According to Biogen Idec, a tenth confirmed case of progressive multifocal leukoencephalopathy (PML, a viral infection of the brain that usually leads to death or severe disability) has occurred among people who have used Tysabri® (natalizumab, Biogen Idec and Elan Pharmaceuticals) after it became available for prescription in July 2006. The case, reported by the company on June 26, 2009, occurred in a person in Europe who had been taking Tysabri for 30 months. The reported duration of use among these ten people has ranged from about 12 to 35 months.
As of the end of March 2009, 40,000 people worldwide were being prescribed Tysabri. Although the absolute risk for PML in patients treated with Tysabri cannot be precisely determined, the frequency to date remains less than the one-in-one thousand risk that was estimated at the time of Tysabri's re-approval in 2006.
It appears that when PML is detected and treated early, it generally improves outcomes. It is important that individuals taking this drug and their doctors be vigilant in monitoring for any occurrence of new, unusual symptoms that might indicate PML.
Typical symptoms associated with PML progress over days to weeks, and can include:
clumsiness and progressive weakness on one side of the body,
disturbances of vision, and
changes in thinking, memory, and orientation leading to confusion and personality changes.
If individuals taking Tysabri experience new, unusual symptoms, they should contact their prescribing physician immediately. Physicians who need guidelines on the protocol to follow when they have a patient on Tysabri who experiences unusual symptoms should contact Biogen Idec.
There is no specific therapy to treat PML, but the best hope is to reconstitute a person's immune responses. Based on small-scale studies supported by Biogen Idec, plasma exchange, a blood-cleansing treatment, has been used to clear the bloodstream of Tysabri. There is insufficient evidence to determine whether plasma exchange can reduce PML symptoms.
With information from the National MS Society (USA)
