Once versus twice daily aspirin after coronary bypass surgery: a randomized trial

The authors randomized 68 patients undergoing CABG to three treatment groups:  

• ASA 81 mg QD
• ASA 325 mg QD
• ASA 162 mg BID

On the 4th day following CABG, the authors measured serum thromboxane B2 (TXB2) as an inverse surrogate for ASA effect.  The order of TXB2 levels were as follows:  162 mg BID << 81 mg BID ≈ 81 mg QD.  Thus, the optimal regimen, according to this small study, would be ASA 162 mg BID.