Filspari (sparsentan) is indicated for reducing urine protein levels (proteinuria) in adults with primary immunoglobulin A nephropathy (IgAN), who are at risk of rapid disease worsening with a urine protein-to-creatinine ratio (UPCR) equal to or more than 1.5g/g.
Developed by the US-based biopharmaceutical companies Travere Therapeutics and partner Ligand Pharmaceuticals, Filspari is a first-of-its-kind once-daily, oral non-immunosuppressive therapy for the treatment of IgAN, a progressive kidney disease.
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In September 2021, Travere granted Vifor Pharma (now CSL Vifor), a Swiss pharmaceutical company, the licence to commercially develop sparsentan in Europe, Australia and New Zealand. Meanwhile, Travere maintained the rights to sparsentan in the US and the rest of the world.
Filspari is available as 200mg and 400mg white to off-white, film-coated, modified oval tablets.
Regulatory approvals for Filspari
The US Food and Drug Administration (FDA) granted accelerated approval to Filspari, based on interim data from the PROTECT Phase III clinical trial in February 2023.
The full approval of Filspari was granted by the FDA in September 2024 based on the PROTECT study’s positive long-term confirmatory findings.
In April 2024, the European Commission granted conditional marketing authorisation for sparsentan for the treatment of IgAN, followed by a standard marketing authorisation (MA) in April 2025, supported by data from the PROTECT trial. The MA applies across every EU member country and also covers Iceland, Liechtenstein and Norway.
In August 2025, the FDA approved updated Risk Evaluation and Mitigation Strategy (REMS) labelling for Filspari for the treatment of IgAN. The revision reduces the frequency of liver function monitoring to once every three months from treatment initiation with sparsentan and removes the requirement for embryo–fetal toxicity monitoring under the REMS.
Filspari is also approved for IgAN in the UK and is temporarily authorised for the same indication in Switzerland.
In April 2026, the FDA approved Filspari as the first and only medicine for the treatment of focal segmental glomerulosclerosis (FSGS). Travere had submitted a supplemental new drug application to the FDA for sparsentan for the treatment of FSGS in March 2025, drawing on the two-year primary efficacy results from the Phase III DUPLEX and Phase II DUET studies.
Filspari also holds an orphan drug designation for the treatment of FSGS in Europe.
IgA nephropathy causes and symptoms
Also called Berger’s disease, IgA nephropathy is a rare kidney disease where immunoglobulin A (IgA), a protein that helps the body fight infection, accumulates in the kidneys. The accumulation disrupts the kidney’s typical filtering processes, resulting in symptoms such as blood in the urine (haematuria), proteinuria and a gradual decline in kidney function.
Additional indications of IgAN include swelling, pain in one or both sides of the back below the ribs, recurrent upper respiratory infections, intestinal disease, swelling (oedema) in hands and feet, low fever and elevated blood pressure.
The symptoms of IgAN may not appear in the early years and can go unnoticed for many years. Symptoms most often appear before the age of 40 years.
IgAN is the most common form of primary glomerulonephritis globally and is a primary contributor to kidney failure arising from glomerular disease, affecting 150,000 people in the US. It also ranks among the most prevalent glomerular diseases in Europe and Japan.
Filspari’s mechanism of action
Sparsentan is the first single-molecule dual endothelin angiotensin II receptor antagonist (DEARA) that selectively targets the two critical pathways, namely endothelin-1 and angiotensin II, involved in the disease progression.
The drug has a high affinity for the endothelin type A receptor (ETAR) and the angiotensin II type 1 receptor (AT1R) and has 500-fold selectivity for these receptors over the endothelin type B and angiotensin II subtype 2 receptors.
Endothelin-1 and angiotensin II are believed to contribute to the pathogenesis of IgAN through the ETAR and AT1R, respectively.
Sparsentan selectively binds to the receptors and blocks the corresponding pathways, reducing proteinuria in adults.
Clinical trials on Filspari
The FDA approval of Filspari was based on the clinically meaningful and statistically significant outcomes in proteinuria compared to irbesartan, an active comparator, in the pivotal PROTECT Phase III clinical trial, the largest head-to-head interventional study in IgAN.
The global, randomised, multi-centre, double-blind, active-controlled clinical trial evaluated the safety and efficacy of 400mg of sparsentan compared to 300mg of irbesartan in 404 adult patients with IgAN and persistent proteinuria, regardless of being treated with angiotensin-converting enzyme or angiotensin receptor blocker therapies.
Patients were randomised to a 1:1 ratio to receive either 400mg Filspari once daily following 200mg once daily for 14 days or 300mg irbesartan once daily following 150mg once daily for 14 days.
The primary endpoint of the study was the relative change from baseline in UPCR at week 36.
At 36 weeks, patients receiving sparsentan achieved a mean reduction of 49.8% in proteinuria from baseline compared to a mean reduction of 15.1% in patients treated with irbesartan.
The key secondary efficacy endpoint for the final analysis was the rate of change in estimated glomerular filtration rate (eGFR) over a 110-week period following initiation of randomised therapy.
In the two-year efficacy results, Filspari slowed the deterioration in renal function from baseline to week 110 versus irbesartan. The average eGFR slope over this period was -3.0mL/min/1.73m²/year with Filspari compared with -4.2mL/min/1.73m²/year for irbesartan, equating to a statistically significant difference of 1.2mL/min/1.73m²/year (p=0.0168).
Filspari was well tolerated and consistent across all clinical trials conducted on it to date. The most common side effects reported in patients during the clinical trial were peripheral oedema, hypotension, dizziness, hyperkalaemia and anaemia.
Additional clinical trials
The Phase III DUPLEX trial is a randomised, multicentre, international, double-blind, active-controlled study that evaluated the safety and efficacy of sparsentan in patients with FSGS. It is reported to be the largest interventional trial in FSGS and the first to compare a novel agent against a maximally dosed active comparator, irbesartan.
In total, 371 participants were randomised in a 1:1 ratio to receive either sparsentan 800mg per day or irbesartan 300mg per day for up to 108 weeks.
At 36 weeks, DUPLEX met its pre-specified interim endpoint of FSGS partial remission of proteinuria (FPRE) with statistical significance. However, the study did not meet its primary efficacy endpoint, which was the eGFR slope over 108 weeks of treatment.
Two-year data from the clinical trial indicated that, at 108 weeks, sparsentan-administered patients demonstrated a reduction in proteinuria, higher rates of partial and complete remission, and a lower incidence of end-stage kidney disease when compared with patients administered with irbesartan.
The earlier Phase II DUET study of sparsentan in FSGS achieved its primary efficacy endpoint in the combined treatment arm, showing more than a two-fold reduction in proteinuria relative to irbesartan.
