Tysabri: New Brain Infections Result in a Safety Update

TysabriThe FDA has confirmed three new cases of a rare but potentially lethal brain inflammation linked to natalizumab (Tysabri, Biogen Idec/Elan), a medication that is used for multiple sclerosis (MS) and Crohn’s disease.

There have been 13 reported cases of progressive multifocal leukoencephalopathy (PML) since mid-2006. All of the PML cases are linked to the drug’s use for MS. Natalizumab drags was approved in November 2004 but was withdrawn from the market in 2005 for 18 months because of PML reports. It was reintroduced in July 2006.
The FDA has updated the safety information for natalizumab and warns that the risk of developing PML appears toncrease with the number of infusions received and that the average number of infusions received before the diagnosis of PML was 25. The agent is delivered through an IV infusion about once a month. The duration of therapy may also play a role in the risk of PML. The current rate of PML in patients who have received at least 24 infusions ranges from 0.4 to 1.3 per 1,000 patients. Biogen claims that there is no definite link to duration of therapy, and the company opposes interrupting treatment because MS symptoms can return.

As of June 30, about 43,300 patients were receiving natalizumab.

The FDA is not requiring changes to the prescribing information or to the risk-management plan. The drug is effective, and patients are informed about the risk of PML before they receive it.

Sources: N Engl J Med 2009;361:1041-1043, 1081-1087; Associated Press, September 22, 2009; The Wall

Street Journal, September 16 and 23, 2009