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INTRODUCTION

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SUMMARY

Antithrombotic drugs are among the most commonly used drugs in medicine and are generally separated into anticoagulants, fibrinolytic agents, and platelet inhibitors based on their primary mechanism of action. For many decades, warfarin, which acts by inhibiting vitamin K action, was the only oral anticoagulant available. Vitamin K antagonists have a prolonged effect, unpredictable pharmacokinetics, and require monitoring, but warfarin was widely used for prevention and treatment. The introduction of novel targeted oral anticoagulants has changed the landscape of anticoagulation. Rivaroxaban, apixaban, and edoxaban are novel oral inhibitors of factor Xa, whereas dabigatran is an orally available inhibitor of thrombin. Unfractionated heparin and the low-molecular-weight heparins are the most commonly used rapidly acting parenteral anticoagulants; they inhibit activated serine proteases through antithrombin. One synthetic agent in this class, fondaparinux, is specific for inhibition of factor Xa, and is effective for prevention and treatment of venous thromboembolism. Several parenteral direct thrombin inhibitors have excellent anticoagulant action and offer an alternative to heparins. A number of fibrinolytic agents are available, all of which convert plasminogen to plasmin to accelerate clot lysis. Differences among them include their degree of fibrin specificity, half-life, and antigenicity. Antiplatelet agents play an important role in prevention and treatment of arterial thrombosis. Aspirin is a cyclooxgenase-1 inhibitor that is effective and widely used in the prevention of stroke and myocardial infarction. Drugs that modulate cyclic adenosine monophosphate levels include dipyridamole, pentoxifylline, and cilostazol, and are primarily used in treatment of peripheral vascular disease. Adenosine diphosphate receptor blockers such as ticlopidine, clopidogrel, and prasugrel are effective in treatment of coronary and peripheral arterial disease. Examples of inhibitors of fibrinogen interaction with αIIbβ3 are abciximab, tirofiban, and eptifibatide. These drugs are highly effective in treatment of patients with acute coronary syndromes.

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Acronyms and Abbreviations:

ACT, activated clotting time; ADP, adenosine diphosphate; aPTT, activated partial thromboplastin time; cAMP, cyclic adenosine monophosphate; COX, cyclooxygenase; CYP, cytochrome P450; DVT, deep vein thrombosis; FFP, fresh-frozen plasma; Gla, γ-carboxyglutamic acid; HIT, heparin-induced thrombocytopenia; INR, international normalized ratio; ISI, international sensitivity index; LMWH, low-molecular-weight heparin; MI, myocardial infarction; NSAID, nonsteroidal antiinflammatory drug; PE, pulmonary embolism; PG, prostaglandin; PGI2, prostacyclin; PRP, platelet-rich plasma; PT, prothrombin time; TNK, tenecteplase; t-PA, tissue-type plasminogen activator; VTE, venous thromboembolism.

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Antithrombotic agents are highly effective and are among the most commonly used drugs in medicine because thrombotic diseases are the leading cause of mortality and morbidity in Western countries. Antithrombotic agents are characterized separately as anticoagulants, antiplatelet agents, or fibrinolytic drugs, depending on their primary mechanism, although there is overlap in their activities and clinical indications (Table 25–1). Their greatest use is in prevention of thrombosis in patients at high risk, but they also have important applications for treating acute thrombosis. For many agents, the risk-to-benefit ratio is narrow, with the result that bleeding complications occur, and bleeding is the most common adverse effect. Consequently, the clinician should carefully ...

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