FDA clears sibeprenlimab for IgA nephropathy on proteinuria, not kidney function

The Food and Drug Administration approved Voyxact (sibeprenlimab-szsi) on 25 November to reduce proteinuria in adults with primary IgA nephropathy at risk of disease progression [s1]. The approval is an accelerated one, granted on the basis of reduced protein in the urine [s1]. The label says plainly what that means: it has not been established whether the drug slows kidney function decline over the long term, and continued approval may depend on a confirmatory trial verifying clinical benefit [s1].

Three weeks earlier, on 8 November, the interim analysis behind the approval was published in the New England Journal of Medicine [s2]. Reading the two documents together is a fairly clean illustration of what an accelerated approval buys and what it defers.

The mechanism

IgA nephropathy is driven in part by A proliferation-inducing ligand, or APRIL, a cytokine considered a key contributor to the disease's pathogenesis [s2]. Sibeprenlimab is a humanised IgG2 monoclonal antibody that selectively binds and inhibits APRIL [s2]. The FDA label describes the product simply as an APRIL blocker [s1].

What the trial showed

VISIONARY is a phase 3, multicentre, double-blind, randomised, placebo-controlled trial [s2]. Adults with biopsy-confirmed IgA nephropathy were assigned 1:1 to subcutaneous sibeprenlimab 400 mg or placebo every four weeks for 100 weeks [s2]. A total of 510 patients were randomised — 259 to sibeprenlimab and 251 to placebo [s2]. The prespecified interim analysis covered the first 320 patients (63%) who had the opportunity to complete a nine-month evaluation: 152 assigned sibeprenlimab and 168 placebo [s1][s2]. At baseline the median age was 42 years (range 18 to 83), 63% were male, 59% were Asian and 38% White [s1].

The primary endpoint for the interim analysis was the 24-hour urinary protein-to-creatinine ratio at nine months compared with baseline [s2]. Sibeprenlimab produced a 50.2% reduction; placebo produced a 2.1% increase [s2]. The adjusted geometric least-squares mean ratio was 51.2% lower with sibeprenlimab than with placebo (96.5% CI 42.9 to 58.2; P<0.001) [s2].

Mechanistic endpoints moved as expected: at week 48, APRIL levels were down 95.8% from baseline and pathogenic galactose-deficient IgA1 down 67.1% [s2].

Safety appeared similar between groups. No deaths were reported, and serious adverse events during the treatment period occurred in 3.5% of sibeprenlimab patients and 4.4% of placebo patients [s2].

What it did not show

The key secondary endpoint — the annualised slope of estimated glomerular filtration rate over 24 months — is to be reported at trial completion, not now [s2]. That endpoint is the one that answers whether patients keep their kidneys longer.

Proteinuria is a validated surrogate in IgA nephropathy in the sense that regulators accept it for accelerated approval, and reducing it is strongly associated with better renal outcomes across the literature. It is not the same as demonstrating those outcomes in this trial with this drug. The FDA label states the position without softening it: the indication is approved under accelerated approval based on reduction of proteinuria, long-term effects on kidney function are not established, and continued approval may be contingent on a confirmatory trial [s1].

One finding in the label adds a wrinkle. During the treatment period in VISIONARY, 88 of 256 evaluable patients (34%) treated with Voyxact developed anti-drug antibodies, and 21 of those 88 (23.9%) developed antibodies with neutralising activity [s1]. Exposure to the drug in patients who developed anti-drug antibodies was roughly 40% lower than in those without them, and the reduction in 24-hour urinary protein-to-creatinine ratio from baseline to month 9 was numerically smaller in patients who developed antibodies (41.6%) than in those who did not (52.7%) [s1]. The label states that the clinical significance of that difference is not clear [s1].

How it is given

The recommended dosage is 400 mg by subcutaneous injection once every four weeks, supplied as a 400 mg/2 mL single-dose prefilled syringe intended for self-administration or administration by a caregiver after proper training [s1]. It is contraindicated in people with serious hypersensitivity to sibeprenlimab-szsi or any excipient [s1].

Two warnings govern use. The drug suppresses the immune system by reducing antibody production, which may raise infection risk; patients should be assessed for active infection before starting and monitored during treatment, and serious infection may warrant interrupting therapy [s1]. Separately, live vaccines are not recommended within 30 days before initiation or during treatment, because safety has not been established and the drug may interfere with vaccine responses [s1]. The most common adverse reactions are upper respiratory tract infection and injection site erythema [s1].

What to watch

The 24-month eGFR slope from the full 510-patient VISIONARY cohort is the result that determines whether this approval converts to a full one. Until it reports, the honest description of Voyxact is a drug that reliably lowers a marker strongly linked to kidney damage in IgA nephropathy, in a well-conducted randomised trial, with the clinical question still open.

This article is informational and not medical advice.

Sources

• [s1] VOYXACT (sibeprenlimab-szsi) injection, for subcutaneous use — Prescribing Information, U.S. Food and Drug Administration, issued November 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/761434s000lbl.pdf
• [s2] Sibeprenlimab in IgA Nephropathy — Interim Analysis of a Phase 3 Trial, The New England Journal of Medicine, 8 November 2025. https://doi.org/10.1056/NEJMoa2512133