FDA approves Sarepta’s disputed drug, overruling staff and advisers

Overruling its own staff and advisers, the Food and Drug Administration on Monday approved the first treatment for Duchenne muscular dystrophy, delivering a victory for families of hundreds of young boys with the deadly muscle-wasting disease and the drug’s developer, Cambridge’s Sarepta Pharmaceuticals Inc.

The decision, described by some stock analysts as virtually unprecedented, came after nine months of delays and a dispute within the FDA on the merits of the drug. It sent Sarepta’s stock soaring and stunned observers who had expected the agency to follow its staff and reject the drug.

Approval of the medicine, which will be sold under the brand name Exondys 51 starting as early as this fall, came after hundreds of patients and their families lobbied for a new approach, packing an emotionally charged FDA advisory committee meeting in April to clamor for Sarepta’s experimental treatment.

“These kids have hope now,” said Christine McSherry of Pembroke, whose 20-year-old son Jett benefitted from Sarepta’s treatment, called eteplirsen, in the clinical trial. “It’s wonderful for the next generation of kids with this terrible disease. It opens the door for more research and more treatments for Duchenne and other genetic diseases.”

Monday’s decision requires Sarepta to conduct a two-year study to confirm that its treatment can improve motor function in Duchenne patients losing the ability to stand and walk. Three earlier Duchenne drug candidates were rejected by the FDA.

Patient advocates argued for a new standard in considering proposed drugs for rare genetic disorders with no other treatments. They said the FDA should not require the same level of data generated in large-scale clinical trials of more common diseases.

Sarepta’s trial involved just 12 patients and didn’t include any patients taking a placebo. Trials for treatments of more common diseases often enroll hundreds of patients, with some given a drug and others a placebo so the two groups can be compared.

But the advocates’ hopes for Sarepta’s therapy appeared to be dashed last spring when the FDA’s advisory panel — made up of independent medical specialists — narrowly declined to recommend approval of eteplirsen.

“We had the feeling we were screaming for the life of these boys and no one could hear us,” said Debra Miller, founder of CureDuchenne of Newport Beach, Calif., one of three patient groups that helped fund Sarepta’s clinical trial. Miller, whose 19-year-old son Hawken suffers from Duchenne, said, “I’m hoping this is a new paradigm for the FDA where they’re actually looking at the patients themselves and not just the numbers on a paper.”

Sarepta’s drug, a weekly infusion, is the first approved medicine to treat the genetic cause of the disease rather than the symptoms. Duchenne strikes about one in 3,500 boys, who typically lose the ability to walk by age 12 and don’t live past age 25. Exondys 51 would treat about 13 percent of those boys, a subset with a gene mutation that makes them unable to produce a protein called dystrophin that can help bolster motor function.

In a conference call with stock analysts, Sarepta chief executive Edward Kaye said the FDA approval would enable the Cambridge company to move forward with other experimental medications for Duchenne and other rare genetic disorders.

“We are far from completing our mission of providing treatments for the vast majority of patients with Duchenne muscular dystrophy,” Kaye said. “Our work has just begun.”

Chief financial officer Sandy Mahatme said the company expects to charge an average price of $300,000 a year per patient for Exondys 51. Executives said they anticipated health insurers would reimburse most patients for the cost, which they described as being in the middle of the typical price range for rare genetic disease treatments.

Shares of Sarepta, an Oregon company that moved to Cambridge in 2012 and now has about 230 employees, surged nearly 74 percent to $48.94 on Monday.

FDA officials declined to discuss their ruling, or whether it might herald a more flexible approach to approving rare disease therapies.

In an unusual move, the agency released a memo from FDA commissioner Robert M. Califf detailing a scientific dispute between Janet Woodcock, director of the agency’s drug evaluation division, and Ellis Unger, whose team reviewed Sarepta’s experimental drug.

Both sides agreed Sarepta’s drug produced measurable increases in dystrophin, but disagreed on the clinical benefit. Califf ultimately sided with Woodcock, who called for “the greatest flexibility possible for FDA while remaining within its statutory framework,” the report said.

Experts were divided on the clinical effectiveness of eteplirsen. Some of the FDA’s staffers and independent authorities questioned the design and adequacy of Sarepta’s clinical study.

Sarepta’s stock was whipsawed in recent months amid speculation of an FDA rift. Division director Woodcock, who personally appeared at the advisory committee meeting in April, signaled her openness to an accelerated approval process for unmet medical need treatments in which “more uncertainty is going to be tolerated” than in conventional drug approvals.

Last week, Dr. Ronald Farkas, who supervised the FDA’s clinical review of eteplirsen and publically expressed doubts about Sarepta’s clinical study, resigned. That departure appeared to clear the way for the FDA’s accelerated approval.

“This decision is extremely unprecedented and follows major disputes among agency personnel regarding their interpretations of very limited . . . data,” biotech analyst Joseph Schwartz at the Boston health care investment bank Leerink Partners wrote in a note to investors. “Ultimately, it appears to us that the FDA bowed to external pressure from patient advocates and others who demanded that a safe and potentially efficacious drug be made available.”

Simos Simeonidis, an analyst with RBC Capital Markets in New York, called the FDA decision “a major game-changer for Sarepta,” suggesting the Cambridge company could now become “one of the most attractive [takeover] targets in biopharma” on the strength of its Duchenne drug and a pipeline of other rare disease compounds that work in a similar way.

Patient advocates had argued that failure to approve the drug could not only worsen life for Duchenne patients but also discourage biotech companies from developing drugs to treat other rare diseases.

McSherry of Pembroke, whose son Jett had been taking Sarepta’s drug in the clinical trial, said the FDA decision means “there’s no fear it can be taken away from him.” McSherry, however, said her excitement was tempered by the knowledge that many other boys with Duchenne lost motor function during the FDA’s long delay.

“It’s really hard for me to celebrate,” she said.

Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.