Viltolarsen Approved for Duchenne Muscular Dystrophy Treatment


The drug is indicated in patients with a confirmed mutation in the DMD gene that is amenable to exon 53 skipping.

The US FDA has approved viltolarsen (Viltepso; NS Pharma) for the treatment of patients with Duchenne muscular dystrophy (DMD) amenable to exon 53 skipping — only the second FDA-approved therapy for this specific DMD gene mutation that affects 8% to 10% of patients with DMD.1

The agent from NS Pharma, delivered via weekly intravenous infusion, was granted accelerated approval via its priority review, fast track, orphan drug, and rare disease designations after its new drug application was accepted earlier this year.2 In March, NS Pharma launched an expanded access program for qualified patients.3

The approval was granted based on findings from a phase 2 clinical trial (NCT02740972) and long-term extension study, details of which were recently published in JAMA Neurology.4 Among 16 participants age 4 to 9, significant drug-induced dystrophin production was observed in both viltolarsen dose cohorts (40 mg/kg per week: mean, 5.7% [range, 3.2—10.3] of normal; 80 mg/kg per week: mean, 5.9% [range, 1.1–14.4] of normal), with 15 (94%) patients achieving dystrophin levels greater than 2% of normal and 14 of 16 (88%) achieving levels greater than 3% of normal.

When compared with natural history controls (n = 65) at 25 weeks, patients treated in the study demonstrated significant improvements in various timed function testes, including time to stand from supine (viltolarsen: —0.19 s; control: 0.66 s), time to run/walk 10 m (viltolarsen: 0.23 m/s; control: –0.04 m/s), and 6-minute walk test (viltolarsen: 28.9 m; control: –65.3 m).

Notably, viltolarsen was generally well-tolerated with no treatment-emergent adverse events (TEAEs) requiring dose reduction, treatment interruption, or treatment discontinuation. The most common AEs observed were upper respiratory tract infection, injection site reaction, cough, and fever. No serious TEAEs or deaths occurred. No kidney toxicity has been observed in trials of viltolarsen; however, this has been observed in administration of other antisense oligonucleotides, and therefore patients’ kidney function should be monitored.

Although the observed increase in dystrophin production associated with treatment with viltolarsen is reasonably likely to predict a clinical benefit in this patient population, a confirmed clinical benefit of this drug has not been established. As part of its accelerated approval, the FDA will require that NS Pharma conduct a confirmatory clinical trial to show that treatment with the drug improves time to stand in patients with DMD amenable to exon 53 skipping.

In this recent NeurologyLive Insights series, neuromuscular disorder experts Crystal Proud, MD, Emma Ciafaloni, MD, and Amy Harper, MD, provide a review of the latest data on viltolarsen in DMD. Watch below.


1. FDA approves targeted treatment for rare duchenne muscular dystrophy mutation. News release. US Food and Drug Administration. August 12, 2020. Accessed August 12, 2020.

2. NDA accepted for filing by the FDA for antisense oligonucleotide viltolarsen (NS-065/NCNP-01). News release. Nippon Shinyaku. February 7, 2020. Accessed February 13, 2020.

3. Expanded access program launched for viltolarsen, an investigational exon 53 skipping antisense oligonucleotide. News release. NS Pharma. March 9, 2020. Accessed March 23, 2020.

4. Clemens PR, Rao VK, Connolly AM, et al. Safety, tolerability, and efficacy of viltolarsen in boys with duchenne muscular dystrophy amenable to exon 53 skipping: a phase 2 randomized clinical trial. JAMA Neurol. 2020;77(8):982—991. doi:10.1001/jamaneurol.2020.1264

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