Biogen idec, Inc. in Massachusetts and its Irish partner, Elan Corp. offer a drug called Tysabri (natalizumab). It works on the body’s immune system and is designed to target only certain cells so as to protect healthy cells from any damage. It is used for multiple sclerosis (MS), to treat it when it relapses. It is also used for Crohn’s disease.
In 2005, the two drug companies withdrew Tysabri from the market after three people developed brain infections and two of them died. The U.S. FDA (Food and Drug Administration) decided in 2006 that it could be placed for sale again because its benefits for M.S. outweigh the slight risk of brain infection. The FDA required stricter prescription guidelines as a way to limit the brain infection risk.
Since 2006, there have been no more reports of brain infection until recently. Thirty-four new cases have been reported (four of them just this week) and one person has died of this brain infection. It is called Progressive Multifocal Leukoencephalopathy (PML).
What is Multiple Sclerosis?
Brain cells communicate with each other with electrical signals sent along nerve cell axons (long fibers). Axons are normally wrapped in a fatty sheath called myelin. When a person has MS, their immune system is attacking the myelin, damaging it, and thereby preventing the brain cells from communicating effectively or at all. The damage causes scars known as scleroses — hence the name multiple sclerosis. The cause of MS is unknown.
What is PML?
Progressive Multifocal Leukoencephalopathy is a viral disease involving many areas of inflammation and damage in the brain’s white matter. It is very rare. It cannot be treated and can be fatal after much brain cell deterioration involving blindness, impaired speech, physical weakness, and cognitive decline. It occurs almost entirely in people with immune deficiency such as AIDS patients and transplant patients taking drugs that suppress the immune system so that their transplant will not be rejected.
The labeling states that the brain infection rate is one in 1,000. “The overall picture is consistent with the rate described in the label,” said Naomi Aoki, a Biogen spokeswoman. “PML remains rare.” She added that the longer a person takes Tysabri, the more likely it may become that they will have PML.
So far, of the 35 PML cases, 11 have been in the U.S., 21 in Europe, and three elsewhere.
It does not appear that Tysabri is necessarily a defective drug. If the labeling is correct and if physicians follow the strict prescription guidelines and monitor their patients properly, perhaps there will never be many cases of PML. All drugs have side effects and most of the time, drug safety is a matter of appropriate and/or FDA-approved use, with the labeling information in mind and warnings observed.
However, there are certainly defective drugs on the market from time to time, which usually get withdrawn after enough cases of severe side effects are reported. It is part of the FDA’s job to monitor such reports and take action when necessary.