Monday, July 31, 2006

Research: Caution flag for Tysabri?

Given that Tysabri will likely be used as long-term therapy, do we know enough about its effects over the long haul?
Expert Opin Pharmacother. 2006 Aug;7(12):1675-8.
Natalizumab in multiple sclerosis: proceed with caution?
Doggrell SA.
Senior Lecturer, School of Science, Charles Darwin University, PO Box 41246, Casuarina, Northern Territory, 0811 Australia.

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the CNS. In a Phase II clinical trial, natalizumab was shown to reduce the relapses in patients with relapsing MS, without improving the disability score. After 1-year of Phase III clinical trials, natalizumab was approved by the FDA for use in relapsing MS but was withdrawn 3 months later, due to two reported cases of progressive multifocal leukoencephalopathy (PML). The completed clinical trials with natalizumab for relapsing MS have recently been reported. In a trial of 1171 subjects with relapsing MS, natalizumab alone was shown to reduce the relapse rate and lesions, without causing PML. Although natalizumab was also shown to reduce the relapse rates and lesions in patients taking IFN-beta, two cases of PML with natalizumab occurred in these patients. An assessment of patients who had taken natalizumab for 1 - 2 years (approximately 3000), showed the incidence of PML to be 1/1000. A drug that is useful in relapsing MS will be used as a long-term therapy in large numbers of patients. For instance, in the 3 months that natalizumab was registered, 5000 patients commenced taking it. In the author's opinion, large numbers of patients should not be allowed to take natalizumab until its safety has been monitored in the long-term use in a clinical trial environment. Link.

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Jaime said...

Very intersting article. I personally am a bit skeptical about Tysabri (only my opinion) at this point. I still think the risk of PML is too high...and with numbers like 1/1000, the number of cases (and deaths) are going to go up.

The last I heard there are something like 350,000 patients with MS in the US (registered with the NMSS....the number is most likely more than that). So according to this statistic 350 americans will develop PML and die. I am not sure that is worth the risk.

It is great that this drug is offering so much hope to people and that it does work...but I agree, more research needs to go into this. I personally would prefer to be in a wheelchair and disabled (all ego set aside) and live than risk being one of those who develop PML and don't.

Beth said...

I don't see what is new in this abstract or what new evidence the author is using to support their opinion it shouldn't be used- the rate of PML hasn't increases since before it was pulled off the market.