The purpose of the study is to test whether an increase of the maintenance dose of clopidogrel from 75 to 150 mg per day results in an additional suppression of ADP-induced platelet aggregation

In patients treated with coronary stents clopidogrel therapy is usually initiated with a 300 to 600 mg loading dose. In the CREDO trial it was shown that a 300 mg loading dose results in a reduction of ischemic events after percutaneous coronary intervention (PCI) if given 6 hours prior to the procedure. An antiplatelet effect similar to that achieved by chronic therapy with 75 mg/day is reached within 2 hours when the high 600 mg loading is administered. The 600 mg loading dose has been shown to be safe and effective in preventing thrombotic events following coronary stent implantation. Recently, it was shown that in patients with stable angina and administration of the 600 mg loading dose at least two hours prior to PCI concomitant therapy with a GP IIb/IIIa antagonist does not result in a further reduction of the incidence of thrombotic events. In contrast to a number of investigations with different loading doses, no trials have been performed comparing different clopidogrel maintenance doses. Recently, it was shown that administration of a 600 mg loading dose in patients already on chronic clopidogrel therapy (75 mg/day) results in an additional significant increase in inhibition of adenosine diphosphate (ADP-) induced platelet aggregation. Therefore, it is possible that an increase of the clopidogrel maintenance dose in patients with chronic clopidogrel therapy also results in a more pronounced inhibition of platelet aggregation.

Inclusion Criteria:

• Patients with chronic aspirin therapy who are treated with percutaneous coronary intervention at least 2 hours after administration of a 600 mg loading dose of clopidogrel

Exclusion Criteria:

• Major alterations of blood count (particularly platelet count < 100x10^9/l, haemoglobin < 10 mg/dl
• Recent bleeding diathesis
• Presence of a hematologic or malignant disorder
• Oral anticoagulation with coumarin derivates
• Use of glycoprotein (GP) IIb/IIIa antagonists during the intervention or during the preceding 14 days
• Therapy with clopidogrel within the last 28 days