Clopidogrel, an inhibitor of ADP induced platelet aggregation and activation, is one of the most commonly used drugs in patients with cardiovascular disease; coronary-stenting would not be possible without the robust anti platelet function of this drug. Clopidogrel is a pro-drug that is transformed through a series of hepatic cytochrome p-450 (CYP) enzymes to an active metabolite. One of these CYP enzymes, 2C19 is subject to competitive inhibition by commonly used proton-pump inhibitors (PPIs). PPIs are commonly used for gastro-esophageal protection in patients treated with clopidogrel. Around 63% of 3,799 patients on clopidogrel received a PPI at TMH in 2008.