Treatment with aspirin 75 to 162 mg daily should be continued indefinitely in the absence of contraindi- cations in patients with SIHD.716,717 (Level of Evidence: A) 2. Treatment with clopidogrel is reasonable when as- pirin is contraindicated in patients with SIHD.718 (Level of Evidence: B) Class IIb 1. Treatment with aspirin 75 to 162 mg daily and clopidogrel 75 mg daily might be reasonable in certain high-risk patients with SIHD.719 (Level of Evidence: B) Class III: No Benefit 1. Dipyridamole is not recommended as antiplatelet therapy for patients with SIHD.720 722 (Level of Evidence: B) 4.4.2.1.1. Antiplatelet Agents. Because platelet aggregation is a key element of the thrombotic response to plaque disrup- tion, platelet inhibition is recommended in patients with SIHD unless contraindicated. Aspirin is a cyclooxygenase inhibitor that produces irreversible blockade of prostaglandin endoperoxide formation. Among 2920 patients with SIHD, a comprehensive meta-analysis of source data revealed an association of aspirin use with a 37% reduction in the risk of serious vascular events, including a 46% decrease in the risk for UA and a 53% decrease in the risk of requiring coronary angioplasty.716 Almost two thirds of the patients included in this meta-analysis were participants in SAPAT (Swedish Angina Pectoris Aspirin Trial), in which patients with SIHD were assigned randomly to aspirin 75 mg per day or placebo for a median of 15 months.717 Aspirin in a dose of 75 to 162 mg daily is equally as effective as 325 mg in secondary prevention and is associated with a lower risk of bleeding. Doses ,75 mg have less proven benefit.716,723 Aspirin is relatively contraindicated in patients with known allergies to nonsteroidal antiinflammatory drugs and in patients with the syndrome of asthma, rhinitis, and nasal polyps. 