Zilganersen (ION373)

March 23, 2026: Ionis Pharmaceuticals, Inc. (NASDAQ: IONS) said the FDA accepted for Priority Review its NDA for zilganersen, an investigational RNA-targeted/antisense oligonucleotide for Alexander disease (AxD). The FDA set a PDUFA target action date of September 22, 2026.

The filing and Priority Review are supported by a global Phase 1–3 randomized, double-blind, controlled multiple-ascending dose study (NCT04849741) in 54 participants ages 1.5–53 across 13 sites in eight countries. In the pivotal 50 mg cohort, zilganersen showed statistically significant stabilization on the primary endpoint of gait speed (10-Meter Walk Test) versus control at week 61 (least squares mean difference 33.3%; p=0.0412), with favorable safety/tolerability. Secondary and exploratory endpoints (including adaptive function, communication, GI symptoms, sleep, and seizures) consistently favored zilganersen.

Ionis said additional pivotal study data will be presented at the 2026 American Academy of Neurology (AAN) annual meeting in Chicago. The FDA previously granted zilganersen Breakthrough Therapy, Orphan Drug, and Rare Pediatric Disease designations; the EMA granted Orphan Drug designation.