On March 12, 2010, the FDA announced that they are adding a black box warning to the Plavix label to advise physicians of the importance of genetics and the availability of testing.
Several recent landmark studies have proven the importance of genotyping in treatment using clopidogrel or Plavix. Researchers have found that patients with variations in a gene called cytochrome P-450 2C19 (CYP2C19) have a 3.58 times greater risk for major adverse cardiovascular events such as death, heart attack, and stroke; the risk was greatest in CYP2C19 poor metabolizers. 
Population Frequency of CYP2C19 Metabolizer Types 
(no or low enzyme levels)
(reduced enzyme levels)
(normal enzyme levels)
*There is wide variability among populations. People of Asian and African ancestry have a greatly increased prevalence of poor metabolizer status.
CYP2C19 is not just involved in the metabolism of clopidogrel, it metabolizes many other medications including antidepressants, barbiturates, proton pump inhibitors, antimalarials, and antitumor drugs.
Who Should Be Tested
The CYP2C19 test for clopidogrel or Plavix is considered appropriate for any patient taking or considering this medication.