Chugai Pharmaceutical has submitted a regulatory application to Japan’s Ministry of Health, Labour and Welfare seeking approval for sparsentan, an oral treatment for patients with IgA nephropathy, a chronic kidney disease that can lead to progressive loss of kidney function.

Sparsentan is a novel small-molecule therapy that simultaneously blocks endothelin receptor type A (ETAR) and angiotensin II type 1 receptor (AT1R). By targeting both pathways in a single drug, the therapy aims to deliver greater reductions in proteinuria—a key marker of kidney damage—while maintaining the convenience of once-daily dosing.

The drug is already approved in other major markets, receiving full approval in the United States under the brand name Filspari in September 2024 and standard marketing authorisation in Europe in April 2025 for the treatment of IgA nephropathy.

According to Chugai, the Japanese filing is supported by findings from the global Phase 3 PROTECT study and a Japanese Phase 3 trial (RE-021-001), both involving patients with persistent proteinuria despite existing treatment options.

Results from the global PROTECT study showed that sparsentan achieved a statistically significant reduction in urine protein-to-creatinine ratio (UPCR), the study’s primary endpoint. At Week 36, patients treated with sparsentan recorded a 49.8 percent reduction in UPCR compared with a 15.1 percent reduction in those receiving the active comparator, irbesartan.

The study also indicated a potential long-term benefit in preserving kidney function, based on measurements of estimated Glomerular Filtration Rate (eGFR), a key indicator of renal health. Researchers reported that sparsentan was generally well tolerated, with commonly observed side effects including hypotension, hyperkalemia, dizziness and peripheral edema.

In the Japanese Phase 3 study, sparsentan achieved a 58.5 percent reduction in UPCR at Week 36, reinforcing the efficacy findings observed in the global trial. The safety profile remained consistent with previous studies, and no new safety concerns specific to Japanese patients were identified.

Dr. Osamu Okuda, President and CEO of Chugai Pharmaceutical, said the therapy’s dual mechanism of action and demonstrated impact on proteinuria could help address an important unmet need in IgA nephropathy, where many patients continue to experience disease progression despite current treatments.

IgA nephropathy is classified as a designated intractable disease in Japan. The condition is characterised by the accumulation of immunoglobulin A (IgA) deposits in the kidneys, which can trigger inflammation and gradual deterioration of kidney function. Existing therapies do not adequately control proteinuria in all patients, leaving a significant need for new treatment options.

If approved, sparsentan could offer a new therapeutic approach for long-term disease management and potentially improve outcomes for patients living with IgA nephropathy.