Some Resistance to Drugs Designed to Prevent Blood Clots Found

Researchers at Sinai Hospital of Baltimore have discovered that patients with overreactive platelets, which may be a risk factor for clotting, do not always respond to current drugs designed to decrease platelet activity. The research is published in the June 19, 2003, issue of Circulation.

"Reactive platelets are very sticky and this can lead to an increased risk of blood clotting," said Paul A. Gurbel, M.D., F.A.C.C., director, Sinai Center for Thrombosis Research, Sinai Hospital of Baltimore. "We have found that one of the leading drugs designed to fight this problem, clopidogrel, as currently administered, does not appear to be an effective treatment for some patients."

For many doctors, clopidogrel with aspirin is widely used and is the regimen of choice to prevent blood clots in patients with hardening of the arteries, also known as atherosclerosis. It is also the regimen used to prevent the formation of blood clots within stents that are implanted to treat blockages in coronary arteries. However, according to Gurbel's research, a significant number of patients did not respond to that line of treatment.

In order to conduct the study, consenting patients of all ages, who were about to undergo elective coronary stenting, were given clopidogrel. All patients were also on aspirin therapy. The results show that two hours after placement of the stent, 63 percent of patients were resistant to the therapy and platelet reactivity was at high levels. Five days after stenting, 31 percent of the total people remained resistant.

The study concludes that a significant percentage of patients are resistant to the current antiplatelet regimen used for preventing blood clots. Researchers suggest further studies be conducted using higher drug doses and the exploration of new drugs to treat the problem.