Anticoagulation

Anticoagulation is the use of medicines to reduce the blood’s ability to clot by interfering with the coagulation cascade. Anticoagulants prevent the formation and growth of clots but do not dissolve existing clots. They are used to lower the risk of stroke, pulmonary embolism, deep vein thrombosis, and other thromboembolic complications.

Most anticoagulants work by targeting thrombin (factor IIa) or factor Xa. Indirect agents such as unfractionated heparin and low-molecular-weight heparin enhance antithrombin activity to inhibit thrombin and Xa. Direct oral anticoagulants (DOACs) include direct factor Xa inhibitors (rivaroxaban, apixaban, edoxaban) and the direct thrombin inhibitor dabigatran. Warfarin, a vitamin K antagonist, reduces production of several coagulation factors and requires routine monitoring.

Common indications include atrial fibrillation, venous thromboembolism (deep vein thrombosis and pulmonary embolism), prophylaxis after many surgeries, and, in some situations, mechanical heart valves or certain hypercoagulable states. The choice of agent depends on renal function, pregnancy status, drug interactions, patient adherence, and bleeding risk.

Monitoring and dosing vary. Warfarin requires regular INR checks; DOACs typically do not require routine coagulation monitoring but dosing may depend on renal function. Unfractionated heparin is monitored with the aPTT, while LMWH dosing is often weight-based and adjusted for renal function.

Reversal and safety considerations include protamine for heparin, and vitamin K for warfarin reversal. Specific antidotes exist for DOACs (idarucizumab for dabigatran; andexanet alfa for Xa inhibitors). Bleeding risk, drug interactions, and dietary vitamin K intake are important factors. In pregnancy, heparin-based therapy is generally preferred over warfarin.