Doubt Cast on Use of Genetic Test Before Plavix

Research review suggests test won't help docs determine who would benefit from heart drug

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By Randy Dotinga

Wednesday, December 28, 2011

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WEDNESDAY, Dec. 28 (HealthDay News) -- A new review of existing research suggests that, despite a federal recommendation, genetic testing won't help physicians determine which heart patients should get Plavix, a blood-thinning drug used to treat certain cardiac conditions.

Plavix, also known as clopidogrel, is used to treat or prevent blood clots due to the clogging of arteries and after such surgical procedures as balloon angioplasty.

But some patients won't experience the drug's clot-preventing benefits if their bodies don't process it properly, potentially leading to heart attack, blood clots in stents and death, according to Dr. Jean-Sebastien Hulot, associate professor of medicine at the Cardiovascular Research Center at Mount Sinai School of Medicine. Or, he said, they could experience the reverse -- excessive bleeding if the medication has too much of an effect. Hulot was not involved with the study, but is familiar with the findings.

The U.S. Food and Drug Administration believes that genetic testing could help identify patients who won't respond well to the drug. But the American Heart Association and the American College of Cardiologists have been skeptical that the genetic testing in question is useful.

In the new review, Dr. Michael V. Holmes of University College London and colleagues examined 32 studies that included over 42,000 patients. They looked for signs of bleeding problems, blood clots in stents and cardiovascular problems.

They also conducted a meta-analysis in which they examined statistics in the studies as a whole.

While they mention some statistical caveats, the researchers found that a specific genetic trait -- linked to the body's ability to respond to the drug -- did not significantly affect the risk of cardiovascular problems.

In a commentary accompanying the study, Dr. Steven E. Nissen, borrowing a phrase from a former chairman of the Federal Reserve, wrote, "It now appears that the FDA warning reflected a case of 'irrational exuberance.'"

Nissen, chair of cardiovascular medicine at the Cleveland Clinic, noted that the review has limitations. But, he added, for the time being physicians should "rarely, if ever" use the genetic testing in question and should "interpret the results with caution."

Hulot, the Mount Sinai School of Medicine professor, is skeptical. He said the findings are "far from convincing" and questioned their statistical validity. He also pointed to an earlier study, also a meta-analysis, that suggested a genetic trait did indeed boost the risk of problems for those who took the drug in certain cases.

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

SOURCES: Jean-Sebastien Hulot, M.D., Ph.D., associate professor of medicine and director, Pharmacogenomics & Personalized Therapeutics, Cardiovascular Research Center, Mount Sinai School of Medicine, New York City; Dec. 28, 2011, Journal of the American Medical Association

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