Updated with new information from 8:18 am EDT.

On Thursday, the U.S. Food and Drug Administration posted an updated but still negative clinical review of eteplirsen, the Duchenne muscular dystrophy drug from Sarepta Therapeutics (SRPT) - Get Sarepta Therapeutics, Inc. Report .

Sarepta shares recently fell 41% to $11.75 Thursday. The stock closed Wednesday at $19.71

The FDA is conducting an outside advisory panel on April 25 to review the eteplirsen data, postponed from Jan. 21 due to a snowstorm. But as in January, the internal assessment by the agency's review team appears to once again cast doubt on the drug's approval chances.

After the Jan. 21 panel postponement, Sarepta submitted new eteplirsen data and pointed out what it believed were errors in the FDA's original review. Thursday, the FDA did not change its opinion.

"... [W]e do not agree with the applicant's characterization of inaccuracies in the initial FDA briefing document," the FDA stated Thursday.

"Although FDA is prepared to be flexible with respect to a devastating illness with no treatment options, we cannot approve drugs for which substantial evidence of effectiveness has not been established," the FDA re-states in a summary of the eteplirsen medical review Thursday. This is the same statement made by the agency in January.

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Sarepta will get a chance on April 25 to rebut the FDA's criticism and present its own case for eteplirsen's approval. The company will be supported by a small army of DMD patients, their families and advocates expected to testify during an open public hearing portion of the advisory panel meeting. Christine McSherry, mother of a child with DMD and executive director of the Jett Foundation, a DMD advocacy group, will speak to the panel members during Sarepta's allowed presentation time.

Top FDA officials Janet Woodcock and Bob Temple are also scheduled to make presentations to the experts on the advisory panel, an unusual move but one that underscores the importance of Monday's hearing. 

In many ways, the FDA's eteplirsen review posted Friday is more negative than the one issued in January. The FDA rebuts, sometimes in sharply critical ways, Sarepta's claims the agency's original review was flawed. Most notably, the FDA is deeply skeptical of Sarepta's attempt to use a data from a retrospective, historical control study of DMD patients to demonstrate the efficacy of eteplirsen.

If Sarepta lacks clinical data to make a convincing case for eteplirsen's approval, it will fall back on the argument that eteplirsen is safe, therefore DMD patients and their families should be allowed to try the drug while an ongoing, confirmatory phase III study moves towards completion.

Two and half hours have been set aside on Monday for an open public hearing where DMD patients and their families are expected to urge the panel experts to recommend eteplirsen's approval. The testimony is likely to be emotional and may counteract the FDA's negative tone. 

I will be provide a live blog of the Sarepta FDA panel on Monday, which will run from 8 am to 6:30 pm EDT.

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; click here to send him an email.