The FDA has greenlit Travere Therapeutics’ Filspari as the only available treatment for focal segmental glomerulosclerosis despite the drug’s loss to Sanofi’s Avapro in a Phase 3 study.
The FDA has given the go-ahead to Travere Therapeutics’ endothelin blocker Filspari for the treatment of focal segmental glomerulosclerosis, a rare and potentially fatal kidney disease that analysts expect could open a market opportunity over $2 billion.
“We expect launch to be strong due to urgency to treat this faster-progressing disease,” analysts at Jefferies wrote to investors on Monday evening, adding that Travere “already has an established commercial footprint.” Filspari was first approved in February 2023 for IgA nephropathy.
Jefferies also expects “limited competition” in the near future, with Travere enjoying at least a three-year headstart versus potential challengers such as BioMarin and Boehringer Ingelheim.
The approval, announced Monday, was granted despite a failed late-stage study. Data from the Phase 3 DUPLEX trial showed that Filspari did not outperform Sanofi’s Avapro at improving kidney function after 108 weeks. However, significantly more patients on Travere’s drug hit partial remission from proteinuria than those on Avapro.
Travere’s package for Filspari’s expansion, which the FDA accepted in May 2025, also included findings from the Phase 2 DUET study, which yielded a more than twofold decrease in proteinuria versus Avapro. Taken together, these data were enough for the FDA to grant Filspari full approval for focal segmental glomerulosclerosis (FSGS), making it the first and currently only drug for the indication, Travere said Monday.
Aside from the late-stage stumble, Filspari in January also had to contend with a delay, with the FDA needing to extend the review by three months to better assess additional submissions. The original target action date for Filspari’s FSGS expansion was set for Jan. 13.
Travere shares spiked nearly 40% in pre-market trading on Tuesday, hovering around $43 apiece.
CEO Eric Dube in a prepared statement called the regulator’s verdict a “historic milestone” for FSGS patients, adding that Filspari will be available “immediately” for doctors to prescribe to their patients.
Around seven of every one million people have FSGS, a rare kidney disorder that scars the small blood vessels in the kidney, in turn impairing the organ’s ability to filter waste from the bloodstream. Patients with FSGS suffer from hypertension, swelling and kidney failure. The disease can become fatal if left unaddressed.
In the U.S., Filspari’s total addressable FSGS population could reach more than 30,000, Dube claimed on Monday. Guggenheim Partners estimated that the drug could earn $32 million in this indication in 2026, with peak FSGS sales exceeding $2 billion before Filspari starts losing patent protections in 2033, according to an April 8 note to investors.
Jefferies on Monday had a more measured projection, expecting around 20,000 patients resulting in a total addressable market of around $960 million by 2032.
Filspari is a small-molecule drug that blocks the endothelin and angiotensin II receptors, which reduces proteinuria and kidney inflammation, while also protecting the kidney from fibrosis and glomerular damage. In IgA nephropathy, the drug’s accelerated approval was converted to traditional approval in September 2024, setting up a 144% year-on-year sales jump in 2025 to hit $322 million in revenue.
