Study of the Efficacy and Safety of Quiklean® and Klean-Prep With Dulcolax® for the Bowel Preparation Prior to Colonoscopy

Inclusion Criteria: 1. Men or women 20 and 74 years of age. 2. Subject who are scheduled for an elective colonoscopy. 3. Ability to complete the entire procedure and to comply with study instructions. 4. Will provide completed and signed written informed consents. Exclusion Criteria: 1. Subjects with severe chronic constipation, defined as fewer than one bowel movement per week for a period \> 1 year. 2. Subjects with known or suspected acute exacerbation of chronic inflammatory bowel disease (IBD). 3. Subjects with significant gastrointestinal disease, such as gastrointestinal obstruction or perforation, active ulcerative colitis, toxic colitis, and toxic megacolon. 4. Subjects with ascites of any etiology. 5. Subjects with renal insufficiency, defined as serum creatinine \> 1.5 times the upper limit of normal (ULN). 6. Subjects with current or history of abdominal surgeries as follow: * Acute surgical abdominal conditions. * Any prior colorectal surgery within previous 3 months at screening, excluding appendectomy, hemorrhoid surgery or prior endoscopic procedures. * History of ileostomy, right or transverse colostomy, subtotal colectomy with ileosimoidostomy, with ≥ 50% of colon removed, excluding right or left hemicolectomy. * History of gastric bypass or stapling history. 7. Subjects with any serious cardiovascular diseases or related interventions as follows: * History or current evidence of prolonged QT, unstable angina pectoris, untreated arrhythmia, or uncontrolled hypertension, cardiomyopathy, congestive heart failure (New York Heart Association (NYHA) Functional Classification, grades 3 and 4). * Myocardial Infarction (MI) within previous 3 months at screening. * Percutaneous transluminal coronary angioplasty (PTCA), or coronary artery bypass graft surgery within previous 3 months at screening. * Subject has undergone cardiovascular stent procedure or carotid artery stenting procedure, and continues to receive an anticoagulant regimen within 1 year prior to screening. * Current use digitalis preparations or any medications known to prolong QT interval. 8. Subjects with history of seizures or at risk of seizure, such as subjects taking medications that lower the seizure threshold (e.g., tricyclic antidepressants), or subjects withdrawing from alcohol or benzodiazepines, subjects with known or suspected hyponatremia. 9. Subject has clinically significant abnormal laboratory values of electrolytes at screening, including phosphorus, sodium, potassium, calcium, chloride, and magnesium. 10. Subjects with history of biopsy-proven acute phosphate nephropathy. 11. Subjects with history of phenylketonuria. 12. Subject has severe dehydration, or severe abdominal pain associated with nausea and vomiting at screening. 13. Subject has problems with swallowing or gastric reflux, or subjects is at risk of aspiration. 14. Subjects is pregnant, lactating women or women of childbearing potential without an effective method of birth control (e.g. oral contraceptive, intrauterine device, surgical sterilization, hysterectomy). 15. Subjects with hypersensitivity to any ingredients in the study medications. 16. Participation in any other investigational study within 30 days prior to receiving study medication.