FDA Approves Zilganersen Injection, First Drug for Alexander Disease

The FDA has approved zilganersen (Zanvastro; Ionis Pharmaceuticals) injection for Alexander disease in pediatric and adult patients, the first therapy ever cleared for the rare neurological disorder and the first to target the protein buildup that drives it. For pharmacists, this fills a total therapeutic void—until now, care was strictly supportive—and introduces an intrathecally administered antisense oligonucleotide that will require specialized handling, dosing coordination, and caregiver counseling.¹

A First-in-Class Approach to a Rare Disease

Alexander disease is a rare, progressive neurological disorder caused by mutations in the gene that produces glial fibrillary acidic protein (GFAP). When the protein is abnormal, it accumulates in the brain's supportive cells and damages the nervous system over time. The FDA notes the disease affects fewer than 1 in a million people and can cause seizures, loss of developmental milestones, difficulty walking, muscle weakness, and increased pressure in the brain.¹

Zilganersen is an antisense oligonucleotide that reduces production of the abnormal GFAP protein before it can accumulate. It is administered as an injection into the spinal canal every 3 months by a trained health care professional. For pharmacists, the intrathecal route and quarterly dosing schedule place this in specialty and health-system settings, where preparation, storage, and administration logistics fall to the pharmacy team.¹

What the Pivotal Study Showed

Efficacy and safety were evaluated in a multicenter, randomized, controlled phase 3 trial (NCT04849741) that enrolled 49 pediatric and adult patients 2 years of age and older, plus an open-label substudy of 4 patients younger than 2 years. In patients aged 5 years and older who had measurable difficulty walking at baseline, those treated with zilganersen showed significantly better walking speed at 61 weeks compared with untreated patients. In children aged 2 to 4 years, a broader motor-skills assessment was used. Treated children improved whereas the control group declined.^1,3

Data presented by Ionis Pharmaceuticals at the 2026 American Academy of Neurology annual meeting quantified the primary result: The 50-mg dose produced a statistically significant stabilization of gait speed on the 10-Meter Walk Test at Week 61, with a least square mean difference of approximately 33.3% versus control (P = .041). In children aged 2 to 4 years, the Gross Motor Function Measure-88 favored treatment (least square mean difference 22.9 points; nominal P = .034).³

For the youngest patients, direct trial data were limited by disease rarity and lack of a concurrent control. Pharmacokinetic modeling confirmed drug levels comparable to those in older children at the same dose, supported by safety data from 4 patients aged under 2 years and from older pediatric patients—allowing the FDA to extend the indication from infancy through adulthood.¹

Safety and Counseling Considerations

The most common adverse events (AEs) are vomiting, back pain, cough, headache, and post-lumbar puncture syndrome. Aseptic meningitis has been reported, and patients and caregivers should be counseled to report symptoms consistent with meningitis to their provider. In the pivotal study, serious treatment-emergent AEs occurred less frequently with zilganersen than with the control (37.5% for the 25-mg or 50-mg groups versus 47.1% pooled control).^1,3

Zilganersen received orphan drug, fast track, breakthrough therapy, and rare pediatric disease and priority review voucher designations.¹

REFERENCES

1. FDA approves first drug to treat Alexander disease. US Food and Drug Administration. News release. September 3, 2026. Accessed September 3, 2026. https://www.fda.gov/news-events/press-announcements/fda-approves-first-drug-treat-alexander-disease

2. A study to evaluate the safety and efficacy of zilganersen (ION373) in patients with Alexander disease (AxD). ClinicalTrials.gov Identifier: NCT04849741. Updated August 21, 2026. Accessed September 3, 2026. https://clinicaltrials.gov/study/NCT04849741

3. Ionis presents new data from pivotal study of zilganersen in Alexander disease (AxD) at AAN 2026 Annual Meeting. Ionis Pharmaceuticals. News release. April 21, 2026. Accessed September 3, 2026. https://ir.ionis.com/news-releases/news-release-details/ionis-presents-new-data-pivotal-study-zilganersen-alexander