Anticoagulation

Anticoagulation is treatment that reduces the blood's ability to form clots. It is used to prevent clots forming in the first place and to stop existing clots from extending or embolising. Despite the everyday phrase, anticoagulants do not thin the blood: they interrupt the coagulation cascade so that fibrin clot forms more slowly and less readily.

The main indications are stroke prevention in atrial fibrillation, treatment and prevention of deep vein thrombosis and pulmonary embolism, prophylaxis in hospitalised patients at raised risk of venous thromboembolism, and thromboembolism prevention in people with mechanical heart valves or certain thrombophilias.

Drug classes

• Direct oral anticoagulants (DOACs): apixaban, rivaroxaban, edoxaban and dabigatran, which inhibit factor Xa or thrombin directly and are given at fixed doses without routine monitoring.
• Vitamin K antagonists: warfarin, which requires regular INR monitoring and dose adjustment and interacts with many drugs and with dietary vitamin K.
• Heparins: low molecular weight heparins such as enoxaparin and dalteparin, and unfractionated heparin, used in acute and inpatient settings.

Balancing benefit and risk

Every anticoagulation decision balances the reduction in thrombotic risk against an increase in bleeding risk. Scores such as CHA2DS2-VASc for stroke risk and ORBIT or HAS-BLED for bleeding risk inform, but do not replace, a shared decision with the patient. Importantly, a high bleeding score is usually a prompt to correct modifiable risk factors rather than a reason to withhold treatment.

Reversal and perioperative care

Reversal agents exist for major bleeding or urgent surgery: vitamin K and prothrombin complex concentrate for warfarin, idarucizumab for dabigatran and andexanet alfa for certain factor Xa inhibitors. Planned procedures require a documented interruption plan that accounts for renal function, the specific drug and the bleeding risk of the operation.