What happened Shares of the rare-disease specialist Sarepta Therapeutics (NASDAQ: SRPT) fell by as much as 20% in pre-market trading today. The drugmaker's shares are cratering in response to a complete response letter issued yesterday by the Food and Drug Administration (FDA) for the Duchenne muscular dystrophy (DMD) drug candidate golodirsen (proposed brand name: Vyondys 53). Sarepta said that the FDA rejected the drug's accelerated regulatory filing over potential safety concerns, such as the risk of infection and kidney toxicity. The biotech's CEO, Doug Ingram, stated in a follow-up press release that the FDA didn't bring up any of these outstanding issues during the drug's formal review, leaving the company "surprised" by this regulatory decision. Image source: Getty Images. So what Wall Street expected golodirsen to eventually tack on a healthy $400 million in annual sales to the drugmaker's top line early in the next decade. With the drug's approval now in doubt, however, these projected sales may never materialize. Viewed in this context, investors' decision to hit the exits this morning is easy to understand. Now what The bad news is that FDA didn't seem to give the company much wiggle room to readily address these safety concerns. Sarepta reportedly plans on sitting down with regulators as soon as possible to figure out a path forward, but the key takeaway is that there may not be a quick fix in this case. In short, the FDA appears to be taking a far more critical stance on golodirsen than it did with the company's other DMD drug, Exondys 51. That means investors might want to avoid this falling knife today. 10 stocks we like better than Sarepta TherapeuticsWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has quadrupled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Sarepta Therapeutics wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of June 1, 2019 George Budwell has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source