Emerging concerns regarding thrombosis within drug-eluting stents has led to reevaluation of trial and practice data by the US Food and Drug Administration (FDA), according to a report issued by the American Heart Association.

Drug-eluting stents were developed to address the problem of restenosis seen with bare-metal stents. However, several recent studies have raised concerns that drug-eluting stents may not be more effective than bare-metal stents because of an increased risk of thrombosis within drug-eluting stents. Most recent data were presented at major medical meetings and are now being published. The FDA will review this and additional information.

There are two separate issues regarding the safety of drug-eluting stents. The first involves antithrombotic therapy after stent placement. Patients who have had a stent procedure should take both aspirin and another anti-platelet agent (most often clopidogrel) for periods of 1 to 12 months, depending on particular circumstances and the type of stent.

Existing joint clinical guidelines from the American Heart Association, American College of Cardiology, and Society for Coronary Angiography Intervention include specific recommendations. Research published earlier this year has shown that many patients are not following appropriate anti-platelet therapy during the first year after their stenting and they are more likely to have a nonfatal or fatal myocardial infarction.

The second issue is less well established at this time. The suggestion has been made that blood clots within drug-eluting stents are more common more than a year after stent placement than with bare-metal stents. There is conflicting data regarding the magnitude and significance of this difference. Some patients in longer-term studies were no longer taking aspirin, which is usually indicated on a lifelong basis for all patients with known coronary artery disease.

Additional studies will probably be required to define the risk of a late thrombotic event in patients with drug-eluting stents and the appropriate therapy to prevent them. In the meantime, it is important that all patients who have undergone stenting procedures continue aspirin indefinitely. Additional therapy should be left to clinical judgment based on individual patient circumstances.

According to American Heart Association President Raymond J. Gibbons, MD, "These recent reports have raised appropriate concerns regarding drug-eluting stents, and more research is needed to determine the long-term efficacy and safety of these devices. Until such information is available, patients should receive appropriate anti-platelet therapy according to existing practice guidelines wherever possible. This will usually require both aspirin and clopidogrel for periods of up to a year after stenting and aspirin indefinitely. Patients should not discontinue either aspirin or clopidogrel within the first year without consulting their treating cardiologist. We are collaborating with five other major medical organizations on an advisory which will appear shortly and will provide further guidance on this important issue."