3 Key Points From Sarepta's Eteplirsen Study Update (And They're Positive)

CAMBRIDGE, Mass. ( TheStreet) -- Three data points stand out for me from Sarepta Therapeutics ( SRPT) eteplirsen update of the phase II study in Duchenne muscular dystrophy:

1. The six boys treated with 30 mg and 50 mg of eteplirsen from the beginning of the study have demonstrated remarkable stability in walking performance. After 96 weeks, the distance walked over six minutes has declined by just 6.3 meters compared to baseline. I'm using mean values.

The 96-week data are no fluke: Here are the changes in six-minute walk distance from baseline for the eteplirsen-treated boys from weeks 74, 84 and 96: -2.2 meters, -9.2 meters, -6.3 meters.

2. The four boys in the study initially treated with a placebo and switched to eteplirsen at week 25 (the crossover group) are also showing stable walking ability now that the effect of the drug has kicked in.

The best way to see the benefit of eteplirsen in these patients is to compare six-minute walk test performance between week 74 and week 96. At week 74, these four boys walked 62.4 meters less than at baseline. At week 96, the drop in walking distance was 67.7 meters. Basically the same.

Why skip the comparison with the week 84 measurement? Because one of the boys in the crossover group broke his ankle and was unable to perform the six-minute walk test for the week 84 analysis, thereby skewing the mean walking performance higher. The mean drop in walking distance at week 84 was -43.2 meters. The boy's broken ankle healed and he was able to perform the six-minute walk test at week 96, so comparing results to week 74 (before the fracture) is a fairer comparison.

Multiple studies have shown DMD boys lose muscle function and the ability to walk over time. Yet these 10 boys treated with eteplirsen are showing a continued stability in walking ability going on almost two years. This is a very impressive result. Two explanations: Eteplirsen is working or Sarepta lucked into selecting 10 boys for its phase II study who happened to have some of the slowest-progressing DMD in history.

3. Eteplirsen's safety record continues to sparkle, with no clinically significant adverse events related to drug, no treatment discontinuations, no hospitalizations. The risk-benefit balance for eteplirsen is helped considerably by what looks like very little of the former.

Sarepta will be presenting these 96-week data at the World Muscle Society meeting next month. This is the same venue where GlaxoSmithKline ( GSK) and Prosensa ( RNA) will present the data from the failed phase III study of drisapersen.

-- Reported by Adam Feuerstein in Boston.

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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.

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