The primary objective of the study is to determine the efficacy of a 72 hour infusion of SUN N4057 (piclozotan) in subjects with clinical findings of an acute ischemic stroke and a magnetic resonance imaging (MRI) demonstrating a measurable penumbra (perfusion-weighted imaging [PWI] minus diffusion-weighted imaging [DWI] volume). Efficacy will be determined by comparing the proportion of subjects with no growth in stroke lesion volume as assessed by DWI at Screening to stroke lesion volume assessed by FLAIR (fluid-attenuated inversion recovery) on Day 28 in the piclozotan group versus the placebo group.