Clopidogrel administration is considered standard of care in patients with stable coronary artery disease post PCI. However , a significant proportion of patients is considered clopidogrel resistant and this is shown to be accompanied by future adverse events. The hypothesis of the study is to define among consecutive outpatient clinics individuals with stable coronary artery disease being on chronic clopidogrel treatment, those that are clopidogrel resistant, as assessed with the VerifyNow point of care assay. Clopidogrel resistant patients will be randomized in a 1:1 fashion to either prasugrel 10mg or clopidogrel 150mg daily. Platelet reactivity will be assessed at Day 14, when treatment crossover will be performed without a washout period. At Day 28 platelet reactivity will be assessed as well.

Inclusion Criteria:

• Age ≥18 years old
• Patients with history of coronary artery disease under chronic (≥ 6 months) clopidogrel treatment
• High on-clopidogrel platelet reactivity (≥235 Platelet Reactivity Units as assessed with the VerifyNow assay)
• Written Informed Consent

Exclusion Criteria:

• History of bleeding diathesis
• History of active bleeding within 6 months before randomization
• Chronic oral anticoagulation treatment
• Contraindications to antiplatelet treatment
• Known platelet function disorders
• Acute coronary syndrome within 30 days before randomization
• Cardiogenic shock
• Planned Percutaneous Coronary Intervention in the next 30 days
• Cancer
• Haemodialysis
• Platelet count < 100000/μL
• Hematocrit < 30%
• High likelihood of being unavailable on the Day 28 visit
• History of stroke
• Known allergy to clopidogrel and/or prasugrel