What Was Approved?
On February 23, 2026, the U.S. Food and Drug Administration approved Loargys (pegzilarginase-nbln) for the treatment of hyperargininemia in adults and pediatric patients 2 years of age and older with Arginase 1 Deficiency, or ARG1-D.
Loargys is used together with dietary protein restriction.
What Is Arginase 1 Deficiency?
Arginase 1 Deficiency is a rare inherited metabolic disorder in which the body does not have enough functional arginase 1 enzyme.
As a result, arginine can build up in the blood.
Over time, elevated arginine levels may contribute to neurologic and developmental complications.
How Does Loargys Work?
Loargys is an enzyme replacement therapy.
It provides an external source of arginase activity and helps lower plasma arginine by converting arginine into other substances the body can process.
How Is Loargys Given?
The recommended starting dose is:
0.1 mg/kg by intravenous infusion once weekly.
The dose may be adjusted based on plasma arginine levels, up to a maximum recommended dose of 0.2 mg/kg once weekly.
After at least eight weeks of weekly intravenous treatment, some patients may be switched to once-weekly subcutaneous administration at the same dose.
Why Was It Granted Accelerated Approval?
Loargys was approved through the FDA’s accelerated approval pathway based on its ability to reduce plasma arginine levels.
Continued approval may depend on a confirmatory study that verifies clinical benefit.
Does Loargys Have a Boxed Warning?
Yes.
Loargys carries a boxed warning for serious hypersensitivity reactions, including anaphylaxis.
Treatment should begin in a healthcare setting with appropriate monitoring and emergency treatment available.
What Are the Common Side Effects?
The most common adverse reactions reported in clinical studies included:
- Vomiting
- Fever
- Infusion-associated reactions
- Constipation
Bottom Line
Loargys (pegzilarginase-nbln) is a newly FDA-approved weekly enzyme replacement therapy for adults and children age 2 and older with Arginase 1 Deficiency and hyperargininemia.
It is used together with dietary protein restriction, and because approval was accelerated and serious allergic reactions can occur, treatment requires specialist supervision and ongoing monitoring.
Sources
- U.S. Food and Drug Administration (FDA) — Novel Drug Approvals for 2026.
- U.S. Food and Drug Administration (FDA) — Loargys (pegzilarginase-nbln) Prescribing Information, February 2026.
- U.S. Food and Drug Administration (FDA) — Loargys Approval Package, February 23, 2026.