Pilot study of the antiplatelet effect of increased clopidogrel maintenance dosing and its relationship to CYP2C19 genotype in patients with high on-treatment reactivity.
OBJECTIVE
The objective of this study was to evaluate the antiplatelet effect of clopidogrel 150 mg/day in patients with high on-treatment reactivity (OTR) and to further assess this effect according to CYP2C19 genotype.


BACKGROUND
High OTR is associated with ischemic events in clopidogrel-treated patients after percutaneous coronary intervention. Alternative dosing regimens might enhance platelet inhibition.


METHODS
Patients with high OTR receiving a standard clopidogrel regimen were identified with the VerifyNow P2Y12 assay and administered clopidogrel 150 mg daily for 7 days, after which OTR was reassessed. Comprehensive CYP2C19 genotyping was performed with the BeadXpress platform (Illumina, San Diego, California) for the *2, *3, *4, *5, *6, *7, *8, and *17 variants.


RESULTS
A total of 41 subjects were enrolled, 20 of whom were carriers of a CYP2C19 loss-of-function (LoF) allele. High-dose clopidogrel significantly reduced OTR from 285 ± 47 P2Y(12) reaction units (PRU) to 220 ± 91 PRU (p < 0.001). There were no significant differences in antiplatelet effect according to CYP2C19 status, although the reduction in reactivity was minimal in the small number of patients homozygous for LoF alleles (n = 3, 28 ± 31 PRU, p = NS). Increasing body mass index was independently and negatively associated with the reduction in OTR (p = 0.009).


CONCLUSIONS
In patients with high OTR, clopidogrel 150 mg/day results in a significant reduction in platelet reactivity. Carriage of an LoF CYP2C19 polymorphism does not seem to have a major influence on dose effect. The observed lack of effect in patients with 2 copies of a CYP2C19 LoF allele must be confirmed by larger studies.
Division of Cardiology, University of Texas Medical School at Houston, Houston, Texas 77030, USA. colin.m.barker@uth.tmc.edu
Colin M
CM
Barker
Sarah S
SS
Murray
Paul S
PS
Teirstein
David E
DE
Kandzari
Eric J
EJ
Topol
Matthew J
MJ
Price
D000368:Aged; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism; D015992:Body Mass Index; D002140:California; D016009:Chi-Square Distribution; D000077144:Clopidogrel; D003324:Coronary Artery Disease / Q000097:blood / Q000188:drug therapy*; D065731:Cytochrome P-450 CYP2C19; D005260:Female; D005838:Genotype; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D010865:Pilot Projects; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics; D010979:Platelet Function Tests; D011110:Polymorphism, Genetic; D011237:Predictive Value of Tests; D058925:Receptors, Purinergic P2Y12 / Q000097:blood / Q000187:drug effects; D018570:Risk Assessment; D012307:Risk Factors; D013988:Ticlopidine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
C548576:P2RY12 protein, human; D010975:Platelet Aggregation Inhibitors; D058925:Receptors, Purinergic P2Y12; D000077144:Clopidogrel; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D013988:Ticlopidine