For the moment it's not available in Canada
"Tysabri, the new innovative treatment for multiple sclerosis, stops the migration of white blood cells to the central nervous system, preventing any damage to the brain. The approval for the new treatment was based on the results of a study of 942 patients in the early phase of multiple sclerosis, a chronic disease of the brain and the spinal cord. The one-year study revealed that the frequency of relapses in patients treated with Tysabari had declined by two third as compared to patients given a placebo. Health Canada has also decided to review the drug on a priority basis and take a decision regarding its approval next year. The drug is expected to receive an impressive market response."