CASPAR : Clopidogrel and Acetyl Salicylic Acid in Bypass Surgery for Peripheral ARterial Disease

Inclusion Criteria: A patient is eligible for inclusion in the study 2-4 days after surgery if all the following criteria are fulfilled: * Informed consent obtained; * Chronic background treatment with daily ASA, whatever the dose, started at least 4 weeks before surgery. A window of a few days without ASA before surgery is acceptable, according to local practice. Post-randomization use of ASA must be between 75 and 100 mg/day. * Unilateral below knee bypass graft (i.e. the distal anastomosis is below the level of the knee joint) for atherosclerotic PAD within the previous 4 days; * Demonstration of initial patency of the index graft by an objective measurement (e.g. intra-operative Doppler scanning, flow measurement, angiography, Duplex scanning) during bypass surgery, or between surgery and the time of randomization; * No clinical evidence of graft occlusion at time of randomization. Exclusion criteria : PAD medical/surgical history * Onset of PAD symptoms before the age of 40 years * Non-atherosclerotic vascular disease (e.g. Buerger's disease, popliteal entrapment syndrome) * Patient receiving aorto-bifemoral, iliac-femoral or crossover (femoral-femoral) grafts, or undergoing peripheral transcutaneous angioplasty (PTA), with or without stenting, during the same surgery. Medical history related to bleeding risk * Current active bleeding at surgical site * Withdrawal of an epidural catheter less than 12 hours before randomization * Current active bleeding or increased risk of bleeding, such as severe hepatic insufficiency, proliferative diabetic retinopathy, peptic ulceration, bleeding diathesis or coagulopathy * Peptic ulceration within 12 months of randomization * Previous or current intracranial hemorrhage or hemorrhagic stroke, or any previous stroke for which the diagnosis of hemorrhagic stroke cannot be excluded * Any history of severe spontaneous bleeding such as gastrointestinal bleeding, gross hematuria, intraocular bleeding Other medical conditions * Previous disabling stroke (severe cerebral deficit such that the patient is bedridden or demented) * NYHA Class IV heart failure * Uncontrolled hypertension: Systolic Blood Pressure (SBP) \> 180 mm Hg, or Diastolic Blood Pressure (DBP) \> 100 mm Hg