Another Tysabri patient contracts PML

Another Tysabri patient has taken ill with the deadly brain infection progressive multifocal leukoencephalopathy, or PML. It's the sixth such case overall, and the third since the multiple sclerosis drug was reintroduced to the market in 2006 under a strict risk management program. This sixth patient, a woman, is alive, as are three of the five previous PML cases linked to Tysabri. About 35,500 patients were taking the drug at the end of last month, according to Biogen Idec.

The Wall Street Journal said the new case would "[darken] the commercial prospects for the medicine." There's no doubt that growth in Tysabri usage already has slowed since the two previous post-reintroduction cases were announced in July. And the latest news sent shares of Biogen, listed on the Nasdaq Stock Market, down 11 percent to $37.40 in after-market trading yesterday. Depository receipts of Biogen's marketing partner, Ireland's Elan, fell 23 percent after the announcement.

The new case also calls into question the theory that strictly governing Tysabri's usage would prevent PML from arising. But even so, the number of cases remains small, compared with the number of patients using the drug.

- read the WSJ story

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