FDA staff unconvinced by Sarepta's muscle wasting drug

(Reuters) - U.S. Food and Drug Administration staff said they were unconvinced about the effectiveness of Sarepta Therapeutics Inc’s drug for a rare muscle wasting disorder, dealing another blow to the quest for a drug to treat the fatal disease.

More than half of Sarepta’s market value evaporated on Friday after the report, which comes a day after the FDA rejected BioMarin Pharmaceutical Inc’s rival drug Kyndrisa.

Sarepta’s drug, eteplirsen, is designed to treat a subset of patients with Duchenne muscular dystrophy (DMD), which hampers muscle movement and affects one in 3,600 newborn boys, with most patients dying by the age of 30.

There are no FDA-approved drugs for DMD, and pressure has been mounting on the U.S. regulator to swiftly approve treatments.

The negative review of Sarepta’s data was not entirely unexpected, given the unfavorable response to BioMarin’s application.

“We expected it to be bad, but not this bad,” Wedbush Securities analyst Heather Behanna told Reuters.

However, it’s not the end of the road for the treatment yet - the situation will become clearer after a panel to the FDA makes its recommendation on the drug on Jan. 22.

Sarepta’s eteplirsen, like Kyndrisa, skips a faulty section of the gene to produce dystrophin, the lack of which is believed to cause DMD.

FDA staff reviewers brought up concerns about Sarepta’s trial design, efficacy, dystrophin measurement methods, and statistical analysis.

Differences in DMD progression between eteplirsen patients and the natural course of the disease were “too small and variable ... to be reliably attributed to drug treatment”, they wrote.

Still, reviewers did not raise concerns with the safety profile of the drug. (

“I’m not writing the Sarepta drug off yet,” WBB Securities analyst Stephen Brozak told Reuters, highlighting previous FDA staff concerns about potentially fatal long-term side effects with BioMarin’s Kyndrisa.

Both drugs target the same subset of DMD patients, which translates into an addressable population of about 1,800 boys in the United States and about 5,000 outside, according to Behanna.

Friday’s documents only questioned the conclusiveness of Sarepta’s data but didn’t really question whether eteplirsen works, Behanna said, adding that in BioMarin’s case reviewers were unconvinced of Kyndrisa’s effectiveness.

“I think there’s still a chance (of approval), but a small chance,” the analyst said.

Shares of Sarepta, which has invested heavily in other DMD drugs targeting multiple mutations, plummeted 58 percent at $13.43 in heavy trading on Friday.

Reporting by Natalie Grover in Bengaluru; Editing by Saumyadeb Chakrabarty