Biogen Idec's hot-selling new multiple sclerosis drug Tecfidera remained effective for patients taking the medicine for at least four years with no new safety problems, according to interim data from a long-term study. Tecfidera, which analysts expect to eventually dominate the MS market, had sales of $192 million in its first quarter on the market - nearly triple average Wall Street expectations. The Endorse extension study followed patients who had taken part in two pivotal Phase III trials that led to the U.S. approval of Tecfidera.