The purpose of this study is to document the safety and effectiveness of high doses of liquids to clean the colon for colonoscopy in patients who had a previous colonoscopy with a poorly cleaned colon.

Most of our patients use a standard dose of Gatorade (64 oz) and a tasteless laxative powder called MiraLAX (306 g) to clean their colons out for a colonoscopy. Occasionally, patients have chosen to use other FDA approved solutions to clean their colons including NuLYTELY, GoLytely, MoviPrep and SuPREP. Rarely patients choose to use high doses of MagCitrate.

Despite drinking all their liquid to clean their colon, a few patients have difficult to clean out colons and the quality of their colonoscopy preparation was not good. No one has ever studied what liquids to give these patients when they have another colonoscopy. Most doctors recommend using higher than standard doses of bowel cleaning liquids, but the safety and effectiveness of these higher doses has never been studied.

Patients will already have been assigned a higher than standard dose of a bowel cleaning liquid of their choice for their planned colonoscopy. This is our standard of care for cleaning out the colons of patients who previous had colonoscopies with colons that were not adequately cleaned. If the patient chooses to participate in this study, the plans to clean their colon will remain unchanged.

Before and during the study: The subject will clean out thier colon in the days before their colonoscopy just as they would have if they were not part of the study. They will be asked to fill out a short questionnaire before the colonoscopy about their experience with the liquid and the clean out process.

We would like to obtain a blood test (basic metabolic profile) that looks at each subject's kidney function within 3 months before their colonoscopy and before the IV is started for the colonoscopy. This involves a simple needle stick to draw 1 teaspoon (5 ml) of blood. If the subject had had blood tests done for other reasons within 3 months of their colonoscopy, these results can be used in place of the first blood sample.

The only research activity is the collection of patient's blood and the questionnaire the subject will fill out before the colonoscopy. The preparation to clean their colon and the actually colonoscopy will be unaffected by this research.

Inclusion Criteria:

• Patients at least 18 years old planning to undergo an elective colonoscopy will be eligible for inclusion in our study if they had a previous colonoscopy with an inadequate preparation.

Exclusion Criteria:

• Patients who are pregnant.
• Patients with ileus, gastrointestinal obstruction, gastric retention, bowel perforation, toxic colitis or toxic megacolon would not be considered elective colonoscopies and are excluded.

Patients in our practice who are undergoing a routine colonoscopy who had an inadequate preparation for colonoscopy in the past