study to evaluate the efficacy of tenapanor as adjunctive therapy to phosphate binder therapy

Conditions: Hyperphosphatemia

Summary: this is a randomized, double-blind, placebo-controlled study to evaluate the effect of tenapanor on change in s-p levels when tenapanor is administered orally, twice daily for 28 days as adjunctive therapy to esrd subjects with hyperphosphatemia on stable phosphate binder therapy.

the study consists of a screening visit; a run-in period of at least 2 weeks and up to 4 weeks, where existing phosphate binder treatment is maintained; and a 4-week double-blind treatment period. at screening, a subject must be on thrice daily phosphate binder therapy and have a serum phosphate (s-p) level ≥5.5 and ≤10.0 mg/dl to qualify for entering the study. s-p will be measured at each visit during the run-in period to enable the evaluation of the s-p randomization criteria. subjects who qualify to enroll in the study will be randomized in a 1:1 ratio to receive tenapanor or placebo while continuing their existing phosphate binder treatment. during the double-blind treatment period, subjects will receive tenapanor or placebo starting at a dose of 30 mg bid

Eligibility criteria:
inclusion criteria: * signed and dated informed consent prior to any study specific procedures. * males or females aged 18 to 80 years, inclusive, at screening * females must be non-pregnant, non-lactating and either be post-menopausal for at least -2 months, have documentation of irreversible surgical sterilization, use of acceptable -contraceptive method, or sexual abstinence, or a sterile sexual partner from screening -until 30 days after the last subject visit. * males must agree to avoid fathering a child (or donating sperm), and therefore be either sterile (documented) or agree to use approved methods of contraception, from the time of enrollment until 30 days after end of study. * chronic maintenance hemodialysis (hd) 3x/week for at least 3 months or chronic maintenance peritoneal dialysis (pd) for a minimum of 6 months. * if receiving active vitamin d or calcimimetics, the dose should have been unchanged for the last 4 weeks prior to screening. * kt/v ≥1.2 at most recent measurement prior to screening. * prescribed and taking phosphate binder medication at least 3 times per day, and the prescribed dose should have been unchanged during the last 4 weeks prior to screening. * serum phosphorus levels must be ≥5.5 and ≤10.0 mg/dl at screening and the end of the run-in period, analyzed at the central laboratory used in the study. exclusion criteria: * severe hyperphosphatemia defined as having an s-p level \>10.0 mg/dl on phosphate-binders at any time point during routine clinical monitoring for the 3 preceding months before screening. * serum/plasma parathyroid hormone \>1200 pg/ml. * clinical signs of hypovolemia at screening as judged by the investigator. * history of inflammatory bowel disease (ibd) or irritable bowel syndrome with diarrhea (ibs-d). * scheduled for living donor kidney transplant or plans to relocate to another center during the study period. * use of an investigational agent within 30 days prior to screening. * involvement in the planning and/or conduct of the study (applies to both ardelyx/contract research organization (cro) staff and/or staff at the study site). * if, in the opinion of the investigator, the subject is unable or unwilling to fulfill the requirements of the protocol or has a condition which would render the results uninterpretable.