Travere Therapeutics, a San Diego-based biotech company, has received full FDA approval for their drug Filspari, which treats immunoglobulin A nephropathy (IgAN), a rare disease where excessive antibody production leads to kidney damage. Previously granted accelerated approval based on its ability to reduce proteinuria—a sign of kidney disease—Filspari’s full approval comes after demonstrating significant long-term benefits in slowing kidney function decline over two years, as observed in a pivotal study.
This study initially failed to meet statistical significance when Filspari was compared against irbesartan, a generic drug used for managing blood pressure and nephropathy. However, after modifying the analysis approach to include data from all participants, regardless of treatment discontinuation, the results achieved statistical significance which led to the full approval.
The updated approval criteria expand the potential patient base for Filspari significantly. Originally, the drug was approved for use in patients hitting a specific threshold of proteinuria, but with full approval, this restriction has been lifted, broadening its usage to a larger group of IgAN patients. Analyst estimates suggest that initially, between 30,000 and 50,000 IgAN patients qualified for treatment under the initial approval criteria; however, this number is now expected to exceed 70,000 due to the removal of the proteinuria threshold. Moreover, revised draft guidelines for IgAN management from Kidney Disease: Improving Global Outcomes (KDIGO) further support the use of Filspari in patients at risk of progressive kidney damage by recommending treatment to achieve even lower proteinuria levels than before.
Filspari’s mechanism involves blocking two specific pathways linked to the progression of IgAN, distinguishing it as the only non-immunosuppressive therapy for the condition. This is a critical differentiator from other treatments such as Calliditas Therapeutics’ Tarpeyo, a corticosteroid with broad immunosuppressive effects that was the first FDA-approved therapy for IgAN. Tarpeyo recently transitioned from accelerated to full approval as well. Another competitor, Novartis, has also entered the field with Fabhalta, which received accelerated approval and operates by targeting a different pathway believed to exacerbate IgAN.
Despite its benefits, Filspari carries a black box warning due to potential liver toxicity. It is distributed under a Risk Evaluation and Mitigation Strategies (REMS) program that includes detailed information about this risk to both clinicians and patients, with advice on monitoring liver enzymes to prevent potential toxicity. Travere has plans to submit a supplemental application to potentially adjust this liver-monitoring protocol.
Commercially, Filspari is showing promise with revenues of $46.9 million recorded in the first half of the year. Its market reach is set to expand with approvals in other global markets ongoing. For instance, the European Commission granted conditional marketing authorization earlier in the year. The rights for commercializing Filspari in Europe, Australia, and New Zealand are held by CSL Vifor, while Renalys Pharma manages rights in select Asian markets. A pivotal study in Japan is expected to conclude in the second half of 2025, potentially opening more markets. Travere stands to gain up to $910 million in milestone payments, plus royalties, from these international partnerships, further cementing Filspari’s position in global IgAN treatment markets.
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