Pharmacogenetics-Based Warfarin Dosing in Patients With Cardiac Valve Replacement: The Effects of CYP2C9 and VKORC1 Gene Polymorphisms

Many lines of evidence suggest that warfarin dosing variability is significantly associated with cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) variant alleles. Therefore, we investigated the influence of CYP2C9*2 (430C/T), *3 (1075A/C) and VKORC1 (-1639G/A) polymorphisms on warfarin dose requirements in patients who underwent cardiac valve surgery during the postoperative period. A total of 100 patients with heart valve replacement who had a prescribed target international normalized ratio (INR) range of 2-3 were enrolled in the study. Genotyping of CYP2C9 and VKORC1 was carried out using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. The demographic and clinical data were collected using a precodified questionnaire and clinical examination and then were analyzed. Our findings revealed that the prevalence of CYP2C9 *2, *3 and VKORC1-1639A alleles in patients were 10.5%, 39%, and 48%, respectively. We also found that patients with CYP2C9 *1 and VKORC1-1639G alleles required the highest dosages of warfarin, while the carriers of CYP2C9 variant *2 and *3 alleles and VKORC1-1639A required less warfarin. Univariate regression analysis showed that age and presence of CYP2C9 *2 allele significantly influenced the daily warfarin dose requirement. Our findings provide additional evidence to support the hypothesis that CYP2C9*2 (430C/T), *3 (1075A/C) and VKORC1 (-1639G/A) polymorphisms explain a considerable proportion of interindividual variability in warfarin dose. Therefore, testing for these variants might be helpful for adjusting patient warfarin dosage to an effective and safe level.