PML Brain Infection from Tysabri Reported in 10th Patient

Biogen Idec Inc. is reporting that another brain infection from Tysabri has been discovered among users of their multiple sclerosis drug, which is at least the 10th case reported in the last three years.

Tysabri (natalizumab) was initially approved for treatment of multiple sclerosis through injection in 2004. However, a Tysabri recall was issued in 2005 after three users developed a rare and life-threatening brain infection, known as progressive multifocal leukoencephalopathy or PML.

The drug was reintroduced in July 2006 with stronger warnings about the potential PML brain infection side effects of Tysabri and it was only made available under strict usage guidelines. Biogen Idec, the drug’s manufacturer, is tracking cases of the rare brain disease associated with Tysabri in an effort to get a solid risk/benefit analysis of the drug by the third anniversary of its return to the market on July 24.

Progressive multifocal leukoencephalopathy is an infection that attacks the central nervous system, damaging and inflaming the white matter areas of the brain. Experts believe that it is caused by the common JC virus, and side effects of Tysabri may reduce the ability of the immune system to combat the virus.

Some researchers suspect that the PML risk is greater for those who have used Tysabri for an extended length of time, giving the JC virus a larger window of opportunity to attack the brain, but that has not been confirmed.

Symptoms of PML brain infections from Tysabri could include confusion, blurred vision, speech and movement difficulties, dizziness and loss of balance. In most cases, PML has a very high fatality rate, however, some Tysabri users have had a better prognosis due to early detection and the use of a plasmapharesis treatment, which removes Tysabri from the system rapidly and allows the immune system to fight off the virus.

The most recent Tysabri user to contract the infection did so after their 30th dose, and was located outside of the U.S.

Earlier this year, reports of PML brain infections from Raptiva, a psoriasis drug marketed by Genentech, Inc., led to that drug being removed from the market. Unlike Tysabri, which has remained available with strong warnings for consumers, it was determined that the risk of Raptiva brain infection side effects outweighed the benefits provided in treating psoriasis.