title: Effects of cytochrome P450 2C9 polymorphisms on phenprocoumon anticoagulation status.
abstract: OBJECTIVE
  Our objective was to assess whether there is an association between the presence of allelic variants of the gene for cytochrome P450 (CYP) 2C9 and anticoagulation problems during the initial phase of phenprocoumon treatment.
  
  
  METHODS
  A prospective follow-up study was performed at 2 anticoagulation clinics in The Netherlands. Included subjects started phenprocoumon during the study period, had their first check of the international normalized ratio (INR) on the third or fourth day of therapy, and had an indication for the low therapeutic range (INR, 2.0-3.5). CYP2C9 genotypes ( CYP2C9*1 , CYP2C9*2 , and CYP2C9*3 ) were assessed, and data on indication, INR checks, comedication, and comorbidity were collected.
  
  
  RESULTS
  After genotyping, 284 subjects were available for analysis. Of these, 186 (65.5%) were homozygous carriers of the CYP2C9 wild-type allele ( CYP2C9*1/*1 ), 61 (21.5%) were carriers of the CYP2C9*2 allele, and 37 (13.0%) were carriers of the CYP2C9*3 allele. Compared with homozygous CYP2C9*1/*1 subjects, carriers of CYP2C9*2 or *3 had an increased risk of severe overanticoagulation (INR >6.0). The hazard ratio for CYP2C9*2 versus CYP2C9*1/*1 was 3.09 (95% confidence interval [CI], 1.56 to 6.13; P=.001), and the hazard ratio for CYP2C9*3 versus CYP2C9*1/*1 was 2.40 (95% CI, 1.03 to 5.57; P=.042). Carriers of CYP2C9*2 also had a lower chance to achieve stability in the follow-up period. The hazard ratio for CYP2C9*2 versus CYP2C9*1/*1 was 0.61 (95% CI, 0.43 to 0.85; P=.003). Carriers of the CYP2C9*2 or *3 allele needed a significantly lower phenprocoumon dosage compared with homozygous CYP2C9*1/*1 subjects.
  
  
  CONCLUSIONS
  The presence of at least 1 CYP2C9*2 or *3 allele in phenprocoumon users is associated with an increased risk of severe overanticoagulation. Similar to warfarin and acenocoumarol, phenprocoumon had a lower dosage requirement in carriers of CYP2C9*2 or *3 compared with that in CYP2C9 wild-type subjects.
authors.affiliation: Department of Pharmacoepidemiology and Pharmacotherapy, University Institute of Pharmaceutical Sciences, Utrecht University, Utrecht. tschalekamp@pharm.uu.nl
authors.forename: Tom
authors.initials: T
authors.lastname: Schalekamp
authors.forename: Mirjam
authors.initials: M
authors.lastname: Oosterhof
authors.forename: Erik
authors.initials: E
authors.lastname: van Meegen
authors.forename: Felix J M
authors.initials: FJ
authors.lastname: van Der Meer
authors.forename: Jean
authors.initials: J
authors.lastname: Conemans
authors.forename: Mirjam
authors.initials: M
authors.lastname: Hermans
authors.forename: Irma
authors.initials: I
authors.lastname: Meijerman
authors.forename: Anthonius
authors.initials: A
authors.lastname: de Boer
mesh_terms: D000368:Aged; D000483:Alleles; D000925:Anticoagulants / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D001777:Blood Coagulation / Q000187:drug effects / Q000235:genetics; D065729:Cytochrome P-450 CYP2C9; D004305:Dose-Response Relationship, Drug; D023381:Endpoint Determination; D005260:Female; D005500:Follow-Up Studies; D005787:Gene Frequency; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010644:Phenprocoumon / Q000494:pharmacology*; D011110:Polymorphism, Genetic / Q000502:physiology; D016016:Proportional Hazards Models; D011446:Prospective Studies
chemical_list: D000925:Anticoagulants; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; D010644:Phenprocoumon