What Was Approved?
On March 24, 2026, the U.S. Food and Drug Administration approved Avlayah (tividenofusp alfa-eknm) for the treatment of neurologic manifestations of Hunter syndrome, also called mucopolysaccharidosis type II or MPS II.
The approval applies when treatment is started in presymptomatic or symptomatic pediatric patients weighing at least 5 kg before advanced neurologic impairment develops.
What Is Hunter Syndrome?
Hunter syndrome is a rare inherited disorder in which certain complex sugars, called glycosaminoglycans, build up in cells.
This buildup can affect multiple organs, including the:
- Brain
- Heart
- Airways
- Bones and joints
Neurologic involvement can lead to progressive developmental and cognitive problems in some patients.
How Is Avlayah Given?
Avlayah is given by intravenous infusion once weekly.
The FDA review describes a starting dose of 3 mg/kg once weekly, with gradual dose increases over several weeks to a maintenance dose of 15 mg/kg once weekly.
Treatment should be administered in an appropriate healthcare setting.
Why Was It Granted Accelerated Approval?
Avlayah received accelerated approval based on reduction of heparan sulfate in cerebrospinal fluid, a biomarker the FDA determined is reasonably likely to predict clinical benefit.
A confirmatory study is still required to verify clinical benefit.
Does Avlayah Have a Boxed Warning?
Yes.
The FDA-approved label carries a boxed warning for serious hypersensitivity reactions, including anaphylaxis.
Treatment should begin in a healthcare setting equipped to recognize and manage severe allergic reactions.
Is Avlayah for Every Patient With Hunter Syndrome?
No.
The FDA-approved indication is specifically limited to pediatric patients who:
- Weigh at least 5 kg
- Are presymptomatic or symptomatic
- Have not yet developed advanced neurologic impairment
The treatment should not be described as a general therapy for all patients with Hunter syndrome.
Bottom Line
Avlayah (tividenofusp alfa-eknm) is a newly FDA-approved weekly intravenous treatment for certain pediatric patients with Hunter syndrome who have neurologic involvement or are at risk for it before advanced neurologic impairment.
Because the approval was accelerated and serious hypersensitivity reactions can occur, treatment requires specialist supervision and ongoing monitoring.
Sources
- U.S. Food and Drug Administration (FDA) — FDA Approves Drug to Treat Neurologic Manifestations of Hunter Syndrome, March 25, 2026.
- U.S. Food and Drug Administration (FDA) — Avlayah (tividenofusp alfa-eknm) Prescribing Information, 2026.
- U.S. Food and Drug Administration (FDA) — Ongoing Accelerated Approvals.