12 Antiplatelet Therapy

Five drugs that inhibit platelet function have been evaluated for their antithrombotic effects in humans. These are aspirin, clofibrate, dipyridamole, hydroxychloroquine and sulphinpyrazone. Aspirin has been shown to reduce the number of transient ischaemic attacks (TIA), strokes and deaths in patients with multiple TIA. The reduction in TIA was greatest in males who were normotensive and when there was an angiographically demonstrated lesion in the carotid artery that accounted for the symptoms. Aspirin reduced venous thrombosis and fatal and non-fatal pulmonary embolism in patients after surgery for fractured hip and after elective hip replacement. There is evidence that the prophylactic effect of aspirin may be greater in male patients. Aspirin reduced the frequency of arteriovenous shunt thrombosis and abolished symptoms in patients with peripheral ischaemia associated with thrombocytosis and spontaneous platelet aggregation. There is no conclusive evidence at present that aspirin is effective in patients with coronary artery disease. Dipyridamole in combination with oral anticoagulants is effective in reducing the frequency of systemic embolism in patients with prosthetic heart valve replacement, but is ineffective in patients with transient cerebral ischaemic attacks or for the prevention of venous thromboembolism. Clofibrate has not been shown to be beneficial in patients with arterial thromboembolism. Hydroxychloroquine is effective in reducing postoperative venous thrombosis in patients undergoing general abdominothoracic surgery but the evidence that it is effective in patients undergoing orthopaedic surgery is inconclusive. Sulphinpyrazone may be effective in reducing the frequency of sudden cardiac deaths in the first year after myocardial infarction when it is started within 25 to 35 days of the initial infarction. Sulphinpyrazone reduced the incidence of arteriovenous shunt thrombosis in patients undergoing chronic haemodialysis and, in combination with anticoagulants, it reduced the frequency of recurrent venous thrombosis.