Source: Biogen Idec

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What: Shares in Biogen Idec (NASDAQ:BIIB) surged higher by 10% after the company announced fourth quarter and full year results, including earnings that exceeded Wall Street analysts' expectations.

So What: Biogen is one of the globe's biggest manufacturers of therapies used to treat multiple sclerosis, a disease of the central nervous system that causes a disruption in communication between the brain and other parts of the body. Since symptoms of MS can be disabling, many patients are prescribed medicine including Biogen's blockbuster therapies Avonex, Tysabri, and Tecfidera.

During the fourth quarter, sales of Biogen's MS drugs totaled $2.18 billion, up from $1.58 billion a year ago. For the full year, sales of these MS treatments reached $7.93 billion, up from $5.41 billion in 2013. The sales surge was led by Tecfidera, which saw its sales jump 130% to $916 million.

Overall, Biogen reported revenue of $2.64 billion in the fourth quarter, but even more importantly, Biogen was able to drop more of its sales to the bottom line than industry watchers were looking for. In the quarter, Biogen's earnings per share hit $4.09, which was $0.31 more than analysts were projecting and 74% more than the company earned during the fourth quarter of 2013.

Now what: The orally administered Tecfidera continues to gain ground against other recently launched oral MS drugs from Novartis and Sanofi. As a result, Tecfidera's sales grew from $876 million in 2013 to $2.9 billion in 2014.

Biogen expects that Tecfidera's momentum will continue to support sales and earnings growth in 2015, but Tecfidera won't be the only drug that Biogen is counting on to send its top and bottom line higher this year.

In November, the FDA approved Plegridy, a twice-monthly injection therapy for MS, and Plegridy's sales were $41 million during the fourth quarter. Biogen also won approval of Alprolix and Eloctate last year. Those drugs are Biogen's first therapies for the treatment of hemophilia, and the two combined to generate sales of nearly $80 million in the fourth quarter. The performance of those drugs last year suggests that they will contribute more meaningfully to Biogen's results in 2015.

The ongoing success of its MS therapies and the potential growth from these newly launched drugs has Biogen guiding investors to expect sales to climb between 14% and 16% this year and for adjusted EPS to reach between $16.60 and $17. If Biogen can deliver on that forecast, investors should have plenty of reasons to be long the company's shares in 2015.