The Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) to Ardelyx regarding the New Drug Application (NDA) for tenapanor for the control of serum phosphorus in adult patients with chronic kidney disease (CKD) on dialysis.

Tenapanor is a first-in-class oral medication designed to block sodium/hydrogen exchanger 3 (NHE3) in the gastrointestinal (GI) tract, reducing the absorption of dietary sodium resulting in increased protons within the cells. The increase in protons causes a selective reduction in phosphate uptake by tightening junctions that regulate phosphate absorption in the GI tract. The NDA included data from three phase 3 trials that evaluated the effects of tenapanor in over 1000 patients. 

In the CRL, the FDA noted that although the submitted data provide substantial evidence demonstrating the efficacy of tenapanor in reducing serum phosphorus in CKD patients on dialysis, the magnitude of the treatment effect is characterized as “small and of unclear clinical significance.” 

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The FDA is requiring the Company conduct an additional clinical trial showing a clinically relevant treatment effect of tenapanor on serum phosphorus or on the clinical outcome thought to be caused by hyperphosphatemia in CKD patients on dialysis. The Agency did not identify any concerns related to the product’s safety.

Mike Raab, president and CEO of Ardelyx, commented: “We continue to believe tenapanor represents an important, first-in-class treatment option for patients with elevated phosphorus. […] In our view, the serum phosphorus lowering data generated with tenapanor in all of our clinical studies is meaningful and clinically significant. We will work with the agency to address the issues raised and, to the extent possible, find an expeditious path forward.”


Ardelyx receives Complete Response Letter from U.S. FDA for New Drug Application for tenapanor for the control of serum phosphorus in adult patients with CKD on dialysis. News release. Ardelyx, Inc. July 29, 2021. Accessed July 30, 2021.

This article originally appeared on MPR