Glaxo grabs coveted breakthrough drug status for muscular dystrophy drug

GlaxoSmithKline ($GSK) has landed the FDA's coveted Breakthrough Therapy designation for drisapersen, a late-stage treatment for Duchenne muscular dystrophy (DMD) that is engaged in a fierce clinical race with Sarepta's ($SRPT) closely watched DMD drug eteplirsen.

GSK says it got a verbal nod from regulators after they reviewed Phase II data. This is GlaxoSmithKline's first Breakthrough Therapy designation, putting the pharma giant in some exclusive company. J&J ($JNJ), Pfizer ($PFE), Merck ($MRK) and others have notched BTD successes--out of a total of 17--in recent months.

The news is also a positive for Prosensa, the Dutch biotech which licensed the drug out to GSK. Prosensa has filed for an IPO, planning to raise about $60 million.

Pushed by lawmakers, FDA officials have been repeatedly vowing to provide an open door for development teams working on these BTDs. The regulators say they'll work with developers every step of the way, reviewing trial designs, data, drug names--everything that can help speed these therapies to the market.

Breakthrough boasting rights can be particularly important to GSK as Sarepta has grabbed investors' attention with some impressive midstage data from a tiny trial. Sarepta has been trying to persuade the FDA to grant an accelerated approval on eteplirsen, which would allow them to beat GSK's therapy to the market. The biotech, though, says it has not applied for breakthrough drug status.

Sarepta's shares were down about 5% this morning.

In the meantime, GlaxoSmithKline has publicly reviewed positive Phase II data for drisapersen. But the pharma giant has had to wrestle with news related to the side effects caused by the therapy.

Among the adverse events recorded, investigators noted an injection site reaction, which is not uncommon in drug trials, as well as signs of proteinuria--an excess level of protein in the urine. Close observers of drisapersen have paid particularly close attention to the proteinuria cases after GlaxoSmithKline discussed cases in Phase III that required hospitalization.

- here's the press release