Overall Risk-Benefit of Tysabri Still Positive, Despite New PML Cases

Two new cases of Tysabri-related progressive multifocal leukoencephalopathy (PML) in patients with multiple sclerosis (MS) were reported yesterday by comarketers Elan and Biogen. In both cases, the diagnosis was established by the detection of JC virus DNA in spinal fluid, along with clinical and MRI findings. The patients had received Tysabri monotherapy for more than a year. These new cases can be added to 2 cases of PML in MS patients who received Tysabri with Avonex (interferon beta-1a; Biogen) and 1 case in a patient with Crohn's disease given Tysabri monotherapy.

Reports of these new PML cases follow the publication in this week's Neurology of the long-term risk-versus-benefit of the agent in patients with relapsing-remitting MS. By assessing quality-adjusted life years (QALYs), investigators from the University of Rochester concluded that the PML risk with Tysabri would have to increase more than 7 times to reduce the drug's net benefit below that of interferon beta. This result is mostly due to the superior reduction of relapses with Tysabri.

The positive analysis notwithstanding, the news of the latest PML cases with Tysabri hit Elan and Biogen hard, with share prices dropping substantially.