Renalys Pharma, Inc., headquartered in Chuo-ku, Tokyo, has announced encouraging topline results from its Phase III clinical trial of sparsentan, an orally administered dual endothelin and angiotensin II receptor antagonist, in Japanese patients with IgA nephropathy. The company plans to submit a New Drug Application in Japan in 2026 based on these findings. The study evaluated the percent change from baseline in the 24-hour urine protein-to-creatinine ratio after 36 weeks of treatment in 35 Japanese patients. Results showed a least-squares geometric mean percent change of negative 58.54 percent with a 95 percent confidence interval of negative 68.75 to negative 45.00 percent, confirming the drug’s effectiveness in this patient population. Sparsentan was well tolerated, with a safety profile consistent with previous international studies and no new safety concerns identified in Japanese patients.
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BT Slingsby, Chairman, CEO, and Co-Founder of Renalys, highlighted the limited treatment options available in Japan and emphasized the urgent need to provide therapies for IgA nephropathy patients. He noted that sparsentan is already approved in the United States and Europe and stressed the importance of delivering this therapy to Japanese patients without delay.
Ryutaro Shimazaki, Chief Development Officer of Renalys, explained that the Phase III trial was conducted as a small-scale bridging study in collaboration with the PMDA, leveraging data from larger international trials. The study included both adults and pediatric patients aged ten and older. Shimazaki added that strong reductions in proteinuria were observed across all age groups, aligning with outcomes from global studies, and expressed gratitude to the patients, investigators, and everyone involved in the study.
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Naoki Kashihara, MD, PhD, President of the Japan Kidney Association, remarked that the development of effective therapies for rare kidney diseases like IgA nephropathy has historically been slow. He welcomed the accelerated progress represented by sparsentan, noting its robust proteinuria-lowering effect and favorable safety profile demonstrated both globally and in Japanese patients. Kashihara also highlighted sparsentan’s potential applications beyond IgA nephropathy, including rare kidney diseases such as FSGS and Alport syndrome, as well as chronic kidney disease.
The Phase III study reinforces the value of international collaboration and evidence-based approaches in rare kidney disease research. By integrating insights from Japanese patient databases with global clinical trial data, Renalys aims to ensure accurate evaluation of clinical endpoints and support future initiatives that improve treatment outcomes for patients with IgA nephropathy and other chronic kidney conditions.
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