Monitoring Antithrombotic Therapy

In health, the haemostatic system is in a constant state of low grade activation, and anticoagulant and antifibrinolytic pathways regulate the system to prevent spontaneous thrombosis. In evolutionary terms, a haemostatic system which is partially activated favours a successful response to injury. Agents such as warfarin and heparin which inhibit the procoagulant effect of the haemostatic system inevitably have anticoagulant effects which favour bleeding. An ideal agent would have specific antithrombotic activity to prevent pathological activation of haemostasis yet would produce negligible global anticoagulant activity so that the haemostatic system could respond appropriately to physiological procoagulant stimuli. During antithrombotic therapy precise dose adjustment is required to establish a clinically suitable effect with a minimal risk of bleeding. Because it is difficult to separate the antithrombotic effects from the global anticoagulant effects of currently available agents, the therapeutic window of such agents tends to be narrow, and dose adjustment requires regular therapeutic monitoring.