Anticoagulants

Anticoagulants are medications that reduce the blood’s ability to form clots by interfering with the coagulation cascade. They do not dissolve existing clots but prevent new clots from forming or growing, reducing the risk of stroke, pulmonary embolism, and other thromboembolic events.

Major classes include:

- Vitamin K antagonists (VKAs), such as warfarin. They inhibit vitamin K–dependent synthesis of clotting factors II, VII, IX, and X, and proteins C and S, leading to anticoagulation. They require regular monitoring of the international normalized ratio (INR) and are influenced by diet and drug interactions.

- Direct oral anticoagulants (DOACs, or NOACs). These include direct factor Xa inhibitors (rivaroxaban, apixaban, edoxaban) and a direct thrombin inhibitor (dabigatran). DOACs offer fixed dosing in many settings and do not require routine INR monitoring, but renal function affects dosing and certain drug interactions exist.

- Heparins. Unfractionated heparin (UFH) and low molecular weight heparins (LMWH, such as enoxaparin, dalteparin) enhance the activity of antithrombin. UFH is monitored with aPTT; LMWHs have more predictable effects and are often used in outpatient settings.

- Fondaparinux. A synthetic pentasaccharide that inhibits factor Xa via antithrombin, used in prevention and treatment of VTE and in certain perioperative settings.

- Other agents such as direct thrombin inhibitors (e.g., argatroban, bivalirudin) used in specific scenarios like heparin-induced thrombocytopenia or during certain procedures.

Common indications include prevention of stroke in nonvalvular atrial fibrillation, treatment and prevention of deep vein thrombosis and pulmonary embolism, and prophylaxis after surgery. Warfarin remains the standard in mechanical heart valves; DOACs are generally avoided in that setting.

Reversal and perioperative management vary by agent and include vitamin K and prothrombin complex concentrates for VKAs, protamine for heparin, and specific reversal agents for certain DOACs. Bleeding risk, renal function, and drug interactions are important considerations in all anticoagulant therapy.

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