Controversies in timing of the first dose of anticoagulant prophylaxis against venous thromboembolism after major orthopedic surgery.

Adjusted doses of oral warfarin sodium or fixed doses of subcutaneous low-molecular-weight heparin (LMWH) are the standard approaches for preventing venous thromboembolism following major orthopedic surgery of the legs. In recent years, new anticoagulants have been compared with either LMWH or warfarin. The optimal timing for the first dose of LMWH prophylaxis and of the new anticoagulants is controversial. Recent clinical trials of LMWH and of …