shortly after it was brought back to the market. The degree of statistical confidence in the PML risk figure declines over time, because there are fewer patients who have been on the drug for two and three years, Aoki says.
So while the incidence appears to be rising, what has changed that’s keeping PML patients alive? One of the big reasons is the strict monitoring program insisted upon by regulators, Sandrock says.
Now that every physician who treats MS has heard a lot about PML, they are trained to look for telltale signs like changes in cognition, changes in personality, or seizures that are not typical symptoms of an MS patient, Sandrock says. Doctors watch for those signs every time a patient comes in for their monthly IV infusion of the drug. If the side effect is suspected, the doctor will withhold the drug and run an MRI test to look for signs that the cause of PML, the JC virus, has entered the brain. If the MRI shows the virus is there, the doctor then does a spinal tap that can confirm the presence of the virus.
“We think we’re catching the virus early now,” Sandrock says, noting that some cases have been detected with extremely low concentrates of virus in the spinal fluid that only a specialty lab at the National Institutes of Health can detect.
Once the virus is detected, doctors do what is called a “plasma exchange,” which basically means that whatever amount of drug is still circulating in the bloodstream gets washed out through a filtering procedure. Doctors then reconstitute the patients’ immune system, which “clears the virus out,” Sandrock says.
So while early detection has helped lower the risk of death, I wanted to know what else Biogen and Elan think holds promise to bring the fatality rate down even further. Analysts suggested earlier this month that regulators might impose a drug “holiday” for patients who stay on Tysabri for long-periods of time. Sandrock didn’t like the sound of this idea, saying there isn’t data to support the notion that such a step will help lower the risk, while it essentially guarantees that a patient’s disabling MS symptoms will come back. But he did note that the company is looking to conduct a clinical trial to test the idea.
Biogen says it is more interested in developing a blood test
