Antithrombotics

Antithrombotics are drugs that reduce abnormal clot formation by interfering with hemostasis. The term covers three main groups: anticoagulants, which slow the coagulation cascade; antiplatelet agents, which inhibit platelet aggregation; and thrombolytics, which dissolve clots that have formed. They are used to prevent or treat thrombosis in cardiovascular and cerebrovascular disease.

Anticoagulants target the coagulation cascade at different points. Vitamin K antagonists (warfarin) reduce vitamin K–dependent factors. Heparins (unfractionated and low-molecular-weight) enhance antithrombin activity. Direct oral anticoagulants (DOACs) such as dabigatran, rivaroxaban, apixaban, and edoxaban inhibit thrombin or factor Xa. Monitoring requirements vary; warfarin needs INR, heparins require aPTT or anti-Xa activity, DOACs usually do not require routine monitoring, though dosing depends on renal function.

Antiplatelet agents prevent arterial thrombosis by inhibiting platelets. Aspirin blocks thromboxane production via COX-1 inhibition. P2Y12 inhibitors (clopidogrel, prasugrel, ticagrelor) prevent ADP-mediated platelet activation. These drugs are common after acute coronary syndromes and stent procedures, but they increase bleeding risk, including gastrointestinal and intracranial hemorrhage.

Thrombolytics promote fibrinolysis to dissolve clots already formed. Agents include alteplase, tenecteplase, and streptokinase. They are used in selected emergencies such as ST-elevation myocardial infarction, massive pulmonary embolism, and certain ischemic strokes. They carry a high risk of major bleeding and require careful patient selection and rapid assessment of contraindications.

Management involves assessing thrombosis versus bleeding risk, adjusting doses for age and kidney or liver function, and considering drug interactions. Reversal options exist for many agents (e.g., vitamin K for warfarin, protamine for heparin; specific antidotes for some DOACs). Patient-specific planning guides the choice and duration of therapy.