Source: BioMarin Pharmaceutical

A key FDA advisory panel is about to debate the effectiveness and safety of BioMarin Pharmaceutical's (NASDAQ:BMRN) drisapersen, a therapy for the treatment of Duchenne muscular dystrophy and based on documents released to the committee by the FDA, the FDA is dubious about the drug's potential.

If the advisory committee concludes that drisapersen's trial results aren't conclusive enough to support an FDA approval, then it could have important repercussions for Sarepta Therapeutics (NASDAQ:SRPT) eteplirsen because eteplirsen and drisapersen work similarly.

First, a bit of background
Duchenne muscular dystrophy (DMD) is a rare disorder in which patients can't produce dystrophin in levels necessary to support muscle development. Absent that muscle development, patients with DMD tend to lose mobility over time and eventually succumb to heart related complications tied to the disease.

Because there is no treatment that directly targets the cause of DMD, the standard of care is corticosteroids which simply delay disease progression.

In an attempt to improve upon current treatment options, considerable effort has focused on developing therapies to restore dystrophin production in these patients.

The majority of that work focuses on skipping specific exons believed to be disrupting dystrophin production and both BioMarin and Sarepta's drugs specifically target skipping exon 51.

Shaky efficacy
BioMarin acquired drisapersen by buying Prosensa Holding N.V. last year for $680 million in cash and promises of another $160 million if drisapersen can claw its way past regulators.

The acquisition is a gamble for BioMarin because trial results for drisapersen have been less than stellar.

Specifically, drisapersen failed to outperform placebo in a phase 3 study, prompting Prosensa's partner at the time, GlaxoSmithKline, to walk away from the collaboration in January 2014.

Typically, a high profile late-stage trial failure and the loss of a well-heeled partner would spell the end for a drug in development, however, because of DMD's significant unmet need for new treatment options and a dire prognosis for patients, advocacy groups successfully lobbied for the FDA to provide a pathway to consider approval anyway.

BioMarin Pharmaceutical

FDA is underwhelmed
In documents released last week, the FDA provided talking points to the advisory committee that suggests the hurdle for approval may be high.

After reviewing two mid stage trial results and the phase 3 data, the FDA came away believing that drisapersen's efficacy was "inconsistent." 

That could be an understatement given that the FDA's report said the first phase 2 trial offered "unimpressive statistical strength" and thus, "the overall persuasiveness of this study appears to be low."

It offered a similarly dim view of the second phase 2 study, saying that the independent persuasiveness of this study is "low."

Looking forward
The advisory committee will debate drisapersen's merits tomorrow and all eyes will be firmly focused on what the members say. The committee will consider both the trial data that has been submitted and hear testimony from patients.

If the testimony is strong enough to overcome the drug's shortcomings in trials, then it could indicate that the FDA will follow the committees recommendation and approve drisapersen. It could also suggest that the FDA will give Sarepta's eteplirsen a green light eventually too. The FDA is set to make its final decision on drisapersen on December 27 and eteplirsen on February 26.