Open-label long-term safety study of tenapanor in pediatric patients with IBS-C.

Open-label long-term safety study of tenapanor in pediatric patients with IBS-C. Eligible patients who complete the parent study will have an option to enroll in this study.

Patients from the parent study will continue tenapanor at the same dose assigned in the parent study which can be titrated to either 50 mg BID or 25 mg BID per guidance in protocol after a patient's first week on the assigned dose. Patients will also return for study visits approximately every 6 weeks for safety assessments.

Inclusion Criteria:

1. ≥6 and <18 years old at enrollment of either parent study
2. Patient completed the parent study immediately with adequate compliance with study procedures in the opinion of the Investigator
3. Females of child-bearing potential must have negative pregnancy test at the last visit of the parent study and confirm the use of appropriate contraception (including abstinence).
4. Subject is ambulatory
5. Written informed consent by parent/guardian/ Legally Authorized Representative (LAR) and a willingness of both subject and parent/guardian/LAR to participate in the study as it is described

Exclusion Criteria:

1. Patient discontinued prematurely from the parent study.
2. Any surgery on the stomach, small intestine or colon, excluding appendectomy or cholecystectomy
3. Pregnant or lactating women
4. If, in the opinion of the Investigator, patient is unable or unwilling to fulfill the requirements of the protocol