This randomized, double-blind, placebo-controlled, ascending single intravenous (IV) bolus-dose study evaluated safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of apixaban, a direct factor Xa (FXa) inhibitor approved for multiple indications. Eight healthy subjects were randomized 3:1 (apixaban:placebo) within each IV dose cohort (0.5, 1.25, 2.5, 3.75, and 5 mg). The 2.5-mg IV panel also received 5 mg of oral apixaban or placebo. Blood samples were collected for PK and PD, including international normalized ratio, modified prothrombin time (mPT), and anti-FXa activity. Apixaban had 66.2% oral bioavailability, dose-proportional exposure, 17 to 26 L steady-state volume of distribution, and 3.2 to 3.5 L/h total plasma clearance. Renal clearance was ≈27%. Anti-FXa activity and mPT changes followed the apixaban plasma concentration-time profile; both were highly correlated with concentration (R2 = 0.99 and R2 = 0.93 for anti-FXa activity and mPT, respectively). International normalized ratio remained within reference range (0.9-1.3). There were no serious or bleeding-related adverse events. Overall, an apixaban single IV bolus was safe and well tolerated over a 10-fold dose range by these subjects. Apixaban had good oral bioavailability, dose-proportional exposure, and constant plasma clearance over a broad dose range, with modest renal clearance. Apixaban PD were consistent with reversible FXa inhibition.