Pegzilarginase-nbln

Arginase 1 deficiency (ARG1-D) is caused by biallelic mutations in the ARG1 gene, which encodes the hepatic enzyme catalyzing the final step of the urea cycle: hydrolysis of L-arginine to L-ornithine and urea. Loss of this activity causes pathological accumulation of plasma arginine and guanidino compounds such as alpha-N-acetylarginine, which are believed to exert direct neurotoxic effects and drive the progressive spastic paraplegia characteristic of ARG1-D.

Pegzilarginase is a recombinant human arginase 1 expressed in Escherichia coli and modified for systemic plasma-based action through two key manufacturing steps:

• Cobalt substitution: The native manganese cofactor is replaced with cobalt, which increases the enzyme's catalytic rate and thermostability relative to the wild-type manganese-containing form.

• PEGylation: Covalent conjugation with polyethylene glycol reduces renal clearance, dampens immune recognition, and substantially extends circulatory half-life.

After intravenous infusion or subcutaneous injection, pegzilarginase acts in the bloodstream rather than within hepatocytes, converting circulating arginine to ornithine and urea and bypassing the absent hepatic enzyme. Sustained arginine reduction also decreases downstream guanidino compound accumulation, which provides the proposed mechanism for the neuromotor improvements observed in clinical trials.

Clinical development of pegzilarginase began with a phase 1/2 open-label study (NCT02488044) enrolling 16 pediatric and adult patients with ARG1-D. That study demonstrated rapid and sustained reductions in plasma arginine over 20 weeks, accompanied by improvements in functional mobility. A subsequent open-label extension enrolled 14 of those patients; 13 transitioned to subcutaneous administration and achieved a median treatment duration of approximately 131 weeks with maintained arginine control.

The pivotal evidence is the PEACE trial (NCT03921541), a phase 3 randomized, double-blind, placebo-controlled study conducted across 19 sites in 7 countries. Thirty-two patients were enrolled between May 2019 and March 2021 (21 pegzilarginase, 11 placebo) as adjuncts to individualized disease management. The primary endpoint — change in plasma arginine at 24 weeks — showed a 76.7% relative reduction versus placebo (p < 0.0001). Geometric mean arginine decreased from 354.0 to 86.4 micromol/L with pegzilarginase versus 464.7 to 426.5 micromol/L with placebo. Normalization to guideline-recommended levels (50–150 micromol/L) was achieved in 90.5% of treated patients versus 0% in the placebo group. Gross Motor Function Measure part E improved by 4.2 points versus a decline of 0.4 points with placebo; 2-minute walk distance increased 7.3 meters (12.8%) versus 2.7 meters (4.1%). Guanidino compound levels fell 53–70%. Benefits were sustained through 48 weeks in the open-label extension.

Pegzilarginase received EU conditional marketing authorization in December 2023 and FDA accelerated approval on February 23, 2026, under the brand name Loargys. Post-marketing confirmatory studies to verify long-term clinical benefit are required as a condition of the accelerated approval.

The approved regimen for Loargys (pegzilarginase-nbln) in patients aged 2 years and older begins at 0.1 mg/kg administered as a once-weekly intravenous infusion over 30 minutes, diluted prior to administration. The permitted dosing range is 0.05 to 0.2 mg/kg per week; doses are individually titrated to achieve a target trough plasma arginine concentration of 50–150 micromol/L at the end of each weekly dosing interval.

After a minimum of 8 weeks of intravenous therapy, patients may transition to an equivalent-dose subcutaneous injection using the same weight-based regimen. The drug is supplied in single-dose vials at two concentrations: 2 mg per 0.4 mL and 5 mg per mL.

All administrations must occur in a healthcare setting equipped for cardiopulmonary resuscitation and hypersensitivity monitoring, particularly for initial doses. Pre-medication with antihistamines may be considered for patients with prior hypersensitivity events. Dietary protein restriction is co-required by the prescribing label and is not optional. Weekly dosing compliance exceeded 93% in the pivotal PEACE trial.

No specific dosage adjustments are described in the current label for renal or hepatic impairment, consistent with the drug's plasma-based rather than hepatic mechanism.

This information is provided for educational reference only and is not a substitute for individualized medical advice from a licensed healthcare provider experienced in metabolic disease management.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

Dietary protein restriction is the only combination with regulatory-level evidence; the FDA label explicitly co-requires it. By limiting dietary arginine intake, protein restriction complements the enzymatic depletion of circulating arginine and may reduce the enzyme dose required to achieve target levels. Arginine-free essential amino acid formula supplementation is standard clinical practice in ARG1-D to prevent nutritional deficiency under restricted dietary intake; this is routinely continued alongside pegzilarginase in clinical practice, though it has not been studied as an independent variable in controlled trials.

Nitrogen-scavenging agents — sodium phenylbutyrate and glycerol phenylbutyrate (Ravicti) — have been used historically in ARG1-D for hyperammonemic episodes, and some patients may continue them alongside pegzilarginase at clinician discretion. No published controlled data evaluate this specific combination; use is based on clinical practice and expert judgment (anecdotal). The prescribing label lists no known drug interactions with pegzilarginase, consistent with its plasma-based mechanism that does not involve hepatic cytochrome P450 metabolism.

Pegzilarginase-nbln is approved by the U.S. Food and Drug Administration for one or more clinical indications. Refer to the prescribing information for full safety and dosing details.

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The FDA prescribing label for Loargys carries a boxed warning for life-threatening hypersensitivity reactions, including anaphylaxis; all administrations must occur in a healthcare setting equipped for resuscitation. Across clinical development, hypersensitivity reactions were reported in 13% of Loargys-treated subjects (6 of 48). Among patients who developed anti-drug antibodies, the rate of hypersensitivity reactions rose to approximately 42%, versus approximately 3% in antibody-negative patients. Reported reactions were managed with antihistamines; epinephrine must be immediately available.

The most frequently reported adverse reactions (incidence greater than 10%) in clinical trials were vomiting, pyrexia, infusion-associated reactions, and constipation. Injection site reactions occurred in approximately 14% of patients receiving subcutaneous administration.

Anti-drug antibodies were detected in approximately 19% of pegzilarginase recipients in the PEACE trial; these were predominantly low-titer and transient, with no sustained clinical impact on efficacy. Hyperammonemic episodes occurred in 14.3% of pegzilarginase patients versus 36.4% of placebo patients in the 24-week double-blind period, suggesting treatment does not increase this risk compared to untreated disease.

No human data exist for use in pregnancy; animal studies at higher exposures demonstrated maternal toxicity and fetal growth deficiencies. Pediatric use is established for ages 2 and older; no data exist for children under 2 years or adults aged 65 and older. No formal contraindications are listed in the current prescribing information.