Biogen Idec Inc. fell after demand for its multiple sclerosis drug Tecfidera showed signs of slowing. Prescriptions fell 6.7 percent in the week ended Aug. 2 to 3,377 from the previous week, IMS Health Inc. said. Tecfidera, said Gabelli & Co.’s Kevin Kedra, is “the newest oral MS product . . . It’s gotten off to a very strong launch, so any signs of them maybe slowing down would be a positive for competitors” like Teva Pharmaceutical, Bloomberg reported. Biogen Idec said it doesn’t comment on sales reports.