Sarepta Therapeutics Inc. SRPT, -3.71% shares fell in the extended session Monday after the drug maker said the Food and Drug Administration raised concerns about its muscular dystrophy treatment. Sarepta shares fell 12% after hours, following a 3.7% decline in the regular session to close at $120.31. The FDA cited a risk of infections in the intravenous sites where the drug was administered and concerns about kidney toxicity. “We are very surprised to have received the complete response letter this afternoon,” said Doug Ingram, Sarepta president and chief executive, in a statement. “Over the entire course of its review, the agency did not raise any issues suggesting the non-approvability of golodirsen, including the issues that formed the basis of the complete response letter.” Sarepta said it was immediately requesting a meeting with the FDA to determine its next steps.