FDA Approves IONIS Drug Zanvastro for Alexander Disease

Ionis Pharmaceuticals (IONS) said the U.S. Food and Drug Administration has approved ZANVASTRO (zilganersen) for the treatment of Alexander disease (AxD) in pediatric and adult patients. It is the first and only disease-modifying treatment for the ultra-rare, progressive and often fatal neurological disorder, where care until now has been limited to managing symptoms. Alongside the approval, the FDA granted Ionis a Rare Pediatric Disease Priority Review Voucher.

ZANVASTRO is an RNA-targeted medicine designed to reduce production of glial fibrillary acidic protein (GFAP), the protein that accumulates toxically in astrocytes as a result of variants in the GFAP gene. The drug is given as a 50 mg intrathecal injection once per quarter, and Ionis said it will be available in the U.S. in the coming weeks.

The approval rests on a global Phase 1-3 study (NCT04849741) that enrolled 54 participants aged 1.5 to 53 years across 13 sites in eight countries, randomized 2:1 to drug or control for a 60-week double-blind period. In patients aged five and older, the 50 mg dose met the primary endpoint with a statistically significant stabilization of gait speed on the 10-Meter Walk Test at Week 61 (least square mean difference 33.3%, p=0.041). Children aged two to four showed improvement on the GMFM-88 motor measure versus control.

Safety was described as favorable, with most adverse events mild or moderate and serious treatment-emergent events occurring less frequently in the ZANVASTRO arm than in the control arm. The label carries a warning for aseptic meningitis, including one serious case that recurred in the open-label extension and required dose interruption and intravenous dexamethasone pretreatment. The most common adverse reactions at an incidence of at least 25% were vomiting, back pain, cough, headache and post-lumbar puncture syndrome.

AxD affects roughly 1 in 1 to 3 million people worldwide and usually leads to death 14 to 25 years after symptom onset. Chief executive Brett Monia called the approval a transformative moment and said it marks the company's first independent launch from our industry-leading neurology pipeline and its second independent launch this year.

Commercially, Ionis retains U.S. rights. In June 2026 the company licensed zilganersen outside the U.S. to Italy's Recordati, with regulatory submissions in Europe and Japan expected in 2027. Ionis said it will support U.S. patients through its Ionis Every Step access program.

The approval adds to a neurology franchise that already includes SPINRAZA, WAINUA and QALSODY, with a clinical-stage portfolio of 12 investigational medicines, seven of them wholly owned. Management will host a webcast on Friday, Sept. 4 at 10:00 a.m. ET to discuss the decision.

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