Platelet function one and three months after coronary bypass surgery in relation to once or twice daily dosing of acetylsalicylic acid.

INTRODUCTION: Current guidelines recommend acetylsalicylic acid (ASA) treatment after coronary artery bypass grafting (CABG) to reduce thrombotic vein graft occlusion. The optimal dosage of ASA is not known.

MATERIALS AND METHODS: Forty-two patients undergoing elective CABG were randomized to receive either ASA 75mg or 160mg once daily (OD) or 75mg twice daily (BID) after the operation. Platelet function testing was performed before, and one and three months after the operation.

RESULTS: White blood cell counts increased during the initial postoperative days whereas platelet counts were initially slightly reduced after the operation but increased after one month without any major changes of mean platelet volumes. Serum thromboxane B2 was more effectively suppressed at one and three months after the operation with ASA 75mg BID or 160mg OD than with 75mg OD (p<0.001). ASA 75mg BID and 160mg OD were equally effective. Adenosine diphosphate stimulated platelet aggregation in whole blood (Multiplate®) was increased one and three months after the operation, and this was counteracted by ASA 75mg BID but not by 75 or 160mg OD. Arachidonic acid-induced aggregation was more effectively inhibited by 75mg BID or 160mg OD compared to 75mg OD at three months.

CONCLUSIONS: Less effective inhibition of platelet activation was obtained with ASA 75mg OD than with ASA 160mg OD or 75mg BID up to three months after CABG. Especially the latter dose is of interest for further studies of efficacy and clinical outcomes after CABG.