Colonoscopy is a basic but important tool to diagnose and treat lesions of the colon. Proper colon cleansing is essential for colonoscopy to be performed with a good quality. Inadequate bowel preparation leads to longer colonoscopic insertion time and patient discomfort, as well as inadequate diagnostic yield of colonic lesions. Frequency of colonoscopy failure due to bad bowel preparation is reported to be 0.3% to 6.5 percent, and the rate increases with liver cirrhosis, constipation, dementia, stroke, or administration of tricyclic antidepressants. In case of colonoscopy failure due to bad bowel preparation, the second colonoscopy can be performed with either adding a colon cleansing solution immediately, or it can be performed after a few days with colon cleansing agent together with prokinetics. These different kinds of bowel preparations after first colonoscopy failure have not been compared.

Inclusion Criteria:

• First colonoscopy failure due to inadequate bowel preparation

Exclusion Criteria:

• younger than 18 years old
• presence of inflammatory bowel disease
• pregnant
• lactating
• refusal