Piling on the Data

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Most investors were convinced awhile ago that Sarepta Therapeutics' (NASDAQ: SRPT  ) eteplirsen is working on the 10 boys with Duchenne muscular dystrophy enrolled in its phase 2 trial. Nevertheless, the biotech keeps piling on the data.

The trial was scheduled to compare eteplirsen to placebo for 25 weeks, after which the placebo group got the drug and both groups entered an extension trial.

We're now at 96 weeks, and both groups are stable compared to the levels they were at when they started getting the drug. The six boys that started in the treatment group have seen the distance they can walk in six minutes decline less than 5%, or 17.5 meters.

The four patients in the crossover group saw an 18.5-meter decline in their six-meter walk test measured from 36 weeks, when the drug should have started working. And that was with one of the boys having a broken ankle that wasn't fully healed. Just looking at the other three boys, the decline was just 4.7 meters.

You could argue that the study is no longer double blind -- everyone knows they're getting the drugs -- so the boys might be trying harder, assuming the drug is helping them. But eventually sheer will won't be able to overcome the biology of the disease that eventually causes Duchenne muscular dystrophy patients to be become unable to walk.

In Prosensa (UNKNOWN: RNA.DL  ) and GlaxoSmithKline's (NYSE: GSK  ) phase 2 trial testing their Duchenne muscular dystrophy drug drisapersen, for instance, the placebo group walked, on average, 24.7 meters less after being in the study for 49 weeks.

We're now double that time frame for the boys in the eteplirsen treatment group. It seems safe to assume they would have seen their walk test decline by more than the 17.5 meters without the drug by now.

"Working on the 10 boys"
Remember that opening sentence of the article? It's clear the drug is working for the boys in the trial.

What about the rest of the Duchenne muscular dystrophy patients with the mutation that eteplirsen treats? While the results are quite impressive, 10 isn't a very large number. We don't really know whether it'll be safe and effective in a larger population.

There's an easy way to find out though: Give eteplirsen to them.

The Food and Drug Administration has two choices at this point. It could approve the drug based on the limited data. Or it could make Sarepta run a larger phase 3 trial to confirm the phase 2 results.

I sure hope the agency approves eteplirsen. What's the worst that happens?

  • The data on the 10 boys is a fluke, and it doesn't help the general population. Considering the lack of alternative treatments, there doesn't seem to be much harm outside of giving people unwarranted hope.
  • The drug isn't safe, and there's a side effect not seen in the 10 boys in the trial. Considering that Duchenne muscular dystrophy is a terminal disease, I think most parents would be more than willing to risk it.

Unfortunately, the FDA has, in general, been more conservative in the past. The agency is charged with approving drugs that have been proven successful not ones that might be. And while the boys will die of Duchenne muscular dystrophy, if eteplirsen is approved, it'll likely be prescribed to patients well before they start declining when the currently unknown side effects might tip the risk-benefit scale.

We'll know soon enough whether the FDA will be more lenient than in the past. Sarepta plans to submit its marketing application to the FDA in the first half of next year. By that point, we could have an additional 26 weeks of data.

Unfortunately, it'll be in the same 10 boys.

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