Zanvastro (zilganersen): FDA approval, pivotal trial and safety
Approved
Type
Oligonucleotide · Intrathecal
FDA-approved use
To treat Alexander disease in pediatric and adult patientsWording from FDA's list of novel approvals.
FDA review
Priority reviewOrphan drug
Company
Ionis
Application
NDA 220210
Specialty
Neurology
At a glance
Zanvastro (zilganersen) is an antisense oligonucleotide approved by the FDA on September 3, 2026 for Alexander disease in pediatric and adult patients. In the pivotal trial, gait speed fell 2.1% with the approved dose versus 35.4% with control at Week 61 (adjusted difference 33.3%, 95% CI 1.44 to 65.25, P=0.041). The main safety point is aseptic meningitis; there is no boxed warning.
What it is and how it works
Zilganersen binds GFAP pre-mRNA and causes its degradation. This lowers synthesis of glial fibrillary acidic protein (GFAP). Alexander disease is caused by pathogenic variants in the GFAP gene. Existing care is supportive and does not target GFAP production.
Multicenter, double-blind, randomized, controlled study with two ascending-dose cohorts. Patients were randomized 2:1 to Zanvastro or control in each cohort. The double-blind period lasted 60 weeks, followed by open-label treatment and a long-term extension. An open-label substudy enrolled patients under 2 years.
Patients
49 patients aged 2 to 65 years with Alexander disease confirmed by clinical phenotype, brain MRI, and a pathogenic GFAP variant. Median age was 11 years. The primary analysis used Stratum 1 (17 on the 50 mg cohort drug arm, 13 control), defined by age, motor symptom onset, and abnormal gross motor skills. Four more patients under 2 years were in the open-label substudy.
Compared with
Control
Primary endpoint
Difference in mean percent change in gait speed on the 10-meter walk test from baseline to Week 61, approved-dose arm versus control, in Stratum 1.
Result
Gait speed changed by -2.1% with Zanvastro versus -35.4% with control. Adjusted least squares mean difference was 33.3% (95% CI 1.44 to 65.25; P=0.041).
Other results
Secondary end points were assessed in all randomized patients. In patients aged 2 to 4 years, motor function was measured with GMFM-88 Dimensions D and E. Those on Zanvastro (n=4) improved and controls (n=3) declined (least squares mean difference 22.9, standard error 5.2).
Safety in the trial
Safety was assessed in 53 patients, with median exposure of 60 weeks. Adverse reactions with the approved dose versus control: vomiting 50% vs 29%, back pain 50% vs 18%, cough 38% vs 18%, headache 29% vs 12%, post-lumbar puncture syndrome 29% vs 6%, arthralgia 25% vs 6%, oropharyngeal pain 21% vs 0%, dysphagia 17% vs 6%. One serious aseptic meningitis event occurred.
How does Zanvastro (zilganersen) compare with the alternatives (Physical and occupational therapy, Antiseizure medications, Antispasticity agents (such as baclofen)) for Alexander disease in pediatric and adult patients? Summarize head-to-head and indirect evidence, efficacy, safety and where each fits, with citations.
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Safety signals
There is no boxed warning. The label warns of aseptic meningitis. One patient had a serious episode that recurred in the open-label period and needed dose interruption and intravenous corticosteroid pretreatment. CSF white cell count and protein kept rising with continued exposure despite premedication, but the patient stayed asymptomatic and stayed on treatment. CSF pleocytosis occurred in 29% of patients on the approved dose versus 18% on control, usually after the first 2 to 4 doses. The most common adverse reactions were vomiting, back pain, cough, headache, and post-lumbar puncture syndrome. Clinicians should work up and treat suspected aseptic meningitis per standard of care.
What it competes with
No other drug is approved to target the cause of Alexander disease. Management is supportive and based on symptoms and complications.
Physical and occupational therapySupports mobility and function but does not change the underlying disease.
Antiseizure medicationsUsed to control seizures when they occur.
Antispasticity agents (such as baclofen)Used to reduce spasticity and improve comfort and care.
Nutritional and feeding supportAddresses swallowing difficulty and nutrition, including gastrostomy when needed.
Bottom line for clinicians
Zanvastro is for patients with Alexander disease confirmed by a pathogenic GFAP variant, including children and adults. The primary result rests on a small trial, and the confidence interval was wide, with a lower bound near zero. Weigh the benefit of slowing gait decline against intrathecal administration burden, post-lumbar puncture effects, and the risk of aseptic meningitis.
Dosing, contraindications and full warnings are in the prescribing information.
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Last updated October 28, 2026 by 2 Minute Medicine.
For healthcare professionals. A summary of public FDA documents and published trials, not medical advice. Check the full prescribing information before prescribing.
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