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   DIR Return to: TYSABRI (natalizumab)
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       #Post#: 1729--------------------------------------------------
       (Abst.) Tysabri-associated PML not preceded by elevated drug con
       centrations
       By: agate Date: June 20, 2017, 7:17 pm
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       From Multiple Sclerosis Journal, June 1, 2017:
       [quote]Natalizumab-associated progressive multifocal
       leukoencephalopathy is not preceded by elevated drug
       concentrations
       Zoé LE van Kempen, Cyra E Leurs, Anke Vennegoor, ...
       Background:
       In recent years, a small but increasing number of neurologists
       choose to extend dose intervals of natalizumab with the aim of
       reducing the risk of progressive multifocal leukoencephalopathy
       (PML). This idea is based on the hypothesis that high drug
       concentrations increase the risk of PML.
       Objective:
       We investigated the relation between longitudinal natalizumab
       concentrations in patients who developed PML and patients who
       did not develop PML.
       Methods:
       In a prospective observational cohort study of 219 patients with
       relapsing–remitting multiple sclerosis treated with natalizumab,
       serum samples were taken every 12 weeks prior to
       natalizumab infusion. In this cohort, 5 patients developed PML
       and were matched with 10 patients from the cohort who did not
       develop PML. Natalizumab concentrations were measured in
       available samples, and the longitudinal results were compared
       between the two patient groups.
       Results:
       Mean natalizumab concentrations in the five patients developing
       PML was 18.9 µg/mL (standard deviation (SD): ±13.4) versus
       23.8 µg/mL (SD: ±11.5) of the control patients.
       Furthermore, we did not observe a clear rise in concentration
       levels in patients subsequently developing PML.
       Conclusion:
       Our results provide preliminary evidence that contradicts the
       hypothesis that exposure to elevated concentrations of
       natalizumab is a relevant risk factor of developing PML.[/quote]
  HTML http://journals.sagepub.com/doi/abs/10.1177/1352458516684023
  HTML http://journals.sagepub.com/doi/abs/10.1177/1352458516684023
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