Fondaparinux is an antithrombotic agent having already received a regulatory approval by the European Authorities in venous thromboembolic event prevention after major orthopaedic surgery, as total hip replacement (THR), total knee replacement (TKR), hip fracture (HF). The bleeding risk associated with this prescription is highly related to renal function evaluated by creatinin clearance (CrCl). In order to reduce the bleeding risk, it has been proposed to prescribe fondaparinux 1.5 mg/day in patients with a CrCl between 20 and 50ml/mn instead of 2.5mg/day (European MMA). In the meantime, this approval is essentially based on simulated pharmakinetic data without any support of clinical data.