Prepare now for the most epic, two-day FDA advisory panel sometime in the middle of 2015: Prosensa (RNA) and Sarepta Therapeutics (SRPT) - Get Report with their respective and competitive exon 51-skipping therapies against Duchenne muscular dystrophy (DMD). There will be live blogging. 

As expected, Prosensa announced Tuesday that it will seek accelerated approval for drisapersen in the U.S. A filing will be submitted "later this year," the company said. Prosensa is also moving forward with plans to seek European approval for drisapersen, which was also expected after regulators there granted conditional approval to PTC Therapeutics' (PTCT) - Get Report DMD drug Translarna

In April, Sarepta made a similar announcement about its intention to seek FDA approval for eteplirsen by year's end. 

The dueling Prosensa and Sarepta FDA filings almost guarantee a mid-2015 advisory panel where experts will review both drugs and vote on approval recommendations. 

As part of its FDA filing strategy, Prosensa says it will also start two confirmatory, post-approval clinical trials of drisapersen. Here's an excerpt from this morning's Prosensa announcement:

The FDA has outlined the following approaches for confirmatory trials, which the Company is urged to initiate both as soon as possible, as quoted from the guidance letter:

1. "A historically-controlled trial might be acceptable to confirm clinical benefit following accelerated approval. We note that a historically-controlled study is likely to provide interpretable evidence of efficacy only if the beneficial effect of drisapersen is large, by clearly showing that performance is better in drisapersen-treated subjects than could be reasonably expected, based on knowledge of the natural history of the disease. The effect size would have to be sufficient to overcome the uncertainty inherent in historically controlled trials, and motivational factors that can affect the results.

2. A randomized, placebo-controlled trial of another exon-skipping drug with a similar mechanism of action, directed at a different exon (e.g., PRO044 or PRO045), with demonstration of a correlation between dystrophin protein production and definitive clinical benefit on 6-minute walk or another measure, could provide confirmatory evidence of drisapersen's clinical benefit if approval were based on a surrogate endpoint."

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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