Summary
High on-clopidogrel platelet reactivity is associated with worse clinical outcome.
Previous data suggest that intrinsic platelet reactivity before initiation of clopidogrel
contributes significantly to on-clopidogrel platelet reactivity. It is unknown whether
intrinsic reactivity can sufficiently predict on-clopidogrel reactivity and therefore
identify patients with insufficient response to clopidogrel before initiation of treatment
and at risk for worse clinical outcome. This analysis included 765 consecutive patients
undergoing elective coronary stent implantation. Platelet reactivity was assessed
by light transmission aggregometry (5 µM ADP) before administration of clopidogrel
600mg and after intake of first maintenance dose of clopidogrel on day 1 following
coronary stenting. Patients were followed for up to seven years. The combined primary
endpoint was death of any cause or non-fatal myocardial infarction. Intrinsic and
on-clopidogrel platelet reactivity were significant correlated (r=0.31; p < 0.001).
Among all tested clinical and genetic factors including the cytochrome P450 2C19*2
polymorphism, intrinsic platelet reactivity was the strongest predictor for on-clopidogrel
platelet reactivity. However, intrinsic platelet reactivity could only explain 8 %
of variability of on-clopidogrel platelet function. Only on-treatment platelet reactivity
was predictive for long-term clinical outcome (HR 1.47, 95 % CI 1.05–2.05; p = 0.02)
whereas intrinsic platelet reactivity was not (HR 1.03, 95 % CI 0.74–1.43; p = 0.86).
In conclusion, intrinsic platelet reactivity before initiation of clopidogrel is the
strongest predictor of early on-clopidogrel platelet reactivity but can only explain
a minor proportion of its variability and is not significantly associated with clinical
outcome. Thus, baseline testing cannot substitute on-clopidogrel platelet function
testing.
Clinical Trial Registration: ClinicalTrials.gov (Identifier: NCT00457236).
Keywords
Clopidogrel - platelet reactivity - risk prediction - mortality - coronary disease