The US Food and Drug Administration (FDA) has granted an orphan drug designation to Ardelyx’s Xphozah (tenapanor) for the treatment of paediatric hyperphosphatemia.

The US-based biopharma will now be in line for tax credits for US-based clinical trials and, if the therapy is approved, the potential for seven years of market exclusivity in the designated indication.

The FDA approved Xphozah for use in controlling serum phosphate in adult chronic kidney disease patients on dialysis who do not respond to or are intolerant to phosphate binder therapy.

Xphozah is an oral phosphate absorption inhibitor. It works by inhibiting the sodium hydrogen exchanger 3 (NHE3), which reduces phosphate absorption through the paracellular pathway. The paracellular pathway is the primary pathway of phosphate absorption.

Hyperphosphatemia is characterised by elevated phosphate levels in the blood. Ardelyx says the condition affects the majority of patients living with chronic kidney disease, with organ dysfunction meaning phosphate is not adequately eliminated from the body.

Currently, elevated levels are first managed with a reduced phosphate diet. If patients do not respond to this, then phosphate binders should be prescribed.  

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Ardelyx CEO Mike Raab said in a 15 November statement: “This designation highlights the importance of evaluating treatment options for all patients with hyperphosphatemia, and we look forward to sharing more details on this important designation by the FDA in the future.”

Xphozah, which is contraindicated in paediatric patients aged under six years old and in those with known or suspected mechanical gastrointestinal obstruction, had a rocky road to FDA approval as an add-on therapy for chronic kidney disease patients on dialysis.

The agency sent a complete response letter in 2021 citing concerns around clinical significance. After a successful appeal to the Office of New Drugs and a new drug application resubmission, the drug came out favourably in a Renal Drug Advisory Committee meeting.

Alongside the approval in October, Ardelyx secured $50m in debt financing from SLR Capital Partners to finance the launch of Xphozah.