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Gene Mutations May Blunt Plavix's Effectiveness, Study Finds

By Steven Reinberg
HealthDay Reporter

TUESDAY, Oct. 26 (HealthDay News) -- People with certain gene variants who take the blood-thinning drug Plavix (clopidogrel) may be at increased risk for serious complications after coronary stent placement, a new study finds.

Having the gene variants seems to reduce the effectiveness of Plavix and put patients at higher risk of developing blood clots in the stent, suffering a heart attack or stroke, or even dying, according to the research.

"Clopidogrel is one of the most commonly prescribed medications worldwide," said lead researcher Dr. Jessica L. Mega, an instructor in medicine at Brigham and Women's Hospital and Harvard Medical School in Boston.

But, "not all patients experience the same anti-clotting effects of the medication. Some of this variation is based on genetic variants in the CYP2C19 gene," she said.

For the study, published in the Oct. 27 issue of the Journal of the American Medical Association, Mega's team conducted a meta-analysis of nine studies involving a total of 9,685 people. In a meta-analysis, researchers review published studies to tease out data about particular outcomes.

In this case, the researchers looked for the effect that variants of the CYP2C19 gene had on people taking the antiplatelet drug and undergoing angioplasty and stent placement to open a blocked artery.

Among the patients studied, 863 died or had a heart attack or stroke, and 84 developed blood clots in their stents.

The researchers found that 71.5 percent of the total patient group had no variant of the CYP2C19 gene. However, 26.3 percent had one variant and 2.2 percent had two variants of the CYP2C19 gene that appeared to affect the body's response to Plavix.

Having one or two variants significantly increased the risk of death, heart attack or stroke, or developing blood clots in the stents, the researchers found.

Plavix uses a liver enzyme to convert the drug to its active form. The genetic variants prevent all of the drug from being converted, which increases the odds of poorer outcomes.

The study was limited, however, in that 95.8 percent of the patients studied were white and individual patient-level data from the studies could not be combined, researchers noted.

Last March, the U.S. Food and Drug Administration said Plavix must carry a "black box" warning on its label, alerting patients and doctors that some people don't metabolize the medication properly.

"Almost one in three patients is not receiving ideal protection from ischemic events when treated with standard doses of clopidogrel for coronary stenting," Mega said.

"Given how widely clopidogrel is used to treat patients with cardiovascular disease, determination of the optimal antiplatelet treatment doses or regimens for individual patients is needed to tailor therapy appropriately," she added.

The findings raise the question of whether routine genetic testing of Plavix patients is needed, but some experts say it's too early for that.

Dr. Gregg Fonarow, an American Heart Association spokesman and professor of cardiology at the University of California, Los Angeles, noted that a clinical alert issued in July by the American College of Cardiology and American Heart stated that "the evidence base is insufficient to recommend routine genetic testing at the present time in clopidogrel-treated patients."

"There is no information that routine testing improves outcome in large subgroups of patients," Fonarow said. "Further studies are needed to determine if routine genetic testing or platelet function testing and alteration of the antiplatelet regimen based on these findings will improve clinical outcomes."

Another expert, Dr. Valentin Fuster, a professor at Mount Sinai School of Medicine in New York City and author of an accompanying journal article, agrees that genetic testing isn't necessary.

"It's very nice that we learn about genetics, but to have a clinical applicability to the patient is still very far off," he said.

More information

For more information on Plavix, visit the U.S. Food and Drug Administration.

SOURCES: Jessica L. Mega, M.D., M.P.H., instructor in medicine, Brigham and Women's Hospital and Harvard Medical School, Boston; Valentin Fuster, M.D., Ph.D., the Richard Gorlin, MD/Heart Research Foundation Professor, Mount Sinai School of Medicine, New York City; Gregg Fonarow, M.D., American Heart Association spokesman and professor, cardiology, University of California, Los Angeles; Oct. 27, 2010, Journal of the American Medical Association

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