Renalys Pharma is vying for the approval of its in-licensed immunoglobulin A (IgA) nephropathy asset, Filspari (sparsentan) in Japan, following the positive results of a Phase III trial.
During the late-stage, small-scale bridging study (jRCT2051240070) conducted in Japan, Filspari met its primary endpoint, triggering a significant 58.54% reduction in patient 24-hour urine protein-to-creatinine ratios (UPCR) over a 36-week treatment period.
The drug was also proven safe and tolerable, with its profile remaining consistent with previous global trials conducted across the US, Europe and Asia.
This will be welcome news for Chugai Pharmaceuticals, which recently handed over up to $202m to make Renalys a subsidiary, meaning it will obtain the exclusive rights to develop and market Filspari across Japan, South Korea and Taiwan.
Following the positive outcome of this trial, Renalys will submit a new drug application (NDA) to the Japanese Pharmaceuticals and Medical Devices Agency (PMDA) in 2026.
Filspari to “address the drug lag”
While a range of IgA nephropathy treatments have reached the market in the last two years – including Novartis Fabhalta (iptacopan) and Calliditas Therapeutics’ Tarpeyo (budesonide) – these drugs have not yet reached Japan.
If Filspari were to gain PMDA approval in IgA nephropathy, it would significantly expand treatment options for Japanese patients, who have relied on renin-angiotensin system blockers and corticosteroids as the main treatment options for years.
In a 26 November statement, Renalys’ chair and CEO BT Slingsby noted that the Filspari’s approval in Japan could also “address the drug lag”, which has seen certain countries wait long periods before gaining access to newer therapies.
Filspari has already reached the US market, having received full approval from the US Food and Drug Administration (FDA) in IgA nephropathy through Travere Therapeutics in 2024. The drug also got the standard regulatory approval from the European Medicines Agency (EMA) via CSL Vifor in April 2025.
Alongside its market penetration across the US and EU, the drug is also used by the UK’s National Health Service (NHS), having gained an endorsement from the UK’s National Institute for Health and Care Excellence (NICE) under CSL Vifor in May 2025.
Renalys obtained the commercialisation rights to Filspari through its in-licensing deal with Travere, which saw Renalys hand over $120m in upfront and milestone payments for the rights to the drug in 13 countries across the APAC region, including Japan. This came before the company was bought out by Chugai.
Moving forward, analysts at GlobalData – parent company of Clinical Trials Arena – forecast that the drug will generate $1.44bn in sales during 2031.
Despite this blockbuster forecast, Novartis’ Fabhalta is expected to eclipse this value, with analysts estimating that the drug will bring in $3.12bn for the Swiss pharma in 2031.
Meanwhile, GlobalData estimates that the chronic kidney disease market will be worth $13.5bn across the seven major markets (7MM: US, France, Germany, Italy, Spain, the UK and Canada) in 2033.
