Shares in Elan Corporation and US partner Biogen Idec Inc fell today on fears a fourth patient taking their multiple sclerosis drug Tysabri may have contracted a deadly brain disease.
The US Food and Drug Administration (FDA) confirmed it was reviewing a link between Tysabri and a possible case of the rare brain infection PML.
"The case is being reviewed," FDA spokeswoman Lenore Gelb said.
The Boston Globereported earlier that Biogen, with which Elan developed the treatment, had told the FDA a fourth patient may have contracted PML.
Elan halted sales of Tysabri, formerly known as Antegren, in February after it emerged one patient had died from PML, and another was believed to have it. A third case of the disease was identified in March.
Shares in Elan were down 17 per cent at €5.28 by lunchtime, off an earlier low of €4.6. In New York, Biogen stock was down 4 per cent at $38.21.
Shares in Swiss rival Serono, which also makes an MS drug, rose on the back of the report.
Elan, responding to the Boston Globereport, said it did not comment on rumours or individual cases going through the safety evaluation process. No one from Biogen was immediately available for comment.