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What happened? The multiple sclerosis drug natalizumab (Tysabri) has gained approval to return to the market.

The Food and Drug Administration (FDA) has agreed with the recommendations an FDA panel made in March 2006 to allow Tysabri to be marketed again. Tysabri was withdrawn in early 2005 due to a possible connection between the drug and a rare — but often fatal — brain disorder.

The drug's manufacturers pulled Tysabri from the market after three people developed a rare condition called progressive multifocal leukoencephalopathy (PML), which destroys the fatty layer that covers nerve fibers in the brain. Two of the three died.

The FDA advisory panel recommended reconsideration of the decision to withdraw, citing the clear benefits that the drug offers to many people with multiple sclerosis — reducing the rate of relapse by nearly 70 percent after one year.

In approving the return of Tysabri under a special distribution program, and to reduce the risk of PML, the FDA attached certain conditions. Among those conditions:

• The drug will be prescribed only by certain specialists, centers and pharmacies registered under a special program, called the TOUCH Prescribing Program.
• Patients have to be enrolled in this program to receive the drug.
• Patients need to follow certain procedures, including regular evaluations.

What does this mean to you? Tysabri will be available for new prescriptions, under special conditions. Discuss the potential risks and benefits with your doctor.