective and better tolerated when compared to PEG preps.7 The safety of the oral sodium phosphate (NaP) preparations becomes the issue. The use of NaP is associated with significant volume contraction and dehydration as well as electrolyte abnormalities. Most healthy individuals, though, will tolerate these preps safely without adverse side effects.

Although usually asymptomatic, hyperphosphatemia is seen in 40 percent and hypokalemia is seen in 20 percent of healthy patients who completed NaP prep.8,9 The increased phosphate levels in most patients is not clinically significant except in patients with underlying chronic renal insufficiency in whom severe hyperphosphatemia can arise. Renal failure has also been seen recently in association with sodium phosphate preps in healthy individuals without any underlying renal dysfunction. Acute phosphate nephropathy causing acute renal failure was reported in 21 patients who had received an oral sodium phosphate solution or Visicol in preparation for colonoscopy. All of these patients progressed to chronic renal failure with four requiring permanent hemodialysis. Factors that seemed to predispose these individuals to renal injury included inadequate hydration, increased age, history of hypertension and use of ACE inhibitors or ARBs (angiotensin receptor blockers).10,11 The FDA has issued an alert regarding the use of oral sodium phosphate products for bowel preparation and the association with acute phosphate nephropathy.

Also reported, hyponatremia and hypocalcemia can occur but are usually not clinically significant. Visicol has been associated, however, with seizures in patients without a history of seizure disorder or known electrolyte abnormalities.12 Sodium phosphate preps have also been associated with a chemical colopathy mimicking inflammatory bowel disease (IBD) with erosions, inflammatory changes and ulceration being encountered in patients who received this prep. This is not clinically significant, but these changes can cause diagnostic uncertain, being mistaken for inflammatory bowel disease.

Current Guidelines

Some patient cohorts are known to have issues with specific preps, so guidelines exist to steer these groups toward the preps that work best for them. For example, since NaP administration is associated with significant changes in volume status and electrolyte abnormalities, its use is contraindicated in patients with advanced liver disease, acute and chronic renal failure, recent myocardial infarction, congestive heart failure (CHF), unstable angina, ileus, malabsorption, ascites and underlying electrolyte abnormalities. PEG-containing colonoscopy preparations are recommended in these situations.13

Elderly patients are at increased risk for hyperphosphatemia and hypokalemia secondary to decreased renal function, comorbidities and concomitant medication use. PEG is likely safer in this patient population, though NaP may be safe in select healthy individuals.

There is little data regarding the safety and efficacy of colonoscopy preparation during pregnancy. Endoscopic procedures are often postponed in this situation if at all possible. The safety of PEG or NaP preparations has not been studied in pregnancy. Both of these preps are FDA Category C for use in pregnancy. No adequate studies have been undertaken to assess safety of colonoscopy preps in this particular situation. Of note, PEG solutions have been used safely to manage constipation in pregnancy.

I do not have personal experience with pediatric patients, as my practice is solely focused on adult gastroenterology. However, the 2006 ASGE guidelines for pediatric colonoscopy preparation discuss three preps for this group of patients: a prep utilizing Fleet enemas and X-Prep, one more commonly used including Miralax at 1.25 mg/kg per day for four days, and a split dosing prep with Fleet Phosphosoda. Each of these preps is deemed safe and adequate for cleansing the colon.13,14

Professional Society Recommendations

In 2006, a consensus statement was put forth by a task force with representation from the American Society for Gastrointestinal Endoscopy (ASGE), the American Society of Colon and Rectal Surgeons (ASCRS), and the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES).

This consensus included an evidence-based analysis of the various colonoscopy preparations, dosing regimens and adjuncts commonly used. Preps utilizing aqueous NaP, NaP tablets, and PEG solutions are all acceptable and well tolerated by most patients. Selection of a particular prep should be based on the safety profile of the prep, the health of the patient, comorbid conditions, and current medications.

In certain patient populations such as the elderly, patients with renal insufficiency, and those with hypertension on ACE inhibitors or ARBs, PEG-based solutions may be safer over NaP-based regimens given the risk of potential electrolyte abnormalities and volume depletion.13

Promoting Patient Compliance

The ideal colonoscopy prep would be inexpensive, safe, acceptable to patients, effective for bowel cleansing affording superb mucosal examination, and would not cause patient discomfort or adverse physiological side effects. Unfortunately, preparations that are currently available do not meet all of these criteria. Even when patients follow all instructions and complete all of their preparation, we are often faced with a poor prep, making visualization of the mucosa suboptimal.

Poor preparation can result in missed lesions, longer procedures and, sometimes, the need for repeat procedures. Major factors in patient compliance with colonoscopy prep include having to drink a large volume of fluid as well as the unpleasant taste of the preparation. Recent studies using split dosing of the standard four liter prep (taking half the prep the evening before the exam and the other half in the early morning the day of the exam) produced comparable results to single dosing and better patient tolerance. A recent study by Ell et al. concluded that the addition of ascorbic acid to a PEG solution reduced the volume necessary for an effective prep and was more acceptable to patients. It is believed that ascorbic acid reduces the effective volume so that patients only have to consume two liters, and it also improves the taste. Ascorbic acid apparently causes an osmotic effect when excess ascorbic acid remaining in the bowel cannot be absorbed.15

Various adjuncts have been tried to make colonoscopy preps more tolerable. Flavoring has been added to PEG solutions, making them more palatable, while sulfate salts have been removed from some, resulting in a less salty taste. Ginger ale has been given with NaP to improve the taste. Gatorade and other carbohydrate-electrolyte solutions, when combined with preps, have been shown to improve taste.

The addition of Reglan has been shown to help decrease nausea and bloating associated with the prep. When bisacodyl, senna or magnesium citrate are added to standard preps, less fluid is needed for adequate colon cleansing, making for an effective more tolerable prep.13

Other measures that can sometimes improve tolerability of the prep include giving a single dose of antiemetic such as phenergan, chilling the solution, or adding Crystal Light. If patients call about intolerance of a prep the evening prior to the colonoscopy, it may also be help to recommend taking a one- or two-hour break, then resuming the prep.

James Pilla, DO, is a gastroenterologist at Three Rivers Endoscopy Center in Moon Township, Pa. Pilla is board-certified in both internal medicine and gastroenterology, and is also an active staff member at Sewickley Valley Hospital and Ohio Valley General Hospital.


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