 Tranexamic acid is administered intravenously to prevent bleeding associated with cardiac surgery and cardiopulmonary bypass. The current dosing regimen for tranexamic acid was empirically derived based upon pharmacokinetics in normal patients receiving the drug. We have developed an assay for tranexamic acid and found that the plasma concentration of tranexamic acid varies greatly between patients and also over time within each patient, especially in patients with renal insufficiency. We have developed an alternative dosing schedule for tranexamic acid that incorporates the effects of renal function on tranexamic acid concentrations. The objective of this preliminary study is to determine if this new dosing schedule can achieve the desired plasma concentration of tranexamic acid and reduce intra and inter patient variability in tranexamic acid plasma concentrations relative to the current dosing schedule. The results of this study will be used in a larger subsequent study of what level of plasma tranexamic acid concentration is needed to prevent bleeding and transfusion of blood products in patients undergoing cardiac surgery. 