Chapter 16: Antithrombotic and Thrombolytic Drugs

Antithrombotic and Thrombolytic Drugs presentation explores the pharmacological management of thromboembolic disorders, emphasizing the critical balance of normal hemostasis and the pathology behind cardiovascular emergencies like myocardial infarction, ischemic stroke, and venous thromboembolism. The discussion begins with the physiological processes of vasospasm, platelet plug formation, and the coagulation cascade, which is a complex series of serine protease activations culminating in fibrin creation. We distinguish between arterial thrombi, which are primarily driven by platelet aggregation over atherosclerotic plaques, and venous thrombi, which result from blood stasis and coagulation factors. The pharmacological landscape is divided into three primary categories: anticoagulants, antiplatelet agents, and thrombolytic drugs. Anticoagulants like warfarin inhibit vitamin K-dependent synthesis of clotting factors II, VII, IX, and X, requiring careful monitoring of the international normalized ratio. In contrast, parenteral agents like heparin and low-molecular-weight heparins such as enoxaparin work by potentiating antithrombin III to inactivate factor Xa and thrombin. Newer direct-acting oral anticoagulants, including the thrombin inhibitor dabigatran and factor Xa inhibitors like rivaroxaban and apixaban, offer predictable pharmacokinetics without the need for routine laboratory oversight. The session also covers antiplatelet therapies, from the irreversible cyclooxygenase inhibition of aspirin to the ADP-receptor blockade of clopidogrel and the potent glycoprotein IIb/IIIa antagonists used in surgical interventions. For acute clot dissolution, we examine thrombolytic agents such as alteplase and tenecteplase, which activate plasminogen to catalyze fibrinolysis during time-sensitive windows for heart attacks and strokes. Finally, the chapter addresses clinical safety, highlighting reversal agents like protamine sulfate for heparin, phytonadione for warfarin, idarucizumab for dabigatran, and antifibrinolytics like aminocaproic acid to manage life-threatening bleeding complications.