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J Thromb Haemost. 2015 Mar;13(3):448-56. doi: 10.1111/jth.12832. Epub 2015 Feb 6.

Multiple daily doses of acetyl-salicylic acid (ASA) overcome reduced platelet response to once-daily ASA after coronary artery bypass graft surgery: a pilot randomized controlled trial.

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Hamilton General Hospital, McMaster University, Hamilton, ON, Canada; Department of Medicine, McMaster University, Hamilton, ON, Canada.



The efficacy of ASA for prevention of graft failure following CABG surgery may be limited by incomplete platelet inhibition due to increased post-operative platelet turnover.


To determine whether acetyl-salicylic acid (ASA) 325 mg once-daily or 81 mg four-times daily overcomes the impaired response to ASA 81 mg once-daily in post-operative coronary artery bypass graft (CABG) patients.


We randomized 110 patients undergoing CABG surgery to either ASA 81 mg once-daily, 81 mg four times daily or 325 mg once-daily and compared their effects on serum thromboxane B2 (TXB2 ) suppression and arachidonate-induced platelet aggregation.


One hundred patients were included in the final analysis. Platelet counts fell after surgery, reached a nadir on day 2, and then gradually increased. Although there was near complete suppression of TXB2 on the second or third post-operative day, TXB2 levels increased in parallel with the rise in platelet count on subsequent days. This increase was most marked in patients receiving ASA 81 mg once-daily and less evident in those receiving ASA four times daily. On post-operative day 4, (i) median TXB2 levels were lower with four times daily ASA than with either ASA 81 mg once-daily (1.1 ng/mL; Quartile(Q) Q1,Q3: 0.5, 2.4 and 13.3 ng/mL; Q1,Q3: 7.8, 30.8 ng/mL, respectively; P < 0.0001) or ASA 325 mg once-daily (3.4 ng/mL; Q1,Q3: 2.0, 8.2 ng/mL; P = 0.002), and (ii) ASA given four times daily was more effective than ASA 81 mg once-daily and 325 mg once-daily at suppressing platelet aggregation.


Four times daily ASA is more effective than ASA 81 and 325 mg once-daily at suppressing serum TXB2 formation and platelet aggregation immediately following CABG surgery.


aspirin; coronary artery bypass; drug resistance; perioperative period; platelet function tests

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