The Food and Drug Administration (FDA) has granted accelerated approval to Viltepso (viltolarsen; NS Pharma) for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 53 skipping.

Viltolarsen is an antisense oligonucleotide of the phosphorodiamidate morpholino oligomers (PMO) subclass. It is designed to bind to exon 53 of dystrophin pre-mRNA resulting in exclusion of this exon during mRNA processing in patients with genetic mutations that are amenable to exon 53 skipping. Exon 53 skipping is intended to allow for production of an internally truncated dystrophin protein in patients with genetic mutations that are amenable to exon 53 skipping.

Viltolarsen was evaluated in 2 clinical studies in a total of 32 male patients with genetically confirmed DMD. The accelerated approval was based on 1 of these studies, a 2-period, dose-finding phase 2 trial that included 16 male patients aged 4 to less than 10 years. Patients received either viltolarsen 40mg/kg or 80mg/kg once weekly for 20 weeks. The primary end point was the change from baseline in dystrophin protein level (measured by % of the dystrophin level in healthy subjects, ie, % of normal) at week 25.

Findings from the study showed that patients treated with viltolarsen 80mg/kg (n=8) achieved an average increase in dystrophin levels from 0.6% of normal at baseline to 5.9% of normal at week 25, with a mean change of dystrophin of 5.3% of normal levels (P =.01), as assessed by validated Western blot. Additionally, viltolarsen 80mg/kg was associated with an increase in dystrophin levels in all patients (100%) and 7 patients (88%) had dystrophin levels of ≥3% of normal.

Based on these findings, the FDA concluded that the increase in dystrophin production was “reasonably likely to predict clinical benefit in patients with DMD who have confirmed mutation of the dystrophin gene amenable to exon 53 skipping.” Continued approval of Viltepso may be contingent on confirmation of its clinical benefit in the phase 3 RACER53 trial, which will assess whether the treatment improves the time to stand for DMD patients with this confirmed mutation.

With regard to safety, the most common adverse reactions were upper respiratory tract infection, injection site reaction, cough, and fever. Additionally, kidney function should be monitored in patients treated with Viltepso; although kidney toxicity was not observed in clinical trials, it has been observed after administration of viltolarsen based on animal data. 

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Viltepso is supplied in a single-dose vial containing 250mg of viltolarsen per 5mL (50mg/mL). The treatment is administered once weekly as a 60-minute intravenous infusion.

Viltepso is expected to be available within the next 2 to 3 weeks.

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  1. FDA approves targeted treatment for rare Duchenne Muscular Dystrophy mutation. Accessed August 12, 2020. 
  2. NS Pharma’s Viltepso™ (viltolarsen) injection now FDA-approved in the US for the treatment of Duchenne muscular dystrophy in patients amenable to exon 53 skipping therapy. Accessed August 12, 2020.
  3. Viltepso [package insert]. Paramus, NJ: NS Pharma; 2020.