Third Case of PML With Tysabri

Another case of progressive multifocal leukoencephalopathy (PML) was reported in a US patient with multiple sclerosis who was treated with Tysabri (natalizumab; Biogen Idec/Elan). According to an SEC report filed yesterday by the drug makers, the diagnosis was made by detecting JC virus DNA in spinal fluid, given disease-consistent clinical signs and MRI findings.

The patient had previously received beta interferons and glatiramer acetate (Copaxone; Teva) for MS, along with methotrexate for a "rheumatological condition." Fourteen infusions of Tysabri, as monotherapy, had been administered.

This newest case can be added to 2 cases of Tysabri-related PML reported in August. These patients had also received extended monotherapy (>1 year) with the monoclonal antibody for MS. PML cases before the market withdrawal of Tysabri in 2005 included 2 cases in MS patients and 1 case in an individual with Crohn's disease.

According to a recent risk-benefit assessment, the risk of PML with Tysabri would have to increase more than 7 times to reduce the drug's net benefit below that of interferon beta. Stockholders apparently don't care.