Monitoring the Anticoagulant Effects of a Low Molecular Weight Heparin Preparation:<i>Correlation of Assays in Orthopedic Surgery Patients Receiving Ardeparin Sodium for Prophylaxis of Deep Venous Thrombosis</i>

This prospective, uncontrolled trial explored the relationship between varying dosages of a low molecular weight heparin (LMWH) preparation, ardeparin sodium (Normiflo, Wyeth-Ayerst, Philadelphia, PA), and anticoagulant effects, monitored by an amidolytic anticoagulation factor Xa (aXa) assay and by global coagulometric methods, including the activated partial thromboplastin time (APTT) and the Heptest (Haemachem, St. Louis, MO). Thirty-three patients undergoing elective unilateral total hip or knee replacement received subcutaneous ardeparin prophylaxis initiated 12 to 18 hours following surgery, administered at a fixed 40-mg dose twice daily, 50 aXa U/kg twice daily or 90 aXa U/kg once daily for up to 14 days. The target antithrombotic aXa levels, determined by amidolytic assay in plasma 6 hours after each ardeparin injection, were most optimally attained and maintained by twice-daily dosing based on body weight and correlated well with incremental increases in Heptest values measured chronometrically. The Heptest results at 12 hours after ardeparin administration indicated that the global anticoagulant effects produced by LMWH are sustained for many hours after subcutaneous dosing.