For patients with mechanical heart valves, atrial fibrillation, or myocardial infarction (MI), oral anticoagulant therapy helps to prevent thromboembolism. However, anticoagulant use also increases the risk of bleeding. That's why Dutch researchers undertook a study of more than 4,000 patients to determine the ideal International Normalized Ratio (INR) at which the risks of thromboembolism and bleeding were lowest.
   Over the 4-year course of the study, the researchers logged the incidence and intensity of adverse events during anticoagulation therapy. Such adverse events occurred roughly 4% per year for all indications. From these data, the researchers calculated the optimal INR to minimize such events, which can improve the safety of oral anticoagulant therapy. For patients with mechanical heart valves, the optimal INR was 2.5 to 2.9. For patients with atrial fibrillation, it was 3.0 to 3.4. For patients who had had an MI, it was 3.5 to 3.9.
   The authors of the study suggested that, for future clinical trials, researchers use a 3.0 INR target for patients with mechanical valves or atrial fibrillation and 3.5 for post-MI patients. (Archives of Internal Medicine, 2009, 169[13]: 1203-1209)

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