Effect of Amlodipine on Anti-platelet Drug Effect in Patients With Coronary Artery Disease

Clopidogrel can reduce risk of cardiovascular disease by inhibiting platelet aggregation. It is metabolized to an active drug by a liver enzyme. Its efficacy may be measured by blood sampling for platelet activity, analyzed by VerifyNow device. Calcium Channel blocker (CCB) is also commonly used for blood pressure and anginal control in these patients. Dihydropyridine group of calcium channel blocker (e.g. amlodipine) inhibits this enzyme. There are observational studies reporting dihydropyridine CCB reducing clopidogrel effect, but the clinical implication is unclear. This study test the hypothesis that there is no significant effect of dihydropyridines CCB on clopidogrel response compared with control. After giving consent, patients with suboptimal blood pressure or anginal control will be randomized to receive either dihydropyridine CCB or non-CCB as placebo. These patient will be follow-up in 1 month.