Polyethylene Glycol Versus Sodium Phosphate for Colon Preparation After Failure of First Preparation for Colonoscopy

The aim of the study is to compare the efficacy of Polyethylene glycol versus sodium phosphate as purgative for colon preparation to colonoscopy, after the failure of preparation with sodium phosphate for first colonoscopy. The hypothesis tested is whether there is advantage for substituting the purgative used, as compared to repeating the colonoscopy with the same purgative.Briefly, patients whose preparation was inadequate, will be allocated randomly to a group that will receive 3L Polyethylene glycol versus a group that will receive sodium phosphate(45ccX2). Both groups will be instructed to extend low-fiber diet to 5 days. Cleanliness of the colon at colonoscopy will be assessed blindly by an experienced endoscopist.