Travere claims first FDA OK in rare kidney disease FSGS
Travere's chief executive, Eric Dube.
Shrugging off an earlier phase 3 disappointment, Travere’s Filspari has become the first FDA-approved treatment for rare kidney disease focal segmental glomerulosclerosis (FSGS).
The company's already-marketed endothelin antagonist therapy Filspari (sparsentan) – approved since 2023 for IgA nephropathy – is now also indicated to reduce proteinuria in patients aged eight and over with FSGS who don't have nephrotic syndrome, an advanced form of the disease.
FSGS is a rare disease characterised by the loss of cells in the kidney responsible for filtering the blood, which generally leads to renal failure. Until now, there were no drugs specifically approved by the FDA for the disease, with patients generally managed off-label using corticosteroids, immunosuppressants, and drugs like renin-angiotensin-aldosterone system (RAAS) inhibitors designed to reduce the load on the kidneys.
Travere estimates that around 30,000 people with FSGS in the US could be eligible for treatment with Filspari, which it claims is the most commonly prescribed IgAN therapy. Sales of the product rocketed 144% to $410 million last year, thanks in part to a reduced FDA requirement for liver monitoring, with the US accounting for $322 million of the total.
FSGS is a much smaller indication than IgAN, which affects around 200,000 people in the US, but provides Filspari with a niche without competition from other targeted therapies, and – by some analyst estimates – could represent a $1 billion market opportunity.
The approval "marks a historic milestone for people living with FSGS, who for the first time have an FDA-approved medicine for this rare and devastating condition," said Travere's chief executive, Eric Dube, who suggested that it expands the eligible patient population for Filspari – which costs around $120,000 a year per patient at list prices – to around 100,000.
The approval is based on the results of the phase 3 DUPLEX study, which compared Filspari to the RAAS drug irbesartan. Travere's drug achieved a 46% reduction in proteinuria at 108 weeks, compared to a 30% reduction with maximum-strength irbesartan.
The results were stronger in less sick patients without nephrotic syndrome, with proteinuria reduced by 48% and 27%, respectively.
Proteinuria wasn't the original primary endpoint for the study, however, and in 2023 Filspari proved no better than irbesartan at improving estimated glomerular filtration rate (eGFR), a tougher clinical measure that charts kidney function over time.
The switch to the proteinuria endpoint was agreed with the FDA, which has awarded Filspari a full approval in FSGS, rather than, as some had suggested might happen, an accelerated approval subject to a confirmatory trial.
There was more good news for FSGS patients earlier this year when Boehringer Ingelheim's TRPC6 inhibitor apecotrep showed efficacy in a phase 2 trial, prompting the company to start a phase 3 programme.
