Detailed narrative
FILSPARI FSGS Approval and Market Opportunity
FILSPARI received full FDA approval for FSGS on April 13, 2026, making it the first and only approved medicine for adults and children 8 years and older with FSGS without nephrotic syndrome. Management highlighted that nephrotic syndrome is a clinical diagnosis defined by high proteinuria (>3.5 g/day), low serum albumin (<3.0 g/dL), and edema; patients missing any one criterion are eligible. This approval significantly expands FILSPARI's market, with over 30,000 eligible FSGS patients in the U.S., contributing to a total estimated 100,000+ eligible patients across IgA nephropathy and FSGS, representing a potential $3 billion peak sales opportunity.
IgA Nephropathy Performance and Clinical Data
The first quarter saw exceptional commercial performance for FILSPARI in IgA nephropathy, with 993 new patient start forms, a new record. Recent data published in C JSON from the PROTECT study showed that IgA nephropathy patients achieving complete proteinuria remission (<0.3 g/g) experienced eGFR decline rates similar to healthy aging (<1 mL/min/year). This reinforces FILSPARI's role as a foundational medicine, aligning with KDIGO guidelines that recommend it as a first-line option for patients at risk of progression.
Pegtibatinase Phase III HARMONY Study Reinitiation
Enrollment in the pivotal Phase III HARMONY study for pegtibatinase in classical homocystinuria (HCU) has been reinitiated, with the first new patient dosed. This milestone keeps the program on track for top-line results in the second half of 2027. The study's primary endpoint, reduction in plasma total homocysteine at 12 weeks, aligns with the successful Phase I/II COMPOSE study, where pegtibatinase demonstrated a 67.1% mean relative reduction. The company believes pegtibatinase has the potential to be the first disease-modifying therapy for the 7,000-10,000 global HCU patients.
Commercial Execution and FSGS Launch Dynamics
The company expects a faster uptake for FILSPARI in FSGS compared to its initial IgA nephropathy launch due to significant prescriber overlap, strong brand awareness, and established payer access (currently over 97% pathway to access). Early feedback and reimbursement approvals for FSGS have been positive, with higher first-pass approval rates than initially seen for IgAN. Management noted that FSGS is a more rare and rapidly progressive disease, which payers understand, and they are not focused on specific FSGS subtypes.
Financial Performance and Expense Drivers
Total U.S. net product sales were $124.5 million, with FILSPARI contributing $105.2 million (up 88% YoY) and THIOLA/THIOLA EC contributing $19.3 million. Total revenue was $127.2 million. R&D expenses increased to $57.1 million (GAAP) due to the HARMONY study restart, and SG&A expenses rose to $80.3 million (GAAP) for the FSGS launch. The company reclassified royalty expense, which was $24.8 million, to a separate line item for transparency. Cash and equivalents stood at $264.7 million as of March 31, 2026, with total liquidity of $352 million including receivables.