Transient ischemic attacks (TIA) are common, with an estimated 250,000-350,000 occurring each year in the US, an incidence about 30-40% that of stroke.  Rapid recovery of cerebral ischemia (reduction of blood flow to the brain) is a defining characteristic of TIA and distinguishes it from completed stroke.  This recovery defines a distinct pathophysiologic feature that generally indicates the presence of previously ischemic tissue still at risk: a characteristic that may be responsible for greater instability. In fact, numerous studies have shown that short-term risk of stroke is high after TIA, particularly in the first few days, even in patients treated with aspirin, the current standard of care. Antithrombotic therapy may play a distinct role in this acute pathophysiology. Effective therapies in those with TIA could significantly reduce the overall burden of stroke if initiated immediately. However, no large-scale trial has evaluated an acute intervention in patients with TIA.

The Primary Specific Aim of this randomized, double-blind, multicenter clinical trial is to determine whether clopidogrel (Plavix) 75 mg/day by mouth after a loading dose of 600 mg is effective in reducing the 90-day risk of major ischemic vascular events (ischemic stroke, myocardial infarction, and ischemic vascular death) when initiated within 12 hours of TIA onset in patients receiving aspirin 50-325 mg/day.