Genetic Test Not Necessary Before Taking Plavix

Genotype testing not needed before taking antiplatelet drug Plavix

(RxWiki News) After an artery-opening procedure following a heart attack, some patients take Plavix (clopidogrel) to treat or prevent a blood clot. Though the drug isn't as effective in some individuals, genetic testing is not needed, a recent study suggests.

U.S. Food and Drug Administration officials had previously recommended genetic testing for genotype CYP2C19 before prescription of clopidogrel to pinpoint patients who may be less likely to respond to the drug.

However, a University College London study did not find a significant association between the drug and cardiovascular events.

"Take antiplatelets as prescribed by your doctor."

Dr. Michael V. Holmes, of University College London, said his review study found that "despite associations between CYP2C19 genotype, clopidogrel metabolism, and platelet aggregation, this systematic review and meta-analysis does not demonstrate a clinically important association of genotype with cardiovascular outcomes with the possible exception of stent thrombosis."

About 40 million patients worldwide take antiplatelet drug clopidogrel, though a genetic variation could mean that the medication would not be effective in certain patients. The American Heart Association and American College of Cardiologists have said previously that there is not enough evidence to support CYP2C19 genotype testing.

During the study researchers reviewed 32 studies that reported clopidogrel metabolism, platelet reactivity or clinically relevant outcomes, including cardiovascular disease events and bleeding, and information on CYP2C19 genotype. More than 42,000 patients were included in those studies, with reports of 3,545 cardiovascular events, 1,413 bleeding events and 579 incidents of stent thrombosis, a rare and potentially deadly complication after stent implantation.

Of those studies, six were randomized trials and the remainder exposed patients to clopidogrel through treatment.

Researchers said the finding that CYP2C19 was not linked to modification of the effect of clopidogrel on cardiovascular events or bleeding was important to understanding of the significance of the genotype.

“In the absence of such a study, physicians should use CYP2C19 or platelet reactivity testing rarely, if ever, and interpret the results with caution," said Dr. Steven E. Nissen, of the Cleveland Clinic Foundation, in an accompanying editorial.

It is still likely that pharmacogenomics has a bright future in cardiovascular medicine, but the pharmacogenomics approach to drug therapy must undergo the same rigorous testing for efficacy and cost-effectiveness that is required for other therapies.

Overzealous adoption based on limited biochemical data does not serve the public interest.”

The study is published in the Dec. 28 issue of the Journal of the American Medical Association.

Review Date: 
December 27, 2011