Outcome Measures: The primary efficacy endpoint for response will be clinical improvement (complete recovery or improvement of 4 points or more on the NIH Stroke Scale) at 24 hours after start of therapy. The primary safety endpoint for determination of toxicity will be any one of the following: symptomatic intracranial hemorrhage (ICH), major systemic hemorrhage, or other serious adverse event related to study drug administration, including death, within 48 hours from start of therapy. The maximum acceptable rate of toxicity will be 10% of patients treated at any dose level and the minimum acceptable rate of response will be 50% of patients at any dose level. The outcomes will be monitored by a Data and Safety Monitoring Committee, which will have the authority to stop or recommend modifications of the trial for safety concerns. Other clinical outcome variables and imaging variables will be recorded and analyzed in secondary and exploratory analyses. If an acceptable dose is identified, then that will be investigated in a subsequent randomized placebo-controlled trial.