Shares in Ardelyx fell more than 26% after it emerged that a Phase II trial assessing its AstraZeneca-partnered kidney drug tenapanor failed to hit targets.

The 154-patient Phase IIa study of tenapanor in Stage 3 chronic kidney disease patients with type 2 diabetes mellitus and albuminuria did not meet the primary endpoint of lowering the urinary albumin-creatinine ratio in patients given then drug, potentially marking the end of its development in this setting.

Ardelyx and AZ signed an agreement in October 2012 to develop and commercialise tenapanor - which is also being assessed in patients with constipation-predominant irritable bowel syndrome and hyperphosphatemia - and AZ has until the end of June to decide whether it wants to pursue development in any of these indications. 

Under the terms of the deal, if AZ pushes on with just the IBS-C indication, Ardelyx will be entitled to a milestone payment of $10 million, but it is chooses to develop tenapanor for any other indication or multiple indications, Ardelyx will be entitled to receive a $20 million milestone payment.

Things are, however, definitely looking a shaky on the CKD front, given this latest setback and earlier findings linking tenapanor to high rates of diarrhoea in patients with CKD.

Ardelyx says it believes “tenapanor can be a best-in-class treatment for IBS-C and hyperphosphataemia and we hope to accelerate the development for these underserved conditions either independently or with AstraZeneca”.