Biogen Idec, of Cambridge, Mass, and Elan, in Dublin, Ireland, viewed their new product as a potential blockbuster. The companies needed just 20,000 patients to break even, according to the February 18, 2006 LA Times.
And Wall Street projected yearly sales to one day reach $3 billion.
However, the rosy financial projections went up in smoke in February 2005, when the drug makers suddenly withdrew Tysabri from the market after 5 patients contracted a rare brain disease called PML, short for Progressive Multifocal Leukoencephalophy.
The most frequently reported other adverse events in the Tysabri clinical trials, overshadowed by the reports of PML, are listed by the FDA to include infections, severe or life threatening allergic reactions, depression (including thoughts of suicide), and gallbladder problems.
"These events occurred at rates ranging from 0.8% to 2.1%," the agency said.
Anita Smith, a patient enrolled in the Tysabri study for treatment of MS, died from PML, and another patient taking Tysabri for Crohn's disease also died of PML.
According to WebMD Medical News, "PML is a progressive disease of the brain and spinal cord that primarily affects people with weakened immune systems."
"The condition is caused by a virus that destroys the sheath that covers the nerves," it said. "Symptoms include mental deterioration, vision loss, speech disturbances, and movement abnormities or paralysis," WebMD reports.
A March 2, 2005, article by Forbes.com titled, The Virus That Took Down Tysabri," explains how a specific virus causes the development of PML.
The JC virus discovered in 1971, was named with the initials of the patient in whom it was found. The virus is present in almost everyone, according to the article, but only destroys the brain when something damages the immune system and allows the virus to run rampant.
By suppressing the immune system, Forbes says, Tysabri allows the JC virus, ordinarily latent in a patients kidney, to travel to the brain via the bloodstream, where it begins uncontrolled replication.
"Since the first description of the disease in 1958, it had remained a rare occurrence," Forbes said, "seen mostly in organ transplant patients whose immune systems were suppressed by drugs." About 5% of people with full-blown AIDS also develop PML
On February 25, 2006, in a new development, News Infirno.com announced a major court ruling in Massachusetts in a wrongful death action filed on behalf of the estate of the 46-year-old wife and mother of two, Anita Smith, that ordered Biogen to produce all medical records on Ms Smith immediately.