The Food and Drug Administration (FDA) has approved Exondys 51 (eteplirsen; Sarepta) injection, the first treatment approved for patients with Duchenne muscular dystrophy (DMD). It is specifically intended for patients who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping.

DMD is a rare genetic disorder caused by an absence of the protein dystrophin, which helps keep muscle cells intact. Initial symptoms are usually observed between 3–5 years of age and worsen over time. 

The accelerated approval for Exondys 51 was based on the surrogate endpoint of dystrophin increase in skeletal muscle seen in some patients treated with Exondys 51. The FDA determined that the data showed an increase in dystrophin production that is reasonably likely to predict clinical benefit in some patients with DMD with a confirmed mutation of the dystrophin gene amenable to exon 51 skipping. The most common side effects reported by patients taking Exondys 51 in the clinical trials were balance disorder and vomiting. 

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As part of the accelerated approval provisions, the Company is required to conduct a clinical trial to confirm the drug’s clinical benefit. The study is intended to assess whether Exondys 51 improves motor function of DMD patients with a confirmed mutation of the dystrophin gene amenable to 51 skipping. 

Exondys 51 was granted fast track designation, priority review, and orphan drug designation. Sarepta was also issued a rare pediatric disease priority review voucher. 

“Patients with a particular type of Duchenne muscular dystrophy will now have access to an approved treatment for this rare and devastating disease,” said Janet Woodcock, M.D., director of the FDA’s Center for Drug Evaluation and Research. “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. 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.” 

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