This study is to investigate the efficacy, safety, and plasma concentration change of ASP0456 in patients with constipation-predominant irritable bowel syndrome.

This study is a multicenter, double-blind, placebo-controlled, parallel-group, comparative study to investigate dose-responses of efficacy, safety, and pharmacokinetics of ASP0456 in patients with constipation-predominant irritable bowel syndrome (IBS-C) according to the Rome III Diagnostic Criteria (2006 revised edition, established by the Rome III Committee) after oral administration of ASP0456.

Inclusion Criteria:

• Patients who had abdominal pain or discomfort repeatedly for at least 3 days per month during the 3 months before screening examination associated with at least 2 out of the following 3 conditions: (1) Improvement with defecation; (2) Onset associated with a change in frequency of stool; and (3) Onset associated with a change in form (appearance) of stool, and had the above symptom (IBS symptom) 6 months or more before the screening examination period.
• Patients with ≥25% of stools hard or lumpy (with each bowel movement occurring without antidiarrheal, laxative, suppository or enema) and <25% of them loose (mushy) or watery during the 3 months before the screening examination.
• Patients who had pancolonoscopy or contrast enema (or sigmoidoscopy) after the onset of IBS symptom and had no organic changes.

Exclusion Criteria:

• Patients with a history of surgical resection of the stomach, gallbladder, small intestine or large intestine
• Patients with other concurrent diseases that may affect the digestive tract passage or large intestinal function
• Patients with other concurrent diseases that may affect the assessment of abdominal pain/discomfort
• Patients with blood pressure, pulse rate, clinical laboratory test, or 12-lead ECG at the time of screening examination that was rated as Grade 2 or greater on the "Severity Criteria for Drug Adverse Reaction" and judged to be clinically significant

Access to anonymized individual participant level data will not be provided for this trial. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.