Study Questions Test For Plavix

A new study questions a well-hyped test for Plavix and the CP2C19 gene variant. The U.S. Food and Drug Administration (FDA) issued a warning on the genetic test last year and, now, that warning is considered by some to have been premature.

The study found that the genetic test might not be all that useful, said The Wall Street Journal, citing research authors and well-respected physicians. The test is meant to help establish how successfully patients process Plavix (clopidogrel) and if they should be prescribed the Bristol-Myers Squibb Co. and Sanofi SA drug or a different treatment, for instance, Effient by Eli Lilly & Co., said The Journal.

We’ve written about the CYP2C19 gene variant before. People with the gene variant are slow metabolizers of the anti-blood clotting drug, Plavix, which makes the medication less effective for them. Heartburn drugs called proton pump inhibitors (Prilosec, Nexium, etc.) are also known to inhibit this gene, raising questions as to whether people taking Plavix should use such drugs.

The issue with Plavix was serious enough to prompt the FDA to order that the drug bear a boxed warning indicating that patients with diminished CYP2C19 function are at greater risk of cardiovascular adverse events after an acute coronary syndrome or percutaneous coronary intervention than normal metabolizers of Plavix. According to the labeling language, it is up to doctors to determine when they should genetically test patients before Plavix administration. They may choose to wait to see how patients react to a particular dose of Plavix and then decide whether to switch to another drug, depending on the outcome.

Enzymes in the body must activate Plavix in order for the drug to be effective; however, patients with the CYP2C19 gene variant seem to process the drug less effectively, according to a number of prior studies, said The Journal. About 30% of all Americans carry the variant, which is believed to affect how patients with the variant are dosed.

The recent findings, from a review of about 32 published studies that involved about 42,000 patients, confirmed that gene variant patients showed a difference in how they activated Plavix, said The Journal. The patients did not reveal a significantly increased rate for heart attack and other cardiac issues, however, said Michael Holmes, lead study author and a researcher in the genetic epidemiology department at University College London, said The Journal.

Aroon Hingorani, another author and director of University College London’s Institute for Cardiovascular Science, said the research results reveal that “there’s insufficient evidence” to support the use of genetic testing to guide how Plavix is prescribed, said The Journal. The study appears in the Journal of the American Medical Association.

This means some former Plavix users who underwent genetic testing and learned they carry the genetic variant, might have been switched off Plavix and on to a costlier drug unnecessarily, and some doctors might have increased Plavix dosing in weak responder patients.

The genetic testing saw an initial 40-fold increase in demand following the FDA’s warning, which tapered down to a 10-fold increase in later months. The test costs $200 – $400, said The Journal.

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