Since NS Pharma launched its Duchenne muscular dystrophy (DMD) drug Viltepso (viltolarsen) in 2020, sales have steadily trended upward, with the company expecting the treatment to generate 20,100 trillion Japanese yen ($128 million) this year.
But the regulatory status of Viltepso may soon be in jeopardy as preliminary results from a confirmatory trial show that it has failed to reach its primary endpoint. In the study of 77 boys, while Viltepso allowed patients to stand faster after 48 weeks of treatment, those in the control group also showed increased velocity in rising to their feet. There was no significant statistical difference between the study groups.
“We are currently conducting further detailed analyses and identifying factors that may have influenced the results,” NS Pharma CEO Tsugio Tanaka said in a release. “Considering the results of prior clinical studies, we have confidence that viltolarsen can be a beneficial treatment for amenable patients with Duchenne.”
New Jersey-based NS Pharma—which is a subsidiary of Japan’s Nippon Shinyaku—said it is investigating the age of the participants, the treatment period and the effect of concomitant drugs including glucocorticoid therapy, which may have influenced the study.
In August of 2020, the FDA granted Viltepso accelerated approval for patients with DMD amenable with exon 53 skipping. The nod was based in part on the results of a phase 2, open-label, long-term extension study of 16 participants between the ages of 4 and 10. After 205 weeks of treatment with viltolarsen, the patients showed statistically significant improvement in their time to stand compared to a historical control group of patients matched for key factors.
Another factor that played into the approval was that patients in two trials showed that viltolarsen provided an increase in dystrophin levels. DMD is a genetic disorder that prevents the production of dystrophin protein, which is crucial to muscle function.
Basing approvals on biomarker data has gotten the FDA in hot water before, including in the DMD field.
Sarepta's FDA approvals for Vyondys 53 and sister med Exondys 51 fueled concerns for some pharma watchers because the company lacked evidence to show that the drugs could actually improve symptoms or fend off disease progression. In both cases, the FDA approved the drugs based on the drugs' ability to spark dystrophin production.
The agency’s own reviewers recommended against approval of Exondys 51, and an FDA panel of independent experts narrowly voted against approval. But the agency approved it anyway, creating a dramatic scene where internal disagreement among FDA staffers led to some high-profile departures. Vyondys 53 was initially rejected, but after the company disputed the FDA's complete response letter, the agency changed its mind.