Isosmotic agents

Sulfate-free PEG-ELS. 

PEG-based lavage solution without sodium sulfate was developed to improve the smell and taste of PEG-ELS. The improved taste was the result of a decrease in potassium concentration, increase in chloride concentration, and complete absence of sodium sulfate. The elimination of sodium sulfate results in a lower luminal sodium concentration. Therefore, the mechanism of action is dependent on the osmotic effects of sulfatefree (SF) PEG-ELS. SF-PEG-ELS is less salty, more palatable, and comparable to PEG-ELS in terms of effective colonic cleansing, overall patient tolerance, and safety.

Low-volume PEG preparations. 

Low-volume PEGELS preparations were formulated to provide a more tolerable bowel preparation with a similar efficacy compared with the original 4-L PEG-ELS preparations. Low-volume 2-L PEG-ELS with ascorbic acid is the only FDA-approved low-volume PEG-ELS preparation commercially available at this time. Studies comparing this preparation with a 4-L PEG-ELS preparation or a sodium phosphate preparation showed similar efficacy. This preparation should be used cautiously in patients with glucose-6-phosphate dehydrogenase deficiency as ascorbic acid may provoke hemolysis in these patients.

Hyposmotic agents

 Another low-volume PEG preparation requires the addition of a commercially available electrolyte solution in the form of a sports drink to PEG-3350 (PEG-SD). It should be emphasized that the combination of a sports drink and PEG-3350 is hyposmotic, is not FDA approved for colonoscopy preparation, and is not equivalent to FDAapproved low-volume 2-L isosmotic PEG-ELS preparations. However, low-volume 2-L PEG-SD (using over-the-counter generic or name brand PEG-3350) is widely used and is often administered with adjuncts such as bisacodyl. Studies that have compared full-volume 4-L PEG-ELS with low-volume 2-L PEG-SD combined with bisacodyl have demonstrated mixed results. One study suggested that there may be a lower adenoma detection rate with the low-volume 2-L PEG-SD/bisacodyl preparation compared with a 4-L PEG-ELS preparation due to differences in bowel preparation quality. A 4-armed study compared 4-L PEG-ELS administered the evening before, split-dose 4-L PEG-ELS, low-volume 2-L PEG-SD administered the evening before, and split-dose low-volume 2-L PEG-SD. This study found that both split-dose regimens were superior to the evening dose-only regimens with no significant preparation quality differences between the 4-L PEG-ELS and the PEG-SD preparations. Other studies comparing a 4-L PEG-ELS preparation with a low-volume 2-L PEG-SD preparation have found no differences in bowel preparation quality 

The safety of PEG-SD combined with bisacodyl has not been well reported to date. It remains unclear whether the addition of bisacodyl is beneficial and whether its use may increase side effects without improving the quality of the preparation. Although there are theoretical concerns regarding mixing PEG-3350 with Crystal Light or Gatorade due to the potential of unabsorbed carbohydrates to be metabolized into explosive gases, no such adverse events have been reported to date. There have been rare reports of hyponatremia. In studies that evaluated the metabolic effects of the PEG-SD preparation compared with a standard PEG-ELS regimen, there were no clinically significant electrolyte changes from baseline due to the bowel preparation. However, a recent study compared the effects of PEG-SD (n Z 180) with an FDA-approved low-volume 2-L PEG-ELS (n Z 184) on serum electrolytes and found that changes from baseline in serum Na, K, and Cl were significantly greater with PEG-SD. The incidence of hyponatremia, the primary endpoint of the study, with PEG-SD was nearly twice that with the low-volume 2-L PEG-ELS (3.9% vs 2.2%, odds ratio 1.82, 95% confidence interval, 0.45-8.62), although this difference was not statistically significantly different. Preparation completion and overall colonic cleansing (per the Aronchick Scale) were similar between the groups

REGIMENS FOR COLONIC CLEANSING BEFORE COLONOSCOPY

 For the purposes of this document, the classification of preparations as high-volume denotes that the preparation requires at least 4 L of cathartic consumption. Preparations described as low-volume preparations require smaller volumes of cathartic consumption, but the reader should understand that the recommended additional fluid intake with so-called low-volume preparations may approach 4 L total liquid volume for optimal preparation results

Isosmotic agents

 High-volume polyethylene glycol preparations. 

Polyethylene glycol (PEG) is an inert polymer of ethylene oxide formulated as a nonabsorbable solution designed to pass through the bowel without net absorption or secretion. Isosmotic preparations that contain PEG are osmotically balanced with nonfermentable electrolyte solutions. Therefore, significant fluid and electrolyte shifts are theoretically minimized by the use of balanced electrolytes. The use of PEG-electrolyte solutions (PEG-ELS) is one of the most common methods of cleansing the colon. Large volumes (4 L) have traditionally been used to achieve a cathartic effect. Although 4-L PEG-ELS is not U.S. Food and Drug Administration (FDA) approved to be administered in a split-dose fashion (single-dosing is approved), there is abundant evidence that the highest-quality preparations are achieved by using 4-L split-dose PEGELS regimens, and this is considered the current criterion standard colonoscopy preparation.

Although PEG-ELS is generally well tolerated, 5% to 15% of patients do not complete the preparation because of poor palatability and/or large volume. In clinical trials, PEG-ELS does not result in significant physiologic changes as measured by patient weight, vital signs, serum electrolytes, blood chemistries, and complete blood counts.PEG-ELS does not alter the histologic features of the colonic mucosa and may be used in patients suspected of having inflammatory bowel disease without obscuring the diagnostic capabilities of colonoscopy or tissue sample analysis.PEG-ELS is considered generally safe for patients with pre-existing electrolyte imbalances and for patients who cannot tolerate a significant sodium load (eg, those with renal failure, congestive heart failure, or advanced liver disease with ascites)

Multiple studies show that the routine addition of prokinetic agents or bisacodyl to 4-L PEG-ELS administration does not improve patient tolerance or colonic cleansing. The additional use of enemas does not offer any improvement in the efficacy of PEG-ELS, but does increase patient discomfort. PEG-ELS gut lavage via nasogastric (NG) tube is the most effective method for colonic cleansing in infants and children. In addition, the use of high-dose (6-8 L) PEG-ELS lavage via an NG tube is effective as a rapid bowel preparation in patients with acute lower GI bleeding.

A disadvantage of 4-L PEG-ELS is the relatively large volume of fluid consumption required, which can cause abdominal fullness and cramping. There is a sulfateassociated taste that is often perceived as unpleasant and is only partially masked by the addition of flavorings. Taking the solution after it is chilled may make it more palatable. These preparations work most effectively when ingested quickly (eg, 240 mL every 10 minutes). Adverse events in patients receiving PEG-ELS have been reported and include nausea with and without vomiting, abdominal pain, rare pulmonary aspiration, Mallory-Weiss tear, pancreatitis, colitis, lavage-induced pill malabsorption, cardiac arythmia, and exacerbation of inappropriate antidiuretic hormone secretion syndrome