The present and future of oral anticoagulants.

The number of patients under oral anticoagulant therapy has markedly increa sed lately, mainly due to those with chronic atrial fibrillation. Progress has been made in the control of oral anticoagulation because sensitive and calibrated commercial reagents for prothrombin time have become available. But bleeding is still a problem in these patients. In our experience, the i ntensity and the duration of the anticoagulant therapy are the most importa nt risk factors for bleeding. The deviation of INR (International Normalize d Ratio) can also be associated with higher risk for bleeding. The limitati ons of oral anticoagulant therapy include frequent laboratory controls for dose adjustment, drug interactions, narrow therapeutic range and the high v ariability in patient response. These limitations prompted the development of new antithrombotic agents. A number of low molecular weight active site inhibitors of thrombin are being developed and one of them is orally bioava ilable, and could become an alternative to vitamin K antagonists.