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Cytochrome P450 2C19 (CYP2C19) Genotype

FDA Announces New Boxed Warning on Plavix - Alerts patients, health care professionals to potential for reduced effectiveness for CYP2C19 “poor metabolizers”



Updated: June 2013
Published: August 2010

CYP2C19 is a liver enzyme that is responsible for metabolizing a wide variety of drugs including the anticoagulant clopidogrel (Plavix), antiulcer drugs such as omeprazole, antiseizure drugs such as mephenytoin, the antimalarial proguanil, and the anxiolytic diazepam.

On March 12, 2010, the US Food and Drug Administration (FDA) added a boxed warning to the anticoagulant drug Plavix, alerting patients and health care professionals that the drug can be less effective in people who cannot metabolize the drug to convert it to its active form.

Why is it important to test for CYP2C19?

  • Plavix reduces the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease by making platelets less likely to form blood clots.
  • Plavix does not have its antiplatelet effects until it is metabolized into its active form by CYP2C19.
  • People who have reduced functioning of their CYP2C19 liver enzyme due to inactivating polymorphisms in their CYP2C19 gene cannot effectively convert Plavix to its active form. As a result, Plavix may be less effective in altering platelet activity in those people. These “poor metabolizers” may not receive the full benefit of Plavix treatment and may remain at risk for heart attack, stroke, and cardiovascular death.
  • It is estimated that 2% to 14 % of the US population are poor metabolizers.

Mayo Medical Laboratories’ Test

2C19S Cytochrome P450 2C19 Genotype by Sequence Analysis

  • Identifies patients who are poor metabolizers or extensive metabolizers of drugs, including Plavix, that are modified by CYP2C19.
  • Detects the *17 allele, which identifies individuals who may be enhanced metabolizers of drugs. A recent report indicates increased risk for bleeding in individuals treated with Plavix who carry the *17 allele.

Clinical References

  1. Food and Drug Administration: FDA Announces New Boxed Warning on Plavix.  2010 Mar 12. Available from www.fda.gov/newsevents/newsroom/pressannouncements/ucm204253.htm
  2. Sibbing D, Koch W, Gebhard D, et al: Cytochrome 2C19*17 allelic variant, platelet aggregation, bleeding events, and stent thrombosis in clopidogrel-treated patients with coronary stent placement. Circulation 2010 Feb 2;121(4):481-483

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