Almost all of the deaths and major cardiovascular events observed in Plavix patients occurred in poor metabolizers of a liver enzyme called CYP2C19, according to data from the GIFT sub study of GRAVITAS presented at American College of Cardiology 2011 annual meeting. Poor metabolizers are people who lack the DNA coding required for their bodies to make CYP2C19, which acts on about 10% of medications. Approximately 2-4% of European origin individuals, 10% of Africans, and up to 20% of Asians are CYP2C19 poor metabolizers. Plavix is a prodrug, taken in an inactive form that requires CYP2C19 to activate it. Additionally, the study found that doubling Plavix dose from 75 to 150 mg improved platelet reactivity results in the one-third of patients who are intermediate metabolizers, but had no impact on poor metabolizers of CYP2C19.
“The thing that hit me in the face was that virtually all of the events were in those [poor
metabolizers].”
- Dr. Gibson, Duke University
Dr. C. Michael Gibson and Dr. Ajay Kirtane from Duke University discussed the study, and both commented that the FDA boxed warning about Plavix genetics was premature until seeing this data. Dr. Kirtane stated, “I’m wondering if maybe we should spend more effort trying to find these non responders for the homozygous gene [poor metabolizers].
Watch the Duke cardiologists discuss the study at www.vimeo.com/22008430
Read details of the study at: www.theheart.org/article/1208199.do
Another case-control study published in October pointed out increased risk of stent thrombosis for patients taking Plavix with variations in a gene called CYP2C19. Patients with adverse events were two times more likely to have half of the gene be non-functional. Called intermediate metabolizers, this represents about one-third of patients. Patients with no CYP2C19 function, called poor metabolizers, were seven times more likely to have an adverse event. About 2-4% of Caucasians, 10% of Africans, and 20% of Asians are poor metabolizers. If you or a loved one is taking Plavix, ask about DNA Drug Sensitivity Testing.
