Travere Therapeutics plans to ask the US Food and Drug Administration (FDA) for approval of its rare kidney disease drug Filspari (sparsentan), despite failing to hit the primary endpoint in its pivotal trial.

Travere’s stock price climbed by 14% following the 11 February announcement, from $21.10 at close on 10 February to $24.07 at open the following day.

Following the Type C meeting with the FDA, Travere said it will submit a supplemental new drug application (sNDA) for Filspari in focal segmental glomerulosclerosis (FSGS), a group of rare diseases involving damage to the glomeruli, or the tiny filters in the kidney. The damage causes scarring to the filters which then stop working properly, allowing protein to leak through the walls of the glomeruli and into the urine.

Filspari was investigated in the Phase III DUPLEX study (NCT03493685), where it failed to hit its primary endpoint. The drug had a 0.3mL favourable difference on the estimated glomerular filtration rate (eGFR) total slope and a 0.9mL annual favourable difference on the eGFR chronic slope compared with the control, Sanofi’s Aprovel (irbesartan). However, it wasn’t statistically significant. eGFR is used to measure how well the kidneys are filtering.

However, Filspari reduced proteinuria by 50% on average after two years, compared to 32% in the control group. Travere says it plans to use the proteinuria measure as an endpoint to ask for FDA approval, citing that a reduction in proteinuria over 24 months is strongly associated with a reduction in the risk of kidney failure. The sDNA submission is expected by the end of Q1 2025.

Filspari – which works by blocking receptors for two proteins called endothelin and angiotensin II – secured approval to treat another kidney disease called IgA nephropathy (IgAN) in September 2024. If it wins a label expansion, it will be the first drug approved specifically for the treatment of FSGS. According to GlobalData’s Pharma Intelligence Center, Filspari is forecast to generate $686m in sales by 2030.

GlobalData is the parent company of Pharmaceutical Technology.

Travere previously sought the FDA’s approval for Filspari as a treatment for FSGS. However, the agency requested additional data to support the sNDA and said the two-year results from the Phase III DUPLEX study were insufficient to support the sNDA.

The FDA’s additional data request drove Travere to implement cash-saving measures in December 2023. The company fired 20% of its staff and announced its intention to focus its resources Filspari’s launch in IgAN.

In the IgAN treatment space, Filspari competes with Calliditas’ Tarpeyo (budesonide), which was awarded full approval for IgAN in December 2023, and Novartis’ Fabhalta (iptacopan), which was granted an accelerated approval in August 2024.