Drugs which inhibit COAGULATION of the blood. They are used to prevent and treat abnormal clotting of the blood, to treat THROMBOSIS, and sometimes to prevent or treat STROKE or TRANSIENT ISCHAEMIC ATTACKS (TIA). Anticoagulant drugs are also prescribed preventively in major surgery to stop abnormal clotting from occurring; HAEMODIALYSIS is another procedure during which these drugs are used. Anticoagulants are also prescribed to prevent thrombi (clots) forming on prosthetic heart valves after heart surgery.

The drugs are particularly effective in the treatment and prevention of venous clotting – for example, deep vein thrombosis (DVT) (see under VEINS, DISEASES OF). They are less effective in preventing thrombosis formation in arteries because of their fast-flowing blood, in which thrombi contain little fibrin (against which the anticoagulants work).The main anticoagulants used are the natural agent HEPARIN (a quick-acting variety and a low-molecular-weight, long-acting type); synthetic oral anticoagulants such as WARFARIN and the less-often-used acenocoumarol and PHENINDIONE; and antiplatelet compounds such as ASPIRIN, clopidogrel dipyridamole and ticlopidines.

Patients taking anticoagulants need careful medical monitoring and they should carry a card with instructions about the use of whatever drug they may be receiving. This is essential information should the individual require treatment for other medical conditions as well as for thrombosis. A class of medicines known as direct oral anticoagulants (DOAC) are used increasingly because they may not require regular blood testing to be performed.