The potentially fatal infection, known as progressive multiform leukoencephalopathy (PML), occurs in an estimated 1.5 per 1,000 patients treated with Tysabri during months 25 to 36. The PML risk was 0.3 per 1,000 patients during the first two years of treatment. After three years, the rate was 0.9 per 1,000. Limited data is available beyond four years.
For the first time the FDA said it had estimated the chances of PML for specific time intervals rather than providing a cumulative risk over years. The new estimates “will allow prescribers to better assess risk based on duration of treatment”, the agency said.
As of the 1st April the total number of PML cases worldwide stands at 111.
COI: I was the UK’s Chief Investigator on the pivotal Natalizumab phase 3 trial and have received consulting fees from Biogen-Idec in relation to the development of Natalizumab for treating MS and managing the risk of PML in subjects on Natalizumab.