The makers of natalizumab (Tysabri) continue to provide updates on the number of people taking the drug who have developed the potentially deadly disease progressive multifocal leukoencephalopathy (PML), previously an AIDS-defining illness.
The latest update as of 2 November 2010 shows that 75 people taking the drug for MS now have PML, 15 of whom have died. This is of great concern, as the drug is being widely prescribed by neurologists, for some people even as a first choice drug. Research has previously suggested that the longer one takes the drug, the greater the chance of PML developing, and this is borne out by the new figures, which confirm the rate of PML is around one in 1000 and gradually rising as people stay on it for longer. Recent data show that this rate is about two per 1000 for those on the drug for more than two years. Once on the drug, there are also issues about how to stop, given that the disease tends to flare up when the drug is ceased.