The U.S. Food and Drug Administration (FDA) has approved apitegromab-mstn (Isembyld) for adults and children ages 2 and older with spinal muscular atrophy (SMA) who are already receiving a survival motor neuron 2 (SMN2)-targeted treatment.

Isembyld is the first FDA-approved SMA therapy designed to directly target muscle loss while working alongside existing treatments. In clinical trials, 1 in 3 people who took the treatment for about a year saw improvements in motor function.

The approval gives some people with SMA another treatment strategy to discuss with their healthcare team.

🗳️ How satisfied are you with your (or your child’s) current SMA treatment plan?

Very satisfied

Somewhat satisfied

Somewhat dissatisfied

Very dissatisfied

Thanks! You've successfully submitted your vote.

Sign up to view the results!

Continue with Facebook

Continue with Google

Continue with Email

By joining, you accept our Terms of Use, and acknowledge our collection, sharing, and use of your data in accordance with our Health Data and Privacy policies.

Already a member? Log In

What Did the Clinical Trial Show?

The FDA’s decision was supported by a yearlong trial. The study included 188 people ages 2 to 21 living with later-onset type 2 or type 3 SMA who were unable to walk. Each participant was already receiving an approved SMN2-targeted treatment, either nusinersen or risdiplam.

Participants received Isembyld or a placebo (inactive treatment) by IV infusion every four weeks for about one year.

The primary analysis focused on 156 children ages 2 to 12. Researchers measured motor function using the Hammersmith Functional Motor Scale Expanded (HFMSE). The HFMSE is a 33-item assessment that measures abilities such as sitting, standing, walking, and other movements used in daily life.

At the approved dose, 34.2 percent of children had at least a three-point improvement in their HFMSE score, compared with 13.5 percent of children who received a placebo — about 1 in 3 versus about 1 in 7.

What Are the Possible Side Effects?

As with any medication, Isembyld may cause side effects. The most common ones include:

The prescribing information warns that bone fractures may occur with or without a fall or other injury.

It’s important to discuss all potential side effects and drug interactions with a healthcare provider before starting a new treatment.

Why Does This Approval Matter for People With SMA?

Current SMA treatments have improved outcomes, but some people continue to have significant movement limitations. Isembyld adds a muscle-targeted approach to treatments that address the motor neuron component of SMA.

If you or your child living with SMA isn’t seeing the benefits you’d hoped for from your current treatment plan, speak with your healthcare provider. Together, you can discuss other treatment options.