A new report in the Journal of the American Medical Association adds to the mounting evidence that genetic variations impact the efficacy of clopidogrel (Plavix ®), a drug used to prevent blood clots in people who have had a heart attack or stroke and also those with peripheral artery disease and unstable angina.Previous research has shown that certain variations in the CYP2C19 gene prevent the body from converting clopidogrel into its active form. That reduces the amount of anti-clotting effect people get from the medication, increasing their risk for heart attacks, strokes and death from cardiovascular causes.(23ndMe customers can learn how their data fits in with this research in a previous Spittoon post or in the Clopidogrel Efficacy Drug Response Report.)The researchers, led by Alan Shuldiner of the University of Maryland School of Medicine, determined that BMI, lipid levels and age account for about 10% of the variation in clopidogrel’s ability to prevent blood clotting. Variation in the CYP2C19 gene accounted for another 12%, meaning that other factors, probably both genetic and non-genetic, are also at work.For patients whose genetics may reduce the benefits of clopidogrel treatment, there are other options. Prasugrel (Effient ®) was recently approved by the FDA and appears not to be affected by the same variations that impact clopidogrel efficacy, although there are some concerns about bleeding caused by this drug. Several other drugs (ticagrelor, cangrelor, elinogrel) that could be used for clotting reduction in place of clopidogrel are currently in clinical trials.Clinical trials have not yet been conducted to show if identifying people with variants of the CYP2C19 before prescribing clopidogrel actually improves health outcomes. If such studies do show a benefit and this type of testing becomes routine, people with these variants might be steered away from clopidogrel by their doctors, which would seem to be a boon for the makers of newer medications.But in an editorial accompanying the study in JAMA, Deepak Bhatt suggests that testing for these variations would also allow physicians to know for whom clopidogrel will work (probably). This would be an important piece of information considering that the patent on clopidogrel is set to expire in 2011, so cheaper generic forms of the drug will be available then.“Although such testing currently is expensive, the cost will decrease and hopefully will coincide with supportive data. Furthermore, if such testing allowed use of a less expensive generic anitplatelet drug, the test might essentially pay for itself,” he writes.