Anticoagulant drugs

Anticoagulant drugs

Anticoagulants are used to prevent the formation or growth of fibrin/erythrocyte thrombi in the venous circulation. They are not useful for treating arterial thrombi which are mainly composed of platelet aggregates.

Anticoagulants can be administered parenterally or orally.

Parenteral anticoagulants:

Heparin (unfractionated or 'standard' heparin) acts rapidly, but also has a short duration of action. This characteristic allows heparin infusion to be used in patients at high risk of bleeding as the anticoagulation effect ends rapidly upon stopping infusion.

Low molecular weight heparins are as effective as unfractionated heparin, but have a lower risk of causing heparin-induced thrombocytopenia. They are also more convenient to use due to their longer duration of action than unfractionated heparin, and are therefore the preferred option for prevention of venous thromboembolism, for example in the treatment of deep-vein thrombosis (DVT), pulmonary embolism (PE), myocardial infarction (MI), unstable coronary artery disease and for the prevention of clotting in extracorporeal circulatory procedures. Example drugs are dalteparin sodium, enoxaparin sodium, and tinzaparin sodium

Heparinoids, such as danaparoid sodium are mixtures of heparin derivatives termed glycosaminoglycans, such as heparan, dermatan, and chondroitin sulphates. Used to reduce the risk of surgical patients of developing DVT.

Argatroban is an oral anticoagulant that acts as a thrombin inhibitor. It is indicated for prophylaxis or treatment of thrombosis in patients with, or at risk of, heparin-induced thrombocytopenia (HIT).

Hirudins, such as desirudin, lepirudin and bivalirudin are derivatives of the salivary anticoagulant found in leeches. These compounds are direct thrombin inhibitors. Bivalirudin is indicated for unstable angina or non-ST-segment elevation MI in patients planned for urgent or early intervention, and as an anticoagulant for patients undergoing percutaneous coronary intervention.

Epoprostenol (prostacyclin PGI2) can be used to prevent platelet aggregation during renal dialysis if heparins are unsuitable or contraindicated. Epoprostenol has a very short half-life so must be administerd by continuous intravenous infusion. Can also be used in conjunction to oral anticoagulation to treat primary pulmonary hypertension resistant to other treatment, under specialist care.

Fondaparinux inhibits activated coagulation factor X and is indicated for prevention of venous thrombus formation in various at-risk patient groups

Oral anticoagulants:

Coumarins (warfarin and acenocoumarol) and phenindione antagonise the effect of vitamin K, but are slow in achieving full anticoagulatory effect (48-72 hours). From this group of drugs, warfarin is the drug of choice. Warfarin is used as prophylaxis of venous thromboembolism in at-risk patients. Keeling D et al. (2011, PMID: 21671894) provide guidelines on using warfarin anticoagulation.

Dabigatran, rivaroxaban and apixaban are oral anticoagulants which are alternatives to warfarin. Rivaroxaban and apixaban inhibit platelet activation and fibrin clot formation via direct, selective and reversible inhibition of Factor Xa. Dabigatran etexilate is a prodrug that is converted to the active dabigatran in vivo. Dabigatran is a specific reversible direct thrombin inhibitor. Regular laboratory testing is not required for either of these drugs. Additionally, there are fewer drug and food interactions with these oral anticoagulants. These represent advantages to the use of these drugs over warfarin.