Biogen Idec's, Elan's shares fall after third case of PML reported among patients taking Tysabri

Biogen Idec announced that a third patient taking Tysabri has been diagnosed with progressive multifocal leukoencephalopathy (PML) since the drug was reintroduced in the US in 2006. The company's shares were down as much as 17 percent Wednesday following the news, while the shares of its marketing partner Elan dropped as much as 27 percent.

In a filing with the US Securities and Exchange Commission, Biogen Idec said a patient with multiple sclerosis was confirmed to have developed PML after 14 injections of Tysabri. The drugmaker also noted that it advised regulatory agencies of the new infection. Regarding the occurrence of PML cases in patients taking Tysabri, Biogen Idec spokesperson Naomi Aoki stated that "the rate is consistent with our expectations, given the information that's in the label,'' which is one per 1000 patients.

In response to the news, analyst Bret Holley of Oppenheimer & Co. explained that "if people hadn't been expecting another case, they were naive." He added, however, that he doesn't believe the news "will negatively affect prescriptions any further.'' Robert W. Baird analyst Christopher Raymond concurred, stating that "while a new Tysabri PML case clearly isn't good news, it should come as little surprise, given the established pattern."

Biogen Idec and Elan announced in July of this year that two patients in the EU with multiple sclerosis had been diagnosed with PML after taking Tysabri.

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