title: Pharmacogenetic testing for clopidogrel using the rapid INFINITI analyzer: a dose-escalation study.
abstract: OBJECTIVE
  Our aim was to assess whether a higher clopidogrel maintenance dose has a greater antiplatelet effect in CYP2C19*2 allele carriers compared with noncarriers.
  
  
  BACKGROUND
  Clopidogrel is a prodrug that is biotransformed by the cytochrome P450 enzymes CYP2C19, 2C9, and 3A4, 2B6, 1A2. The CYPC219*2 loss of function variant has been associated with a reduced antiplatelet response to clopidogrel and a 3-fold risk of stent thrombosis.
  
  
  METHODS
  Forty patients on standard maintenance dosage clopidogrel (75 mg), for 9.4 +/- 9.2 weeks, were enrolled into a dose escalation study. Platelet function was assessed at baseline and after 1 week of 150 mg once daily using the VerifyNow platelet function analyzer (Accumetrics Ltd., San Diego, California). Genomic DNA was hybridized to a BioFilmChip microarray on the INFINITI analyzer (AutoGenomics Inc., Carlsbad, California) and analyzed for the CYP19*2, *4, *17, and CYP2C9*2, *3 polymorphisms.
  
  
  RESULTS
  Platelet inhibition increased over 1 week, mean +8.6 +/- 13.5% (p = 0.0003). Carriers of the CYP2C19*2 allele had significantly reduced platelet inhibition at baseline (median 18%, range 0% to 72%) compared with wildtype (wt) (median 59%, range 11% to 95%, p = 0.01) and at 1 week (p = 0.03). CYP2C19*2 allele carriers had an increase in platelet inhibition of (mean +9 +/- 11%, p = 0.03) and reduction in platelet reactivity (mean -26 +/- 38 platelet response unit, p = 0.04) with a higher dose. Together CYP2C19*2 and CYP2C9*3 loss of function carriers had a greater change in platelet inhibition with 150 mg daily than wt/wt (+10.9% vs. +0.7%, p = 0.04).
  
  
  CONCLUSIONS
  Increasing the dose of clopidogrel in patients with nonresponder polymorphisms can increase antiplatelet response. Personalizing clopidogrel dosing using pharmacogenomics may be an effective method of optimizing treatment.
authors.affiliation: Green Lane Cardiovascular Service, Auckland City Hospital, Auckland, New Zealand. patrickg@theranostics.co.nz
authors.forename: Patrick
authors.initials: P
authors.lastname: Gladding
authors.forename: Harvey
authors.initials: H
authors.lastname: White
authors.forename: Jamie
authors.initials: J
authors.lastname: Voss
authors.forename: John
authors.initials: J
authors.lastname: Ormiston
authors.forename: Jim
authors.initials: J
authors.lastname: Stewart
authors.forename: Peter
authors.initials: P
authors.lastname: Ruygrok
authors.forename: Badi
authors.initials: B
authors.lastname: Bvaldivia
authors.forename: Ruth
authors.initials: R
authors.lastname: Baak
authors.forename: Catherine
authors.initials: C
authors.lastname: White
authors.forename: Mark
authors.initials: M
authors.lastname: Webster
mesh_terms: D000368:Aged; D015906:Angioplasty, Balloon, Coronary; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism; D000077144:Clopidogrel; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance / Q000235:genetics; D004867:Equipment Design; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis / Q000295:instrumentation*; D010597:Pharmacogenetics / Q000295:instrumentation*; D010641:Phenotype; D010974:Platelet Aggregation / Q000187:drug effects* / Q000235:genetics; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage* / Q000378:metabolism; D010979:Platelet Function Tests / Q000295:instrumentation*; D020641:Polymorphism, Single Nucleotide; D057285:Precision Medicine; D011237:Predictive Value of Tests; D016032:Randomized Controlled Trials as Topic; D012189:Retrospective Studies; D013988:Ticlopidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism; D013997:Time Factors
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D013988:Ticlopidine