Estimation of warfarin maintenance dose based on VKORC1 (-1639 G>A) and CYP2C9 genotypes.
BACKGROUND
CYP2C9 polymorphisms are associated with decreased S-warfarin clearance and lower maintenance dosage. Decreased expression of VKORC1 resulting from the -1639G>A substitution has also been implicated in lower warfarin dose requirements. We investigated the additional contribution of this polymorphism to the variance in warfarin dose.


METHODS
Sixty-five patients with stable anticoagulation were genotyped for CYP2C9 and VKORC1 with Tag-It allele-specific primer extension technology. Plasma S-warfarin concentrations and warfarin maintenance dose were compared among patients on the basis of the VKORC1 -1639G>A genotype.


RESULTS
Eighty percent of CYP2C9*1/*1 patients stabilized on <4.0 mg/day warfarin had at least 1 VKORC1 -1639A allele. Mean warfarin doses (SD) were 6.7 (3.3), 4.3 (2.2), and 2.7 (1.2) mg/day for patients with the VKORC1 -1639GG, GA, and AA genotypes, respectively. Steady-state plasma concentrations of S-warfarin were lowest in patients with the VKORC1 -1639AA genotype and demonstrated a positive association with the VKORC1 -1639G allele copy number (trend P = 0.012). A model including VKORC1 and CYP2C9 genotypes, age, sex, and body weight accounted for 61% of the variance in warfarin daily maintenance dose.


CONCLUSIONS
The VKORC1 -1639A allele accounts for low dosage requirements of most patients without a CYP2C9 variant. Higher plasma S-warfarin concentrations corresponding to increased warfarin maintenance dosages support a hypothesis for increased expression of the VKORC1 -1639G allele. VKORC1 and CYP2C9 genotypes, age, sex, and body weight account for the majority of variance in warfarin dose among our study population.
Zhu
Yusheng
Y
Department of Pathology and Laboratory Medicine, University of Louisville School of Medicine, Louisville, KY 40202, USA. zhuyu@musc.edu
Shennan
Michael
M
Reynolds
Kristen K
KK
Johnson
Nancy A
NA
Herrnberger
Matthew R
MR
Valdes
Roland
R
Linder
Mark W
MW
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D065729:Cytochrome P-450 CYP2C9; D005260:Female; D018628:Gene Dosage; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics*; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000008:administration & dosage*
D000925:Anticoagulants; D014859:Warfarin; 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