Sarepta Therapeutics ($SRPT) was up by about 75% in early trading on news that its Duchenne muscular dystrophy (DMD) treatment Exondys 51 (eteplirsen) has been approved by the U.S. Food and Drug Administration. The controversial drug faced multiple delays with the agency along the way due to efficacy concerns.
Shares quickly fell back to a gain of around 50% only to surge again as investors digested the terms of the FDA’s accelerated approval, which requires a confirmatory clinical trial to demonstrate efficacy. The agency is requiring an additional two-year randomized, controlled trial of eteplirsen; it’s slated to be dose-ranging from the approved dose of 30 mg/kg weekly up to a much higher dosage of 30 mg/kg daily.
The injection is approved specifically for DMD patients with a mutation of the dystrophin gene amenable to exon 51 skipping, which affects about 13% of the population.
The confirmatory trial will be in that specific population with a primary endpoint based on the North Star Ambulatory Assessment, with a secondary endpoint of dystrophin levels as a percent of normal as determined by a tissue biopsy.
The FDA concluded that the existing data based on skeletal muscle biopsy demonstrated an increase in dystrophin production; it then said this is “reasonably likely to predict clinical benefit in some patients.” But it added decisively that any clinical benefit, including improved motor function, has not been established.
“Patients with a particular type of Duchenne muscular dystrophy will now have access to an approved treatment for this rare and devastating disease,” said Dr. Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research, in a statement. “In rare diseases, new drug development is especially challenging due to the small numbers of people affected by each disease and the lack of medical understanding of many disorders.”
She added, “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.”
Sarepta is slated to submit a draft protocol for the upcoming trial in October with a final protocol submission due in April 2017. The trial is slated to complete in November 2020 with final data due by May 2021, according to the approval letter.
The rare genetic disorder DMD is characterized by progressive muscle deterioration and weakness; it occurs in one out of about every 3,600 male infants worldwide. DMD patients are typically wheelchair-bound by their early teens and often die in their 20s or 30s.
The accelerated approval process was beset by myriad delays throughout this year as the FDA weighed how to proceed with this potential treatment that lacked compelling efficacy data, but seems to offer some potential in this terrible disease that previously had no approved treatment.