Rare Disease Report

FDA Not Ready to Decide on Sarepta's Duchenne Drug

MAY 24, 2016
James Radke, PhD
You know that scene where a person in a wheelchair is waiting outside the handicapped bathroom stall while a non-handicapped person sits in the stall reading a magazine?

The FDA is not ready to make a decision about eteplirsen yet. Today, Sarepta Therapeutics announced that the FDA notified the company that they need more time to review the orphan drug eteplirsen for the treatment of patients with Duchenne muscular dystrophy amenable to exon 51 skipping therapy.
No date has been provided and the FDA has “communicated that they will continue to work past the PDUFA goal date (May 26th) and strive to complete their work in as timely a manner as possible.”
This is not the first delay that the FDA has announced for the review of this drug. Initially, there was an Advisory Committee Meeting scheduled for January 22 but that got delayed due to a snow storm that hit the Washington DC area. A month and a half later, the FDA announced the new meeting would take place April 25th.  During that meeting, a record 52 people spoke during the public forum in favor of the drug being approved while the FDA briefing documents for that meeting were highly critical of the data. The voting at that meeting was mixed with half the committee in favor of the drug and half of them not.

FDA has had the NDA since August 25, 2015. A normal review process for an orphan drug is 6 months.

The delay is a good thing?

In early morning trading, shares of Sarepta are up 22% which would imply that the delay in the review process is a good sign that the FDA is taking into account the patients’ testimonies rather than just focusing on the NDA data that the FDA has previously been critical of in their briefing documents.

Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by lack of a functional dystrophin protein, a protein that helps keep muscle cells intact. Patients with progressive muscle disorder experience symptoms in early childhood, losing the ability to walk as early as age 10. These patients, mostly boys, experience life-threatening heart and lung complications in their late teens and twenties.
There are many subsets of the DMD population based on the type of mutation found in the dystrophin gene. There are currently no drugs approved in the US to directly treat any of these groups.

The promise of eteplirsen and other exon skipping drugs

Eteplirsen is designed to enable RNA to skip over the part of the DNA with a problematic mutation, enabling a functional (though shorter) dystrophin protein to be produced. Specifically, the drug skips a portion of the DNA known as exon 51. About 13% of the 35,000 DMD patients in the US and Europe have a mutation that might theoretically respond to a drug such as eteplirsen. According to Sarepta, the drug’s developer, up to 80% of patients with DMD might respond to this class of drugs, others of which are in development.

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