Sarepta's Next Step: Early FDA Approval

BOSTON ( TheStreet) -- Some additional thoughts and observations on Sarepta Therapeutics ( SRPT) and the outstanding results from the eteplirsen study in Duchenne muscular dystrophy announced today.

Sarepta shares are up $16.82, or 112%, to $31.81. Well deserved.

I wrote the following last month when previewing the 48-week results:

"Positive results will show a continuation of the slower decline (stabilization) in 6MWT performance for the patients in the original 50 mg eteplirsen group. If these patients actually improve on the 6MWT at 48 weeks compared to 36 weeks, it's a home run."

Today's data were not only a home run, they were a grand slam. The 50 mg eteplirsen group actually improved walking distance over baseline. Incredible! The 6MWT results for these four boys increased from -12 meters at 36 weeks to +21 meters at 48 weeks. This is an unprecedented result for DMD patients because current treatments at best only slow the progression of disease.

Equally as stunning were the results from the group of patients who started on placebo then switched to eteplirsen after 24 weeks. I wrote this in my preview:

"Likewise, stabilization or slowing declines in 6MWT performance for the placebo/delayed treatment group would also be positive. Remember, these patients were on placebo for 24 weeks before switching to eteplirsen. It would be great to see improvements in walking ability coming after 24 weeks of eteplirsen therapy."

Sure enough, we saw an improvement in walking ability from 36 to 48 weeks of about 10 meters. Again, remarkable because the slope of the 6MWT curve changed direction. On this morning's conference call, we learned that three of the four patients in the placebo/delayed treatment group showed "stabilization" at 48 weeks, meaning a change of +/- 10 meters on the 6MWT.

Can Sarepta make a convincing argument in front of FDA to grant early, accelerated approval of eteplirsen based on this tiny phase II study?

I say yes, although not easy even with Wednesday's stellar data. Being able to tie significant increases in dystrophin production to improved walking ability will be a big help. The FDA's new mandate to accelerate approval of new drugs for rare diseases works in Sarepta's favor, as will intense lobbying from DMD patients and their advocates. Can you imagine the phone calls and letters FDA will receive from DMD patients after today?

On the negative side, you can't dismiss the risk that comes from a tiny study of just 12 patients. The data are not pristine -- remember the two patients in the 30 mg eteplirsen dose who were excluded from the analysis because they experienced rapid declines in walking ability. FDA may simply conclude that more clinical data is needed for approval.

Manufacturing could be an issue. It's something investors often overlook but remember FDA can't approve a drug unless reliable manufacturing at commercial scale is in place. Sarepta is right now working on ramping up its eteplirsen manufacturing capacity but this process takes time. If there are delays in manufacturing scale-up, approval could be delayed.

Sarepta does face competition from a similar drug developed by GlaxoSmithKline ( GSK) and a partner in a phase III study. We should see results from this study relatively soon. A key question will be safety. The Glaxo DMD drug has shown some evidence of kidney toxicity in the past. If that persists, Sarepta's eteplirsen could be deemed superior.

Are there unresolved risks to the Sarepta story? Sure. Are these risks small next to the stellar eteplirsen data announced Wednesday and the $400-500 million market opportunity for the drug in the U.S.? Absolutely.

-- Reported by Adam Feuerstein in Boston.

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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