Natalizumab-associated PML Update: March 2013

#MSBlog: March natalizumab PML update; 343 confirmed cases with a 23% mortality rate on a denominator of more than 112,000 treated MSers.

“As of the 5th March 2013 there have been 343 confirmed cases of natalizumab-associated PML; 79 (23%) MSers have died because of PML and 264 (77%) are alive. Of the MSers who survive the majority are significantly disabled. These figures are on a denominator of over 112,000 MSers treated with Natalizumab to date.”

The following presentation has been kindly provided by Biogen-Idec and contains more detailed figures.

CoI: multiple

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.


  • Dear Prof G,

    Tysabri is given every 4 weeks, does it make a difference if the infusions are given at 5 weekly intervals instead of 4weekly? I normally have infusions every 4 weeks, but due to the large number of Monday bank holidays my infusions are being put at 5 weekly intervals.

    • 5-weekly is a not a problem for a few weeks. It takes several months for natalizumab to washout. Some MSers notice the drug wearing off in the week prior to the next infusion. We assume in these MSers the saturation on the lymphocytes drops allowing re-trafficking of some cells and inflammation that makes MSers feels unwell. The latter is a hypothesis that needs testing. If you are one of these sorts of MSers you won't like a 5-week break.

  • Dear Professor Giovannoni,

    Many thanks for making the Biogen March presentation available.

    Would you know why Biogen don't include Interferon's as an IS factor and if they did – any sense of what that might do to the 1 in 192 number for Anti JCV positive MS patient with over 48 months treatment, currently categorised as no Prior IS use.

    Many thanks for any insights you can provide.

    Kind regards

    Matt Kavanagh (Dublin()

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