Test Being Developed For Deadly Brain Infection Linked to MS Drug Tysabri

Drug maker Biogen Idec Inc. is close to finalizing a new test to detect a virus which can cause a deadly brain infection in patients taking its multiple sclerosis drug, Tysabri.

The antibody-based test, which may be ready for the public by the end of 2009, is designed to detect the JC virus, which is linked to causing progressive multifocal leukoencephalopathy (PML). Tysabri and other drugs treat MS, psoriasis, and other inflammatory conditions by lowering the body’s immune system. However, in doing so, immune-suppression drugs may leave patients more susceptible to infections, including PML.

Tysabri: A Big Earner for Biogen

Tysabri is a top-selling drug for Biogen, earning the company $813 million in sales in 2008, but the drug has not been without controversy. Tysabri was launched in 2005 but was quickly withdrawn after patients taking it developed PML. The drug was later allowed back on the market after stricter safety warnings about the risk of PML were added to the drug’s packaging.

Less than 100,000 people in the United States are expected to be taking Tysabri by the end of 2010, company officials said.

Biogen estimates that the rate of PML in Tysabri patients is about 1 in 4,000 over 12 months of exposure. That rate is considerably lower than earlier estimates of 1 in 1,000. However, five cases of PML have been reported in Tysabri patients since July 2008 and one patient has died.

PML Treatment Options

PML patients may be able to undergo a treatment called plasma exchange, which removes Tysabri from their blood, and can slow or stop the progression of PML. Some patients who develop the life-threatening infection have stopped taking Tysabri for a time, raising their immune system in an effort to control PML. However, Biogen recommend against taking “drug holidays” and say breaks in taking the drug decrease its effectiveness.

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