BioPharma, Pharma

FDA turns down Ardelyx’s chronic kidney disease drug and asks for another trial

Ardelyx drug tenapanor was rejected by the FDA as a treatment for a complication experienced by chronic kidney disease patients. The regulatory decision came two weeks after the company received an FDA letter citing deficiencies in the drug application.

Urinary system, bladder, kidney


Ardelyx wants to offer chronic kidney disease patients a new, more convenient option for addressing a complication of their condition. The FDA on Thursday put a crimp in those plans, rejecting the biotech’s drug and asking the company to conduct another clinical trial to demonstrate the therapy’s effect.

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The company said the agency’s letter stated it is willing to meet with the company to discuss the options for seeking regulatory approval for the drug, tenapanor. Ardelyx, which splits its operations between Fremont, California and Waltham, Massachusetts, said that it plans to request a meeting with the FDA as soon as possible.

Chronic kidney disease patients can develop a buildup of phosphate levels in the blood. The main treatment options are phosphate binders, medications that bind to phosphate and prevent its absorption by the body. But phosphate binders must be taken as multiple pills with every meal. Tenapanor is a single pill developed for twice-a-day dosing. In addition to convenience, the Ardelyx drug is also hoped to offer better efficacy.

The Ardelyx drug is not a phosphate binder. The small molecule is designed to act locally in the gut to block a protein called sodium hydrogen exchange 3. Doing so tightens junctions of epithelial cells that line the gut, which in turn reduces the uptake of phosphate, according to the company. Ardelyx tested the drug in three Phase 3 studies enrolling more than 1,000 patients total. Two of the studies tested the drug by itself and one evaluated the pill in combination with phosphate binders.

Complete response letters aren’t public documents. According to Ardelyx’s telling of the correspondence, the FDA agrees that the data provide “substantial evidence that tenapanor is effective in reducing serum phosphorus in [chronic kidney disease] patients on dialysis.” But the company said the agency characterizes the magnitude of the treatment effect as “small and of unclear clinical significance.” To show a clinically relevant effect, the FDA said that the company must conduct another study. Ardelyx said that the FDA did not cite any safety or manufacturing issues in its letter.

“We do not agree with the FDA’s subjective assessment on the clinical relevance of the treatment effect of tenapanor in our studies which met all clinical endpoints agreed upon by the FDA,” Mike Raab, president and CEO of Ardelyx, said in a prepared statement. “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.”

Signs that the new drug application might be in trouble emerged in the spring. In April, the FDA asked Ardelyx for more analyses of the clinical data to better understand how the drug compared to already approved therapies. The requested information was a major amendment to the application, triggering an extension of the target decision date by three months.

Last week, Ardelyx disclosed that the regulator sent another letter stating that its review of the application “identified deficiencies that preclude discussion of labeling and post-marketing requirements/commitments at this time.” In a regulatory filing, Ardelyx said the FDA wrote that a key issue is “the size of the treatment effect and its clinical relevance.” The company’s request for a meeting to discuss the matter was denied.

Tenapanor is the most advanced drug candidate from Ardelyx, a biotech that develops medicines addressing kidney and cardiorenal diseases. At the end of the second quarter of this year, Ardelyx reported a $171.8 million cash position.

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