Cohort Study of Clopidogrel and Proton Pump Inhibitors

Patients who have experienced and survived non-ST segment elevation acute coronary syndromes are often prescribed a combination of aspirin and clopidogrel to thin the blood and prevent further acute coronary episodes. Both clopidogrel and aspirin may cause stomach bleeds and so a prophylactic proton pump inhibitor is frequently co-prescribed in order to prevent such bleeds. Recent mechanistic and observational studies suggest proton pump inhibitors may reduce the effectiveness of clopidogrel and so patients may not benefit as much as expected from combined aspirin and clopidogrel. The investigators propose a cohort study of patients prescribed clopidogrel + aspirin. Amongst these patients the investigators will measure the relative rate of acute coronary syndrome and death comparing patients with and without proton pump inhibitor treatment. To provide a more complete picture of the risks and benefits of treatment the investigators will also measure the relative rate of stomach bleeds in the same groups of patients. In addition, whether the inhibitory effect of proton pump inhibitors on the protective effect of clopidogrel is due to their inhibition of drug metabolising enzymes will be explored by assessing the effects of other drugs that inhibit the same enzymes.