*Yousry TA, et al. N Engl J Med. 2006;354:924-933.
Observed clinical trial rate in patients who received a mean of 17.9 monthly doses of natalizumab. The post-marketing rate is calculated as the number of PML cases since reintroduction in patients that have had at least 1 dose of natalizumab.
Incidence estimates by treatment duration are calculated based on natalizumab exposure through July 31, 2011 and 150 confirmed cases as of August 4, 2011. The incidence for each time period is calculated as the number of PML cases divided by the number of patients exposed to natalizumab (e.g. for ≥24 infusions all PML cases diagnosed with exposure of 24 infusions or more divided by the total number of patients exposed to at least 24 infusions).
As of August 4, 2011:
- 29 patients have died (19%); most of the deaths have occurred within approximately 2 months after PML diagnosis
- 121 patients are alive (81%)
**Based on natalizumab exposure data as of February 28, 2011; PML incidence data based on 102 confirmed PML cases as of March 4, 2011; prior IS data in overall natalizumab-treated patients based on proportion of patients with IS use prior to natalizumab therapy in TYGRIS study as of November 23, 2010; and prior IS data in PML patients as of March 4, 2011 (with 102 confirmed PML cases of which only 88 had known prior IS status available and had natalizumab exposure between 1 and 48 doses).
Source: Biogen Idec, data on file.