UPDATE 3-Sarepta's new Duchenne drug outperforms bestseller Exondys in trial

(Adds share movement in paragraph 5, analyst comment in paragraph 6, adverse event in paragraph 7)

By Christy Santhosh

Jan 29 (Reuters) - Sarepta Therapeutics said on Monday its new experimental drug for Duchenne muscular dystrophy (DMD) was far more effective in increasing levels of a key protein than its bestselling medicine Exondys 51.

DMD is a genetic muscle wasting disorder that affects an estimated one-in-3,500 male births worldwide, and most patients lack the protein dystrophin which keeps muscles intact.

The drug SRP-5051 and Exondys 51 both belong to a class of "exon-skipping" therapies, which work by skipping specific parts of genes, called exons, helping the body make shorter forms of dystrophin. Both drugs are given to specific patients who can be treated by skipping exon 51.

Sarepta said the new drug, when given every four weeks, showed an over 12-fold increase in dystrophin expression and a nearly 25-fold increase in exon skipping after 28 weeks compared to weekly dosing of Exondys 51.

Shares of the company were up 2% in early trade.

Leerink Partners analyst Joseph Schwartz said the 5.17% mean dystrophin expression seen in the mid-stage trial with the drug cleared the 5% bar set by the company's management, but raised concern about its safety.

Seven serious adverse events were reported in the 20-patient trial, of which four patients had low levels of magnesium and three had low potassium levels.

Exondys 51 was Sarepta's biggest product, generating revenue of $409.6 million in the first nine months of 2023.

The company's portfolio also consists of two more DMD drugs, Vyondys and Amondys, which are used to treat patients by skipping exon 53 and 45, respectively.

The company also secured the U.S. Food and Drug Administration's accelerated approval in June last year for a gene-therapy to treat four to five-year olds with DMD. It is currently awaiting full approval for the therapy.

Based on results from the trial for SRP-5051, Sarepta has requested for a meeting with the FDA which is expected to occur in the third quarter of 2024. (Reporting by Leroy Leo and Christy Santhosh in Bengaluru; Editing by Shailesh Kuber)