Monitoring for anti-Xa activity for prophylactic administration of Fondaparinux in patients with artificial joint replacement.

The efficacy of measuring anti-Xa activity was evaluated in major orthopedic surgery patients receiving thrombo-prophylaxis with Fondaparinux. Although 98 orthopedic patients including those receiving total hip replacement (THR) and total knee replacement (TKR) were treated with 1.5 mg of Fondaparinux for prophylaxis of deep vein thrombosis (DVT). Sixteen patients developed DVT, but none was associated with a fatal pulmonary embolism. There was a wide range of anti-Xa activity, but there were no patients with less than 0.15 mg/l or more than 0.90 mg/l. Anti-Xa activity gradually increased from days 1 to 8 and showed no significant difference between patients with and without DVT. Anti-Xa activity was correlated with weight, height, body mass index, and antithrombin activity. Postoperative plasma levels of D: -dimer and soluble fibrin (SF) were markedly high, and those were significantly reduced at days 1 and 4 of treatment with Fondaparinux. Plasma levels of SF were significantly reduced at days 8 and 15, but D: -dimer was not. These findings suggested that there was continued thrombin generation after the injection of Fondaparinux until day 8 and secondary fibrinolysis occurred on day 8. In conclusion, 1.5 mg of Fondaparinux may not be sufficient for the prophylaxis of silent DVT, but it was found to be useful for that of fatal pulmonary embolism. Consequently, monitoring anti-Xa activity may be unnecessary for the administration of Fondaparinux at such doses.