It's rare to find a drug that affects two companies as much as Tysabri does Biogen Idec
When drug partnerships are involved, there's usually a big guy and a little guy. But in this case it's two medium-sized guys strapped to the coattails of Tysabri.
Fortunately, those tails are still holding strong. Sales of Tysabri were up 20% in the first quarter, which allowed Biogen to post a 9% gain in revenue and Elan to hold revenue flat despite declining sales of multiple legacy products.
To keep the momentum, Biogen and Elan have to bring their test for the JC virus to market. The virus causes a potentially deadly brain infection called progressive multifocal leukoencephalopathy, or PML, in patients whose immune systems are tuned down by Tysabri. The test will cause some JC-virus-positive patients to stop taking the drug, but the expectation is that there are many more JC-virus-negative patients that aren't taking Tysabri simply because they think the unknown risk is too high.
While Tysabri is immensely important to both companies right now, neither company is resting on its laurels.
Biogen is developing an oral multiple sclerosis drug, BG-12, which passed its first trial and the initial data look really good.
Elan has an Alzheimer's disease drug, bapineuzumab, in phase 3 development in combination with Johnson & Johnson
Biogen's and Elan's investors will need to keep their heads on a swivel, keeping track of both Tysabri sales as well as the upcoming drugs to take its place.
Keep track of Biogen and Elan as they try to keep expanding sales of their most-important drug. Click on their names to add them to My Watchlist, which will help you keep track of all our Foolish analysis on the companies.