On September 3, 2026, Ionis Pharmaceuticals, Inc. announced that the U.S. Food and Drug Administration (FDA) has approved ZANVASTRO (zilganersen) for the treatment of Alexander disease (AxD) in pediatric and adult patients. According to the filing, ZANVASTRO is the first and only disease-modifying treatment for AxD, an ultra-rare, progressive, and often fatal neurological disorder.
The FDA approval was based on results from a pivotal study involving 54 participants aged 1.5 to 53 years. The study met its primary endpoint in individuals 5 years of age and older, demonstrating that ZANVASTRO 50 mg provided statistically significant and clinically meaningful stabilization of gait speed compared to control at Week 61. The least square mean difference was 33.3% with a p-value of 0.041. Additionally, ZANVASTRO demonstrated improvement in gross motor function in patients aged 2 to 4 years as assessed by the Gross Motor Function Measure-88.
The filing details the administration of ZANVASTRO as a 50 mg intrathecal injection administered quarterly. The therapy is designed to reduce the production of glial fibrillary acidic protein (GFAP), which accumulates in astrocytes due to changes in the GFAP gene. AxD affects approximately 1 in 1 to 3 million people worldwide and is characterized by progressive motor and cognitive dysfunction.
Regarding safety, the filing notes that ZANVASTRO demonstrated a favorable profile with most adverse events being mild or moderate. Serious treatment-emergent adverse events occurred less frequently in the ZANVASTRO group compared to control. The FDA granted Ionis a Priority Review Voucher in conjunction with the approval. In June 2026, Ionis entered into a license agreement with Recordati, granting Recordati exclusive rights to develop and commercialize zilganersen in all countries outside the U.S.
