Ionis Pharmaceuticals wins FDA approval for first Alexander disease treatment, priced at $285,000 per dose

Sep 3, 2026

The FDA has approved Ionis Pharmaceuticals' Zanvastro (zilganersen) as the first-ever treatment for Alexander disease, a rare and fatal neurodegenerative disorder. Priced at $285,000 per dose, the quarterly spinal injection stabilized motor function in a Phase 3 trial, halting the typical 33% decline in walking speed. The landmark approval marks Ionis' first independent commercial launch in neurology, establishing a critical foundation for its solo rare-disease pipeline.

Zanvastro FDA approval

▪Zanvastro is approved by the U.S. Food and Drug Administration for patients of all ages, including children and adults, with Alexander disease.
▪The U.S. Food and Drug Administration approved Ionis Pharmaceuticals' Zanvastro, also known as zilganersen, on September 3, 2026, as the first approved treatment for Alexander disease.
▪The U.S. Food and Drug Administration approved Zanvastro more than two weeks ahead of its scheduled September 22, 2026 Prescription Drug User Fee Act action date.

Alexander disease pathology

▪Alexander disease is an extremely rare, neurodegenerative genetic disorder caused by mutations in the GFAP gene that lead to toxic protein accumulation in glial cells.
▪Alexander disease affects fewer than 1,000 people in the United States, with some estimates placing global prevalence as low as one in 3 million people.

Zilganersen clinical trial results

▪In a pivotal Phase 3 clinical trial of 49 patients aged 5 and older, patients treated with a 50 mg dose of Zanvastro showed statistically significant stabilization of walking speed at week 61 compared to untreated patients.
▪In a clinical trial control group of untreated Alexander disease patients, walking speed declined by 33% over 61 weeks.
▪An open-label clinical substudy of four children under the age of 2 treated with Zanvastro showed improvements in motor skills, including standing, walking, running, and jumping.

Drug pricing expectations

▪Ionis Pharmaceuticals announced on September 4, 2026, that it would price Zanvastro at $285,000 per dose.
▪Zanvastro is administered as an injection into the spinal canal every three months by a healthcare professional.
▪Ionis Pharmaceuticals expects peak sales for Zanvastro to exceed $100 million and plans to make the drug available in the United States in the weeks following approval.

Patient advocacy stories

▪Elise Pearson, who was diagnosed with Alexander disease in 2014, participated in the clinical trial for zilganersen and celebrated her 15th birthday on September 1, 2026.
▪Jenny Pearson founded the nonprofit Elise's Corner to raise research funds after her daughter Elise was diagnosed with Alexander disease in 2014.

Ionis neurology pipeline

▪Ultragenyx Pharmaceutical's competing Angelman syndrome drug candidate, apazunersen, failed to improve cognition in a Phase 3 clinical trial, as reported on September 3, 2026.
▪Ionis Pharmaceuticals is developing obudanersen for Angelman syndrome, with late-stage Phase 3 trial data expected to read out in the second half of 2027.
▪Zanvastro represents the first independent commercial launch in neurology for Ionis Pharmaceuticals, which previously partnered with Biogen on neurological drugs like Spinraza and Qalsody.