4-Week, Multi-center Dose-Ranging Study for the IBS-C in Pts. 6 to <12 Yrs

This study consists of 2 week screening period in which subjects who have consented will be evaluated for eligibility per protocol requirements. During this 2 week screening period subjects will be given access to ediary in which they will be required to self report symptoms of IBS-C daily. Information in ediary will also be used to determine eligibility prior to enrollment. During the 4 week RTP (Randomized treatment period), subjects will be randomized in in a ratio of 5:1 to receive tenapanor or matching placebo for 4 weeks. During the RTP, patients will continue recording daily assessments in the eDiary system as instructed and compliance with eDiary entries will be monitored. Patients will return for study visit every weeks (Visits 3-6) and will undergo safety assessments as per the protocol. At the end of this 4 week period, subjects will complete 2 week treatment free follow-up period and safety assessments per protocol will be conducted at the end of this 2 week period. The study plans to enroll up to 6 cohorts of eligible patients sequentially, starting from Cohort 1 with 12 patients randomized in to receive tenapanor 2 mg BID or matching placebo for 4 weeks. Subsequent cohorts will assess increasing tenapanor doses, following a dose escalation order. The study will proceed to the next dosing cohort if the current cohort completes the 4-week RTP and does not meet any of the dose escalation stopping criteria pre-specified in the protocol.