Sarepta Fans: A Single Data Slide Raises Questions About Glaxo's DMD Drug

NEW YORK ( TheStreet) -- I spent a lot of time last night examining the efficacy curves depicted in the photo posted above. This is the money shot from Thursday's presentation by GlaxoSmithKline ( GSK) of the first placebo-controlled data on its Duchenne muscular dystrophy (DMD) drug drisapersen. I trekked out to idyllic Cold Spring Harbor Laboratories, along with a sizable contingent from Wall Street, to scrutinize the drisapersen data first hand.

Not surprisingly, we were all really there because of the intense investor interest in Sarepta Therapeutics ( SRPT) and its competing DMD drug eteplirsen. Sarepta folks, including CEO Chris Garabedian, attended the drisapersen presentation, too.

Let's examine the data contained in the slide above to see what it tells us about drisapersen, and perhaps eteplirsen as well.

The curves represent results of the six-minute walk test over time. Look at the green line. These are the 18 DMD patients treated with continuous drisapersen. From Day 1 of the study through week 13 and week 25, these patients walk further in six minutes than they did at baseline. The green line goes up to the right. That's a positive result.

Now, compare the green line to the blue line, which represents 18 DMD patients treated with a placebo. From Day 1 through week 13, the blue line is flat, then declines slightly to week 25. These patients can't walk as far in six minutes than they did at baseline.

The difference in walking ability at week 25 between the patients treated with continuous drisapersen and placebo is 35 meters, which was statistically significant, meeting the primary endpoint of the study. These are the data that support drisapersen's benefit to DMD patients.

Or, perhaps not.

Glaxo conducted this placebo-controlled study of drisapersen under blinded conditions, meaning patients were not supposed to know if they were being treated with drug or placebo. In reality, the study was not blinded because the drisapersen injection is very painful. Talk to parents of boys in the study (as I have) and they'll tell you they knew if their kids were on drisapersen or placebo from the first day of the study.

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