MONDAY, Aug. 4, 2008 (HealthDay News) -- The widely used anti-clotting drug Plavix appears to have a stronger effect in people who smoke, a study indicates.
Plavix (clopidogrel) is often given to heart attack patients after the attack. It inhibits formation of clots by blood cells called platelets.
The study of 259 people given Plavix because of coronary conditions found that those who smoked had significantly less clot formation than nonsmokers.
But it's still too early to say that doctors should include smoking among the factors that affect whether Plavix should be prescribed or how large the dose should be, said study lead author Dr. Paul A. Gurbel, associate professor of medicine at Johns Hopkins University and director of the Sinai Center for Thrombosis Research, Baltimore.
"I don't know if we can jump to that conclusion yet," Gurbel said. "We need to study this further. We do know from two large-scale clinical trials that smokers benefited more when they got Plavix therapy. Maybe smoking does something to make Plavix work better."
That "something" probably occurs in the liver, where the drug is metabolized, Gurbel said. Cigarette smoking increases the production of CYP1A2, a liver enzyme that converts the drug to its active form, he said.
"Current smoking was an independent predictor of low platelet aggregation," the journal report said.
Of course, lower clotting action can sometimes mean a higher risk for bleeding. But Gurbel said that, based on these early findings, "we don't know if [smoking patients] will bleed more."
The findings were expected to be published in the Aug. 12 issue of the Journal of the American College of Cardiology.
Plavix is widely used to prevent coronary problems and is commonly prescribed after a heart attack. A standard recommendation for heart attack patients includes a year of combined therapy with Plavix and aspirin, another clot-preventing drug.
The indication that smoking reduces platelet stickiness in people given Plavix "is certainly observational at this point" and requires proof in a large, controlled trial, Gurbel said.
"Were trying to get funding for a trial right now," he said.
The trial he envisions would enroll a large group of smokers who would all be prescribed Plavix. "Then we would remove the smoking in half the group," Gurbel said. "We would see whether that removal adds support for our observation."
The hardest part of such a trial would be to get half a group of smokers to quit, Gurbel acknowledged.
"And were definitely not telling people to smoke if they have heart disease," he said. Smoking is high on the list of risk factors for heart attack, stroke and other cardiovascular problems, Gurbel noted.
The study was funded in part by a grant from drug maker Daiichi Sankyo Inc.
For move on Plavix, head to the U.S. National Library of Medicine.