The U.S. Food and Drug Administration (FDA) has granted full approval to Travere Therapeutics' Filspari (sparsentan) for slowing kidney function decline in adults with primary immunoglobulin A nephropathy (IgAN) who are at risk of disease progression. This decision expands the drug's availability and reinforces its role in managing this rare kidney disease.
Clinical Significance
IgAN, also known as Berger's disease, affects up to 150,000 people in the U.S. It occurs when IgA accumulates in the kidneys, causing damage and impairing their filtering function, leading to blood and protein leakage into the urine. The full approval of Filspari offers a significant advancement in treatment, providing a non-immunosuppressive option that directly targets glomerular injury.
PROTECT Study Results
The FDA's decision was supported by positive long-term confirmatory results from the Phase 3 PROTECT study. In this study, Filspari significantly slowed kidney function decline over two years compared to irbesartan, an angiotensin II receptor blocker (ARB). The modified intention-to-treat (ITT) analysis, favored by the FDA, included data from all 404 randomized patients, regardless of treatment discontinuation.
The mean eGFR slope from baseline to week 110 was -3.0 mL/min/1.73 m²/year for Filspari and -4.2 mL/min/1.73 m²/year for irbesartan, corresponding to a statistically significant treatment effect of 1.2 mL/min/1.73 m²/year (p=0.0168). This demonstrates a superior preservation of kidney function with Filspari.
Treatment Landscape
Filspari, an oral, once-daily, non-immunosuppressive medication, blocks two critical pathways of IgAN disease progression: endothelin-1 and angiotensin II. Travere CEO Eric Dube, Ph.D., stated that the full approval enables physicians to confidently prescribe Filspari more broadly as a treatment that can provide superior preservation of kidney function and replace current standard of care.
The full approval also removes a specific urine protein level requirement from Filspari’s label, expanding the market to include a broader set of IgAN patients at risk of disease progression. This adjustment will allow Filspari to reach more patients who are at lower risk of progression.
Safety and Monitoring
Filspari carries a boxed warning for hepatotoxicity and embryo-fetal toxicity. Patients are required to undergo liver function tests monthly for the first year and then every three months during treatment. Travere is planning to eventually ask the FDA to modify that requirement.
Competition
Filspari faces competition from other approved therapies for IgAN, including Calliditas Therapeutics' Tarpeyo (budesonide) and Novartis' Fabhalta (iptacopan). Tarpeyo received full FDA approval in December 2023, while Fabhalta received accelerated approval in August 2024.
Future Directions
Travere is exploring potential combinations for Filspari, including with SGLT-2 inhibitors, in IgAN. The company is also collecting more data on Filspari, including its real-world experience, to potentially ask the FDA to modify the liver monitoring requirement in the future.
