The US Food and Drug Administration recently recommended that CYP2C19 genotyping be
considered prior to prescribing clopidogrel, but the American Heart Association and
American College of Cardiologists have argued evidence is insufficient to support
CYP2C19 genotype testing.
To appraise evidence on the association of CYP2C19 genotype and clopidogrel response
through systematic review and meta-analysis.
PubMed and EMBASE from their inception to October 2011.
Studies that reported clopidogrel metabolism, platelet reactivity or clinically relevant
outcomes (cardiovascular disease [CVD] events and bleeding), and information on CYP2C19
genotype were included.
We extracted information on study design, genotyping, and disease outcomes and investigated
sources of bias.
We retrieved 32 studies of 42,016 patients reporting 3545 CVD events, 579 stent thromboses,
and 1413 bleeding events. Six studies were randomized trials ("effect-modification"
design) and the remaining 26 reported individuals exposed to clopidogrel ("treatment-only"
design). In treatment-only analysis, individuals with 1 or more CYP2C19 alleles associated
with lower enzyme activity had lower levels of active clopidogrel metabolites, less
platelet inhibition, lower risk of bleeding (relative risk [RR], 0.84; 95% CI, 0.75-0.94;
absolute risk reduction of 5-8 events per 1000 individuals), and higher risk of CVD
events (RR, 1.18; 95% CI, 1.09-1.28; absolute risk increase of 8-12 events per 1000
individuals). However, there was evidence of small-study bias (Harbord test P = .001).
When analyses were restricted to studies with 200 or more events, the point estimate
was attenuated (RR, 0.97; 95% CI, 0.86-1.09). In effect-modification studies, CYP2C19
genotype was not associated with modification of the effect of clopidogrel on CVD
end points or bleeding (P > .05 for interaction for both). Other limitations included
selective outcome reporting and potential for genotype misclassification due to problems
with the * allele nomenclature for cytochrome enzymes.
Although there was an association between the CYP2C19 genotype and clopidogrel responsiveness,
overall there was no significant association of genotype with cardiovascular events.