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Controversial Drug EXONDYS 51 Gets FDA Approval…For Now

Controversial Drug EXONDYS 51 Gets FDA Approval…For Now

Perhaps bowing to outside pressures, the FDA approved Exondys 51 (etepliren) on September 19. This is the first drug approved to treat patients with Duchenne muscular dystrophy (DMD).

Exondys 51 is specifically indicated for patients who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping, the most common type of muscular dystrophy which affects about 13 percent of the population with DMD.

It was only back in April that the FDA’s own panel of advisors voted 7-3 against recommending the drug, reporting that there was little efficacy. Also figuring into their vote of no confidence was that the study by Exondys 51 maker Sarepta Therapeutics was limited to just 12 boys.

A public backlash ensued from DMD advocates and politicians clamoring for its approval, especially when Sarepta submitted additional data (after the FDA vote) that did show a “statistically significant increase in dystrophin.”

The term “statistically significant” has caused a major schism at the FDA that threatens to go well beyond Exondys 51. In his case against approving the drug, Ellis Unger, director of the Office of Drug Evaluation, argued whether “an exceptionally small magnitude” implies clinical benefit, adding “This decision could be precedent setting with respect to accelerated approval, i.e., where the bar should be set for changes in a pharmacodynamic biomarker that are deemed ‘reasonably likely to predict clinical benefit.’ Moreover, to my knowledge, this could be the first time a Center Director has overruled a review team (and an advisory committee) on a question of whether effectiveness has been demonstrated.”

FDA Commissioner Robert Califf concurred with Janet Woodcock, director of the Center for Drug Evaluation and Research, in overruling Unger and the FDA panel, noting their concerns in the official statement summing up the FDA’s decision:

“In this case, flexibility is warranted because of the life-threatening nature of the disease; the lack of available therapy; the fact that the intended population is a small subset of an already rare disease; and the fact that this is a life-limiting disease of children. These factors, combined with the dystrophin production data – and the drug’s low risk profile – led the Agency to approve the drug under the accelerated approval pathway.”

However, a major condition was placed in the FDA’s accelerated approval provisions. Sarepta Therapeutics must conduct a new clinical trial, and if the subsequent trial fails to verify clinical benefit the FDA could summarily reverse its endorsement. And so, the controversial drug Exondys 51 has its FDA approval…for now.

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Brought to you by Jason Marcewicz, Special Projects Manager

Advanced Medical Strategies

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