Mar 23, 2011
By BRADLEY J. FIKES
Higher than normal doses of the anti-clotting drug Plavix produce no effect on cardiovascular injury or death in heart patients at risk for blood clots, according to a large new study led by a Scripps Health researcher.
Researchers said the study is the largest conducted on customized antiplatelet therapy. Results were published in the March 16 issue of the Journal of the American Medical Association.
The negative results leave researchers without any clearer path to better treat cardiovascular patients at risk because of high blood platelet activity. Cardiovascular disease is the nation’s leading cause of death; according to the National Heart, Lung and Blood Institute, 1.25 million heart attacks take place each year in the United States. About 34 percent of those who have heart attacks die from them.
Plavix and aspirin are routinely prescribed to heart patients who have been implanted with coronary stents, flexible mesh tubes that open up blocked blood vessels that nourish the heart. The blood thinner reduces the activity of clot-forming platelets by making them “slipperier,” said Scripps Health cardiologist Matthew J. Price, the study’s first author.
Plavix helps reduce reblockage for many patients, but not all, Price said. So the trial tested whether the higher doses of Plavix, generically known as clopidogrel, were given to patients with higher-than-normal platelet activity, known as nonresponders.
“Studies have shown there appears to be a link between not responding to clopidogrel and clotting events,” Price said. Scripps routinely performs genetic testing for responsiveness before implanting stents.
The study, called GRAVITAS (Gauging Responsiveness with a VerifyNow Assay Impact on Thrombosis and Safety), enrolled 2,214 patients with high platelet activity in a randomized trial. The patients had been implanted with drug-eluting (-emitting) stents and had received balloon angioplasty.
Patients either got the standard dose of Plavix, 75 milligrams, or a double dose, 150 milligrams plus an initial dose of 600 milligrams, and were followed for six months. Doctors compared their rates of death from cardiovascular causes, nonfatal heart attacks, and blood clots in the stents, known as stent thrombosis.
It’s not entirely clear why the higher dose of Plavix didn’t produce additional benefit, said Price, of the Scripps Translational Science Institute. The institute, part of Scripps Health, aims to speed up the often cumbersome process of turning basic research into treatments.
It could be that those with high platelet activity need an even higher dose of the drug, Price said. Alternately, he said, Plavix may just not have any effect, no matter what the dose, on the “nonresponders.”