Effect of prolonged treatment with acetylsalicylic acid and dipyridamole on platelet thromboxane A2 production in atherosclerotic subjects.

We evaluated the effect of four weeks treatment with 90 mg and 1500 mg of acetylsalicylic acid (ASA), 990 mg of ASA together with 225 mg of dipyridamole and 225 mg of dipyridamole daily on the production of thromboxane A2 (TxA2) by platelets of atherosclerotic subjects. All doses of ASA studied inhibited 99% or more of TxA2 production from the third day to the end of the treatment, whereas dipyridamole did not have any effect. After the treatment, TxA2 production recovered in two weeks. Our results argue against the clinical relevance of the recent suggestions that salicylate accumulating during prolonged treatment with ASA could reduce the effect of the parent drug on the synthesis of TxA2 by platelets. Our data also dispute the inhibition of TxA2 synthesis as an antithrombotic mechanism of dipyridamole.