Adverse effects and drug interactions of antithrombotic agents used in prevention of ischaemic stroke

Stroke is the third most common cause of death in the US. Primary prevention of stroke can be achieved by control of risk factors including hypertension, diabetes mellitus, elevated cholesterol levels and smoking. Approximately one-third of all ischaemic strokes occur in patients with a history of stroke or transient ischaemic attack (TIA). The mainstay of secondary prevention of ischaemic stroke is the addition of medical therapy with antithrombotic agents to control the risk factors for stroke. Antithrombotic therapy is associated with significant medical complications, particularly bleeding.Low-dose aspirin (acetylsalicylic acid) has been shown to be as effective as high-dose aspirin in the prevention of stroke, with fewer adverse bleeding events. Aspirin has been shown to be as effective as warfarin in the prevention of noncardioembolic ischaemic stroke, with significantly fewer bleeding complications. Ticlopidine may be more effective in preventing stroke than aspirin, but is associated with unacceptable haematological complications. Clopidogrel may have some benefit over aspirin in preventing myocardial infarction, but has not been shown to be superior to aspirin in the prevention of stroke. The combination of clopidogrel and aspirin may be more effective than aspirin alone in acute coronary syndromes, but the incidence of adverse bleeding is significantly higher. Furthermore, the combination of aspirin with clopidogrel has not been shown to be more effective for prevention of recurrent stroke than clopidogrel alone, while the rate of bleeding complications was significantly higher with combination therapy. The combination of aspirin and extended-release dipyridamole has been demonstrated to be more effective than aspirin alone, with the same rate of adverse bleeding complications as low-dose aspirin. When selecting the appropriate antithrombotic agent for secondary prevention of stroke, the adverse event profile of the drug must be taken into account when assessing the overall efficacy of the treatment plan.