 After sigmoidoscopy is completed, patients will be monitored in the recovery room of endoscopy suite till patients are out of sedative effect.Safety Assessment Health assessment, including vital signs, physical examination and clinical laboratory testing electrolyte test and CBC will be performed at baseline; before sigmoidoscopy and electrolyte will be repeated within 10-30 minutes after dosing. Patients will be monitored after drug administration to determine any adverse events. Patients are encouraged to report any unusual feeling or adverse event to endoscopy research staff or research assistant. Patients will be monitored for pruritus, dehydration, nausea,vomiting, abdominal pain, abdominal distension, diarrhea, gastrointestinal pain and any other adverse 