The US Food and Drug Administration has granted a conditional approval to Sarepta's Exondys 51, the first drug cleared to treat patients with Duchenne muscular dystrophy (DMD).

Exondys 51 (eteplirsen) addresses the underlying cause of DMD by enabling the production of a functional dystrophin protein, and clinical studies have demonstrated a broadly favourable safety and tolerability profile as well as efficacy for the drug.

The injection is specifically indicated for patients who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping, which affects about 13 percent of the DMD population.

The FDA concluded that the data submitted by Sarepta demonstrated an increase in dystrophin production that is reasonably likely to predict clinical benefit in some patients with DMD who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping.

But it also stressed that a clinical benefit has not been established, and that Sarepta must conduct a further clinical trial to convert the conditional approval into a full one.

"Patients with a particular type of Duchenne muscular dystrophy will now have access to an approved treatment for this rare and devastating disease," said Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research. "Accelerated approval makes this drug available to patients based on initial data, but we eagerly await learning more about the efficacy of this drug through a confirmatory clinical trial that the company must conduct after approval."

"We will continue to leverage what we have learned from Exondys 51 to facilitate future development of potential new treatments targeting additional exons with the goal of one day treating all DMD patients amenable to exon skipping," the firm noted.

The FDA is also currently reviewing BioMarin's experimental DMD drug drisapersen in the same setting, on which it is expected to make a decision by the end of the year.