The objective of this study is to verify the efficacy and investigate the safety of the study drug when ASP0456 is administered orally for 4 weeks and 52 weeks.

This study consists of two parts. In Part I, ASP0456 or placebo will be administered orally in a blind manner. In Part II, the long-term safety and efficacy of ASP0456 will be evaluated in patients who have participated in the study and completed the Part I.

Inclusion Criteria:

• Patients with SBM frequency for < 3 times/week, since ≥ 6 months prior to preliminary enrollment
• Patients with one or more related symptoms for ≥ 6 months prior to preliminary enrollment
• Patients at whom loose (mushy) or watery stools are rarely present without the use of laxatives for ≥ 6 months prior to preliminary enrollment
• Patients who underwent pancolonoscopy or contrast enema after development of the CC symptoms and within 5 years prior to preliminary enrollment, and in whom no organic change was observed which dose not influence on CC symptoms
• Female patients must be either:

If of non-childbearing potential:

• Post-menopausal at the preliminary enrollment, or documented surgically sterile Or, if of childbearing potential,

• Agree not to try to become pregnant during the study and for 28 days after the final study drug administration

• And have a negative urine pregnancy test at screening

• And, if heterosexually active, agree to consistently use two forms of highly effective birth control throughout the study period and for 28 days after the final study drug administration

  • Female patients must agree not to breastfeed throughout the study period and for 28 days after the final study drug administration
  • Female patients must not donate ova starting throughout the study period and for 28 days after the final study drug administration
  • Male subject and their female spouse/partners who are of childbearing potential must be using two forms of highly effective form of birth control starting at Screening and continue throughout the study period, and for 28 days after the final study drug administration
  • Male subject must not donate sperm starting at Screening and throughout the study period and, for 28 days after the final study drug administration

Exclusion Criteria:

• Patients who have met the Rome III diagnostic criteria for IBS; with recurrent abdominal pain or discomfort for ≥ 3 days/month in the last 3 months prior to preliminary enrollment, associated with ≥ 2 of the 3 characteristics described below and with the symptoms (IBS symptoms) described above for ≥ 6 months prior to preliminary enrollment

  1. Improvement with defecation
  2. Onset associated with a change in frequency of stool
  3. Onset associated with a change in form (appearance) of stool

• Patients with a history of surgical resection of the stomach, gallbladder, small intestine, or large intestine

• Patients with a history or current evidence of inflammatory bowel disease or ischemic colitis

• Patients with concurrent infectious enteritis, hyperthyroidism or hypothyroidism, constipation due to anorectal dysfunction, drug-induced constipation, constipation due to other organic diseases or active peptic ulcer

• Patients with apparent mechanical obstruction

• Patients with megacolon or megarectum

• For female patients, patients with concurrent endometriosis or adenomyosis

• Patients who are considered to have severe depression or a severe anxiety disorder that can affect the efficacy evaluation of the study drug

• Patients with a history of abuse of drugs or alcohol, or current abuse of drugs or alcohol

• Patients who used/underwent or are scheduled to use/undergo prohibited concomitant drugs or therapies, or in whom prohibited examinations were conducted or are scheduled to be conducted 3 days prior to the start of the bowel habit observation period

• Patients with a history or current evidence of malignant tumors

• Patients with concurrent serious cardiovascular diseases, respiratory diseases, renal diseases, hepatic diseases, gastrointestinal disorders, blood diseases, or neurological/psychiatric diseases

• Patients with a history of drug allergies

• Patients who have participated in the clinical trial of ASP0456 or have been administered ASP0456

• Patients who have participated or are participating in another clinical trial or post-marketing clinical study of other ethical drugs or medical devices within 12 weeks prior to obtaining informed consent

Access to anonymized individual participant level data collected during the study, in addition to study-related supporting documentation, is planned for studies conducted with approved product indications and formulations, as well as products terminated during development. Studies conducted with product indications or formulations that remain active in development are assessed after study completion to determine if Individual Participant Data can be shared. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.

Access to participant level data is offered to researchers after publication of the primary manuscript (if applicable) and is available as long as Astellas has legal authority to provide the data.

Researchers must submit a proposal to conduct a scientifically relevant analysis of the study data. The research proposal is reviewed by an Independent Research Panel. If the proposal is approved, access to the study data is provided in a secure data sharing environment after receipt of a signed Data Sharing Agreement.