If you thought that the great run so far in 2013 was over for Biogen Idec (NASDAQ:BIIB), think again. Shares soared more than 40% year to date before beginning to pull back somewhat over the last few days. However, the biotech's just-announced first-quarter results should keep the stock rolling. Shares were up 3% in midday trading. Here are the highlights.

By the numbers
Biogen reported first quarter non-GAAP diluted earnings per share of $1.97, up 41% compared to the first quarter of 2012. That result easily topped the average analyst estimate of $1.61. Non-GAAP net income was $469 million, 39% higher than the figure from first quarter of 2012.

GAAP diluted earnings per share for the quarter came in at $1.79, an increase of 43% year over year. The company reported GAAP net income of $427 million, a gain of 41% compared to the same quarter last year.

Total revenue for the last quarter increased 10% year over year to $1.4 billion. This result was roughly in line with the average analyst revenue estimate of $1.42 billion.

The biotech boasted a nice cash stockpile as of the end of the first quarter. Biogen reported over $3.6 billion in cash, cash equivalents, reverse repurchase agreements, and marketable securities as of March 31. However, that amount was reduced just a few days later with the $3.25 billion acquisition of full rights for Tysabri from Elan.

Behind the numbers
These solid results stemmed primarily from Biogen's top two products -- Avonex and Tysabri. Avonex sales during the first quarter totaled $746 million. That's up 13% from the same quarter in 2012.

Tysabri wasn't far behind, with 9% year-over-year growth. Sales of the biotech's second-highest grossing multiple sclerosis drug came in at $312 million for the quarter.

Combined sales of Fampyra and Fumaderm during the first quarter totaled $38 million. This result was 35% higher than the $28 million recorded in the same quarter of 2012.

The only negative news came from Rituxan. Sales for the drug declined 7% from the first quarter of 2012, to $265 million. This drop reflected a $42 million hit that Biogen took related to damages assessed against its partner Genentech from arbitration with Hoechst GmbH.

Looking ahead
Biogen upped its full-year earnings guidance to a range of $7.80 to $7.90 per share, from $7.15 to $7.25 per share given earlier. The company also announced 2013 revenue growth expectations of 16% to 18%, significantly higher than the 10% figure provided previously.

There are a several factors that I think portend a continued bright future for Biogen. First, I like that the company bought full rights to Tysabri from Elan. It will split profits with Elan through April 30, and then pay royalties going forward.

Another big driver of Biogen's success comes from its new multiple sclerosis tablet, Tecfidera. The FDA approved Tecfidera on March 27, so there wasn't any revenue to report in the first quarter. However, I expect we'll begin seeing nice initial sales numbers beginning in the second quarter, and things should really take off from there.

I'll be quite surprised if Tecfidera doesn't top sales of rival multiple sclerosis pills from Novartis and Sanofi. Analysts expect Novartis' Gilenya to reach sales of $2.3 billion by 2016. Credit Suisse thinks that Sanofi's Aubagio will hit peak annual sales of $1.2 billion. However, Tecfidera's safety profile gives it a leg up in my view.

Biogen's pipeline also looks very promising. The company recently submitted Biologic License Applications, or BLAs, to the FDA for two biologics, one treating hemophilia A and the other for hemophilia B. I think both have strong chances for ultimate approval.

All in all, things look very good for Biogen right now. My suspicion is that the terrific run this biotech has had thus far in 2013 has a long way to go.

Fool contributor Keith Speights has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.