Dimerix Locks in >90% Statistical Power on Path to March 2028 Trial Readout
Dimerix confirms ACTION3 Phase 3 study maintains strong statistical power for primary endpoint
Dimerix Limited (ASX: DXB) has announced that an external blinded statistical review confirms the ACTION3 Phase 3 study remains appropriately powered with >90% statistical probability to demonstrate a treatment effect for its proteinuria primary endpoint. The review validates the study design ahead of trial completion, with the last patient expected to receive their final dose in March 2028.
In practical terms, if DMX-200 continues to reduce proteinuria in trial patients as anticipated, the >90% power means there is greater than a nine-in-ten chance the study will successfully demonstrate a statistically significant treatment effect at conclusion. Dimerix and its commercialisation partners will continue ACTION3 to the final proteinuria endpoint to maximise the likelihood of successful study outcomes and regulatory approval, a strategic decision supported by recent FDA guidance confirming proteinuria is an appropriate endpoint for full regulatory approval of DMX-200.
The announcement removes a key execution uncertainty for investors. With 333 adult patients fully recruited and the study maintaining robust statistical power, the pathway to traditional approval remains on track. The FDA has previously confirmed that the proposed primary endpoint of percent reduction in proteinuria compared to placebo is suitable to support traditional approval via the 505(b)(1) pathway, with change in eGFR as a secondary endpoint.
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What is statistical power and why does it matter for clinical trials?
Statistical power is the probability that a clinical trial will detect a real treatment effect if one exists. It functions as a measure of a study’s sensitivity—the likelihood it will successfully identify a meaningful difference between treatment and placebo groups when such a difference genuinely exists in the patient population.
Industry standard statistical power for Phase 3 trials typically sits at 80%, meaning there is an 80% probability of detecting a treatment effect. The ACTION3 study’s >90% power exceeds this benchmark, providing an additional margin of confidence in the study design. Higher statistical power reduces the risk of a trial failing due to inadequate study design rather than drug performance, a crucial distinction for investors evaluating clinical-stage assets.
For shareholders, this translates to greater certainty that if ACTION3 fails to meet its primary endpoint, it would reflect drug performance rather than a flawed trial structure. The blinded statistical review validates that Dimerix has appropriately sized the study and selected endpoints capable of detecting the anticipated treatment effect, de-risking execution ahead of the final data readout.
Evolving FSGS landscape validates proteinuria endpoint strategy
Dimerix and its commercialisation partners assessed changes to the Focal Segmental Glomerulosclerosis (FSGS) treatment landscape since ACTION3 initiated in 2022, with multiple external developments validating proteinuria as the primary endpoint. Evidence from the PARASOL working group provided support for proteinuria as a candidate surrogate endpoint for FSGS, while the FDA delivered positive feedback confirming proteinuria is appropriate for full DMX-200 approval. Most notably, the FDA approved another FSGS therapy in April 2026 based on a proteinuria endpoint, establishing recent regulatory precedent.
A key finding from the PARASOL working group analysis was that proteinuria required smaller sample sizes and demonstrated less variability than eGFR for FSGS clinical trials, potentially reducing risk for downstream marketing approval. Collectively, the PARASOL working group analysis, the National Registry of Rare Kidney Diseases UK (RaDaR) analyses, Kaiser Permanente analyses, third-party FSGS study data, and input from key opinion leaders all suggest that measuring proteinuria change from baseline is a more statistically achievable endpoint for DMX-200 than eGFR endpoints.
| Factor | Proteinuria Endpoint | eGFR Endpoint |
|---|---|---|
| Sample size required | Smaller | Larger |
| Variability | Lower | Higher |
| Regulatory precedent | FDA-approved FSGS therapy (April 2026) | Limited |
| Statistical achievability | Higher | Lower |
Why Dimerix ruled out accelerated approval pathway
The company evaluated the accelerated approval pathway but determined it would not represent the most strategic course for the trial. While accelerated approval based on proteinuria could theoretically bring DMX-200 to market sooner, it would likely require an eGFR-based confirmatory endpoint, introducing multiple execution risks and costs.
Pursuing accelerated approval would necessitate increased costs, a lengthened study timeline, and the splitting of alpha (the statistical significance threshold), potentially reducing the probability of success for the final endpoint. Given these downsides, Dimerix and its commercialisation partners concluded that conducting the interim analysis required for an accelerated approval application would add risk rather than value.
Dr Jeff Castelli, Chief Development Officer, Amicus Therapeutics
“The move to having proteinuria as the ACTION3 primary endpoint for traditional approval increases the likelihood of a successful marketing approval and avoids the very real risks associated with use of eGFR endpoints. The required additional activities, cost and increased risk associated with accelerated approval would not be value generating in our view.”
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ACTION3 study progress and upcoming milestones
The ACTION3 Phase 3 clinical trial adult cohort is fully recruited with 333 patients, and the last patient is expected to receive their final dose in March 2028. Recruitment of paediatric patients aged 12-17 years old remains ongoing as an independent cohort in the trial, and if successful, may allow Dimerix to expand its application for DMX-200 to adolescents in key territories.
The study has delivered positive safety and efficacy signals to date:
- The ACTION3 Phase 3 study passed a formal futility analysis of the proteinuria endpoint in March 2024, demonstrating DMX-200 was performing better than placebo at that point in time
- A further seven Independent Data Monitoring Committee (IDMC) reviews to date have not identified safety issues or requested changes to the protocol
- No safety concerns have been raised across multiple independent reviews
Dr David Fuller, Chief Medical Officer, Dimerix
“The understanding of the FSGS disease and appropriate surrogate clinical endpoints has evolved significantly since the initiation of the ACTION3 study and justified a comprehensive review of all considerations. By focussing on proteinuria, it significantly reduces the clinical and commercial risk for traditional approval. Given the successful blinded interim futility analysis in 2024, we know that DMX-200 was performing better than placebo in reducing proteinuria at that point in time, and with seven independent data monitoring committee reviews completed, we are confident that DMX-200 is well tolerated.”
Regulatory pathway and commercial positioning
The FDA has confirmed that the proposed primary endpoint of percent reduction in proteinuria compared to placebo is suitable to support traditional approval of DMX-200 via the 505(b)(1) pathway, with change in eGFR as a secondary endpoint. Dimerix is advancing licensing discussions with potential partners in territories not already licensed, while the company benefits from granted patents in various territories until 2032, with patent applications submitted globally that may extend patent protection to 2045. DMX-200 has received Orphan Drug Designation in the United States, Europe, UK and Japan.
The market opportunity for DMX-200 is substantial:
- More than 40,000 people are estimated to be living with FSGS in the United States
- There were no therapies specifically approved for FSGS in the US until the recent April 2026 approval
- In patients with progressive or treatment-resistant FSGS, disease progression can lead to end-stage kidney disease within five years
- Up to 60% disease recurrence rate after kidney transplantation
Traditional approval with strong statistical power positions DMX-200 for a streamlined regulatory process with reduced execution risk. The Orphan Drug Designation provides market exclusivity benefits that could prove material in a rare disease indication with limited approved treatment options. With the blinded statistical review now complete, Dimerix has removed a key uncertainty from the ACTION3 trial pathway, allowing investors to focus on trial execution through to the March 2028 completion date.
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