A synthetic anticoagulant (see ANTICOAGULANTS). Given by mouth, it is used to prevent the formation of clots in the blood in rheumatic heart disease and atrial fibrillation (see HEART, DISEASES OF); as prophylaxis after insertion of a prosthetic heart valve; and as prophylaxis and treatment of venous thrombosis and pulmonary embolism. It is slower in action than WARFARIN, not achieving its full anticoagulant effect until up to 48 hours after the initial dose. The drug should be avoided in patients with renal or hepatic impairment, and whenever severe hypersensitivity reactions have previously occurred. Adverse effects include rashes, fever, LEUCOPENIA, AGRANULOCYTOSIS, diarrhoea and pink urine; breast feeding should be avoided.