The Tysabri Game Plan -READ MORE: "Some analysts, such as Deborah Knobelman of Piper Jaffray expect the FDA to approve a re-entry of Tysabri but with significant restrictions. Her firm's recent survey of 140 neurologists revealed that doctors continue to be wary of safety risks: More than three-quarters of the neurologists polled said they would prescribe the drug--but to just 10% of their patients.Still, with a hefty price tag of about $23,500 for one year of treatment, even 10% of multiple sclerosis patients translates roughly to 34,000 patients in the U.S., according to Piper Jaffray. This bodes well for Elan, since it needs about 20,000 patients on Tysabri to stay out of the red, said Chief Financial Officer Shane Cooke in January during the company's fourth-quarter earnings call.

And while the FDA usually follows the advice of advisory committees, it's not always a slam-dunk. This was seen after an advisory panel's February 2005 blessing of painkillers Celebrex, Bextra and Vioxx, a class of drugs known as COX-2 inhibitors.

Two months after the committee said the drugs should be made available despite increased risks of heart attacks, the FDA banned Pfizer's (nyse: PFE - news - people ) Bextra and placed its strongest warning label on the company's other drug, Celebrex, while Merck's (nyse: MRK - news - people ) hopes for a Vioxx return were dashed."