Aspirin and Other Platelet Active Drugs

Relationship Among Dose, Effectiveness, and Side Effects

Thus, aspirin is an effective antithrombotic agent in doses between 100 mg/day and 1.2 g/day. There is no evidence that low doses (160-325 mg/day) are either more effective or less effective than high doses (900-1,500 mg/day). There is evidence, however, that low doses produce fewer gastric side effects. The results of biochemical studies on its mechanism of action, the dose-related side effects of aspirin, and the results of clinical studies evaluating antithrombotic effects all support the use of low doses of aspirin in the treatment of thromboembolic disorders in which the drug has been found to be effective. There is also now suggestive evidence from the UK-TIA study that aspirin is effective in patients with transient cerebral ischemia in a dose of 300 mg/day (level I), although most of the evidence for effectiveness has been obtained with higher doses (eg, approximately 1,000 mg/day).

Although a preliminary report of a study evaluating the effectiveness of aspirin (325 mg every second day) in the primary prevention of myocardial infarction suggests a beneficial effect of aspirin (level I), it would be prudent at this stage to limit the use of prophylactic aspirin to patients at high risk for coronary artery disease and cerebrovascular disease.

A greater benefit for aspirin has been reported in males in some studies, although this finding has not been consistent. At present, there is no convincing evidence from clinical studies that the addition of dipyridamole to aspirin improves its clinical efficacy. A critical review of the alleged antithrombotic action of dipyridamole has recently been published by Fitzgerald.