Aspirin: new cardiovascular uses for an old drug.

Inhibition of TXA2-dependent platelet function by aspirin may lead to prevention of thrombosis as well as to excess bleeding. The balance between the two depends critically on the absolute thrombotic versus hemorrhagic risk of the patient. As the risk of experiencing a major vascular event increases, so does the absolute benefit of antiplatelet prophylaxis with aspirin [Figure-see text]. The antithrombotic effect of aspirin does not appear to be dose related over a wide range of daily doses (30 to 1,300 mg), an observation consistent with saturability of platelet COX-1 inhibition by aspirin at very low doses. In contrast, GI toxicity of the drug does appear to be dose related, consistent with dose- and dosing interval-dependent inhibition of COX-1 activity in the nucleated lining cells of the GI mucosa. Thus, aspirin once daily is recommended in all clinical conditions where antiplatelet therapy is effective. Because of safety considerations, physicians are encouraged to use the lowest dose of aspirin shown effective in each clinical setting [Table-see text].