2. Avonex
Biogen Idec
2013 Revenue:
$3.00 billion

Once-weekly injectable Avonex was groundbreaking when it first grabbed the FDA's green light back in 1996. Now, however, with oral competition looming--including that from fellow Biogen ($BIIB) drug Tecfidera--the company has had to raise prices to keep sales growing.

In 2013, sales grew by 3.2%, with nearly two-thirds of its global haul generated in the U.S. The stateside revenue increase came primarily from price hikes; those were partially offset by an 8% decrease in unit sales volume, thanks partly to patients who switched to Biogen's new pill. And as Biogen said in its last 10-K, it only expects the competition to keep on building.

But as of August, Biogen has approval for a longer-lasting version of Avonex that will help it fight for its piece of the pie. Dubbed Plegridy, the drug requires injection only once every two weeks--a factor Biogen commercial chief Tony Kingsley recently told Reuters gives it "the potential to be the leading interferon on the market." -- Carly Helfand (email | Twitter)

For more:
Biogen ready to steal market share with newly minted MS drug Plegridy
Biogen Idec secures FDA nod for Avonex delivery accessory
Biogen Idec lengthens shelf life of Avonex