Onasemnogene abeparvovec

Mechanism of action

Onasemnogene abeparvovec is an adeno-associated virus vector carrying a fully functional copy of the human SMN gene. After a single intravenous infusion, the vector reaches motor neurons and the new gene makes SMN protein, replacing what the mutated SMN1 genes cannot produce. With enough SMN, motor neurons survive, which improves movement, motor milestones and survival in infantile-onset SMA.

1. A single intravenous infusion of the viral vector
2. The vector delivers a working SMN gene into motor neurons
3. Motor neurons make their own SMN protein
4. Motor neurons survive: better movement and survival

Indications

• Spinal muscular atrophy (SMN1 mutations) in children less than two years old, with genetic confirmation Spinal muscular atrophy →

Adverse effects

Common

• Raised liver enzymes
• Vomiting
• Infusion reactions: hives, itching, rash, fast heartbeat, fast breathing

Contraindications

• Hypersensitivity to the product or any of its components

Key interactions

Vaccines during the corticosteroid course

Some vaccines are contraindicated at immunosuppressive steroid doses; the vaccination schedule is adjusted with the treating team.

What is monitored

• Liver function tests before the infusion and for at least three months afterwards
• Platelet count and signs of bleeding
• Vital signs during and after the infusion
• Signs of infection, which can make adverse reactions worse

Administration and safety

• A single intravenous infusion given by a doctor or nurse in a health-care setting, with monitoring during and after.
• A corticosteroid is started the day before and continued for at least a month afterwards to protect the liver.
• Genetic testing confirms eligibility beforehand; age-appropriate vaccines are reviewed before treatment.
• For a month after the infusion, carers wash their hands after contact with body fluids or waste and discard soiled materials in sealed bags.

Pregnancy and breastfeeding

It is given to infants and young children; pregnancy data do not apply to its use.

Nursing care

• Check baseline liver tests, platelets and kidney and heart history before the infusion.
• Watch for hives, vomiting, tachycardia or fast breathing during the infusion.
• Teach carers to give every corticosteroid dose and to report jaundice, dark urine, drowsiness or bruising.
• Teach hand hygiene and safe disposal of nappies and soiled materials.

Pharmacokinetics

Absorption

A single intravenous infusion; the dose is based on body weight.

Elimination

Vector shed in body fluids and waste for a period after the infusion.

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Connections

← Back to the class: Spinal muscular atrophy (SMA) therapies

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Onasemnogene abeparvovec-xioi Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); FDA approves innovative gene therapy to treat pediatric patients with spinal muscular atrophy, a rare disease and leading genetic cause of infant mortality (U.S. Food and Drug Administration, 2019); Spinal muscular atrophy: MedlinePlus Genetics (MedlinePlus Genetics (U.S. National Library of Medicine), 2018); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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