Figure 1: Study design. The solid black line indicates the period following hospital discharge after treatment of acute myocardial infarction. We excluded patients who did not receive a prescription for clopidogrel within 3 days of the discharge date (upward arrow). Among the remaining patients, cases were those readmitted because of myocardial infarction within 90 days after discharge. We attempted to identify 3 matched controls, with no myocardial infarction before the same date (the index date, indicated by downward arrow) for each case. Use of proton pump inhibitors before the index date was categorized as current (within 30 days), previous (31–90 days) or remote (91–180 days).