TYSABRI: HARVARD MED SCHOOL'S TOP 10 STORIES OF 2006


7. Drug approvals — with strings attached. Hopes were high when natalizumab (Tysabri) was introduced in 2004. The new monoclonal antibody treatment promised to treat multiple sclerosis by binding to immune system cells that attack the myelin covering of nerves in the brain and spinal cord. The crash landing came a few months later: Tysabri was withdrawn after being linked to three cases of an unusual brain infection (progressive multifocal leukoencephalopathy).

In 2006, the FDA allowed the drug back on the market, with restrictions. Doctors prescribing it must register with the manufacturer. The monthly infusions can only be given at authorized sites. Patients must also be registered in a special Tysabri program. Alosetron (Lotronex), the irritable bowel syndrome drug, followed a similar path earlier: The big splash, the hasty retreat off the market, a return with restrictions.

Drug approvals have generally been binary, yea or nay, with doctors free to prescribe any approved drug. With Tysabri and Lotronex, we’re moving toward modified approvals with requirements for monitoring attached.