title: VKORC1 and CYP2C9 genotypes and phenprocoumon anticoagulation status: interaction between both genotypes affects dose requirement.
abstract: In a prospective follow-up study of the effects of VKORC1 and CYP2C9 genotypes on the anticoagulation status of patients, we assessed the CYP2C9 and the VKORC1 C1173T genotypes of patients during the initial 6 months of phenprocoumon treatment. We used linear regression models and Cox proportional hazard models to determine the effects of the VKORC1 and CYP2C9 genotypes on phenprocoumon dose requirements, overanticoagulation, and time to achieve stability. Allele frequencies of interest within the cohort (N=281) were 40.8% VKORC1 T-1173, 12.8% CYP2C9*2, and 6.9% CYP2C9*3. In patients with the VKORC1 CC genotype, carriers of a CYP2C9 polymorphism needed dosages that were nearly 30% lower than those for CYP2C9*1/*1 patients (P<0.001). In patients with a VKORC1 polymorphism, differences between carriers of a CYP2C9 polymorphism and CYP2C9*1/*1 were far smaller and largely not statistically significant. A larger part of the variability in dose requirement was explained by the VKORC1 genotype than by the CYP2C9 genotype (28.7% and 7.2%, respectively). Carriers of a combination of a CYP2C9 polymorphism and a VKORC1 polymorphism had a strongly increased risk of severe overanticoagulation (hazard ratio (HR) 7.20, P=0.002). Only carriers of a CYP2C9*2 allele had a decreased chance to achieve stability compared to CYP2C9*1/*1 patients (HR 0.61, P=0.004). In conclusion, the VKORC1 genotype modifies the effect of the CYP2C9 genotype on phenprocoumon dose requirements. A combination of polymorphisms of both genotypes is associated with a strongly increased risk of overanticoagulation, whereas delayed stabilization is mainly associated with the CYP2C9 genotype.
authors.affiliation: Division of Pharmacoepidemiology and Pharmacotherapy, Utrecht Institute for Pharmaceutical Sciences (UIPS), Faculty of Science, Utrecht University, Utrecht, The Netherlands. t.schalekamp@pharm.uu.nl
authors.forename: T
authors.initials: T
authors.lastname: Schalekamp
authors.forename: B P
authors.initials: BP
authors.lastname: Brassé
authors.forename: J F M
authors.initials: JF
authors.lastname: Roijers
authors.forename: E
authors.initials: E
authors.lastname: van Meegen
authors.forename: F J M
authors.initials: FJ
authors.lastname: van der Meer
authors.forename: E M
authors.initials: EM
authors.lastname: van Wijk
authors.forename: A C G
authors.initials: AC
authors.lastname: Egberts
authors.forename: A
authors.initials: A
authors.lastname: de Boer
mesh_terms: D000368:Aged; D000483:Alleles; D000925:Anticoagulants / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D016009:Chi-Square Distribution; D065729:Cytochrome P-450 CYP2C9; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D053208:Kaplan-Meier Estimate; D015810:Linkage Disequilibrium; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics*; D010644:Phenprocoumon / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D011110:Polymorphism, Genetic; D011446:Prospective Studies; D013997:Time Factors; D016896:Treatment Outcome; D064417:Vitamin K Epoxide Reductases
chemical_list: D000925:Anticoagulants; D006899:Mixed Function Oxygenases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C578523:VKORC1 protein, human; D064417:Vitamin K Epoxide Reductases; D010644:Phenprocoumon