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What: Shares of Biogen Idec (NASDAQ:BIIB), a global biopharmaceutical company with a primary focus on developing therapies to treat multiple sclerosis, rallied 15% in January, based on data from S&P Capital IQ, after announcing better-than-expected fourth-quarter earnings results.

So what: For the quarter Biogen Idec produced $2.64 billion in revenue, up 34% from Q4 2013, and delivered adjusted EPS of $4.09, up 74% from the year-ago quarter. Although Biogen Idec's revenue figure was more or less in-line with Street estimates, Biogen crushed the $3.78 in adjusted EPS that analysts had forecast.

Source: Biogen Idec.

The primary growth driver for Q4 remained twice-daily MS pill Tecfidera whose sales grew to $916 million and is on pace to top $4 billion in revenue next year. Analysts had been looking for just $880 million in Tecfidera sales for Q4. Recently launched hemophilia drugs Alprolix and Eloctate brought in a respectable $40 million and $37 million as well.

Looking ahead, Biogen Idec offered guidance in 2015 of 14% to 16% revenue growth and adjusted EPS of $16.60 to $17 per share. By comparison, Wall Street was locked in with an estimate of $16.37 per share, so this is another nice beat and the third straight quarter that Biogen has absolutely crushed Wall Street's projections.

Now what: This was nothing more than business as usual for Biogen Idec which has remained an impressive force in MS therapies for years. Tecfidera's favorable safety profile relative to competing drugs Aubagio and Gilenya should allow it to continue to attract market share.

Additionally, ongoing research into new drug candidates, such as BIIB037 for Alzheimer's disease and its optic neuritis drug hopeful anti-Lingo-1, could provide the extra kick to send Biogen's shares even higher with a steady foundation being laid down by its MS product portfolio.

On the flipside, competitors such as Alkermes are out to create drugs similar to Tecfidera that may be even safer, potentially threatening Tecfidera's MS dominance later this decade. Also, at 23 times 2015's EPS Biogen is no longer the great value it once was.

After a monumental run over the last couple of years I'd begin paring my expectations back on Biogen Idec and its future growth prospects just a bit. While it can still count on Tecfidera and a number of other portfolio products, it'll need near-flawless growth prospects if it hopes to crest and hold the $400 per share mark.