The market for multiple sclerosis medications is growing ever more crowded, especially with the advent of oral MS drugs, which are grabbing market share. One such pill is Biogen Idec's ($BIIB) Tecfidera, whiched raked in $192 million in sales its first quarter on the market--more than twice what some analysts expected. But Tecfidera is not stopping there. An investor note from Leerink Swann says the drug showed a 4.3% week-over-week increase in new prescriptions for the week ended July 26. While analyst Dr. Marko Kozul cautions that early data "may not be the best of Tecfidera's launch and long-term potential," he also calls the drug's launch "very impressive" overall.