This study is designed to prove the superiority of the triflusal in preventing recurrent stroke over the clopidogrel in ischemic stroke patient with poor or intermediate metabolizer of CYP2C19 polymorphism. Also we plan to prove that clopidogrel resistance is related to CYP2C19 polymorphism by comparing the ischemic preventive effect of clopidogrel between groups of different CYP2C19 polymorphism.