Zolgensma (onasemnogene abeparvovec-xioi) is a brand-name drug prescribed for spinal muscular atrophy in certain children. Zolgensma comes as a liquid suspension for intravenous (IV) infusion. It’s given by a healthcare professional as a single dose.

Zolgensma is a biologic medication and belongs to a drug class called gene therapy. (The reason “-xioi” appears at the end of the drug’s name is to show it’s distinct from similar medications that may be created in the future. Zolgensma is not available in a biosimilar version.)

Zolgensma is approved by the Food and Drug Administration (FDA) to treat spinal muscular atrophy (SMA) caused by changes in the SMN1 gene in certain children ages 2 years and younger.

Keep reading for specific information about the dosage of Zolgensma, including its strength and how the medication is given. For a comprehensive look at Zolgensma, including its limitations of use, see this article.

Note: This article describes the typical dosage of Zolgensma provided by the drug’s manufacturer. However, your child’s doctor will prescribe the Zolgensma dosage that’s right for them.

The information below is about the recommended dosage of Zolgensma.

Zolgensma form

Zolgensma comes as a liquid suspension that’s given as an IV infusion. It’s always given by a healthcare professional.

Zolgensma strength

Zolgensma comes in one strength of 2 x 1013 vector genomes (vg) per milliliter (mL).

Zolgensma contains a functional copy of the SMN1 gene in a virus vector. The unit of measure (vg per mL) indicates the number of viral vector particles in each milliliter of the drug.

Typical dosage

The following information describes the dosage that’s commonly prescribed or recommended.

Dosage for SMA

Zolgensma is prescribed to treat SMA in certain children ages 2 years and younger. The dosage is based on the child’s body weight in kilograms (kg). For reference, 1 kg equals about 2.2 pounds (lb).

The typical dose of Zolgensma is 1.1 x 1014 vg per kg of body weight and will be calculated by your child’s doctor. Your child will receive only one dose of the drug.

Talk with your child’s doctor if you have questions about their dosage.

How Zolgensma is administered

Your child’s doctor or another healthcare professional will give the IV infusion of Zolgensma. They’ll infuse the drug into a vein in your child’s arm or leg.

You’ll likely go to an infusion center or a hospital for your child to receive the infusion. The infusion takes about 60 minutes.

To help reduce the risk of liver injury, your child will take a corticosteroid starting 1 day before their infusion and for at least 30 days after the dose is administered.

Note that Zolgensma has a boxed warning about the risk of serious liver damage. A boxed warning is the most serious warning from the FDA. For details, see “Boxed warning: Serious liver damage” at the top of this article.

If you have questions about how Zolgensma is given, talk with your child’s doctor or pharmacist.

Long-term treatment

Zolgensma is given as a one-time infusion and is meant to be a long-term treatment for SMA. Clinical trials haven’t looked at the drug’s effectiveness with more than one dose. For more information, see the Zolgensma prescribing information.

Talk with your child’s doctor if you have questions about what to expect with Zolgensma treatment.


It’s important to read the Zolgensma label and other paperwork that may come with the drug. This may also be referred to as the medication guide or patient package insert. If your doctor doesn’t provide the paperwork before the infusion appointment, you can ask them to print a copy.

If you need help reading or understanding this information, ask your doctor or a pharmacist. For example, some pharmacies offer labels with large print, braille, or a code you scan with a smartphone to convert text to speech.

Below are some frequently asked questions about Zolgensma.

How long does it take for Zolgensma to start working?

Zolgensma starts to work after your child receives their dose. In clinical trials, improvement in SMA symptoms was assessed based on the child’s development as they aged. Improvements were seen as early as 9 months old.

The doctor will monitor your child during treatment to check whether the drug is working to treat their condition.

Talk with your child’s doctor if you have questions about what to expect with Zolgensma treatment. You can also refer to this article about SMA gene therapy.

Can my child receive a second dose of Zolgensma?

No, Zolgensma is given as a single dose. Clinical trials of Zolgensma haven’t looked at the safety or effectiveness of a second dose. The medication is designed to work as a long-term treatment for SMA. A study from 2021 has shown Zolgensma may work beyond 5 years.

Talk with your child’s doctor if you have questions about Zolgensma’s dosage.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.