Filspari wins first FDA nod for FSGS Proteinuria

On April 14, 2026, the FDA granted full approval to Filspari (sparsentan) to reduce proteinuria in adults and pediatric patients aged 8 years and older with focal segmental glomerulosclerosis (FSGS) without nephrotic syndrome - the first medicine ever approved specifically for the disease. The approval extends Travere Therapeutics' indication beyond IgA nephropathy (IgAN) into a second rare kidney disease and expands its total addressable US population to more than 100,000 patients across both conditions.

The Evidence

The Phase III DUPLEX study enrolled 371 patients aged 8 to 75 with biopsy-proven or genetic FSGS, randomised 1:1 to sparsentan 800mg daily or irbesartan 300mg daily for 108 weeks. Filspari produced a 46% reduction in proteinuria from baseline to week 108 versus 30% for irbesartan across the full study population; in the approved without-nephrotic-syndrome population the reduction was 48% versus 27%, with a 1.1 ml/min/1.73m2 mean difference in estimated glomerular filtration rate (eGFR) change. The approval rests on proteinuria reduction as a surrogate endpoint. The study's primary endpoint of eGFR slope, the harder measure of kidney function preservation, showed no significant difference between treatment groups at week 108. Sparsentan works through dual blockade of endothelin A and angiotensin II receptors, two pathways implicated in the glomerular scarring that drives FSGS progression.

The Regulatory Path

Travere's original PDUFA date was January 2026. The FDA requested additional data to characterise clinical benefit, Travere responded, and full approval followed in April, reflecting a three-month delay that introduced uncertainty into the commercial timeline.

What This Means

The commercial position is structurally advantageous. With no approved comparator in FSGS, Filspari enters a market without an established payer reference point, limiting the leverage payers typically use to constrain launch pricing. Off-label steroid regimens, the previous standard of care, carry significant tolerability limitations that weaken the case for formulary restriction. The primary endpoint miss, however, is a detail payers and health technology assessment bodies will not overlook: the approval rests on a surrogate measure of kidney protein leakage rather than demonstrated preservation of kidney function. That distinction will define the reimbursement conversation in markets outside the US. For competing programmes in FSGS and rare nephrology more broadly, the FDA's willingness to approve on proteinuria reduction alone materially shortens the evidentiary bar and changes the design calculus for the next generation of trials.

Sources: Travere Therapeutics press release, 13 April 2026 

Rheault MN et al. Sparsentan versus irbesartan in focal segmental glomerulosclerosis. NEJM. doi:10.1056/NEJMoa2308550

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