Chugai Files Regulatory Application in Japan for Sparsentan in IgA Nephropathy

Chugai Seeks Approval for New IgA Nephropathy Treatment
Chugai Pharmaceutical has announced the submission of a regulatory application to Japan’s Ministry of Health, Labour and Welfare (MHLW) for sparsentan, an oral treatment being developed for patients with IgA nephropathy.
The filing marks an important step for the company as it looks to bring a new treatment option to patients living with this chronic kidney disease. Sparsentan has already gained approval in other major markets, including the United States and Europe, and is now being reviewed for use in Japan.
What Is Sparsentan?
Sparsentan is an oral small-molecule medicine designed to target two pathways involved in kidney disease progression.
The drug blocks both the endothelin receptor type A (ETAR) and the angiotensin II type 1 receptor (AT1R) within a single molecule. By targeting both pathways at the same time, sparsentan aims to reduce proteinuria more effectively than conventional treatments that focus only on the renin-angiotensin system.
Another advantage of the therapy is its once-daily dosing schedule, which is similar to commonly used kidney disease medications.
The treatment is marketed as Filspari in other regions and received full approval in the United States for IgA nephropathy in September 2024. It also received standard marketing authorization in Europe in April 2025.
Why New Treatment Options Are Needed
IgA nephropathy is a chronic kidney disease that can gradually lead to loss of kidney function over time. It is classified as a designated intractable disease in Japan.
Many patients continue to experience persistent proteinuria despite receiving currently available treatments. Ongoing protein leakage in the urine is associated with worsening kidney damage and an increased risk of disease progression.
For these patients, preserving kidney function over the long term remains a major treatment challenge.
Application Supported by Global and Japanese Phase III Studies
The Japanese regulatory submission is supported by results from two Phase III clinical studies.
The first is the global PROTECT study, which was conducted in patients with IgA nephropathy outside Japan. The second is the Japanese RE-021-001 study, which evaluated sparsentan in Japanese patients with persistent proteinuria.
Both studies investigated the drug's ability to reduce proteinuria and support kidney health.
Global Phase III Study Shows Significant Reduction in Proteinuria
In the global PROTECT study, sparsentan achieved the primary endpoint by demonstrating a statistically significant reduction in urine protein/creatinine ratio (UPCR) at Week 36 compared with the active control treatment, irbesartan.
Patients receiving sparsentan experienced a 49.8% reduction in UPCR from baseline, while patients receiving irbesartan showed a 15.1% reduction.
The difference between the two groups was statistically significant, with a p-value of less than 0.0001.
Researchers also evaluated the total slope of estimated glomerular filtration rate (eGFR), a key measure of kidney function. Results suggested that sparsentan may offer long-term benefits in preserving kidney function.
Japanese Study Confirms Consistent Results
The Japanese Phase III study produced findings that were consistent with those observed globally.
At Week 36, patients treated with sparsentan achieved a 58.5% reduction in urine protein/creatinine ratio from baseline.
These results further supported the drug's effectiveness in Japanese patients and reinforced the findings from the PROTECT study.
According to the company, the data demonstrated that sparsentan can significantly reduce proteinuria in patients with IgA nephropathy.
Safety Profile Remains Consistent
Sparsentan was generally well tolerated across the clinical studies.
The safety profile observed during both the global and Japanese studies was consistent with findings from previous clinical research.
Common treatment-emergent adverse events reported during the double-blind period included hypotension, hyperkalemia, dizziness, and peripheral edema.
In the Japanese study, no new safety concerns specific to Japanese patients were identified.
Chugai Highlights Potential Benefits for Long-Term Disease Management
Dr. Osamu Okuda, President and CEO of Chugai Pharmaceutical, stated that sparsentan's dual mechanism of action represents a novel approach for patients with IgA nephropathy.
He noted that clinical studies have shown significant reductions in proteinuria and results suggesting the potential to preserve kidney function over time. Combined with the convenience of once-daily dosing, the company believes sparsentan could support long-term disease management and help strengthen the treatment landscape for patients living with IgA nephropathy.

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