If the quick and steep decline in the walking ability of the Sarepta placebo patients is an anomaly, FDA may decide that another clinical study of eteplirsen is needed before the drug can be approved.

Fortunately for Sarepta, it's entirely possible (perhaps even probable) that both sets of placebo data are real.

Glaxo enrolled DMD patients with a mean age of 7 years. Some kids in the study were as young as 5 years old. Their baseline walking ability was also relatively strong. Younger, healthier DMD patients walk better, which could easily explain the stable walking ability of the placebo patients.

By contrast, the DMD patients enrolled in the eteplirsen study averaged 8-9 years and entered with more advanced disease. DMD kids like these are expected to show more rapid declines in walking ability.

Lastly, let's look at drisapersen's safety. Seventy percent of drisapersen-treated patients reported renal toxicity in the study. This is a hint at the more serious treatment discontinuations and hospitalizations that we know occurred among drisapersen-treated patients in the larger phase III study. These data underscore what looks like an important advantage for Sarepta's eteplirsen.

-- Reported by Adam Feuerstein in Boston.

Follow Adam Feuerstein on Twitter.
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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