Travere's Filspari misses the mark in key trial, but market removal looks unlikely: analysts

Six months after Travere Therapeutics’ Filspari won an accelerated nod to treat patients with a rare kidney disease, the first-of-its-kind drug narrowly failed its confirmatory trial.

While the results bode poorly for a full FDA approval anytime soon, Travere may take some solace in the fact that the drug’s removal from market looks unlikely, at least according to two groups of analysts.

The readout comes from Travere’s phase 3 PROTECT study pitting Filspari (sparsentan) against the popular angiotensin II receptor blocker irbesartan in patients with primary immunoglobulin A nephropathy (IgAN).

In the study, Filspari failed to reach statistical significance over irbesartan when it came to kidney function outcomes as measured by the estimated glomerular filtration rate (eGFR).

It wasn’t all bad news for Filspari, which demonstrated long-term kidney function preservation and achieved a clinically meaningful difference on the eGFR slope versus irbesartan.

The drug also hit statistical significance on its eGFR endpoint for the purposes of its regulatory review in the EU, Travere said.

A trial win could have teed up a conversion of Filspari’s accelerated approval into a full, traditional green light. With that prospect now on ice, Travere says it plans to apply for full U.S. approval in the first half of 2024.

Filspari won its accelerated approval back in February. At that time, the FDA endorsed the drug on earlier data from PROTECT, which showed Filspari significantly reduced proteinuria compared with irbesartan after 36 weeks of treatment. 

Patients on Filspari achieved mean proteinuria reductions of 49.8% from baseline versus a 15.1% reduction for the control group.

Analysts were disappointed by the med’s eGFR miss. The team at William Blair blamed the trial flop on the “historically strong performance of irbesartan,” which “ultimately hurt the ability for Filspari to hit a statistically significant difference versus the active control.”

Leerink Partners analysts, meanwhile, called the readout “very disappointing.” The results also introduce “some regulatory risk” given the drug’s accelerated approval status.

Both groups of analysts suggested the drug likely won't be pulled from the market. William Blair analysts cited Filspari's position as the first and only non-immunosuppressive therapy for IgAN, while the Leerink team touted the results as "clinically meaningful."

The results could prompt more pricing or reimbursement pushback, though, the analysts figure.

Travere's stock price was down roughly 42% as of Thursday afternoon.