Irish drug firm Elan will hear today whether a drug key to its future will be licensed for use in the United States.
The multiple sclerosis drug Tysabri, developed with US drug maker Biogen, was withdrawn last year after it was linked to a rare brain infection.
The US Food and Drug Administration (FDA) will hear from outside experts today and tomorrow advising on whether the drug can return to the market.
It is unknown whether Tysabri increases the chances of a life-threatening brain infection when used alone, or if the problem occurs only when it is combined with other drugs that may suppress the immune system, an FDA report said yesterday.
The drug's makers should impose strict patient monitoring requirements if Tysabri is allowed to return, the FDA added. Biogen has proposed creation of a patient registry.
The analysis was released ahead of the advisory panel meeting, which will issue a recommendation which the FDA usually follows.
Elan and Biogen voluntarily pulled the drug from the market in February 2005 after three patients developed a rare brain and spinal-cord infection known as progressive multifocal leukoencephalopathy, or PML. Two of them died.
In two of the cases, the patients also were taking Biogen's older MS drug, Avonex, at the same time.
While acknowledging that Tysabri offers unique benefits, the report said many MS patients have a "relatively benign disorder" and Tysabri may be too risky for them.
MS is a progressive autoimmune disease that can cause blurred vision, weakness, poor muscle co-ordination and loss of memory and mental function as nerves lose their insulating sheath.
The expert panel's findings are likely to have a significant effect on the share price of both Biogen and Elan.