Half Dose of Prasugrel and Ticagrelor in Acute Coronary Syndrome (HOPE-TAILOR)

Inclusion Criteria: * Patients present with acute coronary syndrome undergoing primary PCI. * Patients receive DAPT (conventional dose of P2Y12 inhibitors+aspirin) at least 1 month. * Patients provide written informed consent prior to enrollment. Exclusion Criteria: * Low body weight (\<60kg). * History of transient ischemic attack or stroke. * History of upper gastrointestinal bleeding in recent 6 months. * Renal dysfunction defined as serum creatinine \> 2.5 mg/dl * Severe hepatic dysfunction defined as serum transaminase \> 3 times normal limit * On treatment with oral anticoagulant (Vitamin K antagonists, dabigatran, rivaroxaban). * Bleeding tendency. * Thrombocytopenia defined by platelet \< 100,000/ml. * Anemia defined by hemoglobin \< 10 g/dl. * Current treatment with drugs interfering with CYP3A4 metabolism (to avoid interaction with Ticagrelor): Ketoconazole, itraconazole, voriconazole, clarithromycin, nefazodone, ritonavir, saquinavir, nelfinavir, indinavir, atazanavir, and telithromycin. * Known severe chronic obstructive pulmonary disease or bradycardia (sick sinus syndrome (SSS) or high degree AV block without pacemaker protection). * Contraindication for study drugs.