(RxWiki News) Multiple sclerosis does its damage in a patient's brain, and that's where most drugs are targeted. But one drug holds the dangerous risk of a severe brain infection for some patients.
Tysabri, a drug designed to treat multiple sclerosis (MS), is known to increase the risk of progressive multifocal leukoencephalopathy (PML), a brain infection. A new study focuses on a blood test that has the potential to identify a patient's individual risk to the virus that causes PML.
The hope is that this test could help predict risk and guide the patient to a safe, effective treatment.
"Before taking Tysabri, discuss the risks with your doctor."
The study, nicknamed STRATIFY-1, is being conducted by Biogen Idec, the maker of Tysabri (natalizumab). The company had previously announced that there had been 49 confirmed cases of PML in patients who used Tysabri, as of May 2010.
PML is a rare disorder, which is potentially life-threatening. It damages myelin, the material that protects the nerve cells in the brain's white matter. Myelin is also a target for MS.
Biogen scientists developed a blood serum test, which is designed to test for antibodies of the virus that causes PML. The virus is called John Cunningham virus, or JCV.
Out of 1,096 people with relapsing MS who are either being treated with or considering treatment with Tysabri, the researchers found that 56 percent had evidence of JC virus antibodies.
Women had a lower prevalence than men, and the likelihood that the patient had antibodies increased with age.
The test had a relatively low false-negative rate of 2.7 percent. That means that 3 out of 100 times, the blood test did not detect evidence of the antibodies, but the presence of the virus' DNA had been found by a urine test.
Finding JC virus antibodies means that the patient has been infected or exposed to the virus, which lies dormant. Patients with antibodies are at an increased risk for the virus, and that suggests that they might try to avoid taking Tysabri.
Tysabri is designed to prevent the movement of damaging immune cells into the brain and spinal cord. In two clinical trials, patients had a reduced risk of disability progression, and had fewer relapses, or attacks, than participants taking a placebo.
Currently, Tysabri is used to treat MS only when alternative treatments have failed. That's due to the risk of PML. There's a procedure to make sure that the patient is aware of the risks, and that the medication is still safe and appropriate for them.
The study was published in the Annals of Neurology in December 2011.
