FILE PHOTO: A sign marks the offices of Sarepta Therapeutics in Cambridge, Massachusetts, U.S., July 22, 2025. REUTERS/Brian Snyder/File Photo

(Reuters) -Sarepta Therapeutics' shares plunged nearly 40% in premarket trading on Tuesday as failure of two of its approved drugs for a muscle wasting disorder in a key trial raised concerns about the strength of the company's portfolio.

The latest setback compounds Sarepta's woes as it is already facing intense scrutiny over its top-selling gene therapy, Elevidys, following deaths of two patients earlier this year. The company's stock has lost about 80% of its value this year.

Sarepta was testing its therapies, Amondys 45 and Vyondys 53, in a trial aimed at seeking confirmation of their effectiveness in treating Duchenne muscular dystrophy. Confirmatory trials such as these are considered key part of regulatory submissions for a full approval of drugs.

DMD is a rare disorder that typically affects boys, causing skeletal and heart muscle weakness that quickly gets worse with time.

Sarepta, a specialist in DMD treatments, attributed the trial's failure to dose interruptions during the COVID-19 pandemic.

"It is certainly believable that dose interruptions diluted the effect size, but the fact remains that the results from this post-hoc analysis are also not especially compelling," said Bernstein analyst William Pickering.

Sarepta plans to meet with the U.S. Food and Drug Administration to discuss converting the drugs' current accelerated approvals into full approvals, the company said.

While analysts noted the trial miss was not entirely unexpected, they warned it could further cloud the outlook for Sarepta's base business and increase regulatory, payer, and physician scrutiny.

(Reporting by Mariam Sunny and Joel Jose in Bengaluru; Editing by Saumyadeb Chakrabarty and Leroy Leo)