The Dose--Plasma Concentration Relationship of Tranexamic Acid during Surgery

Plasma specimens from 59 patients undergoing cardiac operations utilizing extracorporeal circulation underwent determination of tranexamic acid concentration to explore the effect of dose administered to plasma concentration. Each patient received one of five doses of tranexamic acid in double-blinded, randomized fashion, ranging from 2.5 to 40 mg kg(minus sign1) for the loading dose and from 0.25 to 4.0 mg kg(minus sign1) h(minus sign1) for a subsequent infusion. Plasma collections occurred after completion of the loading dose, during extracorporeal circulation, before protamine infusion, after protamine infusion, and following arrival in the intensive care unit. The samples were analyzed using high-performance liquid chromatography. The logarithm of plasma concentration varied linearly with the logarithm of dose administered at each sampling time (r(2) values 0.82, 0.95, 0.89, 0.74 and 0.93 for the respective collection times). Plasma concentrations did not decrease during extracorporeal circulation despite absence of tranexamic acid in the pump prime. However, concentrations varied inexplicably following protamine administration and decreased in the intensive care unit.