Objective To evaluate the efficacy and safety of a 600 mg loading dose of clopidogrel followed by 150 mg as maintenance dose in patients with acute coronary syndrome (ACS) undergoing drugeluting stent (DES) implantation.  Methods Totally 608 consecutive ACS patients undergoing DES implantation were enrolled in our hospital from December 2004 to December 2005. A 600 mg loading dose was administered before percutaneous coronary intervention (PCI)

and then the patients were randomized to receive clopidogrel 75 mg （n=307）or 150 mg （n=301）per day for 30 d in addition to 300 mg aspirin daily. From 30 d to 12 months after the operation

all patients received 75 mg/d clopidogrel and were followed up for a mean period of 18 months.  Results The ratios of fatal or non-fatal myocardial infarction (MI) and target vessel revascularization (TVR) were significantly lower in the 150 mg group than in the 75 mg group (3.7% vs 8.1%

P= 0.025; 9% vs 14.7%

P=0.033). So the overall incidence of primary end point including death

MI and TVR was obviously lower in the 150 mg group than in the 75 mg group (13% vs 20.2%

absolute risk reduction 7.2%

P=0.017). There was no significant difference in the incidence of all-cause death between 2 groups (2.7% vs 4.2%

P=0.375). While for secondary end points such as major and minor bleeding events

no significant difference was seen between 2 groups (2.3% vs 1.6%

P=0.574; 9.0% vs 6.8%

P=0.368). So was the need for blood transfusions (2.0% vs 1.3%

P=0.542).  Conclusion A high clopidogrel maintenance dose of 150 mg daily for the first month after PCI procedure following a 600 mg loading dose reduces the risk of adverse events in patients with ACS undergoing DES implantation and appears to be safe.