Few doctors knew much about a rare brain infection called PML back in 2005, when two patients on a hot new multiple sclerosis drug from Biogen Idec and Elan died from the side effect. The infection, at the time, was generally considered a death sentence. But now with three years of data from more than 60,000 patients worldwide who have taken natalizumab (Tysabri) under strict monitoring by physicians, a new picture is emerging that shows PML is still very much a serious threat, but that it isn’t nearly as deadly as first feared.
While each and every confirmed case of PML, known formally as progressive multifocal leukoencephalopathy, scares investors in Cambridge, MA-based Biogen (NASDAQ: [[ticker:BIIB]]) and Ireland-based Elan (NYSE: [[ticker:ELN]]), I sought to assemble a big picture view of exactly how deadly PML really is when I interviewed Al Sandrock last week. He’s the senior vice president of neurology R&D at Biogen, and an assistant clinical professor of neurology at Harvard Medical School.
Before diving too far into the numbers about the risk of Tysabri, a little background is required. This drug, an antibody treatment designed to block certain white blood cells that cause MS when they attack nerves, has a history of also making patients vulnerable to infection. Biogen and Elan yanked it off the market in February 2005 after two cases of the brain disease were confirmed among patients taking the drug; a month later, a third case was confirmed. But legions of patients still demanded the drug, considered to be the most effective medicine on the market at reducing the disabling nerve damage from multiple sclerosis flare-ups. The FDA allowed the drug to return to the market in July 2006 after determining its benefits outweighed the risks, but it also forced doctors into a strict monitoring program to keep an eye out for the early signs of PML.
This matters not just for doctors and patients, but for Biogen’s and Elan’s financial futures. The drug, Biogen’s fastest-growing product, generated $560 million in sales in the first nine months of this year. (The importance of this drug is one reason why investors get so ticked at Biogen when it isn’t exactly forthcoming about every newly diagnosed case, but that’s a bone to pick another day.)
When the drug came back on the market, its FDA-approved prescribing information contained a prominent warning that about 1 out of every 1,000 patients on the drug were likely to get PML. But that was really just a forecast, and the actual risk-benefit balance for this drug is really a moving target that shifts over time when a new case is confirmed. So I sought to build a simple chart when I spoke to Sandrock that provides a snapshot of PML cases in February 2005, when the drug was pulled off the market because of the PML risk, versus those confirmed as of yesterday. Here’s what I gathered:
|
Number of patients |
Number of |
Deaths | |
| February 2005 |
3,000 | 3 | 2 |
| Nov. 18, 2009 | 63,000 | 27 | 5 |
The February 2005 figures came from clinical trial data and formed the foundation for the FDA-required warning of the 1-in-1,000 chance of getting PML. The more recent figures include all the experience of patients who have gotten the drug since it was returned to the market in July 2006. The thing that jumped out at me was the fact that only five of the 27 confirmed patients with PML have died—meaning that the current survival rate stands at over 80 percent.
That curious fact has been buried under a rash of scary headlines
