OTSKY VOYXACT: GlomCon Data Locks In +0.3 eGFR Slope

Otsuka (OTSKY) presented the full 24-month VISIONARY Phase 3 dataset at GlomCon Hawaii, and the numbers deliver on the July topline. VOYXACT (sibeprenlimab-szsi) showed an annualized eGFR slope of +0.3 mL/min/1.73 m²/year versus -4.2 on placebo, a treatment effect of +4.5 (95% CI, 3.6 to 5.4; p<0.0001). Kidney function essentially stabilized at a near-physiologic rate of decline. For a disease where patients typically lose 3-5 mL/min/year on optimized supportive care, a slope that rounds to zero is a new standard.

OTSKY, the ADR for Otsuka Holdings, closed at $40.49 on volume of roughly 18,000 shares. The ADR trades over the counter. Otsuka’s primary listing is the Tokyo Stock Exchange.

What the GlomCon data adds

The topline in July confirmed eGFR stabilization. The GlomCon presentation put exact numbers on it. The least square mean change from baseline at 24 months was +1.3 mL/min/1.73 m² with VOYXACT versus -7.9 for placebo, a treatment difference of +9.2 (95% CI, 7.1 to 11.4; p<0.0001). Patients on VOYXACT gained kidney function over two years. Patients on placebo lost nearly 8 points.

The safety profile through 24 months remained comparable to placebo. Overall adverse events were 90.7% versus 90.0%. Infection rates were 51.4% versus 51.0%. Serious infections were lower on VOYXACT, at 1.9% versus 4.0%, and both serious adverse events and discontinuations favored the drug.

VOYXACT is the only selective APRIL inhibitor on the market, reducing pathogenic galactose-deficient IgA1 production without broad B-cell depletion. The FDA granted accelerated approval in November 2025. Otsuka has started a rolling sBLA submission for traditional approval.

The IgAN competitive field just got a data leader

The IgAN market now has four entrants with distinct mechanisms. Vera’s Trutakna (atacicept) blocks BAFF and APRIL but has reported only 9-month proteinuria data, with eGFR results still pending. Novartis’ Fabhalta (iptacopan), a complement factor B inhibitor, holds traditional approval with eGFR data maturing. Vertex’s povetacicept, another BAFF/APRIL inhibitor, has a November 30 PDUFA date with 36-week proteinuria data but 2-year eGFR still outstanding. VOYXACT is the only one with 24-month eGFR results in hand, and the numbers beat the KDIGO treatment target of under 1 mL/min/1.73 m²/year.

The caveat is the accelerated approval gap. Fabhalta already has traditional approval. VOYXACT and Trutakna both need confirmatory eGFR data to convert; VOYXACT just delivered. The sBLA timeline is not yet public, but the dataset gives Otsuka the most mature filing package in the APRIL inhibitor class.

For the setup to these results, see the earlier preview of the VISIONARY dataset.

Source: Otsuka press release | VISIONARY on ClinicalTrials.gov

What It Means for the Trade

The GlomCon presentation converts VOYXACT from “promising accelerated approval” to “the data leader in IgAN,” and in a market where four mechanisms are fighting for the same nephrologists, mature eGFR data is the currency that wins formulary and guideline placement. A +0.3 slope versus -4.2 for placebo (treatment effect +4.5, p<0.0001) is not just statistical — it is a kidney-function stabilization that rounds to physiologic decline. No competitor can currently make that claim with 24-month data: Fabhalta’s eGFR package is still maturing, Trutakna has 9-month proteinuria data only, and povetacicept’s PDUFA rests on 36-week proteinuria. Those are cross-trial comparisons, to be clear — different trials, different populations — but the market reads cross-trial anyway, and right now it reads Otsuka first.

For OTSKY, the ADR is nearly untradeable and Otsuka’s real listing is Tokyo — the read matters for the yen stock. The commercial stakes are large regardless: IgAN is the most common primary glomerulopathy driving patients toward dialysis, and a drug that preserves eGFR at this magnitude becomes chronology-defining therapy rather than an add-on.

Mechanism and Market Context

Why the slope matters more than proteinuria: eGFR slope is the endpoint the FDA now treats as the surrogate for kidney failure, and the difference between -4.2 (placebo) and +0.3 (VOYXACT) is the difference between dialysis in a decade and kidney function that outlives the trial. Proteinuria reductions can wobble; slopes compound. That is why the 24-month LS mean change (+1.3 on drug versus -7.9 on placebo) is the single most commercially important number in the IgAN field.

Mechanistically, the selectivity is the differentiator worth watching. APRIL drives production of galactose-deficient IgA1, the pathogenic species at the top of the IgAN cascade. Blocking APRIL without broad B-cell depletion means immune competence survives — the VISIONARY safety data support it (infection rates 51.4% versus 51.0%, serious infections lower on drug) — which matters for a chronic therapy dosed for years. The rolling sBLA for traditional approval is now backed by exactly the dataset the accelerated-approval framework demanded.

Risks and What Could Go Wrong

1. sBLA conversion timing. Traditional approval is the commercial unlock (full guideline placement, broader payer comfort), and the review clock has not started publicly; a slow filing cedes the “first traditional approval” race to Fabhalta, which already holds it.
2. Competitive catch-up. Povetacicept’s November 30 PDUFA will land with full IgAN-market attention; Vertex’s commercial machine can compress VOYXACT’s lead even with less mature data.
3. Long-tail safety. APRIL inhibition for a lifetime is uncharacterized; the 24-month profile is clean but the class question is decades, not years.
4. Slope sustainability. Two years of near-zero decline is not five years; the extension data will be scrutinized for a wobble.

Own Otsuka (in Tokyo, realistically) for the data lead; trade nothing on the ADR’s liquidity.