• Myocardial infarction
• Unstable angina
• Cerebral infarction
• Transitory cerebral ischaemia
• Percutaneous or surgical vascular intervention
• Sudden deterioration of symptoms
• Amputation
• Death

1000 patients with atherosclerosis of lower limbs are examined to evaluate the activity of the platelets during the standard treatment, including aspirin. A minor group will receive clopidogrel instead of aspirin for 2 weeks.

The main hypothesis is that high platelet activity at the beginning of the study is associated with a higher risk of atherothrombosis. Follow up time is 6 years.

Patients with atherosclerosis of the lower limbs are at high risk of atherothrombosis, mainly heart attack and stroke. The medical treatment of these patients include platelet inhibiting drugs, usually aspirin, to reduce the risk of blood clot formation. Clopidogrel is another platelet inhibiting drug, which is prescribed less often, primarily because of the high costs compared to aspirin.

Phenomena of 'resistance' to these drugs have been described by numerous investigators. Essentially resistance means that the effect of the drug described is less than expected or missing, when described by various laboratory methods. We still do not know which way resistance is best described, and we still do not know if patients who are 'resistant' to either drug are less protected against future heart attacks or strokes.

Main objectives:

• To measure the activity of platelets in these patients during aspirin treatment.
• To measure the activity of platelets in a minor population of these patients during clopidogrel treatment.
• To evaluate the prognostic significance of resistance to aspirin in these patients.

Secondary objectives:

• To describe the relation between drug resistance and the level of inflammatory markers in the blood.

Methods:

Platelet activity is measured by the PFA-100 (Dade Behring) and by traditional turbidimetric aggregation.

Patients:

Number needed is 1000.

Follow up:

6 years

Endpoints:

Myocardial infarction, unstable angina, cerebral infarction, transitory cerebral ischaemia, sudden deterioration of symptoms, percutaneous or surgical vascular intervention, amputation, death.

Inclusion Criteria:

• Atherosclerosis of the lower limbs, defined by one of the following criteria: Ancle-Brachial Pressure Index (ABPI)< 0.9, intermittent claudication, ischaemic pain at rest, ischaemic ulcers or gangrene.
• Age > 18 years
• For fertile women: Use of safe contraception (intrauterine contraceptive device, the pill, hormonal skin patches, progestogen injections, progestogen implant, vaginal ring)

Exclusion Criteria:

• Allergy to either Aspirin or Clopidogrel
• Known bleeding disorder
• Platelet count < 140 mia/L or > 400 mia/L
• Intake of NSAID's, SSRI's or Dipyridamol within the preceding 14 days
• Not radically treated gastrointestinal ulceration within the last 6 month
• Greater surgical procedures performed within the last 3 month
• Severe renal disease
• Severe hepatic disease
• Breast feeding
• Pregnancy