Effect of Natalizumab on Infarct Volume in Acute Ischemic Stroke

The primary objective of the study is to determine whether one 300 mg dose of intravenous (IV) natalizumab reduces change in infarct volume from Baseline to Day 5 on magnetic resonance imaging (MRI) in participants with acute ischemic stroke when given at ≤6 hours or at \>6 to ≤9 hours from when they were last known normal (LKN). The secondary objectives of this study in this study population are as follows: to assess the efficacy of natalizumab on change in infarct volume from Baseline to Day 30; to assess efficacy of natalizumab on change in infarct volume from 24 hours to Day 5 and Day 30; to assess the efficacy of natalizumab on clinical measures of stroke outcome; to assess the safety of natalizumab in participants with acute ischemic stroke.