3 September 2019 - It is hard to discern the true state of drug regulation from the outside, but two recent decisions by the FDA — to approve one drug but reject another — offer a rare glimpse into that world.

Exondys 51 and Vyondys 53, both developed by Sarepta Therapeutics, are intended to treat a severe form of muscular dystrophy, though in different subgroups of patients. Exondys 51 gained FDA approval in 2016 amid great controversy. Agency officials were divided because evidence of the treatment’s benefits was especially thin. Its approval came with a condition requiring Sarepta to carry out a post-approval clinical trial to confirm the drug’s effectiveness.

Despite sales of $300 million in 2018 alone, however, the company has yet to begin the post-approval trial. Within days of this delay becoming public, Sarepta announced that the FDA had rejected Vyondys 53 from entering the market.

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