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How long does it take for Viltepso to work?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Feb 28, 2023.

Official answer


The length of time it takes for Viltepso (viltolarsen) to work in Duchenne muscular dystrophy (DMD) is still being evaluated in an ongoing study.

In small studies submitted to the FDA for Viltepso accelerated approval, dystrophin levels increased to about 6% of normal in patients receiving Viltepso (80 mg/kg/wk) compared to a 0.6% increase at baseline (the beginning of the study) after 20 to 24 weeks of treatment, a statistically significant effect. Researchers believe that this increase in dystrophin may predict clinical benefit in patients, but that is not yet proven.

Viltepso is given by a healthcare provider once every week by an intravenous, or IV infusion through a needle in the vein. The infusion takes about one hour.

Viltepso studies

Viltepso (viltolarsen) was approved in August 2020 under the FDA accelerated approval program. This program allows patients to use a promising new drug while the company that makes the medicine continues to study the drug to confirm that it works well. Continued approval for Viltepso may depend upon its benefits proven in these clinical research studies.

Viltepso is indicated for the treatment of Duchenne muscular dystrophy (DMD) in patients amenable to exon 53 skipping. When exons are missing, cells do not have the proper instructions to make dystrophin, which leads to a type of muscle damage that causes DMD. Viltepso is the first exon 53 skipping therapy to demonstrate an increase in dystrophin in children as young as four years old.

Approval was based on a “marker”, not an evaluation of clinical benefits. Studies showed an increase in dystrophin protein production in skeletal muscle observed in patients treated with Viltepso. Dystrophin helps to strengthen and protect muscles in patients with Duchenne muscular dystrophy (DMD).

For accelerated approval, researchers studied 16 patients aged four to less than 10 years of age.

  • In this study, 100% of patients (8 of 8) who received the recommended dose of Viltepso 80 mg/kg/wk showed an increase in dystrophin levels in muscle biopsies after treatment with Viltepso.
  • In 7 of 8 patients (88%), an increase of dystrophin levels of 3% of greater or greater than normal was demonstrated.
  • Overall, the increase in dystrophin ranged from 0.69% to 13.91% of normal, with a mean of 5.9%.

NS Pharma, the manufacturer of Viltepso, continues to study the safety and efficacy of Viltepso in the confirmatory Phase 3 RACER53 trial. This study was initiated in October 2019 and may still be enrolling patients. Speak with your healthcare provider about any ongoing clinical trials.

How does Viltepso work?

Viltepso works in Duchenne muscular dystrophy (DMD) by “hiding” exon 53, causing cells to bypass this exon and allowing the remaining exons (a portion of a gene) to fit together properly and form a shortened version of the dystrophin protein.

  • Duchenne muscular dystrophy (DMD) is caused by a genetic mutation to the dystrophin gene that results in missing exons (a portion of the gene).
  • When exons are missing, cells do not have the proper instructions to make dystrophin, which leads to a type of muscle damage that causes DMD.
  • Patients with a confirmed mutation of the DMD gene that is amenable to exon 53 skipping may be able to receive treatment with Viltepso.

Corticosteroid drugs such as Emflaza (deflazacort) may also be used to treat patients with Duchenne muscular dystrophy (DMD). These medicines are beneficial as they can help improve motor skills and walking, muscle strength, and breathing. They may also help to reduce the risk of curvature of the spine (scoliosis) and improve heart function and length of survival, although not all studies have found an association.

Learn more: Which medicines are used to treat Duchenne muscular dystrophy (DMD)?

Is there a cure for DMD?

No, there is no cure for Duchenne muscular dystrophy (DMD) at this time. DMD is a rare and fatal genetic disorder primarily affecting males, starting early childhood between the ages of 2 and 3 years of age.

Early signs of DMD may include delayed ability to sit, stand or walk. DMD results in progressive muscle weakness from early childhood and leads to premature death in the mid-twenties to thirties due to heart and lung failure.

It is estimated that about 10% of patients with DMD have a genetic mutation amenable to exon 53 skipping of the dystrophin gene, and about 13% of patients have a mutation amenable to exon 51 skipping.

This is not all the information you need to know about Viltepso (viltolarsen) for safe and effective use and does not take the place of talking to your doctor about your treatment. Review the full Viltepso information here, and discuss this information and any questions you have with your doctor or other health care provider.


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