Wednesday, 22 March 2017


 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

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