Cecil B. Pickett, Ph.D., president of Biogen Idec, said in a conference call with analysts that the two PML cases are the first since the drug was reintroduced to the U.S. market in 2006.
He said an estimated 32,000 MS patients worldwide are receiving the drug. He said 13,900 of them have taken it for more than 12 months, and 6,600 have used it for more than 18 months.
The company said that more than 17,000 U.S. patients take the drug.
Biogen Idec and Elan developed the drug, and Dr. Pickett said the companies received confirmation of the first case on Wednesday and the second case was confirmed yesterday.
In both cases PML was confirmed in the presence of symptoms, MRI evaluation, and confirmed JC viral DNA in cerebrospinal fluid.
One patient was described as "stable, ambulatory, and at home," while the other was described as hospitalized, but clinically stable.
The drug was initially approved by the FDA in November 2004, but was withdrawn from the market in February 2005 after three patients developed PML. Two of those patients died.The drug was reintroduced under a special restricted distribution plan that requires a registry for all patients as well as follow-up at three and six months after initial infusion and follow-up every six months thereafter.
Alfred Sandrock, M.D., Ph.D., senior vice president for neurology research and development at Biogen Idec, said the first patient had aggressive relapsing MS and was treatment naive when he began therapy in December 2006.
He developed a focal twitch and left-sided weakness after 17 months on natalizumab monotherapy, but had no cognitive symptoms.
Initial MRI was equivocal and initial CSF testing was negative, but despite the absence of JC viral DNA in the CSF, plasma exchange was initiated. The patient underwent five plasmapheresis treatments over the course of 10 days.
"A second CSF test confirmed the presence of JC virus DNA," Dr. Sandrock said. He said the patient was stable, at home, but the focal twitch and left-sided weakness remained.
The second patient was diagnosed with MS in 1992 and had a long history of therapeutic interventions, prior to initiation of natalizumab. This patient developed left-side hemiparesis over the course of two months.
Dr. Sandrock said tests confirmed JV viral DNA in this patient's CSF and the patient is scheduled to begin plasmapheresis treatment.Additional Multiple Sclerosis Coverage
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