VKORC1 And CYP2C9 Polymorphisms Are Associated With Response To Warfarin During Initial Anticoagulation In Chinese

BackgroundOral anticoagulation with the vitamin K antagonist warfarin reduces the rate ofthromboembolic events for patients in a variety of clinical settings. However, warfarin therapy is challenging because there is wide variation among patients in response and therefore in dose requirement. To achieve and maintain an optimal warfarin dose, the prothrombin time and the international normalized ratio (INR) are monitored, and dose are adjusted to maintain each patient's INR within a narrow therapeutic range.Polymorphisms in the gene encoding the cytochrome P-450 2C9 enzyme (CYP2C9) are known to contribute to variability in sensitivity to warfarin. Patients with certain common genetic variants of CYP2C9 require a lower dose of warfarin and a longer time to reach a stable dose. They are also at higher risk for over-anticoagulation and serious bleeding.VKORC1 is the target of coumarin anticoagulants. VK0RC1 polymorphisms are associated with a need for lower doses of warfarin during long-term therapy, and in some studies, were found to contribute to variation in dose requirement more than CYP2C9 variants.However, there is little information about the relative contributions of VKORC1 and CYP2C9 to the anticoagulation response in patients during the initiation of warfarin therapy.Part 1: Study in healthy Chinese volunteersObjectivesTo evaluate the effect of VKORC1 polymorphisms on the INR value and the plasma warfarin free concentration of healthy Chinese volunteers in two dosage groups. Subjects and methodsTwenty-four healthy Chinese volunteers were grouped according to their VKORC1 genotype. Twelve subjects were in the 3mg group and 12 were in the 6 mg group. VKORC1 genotypes were determined by a polymerase chain reaction (PCR) based restriction fragment length polymorphism (RFLP) assay and sequencing. The international normalized ratio (INR) was measured with an ACL9000 coagulation analyser. Plasma warfarin free concentration was measured with LC/MS/MS.Results1. In initial anticoagulation period, as compared with the -1639AA and 1173TT carriers, the -1639AG and 1173TC carriers had a low INR value The differences between genotypes with regard to INR values were more obvious in the 3mg subjects (p<0.05), and were not significantly different among the 6mg subjects (p>0.05).2. No difference of plasma warfarin free concentration between genotypes was observed in each dosage group.Part 2: Study in Chinese patients with prosthetic heart valvesObjectivesTo evaluate the effect of VKORC1 and CYP2C9 polymorphisms on the initial response to warfarin in Chinese patients with prosthetic heart valvesSubjects and methods1. Subjects: 254 patients taking prosthetic heart valve replacement and been administrated with warfarin after operation2. Analysis with VKORC1 polymorphisms, CYP2C9 polymorphisms, demographic characteristics and clinical information.Results1. The VKORC1 polymorphisms are associated with warfarin total dose of the first 5 days after operation.2. The VKORC1 polymorphisms are associated with INR within the therapeutic window in day 6 after operation. 3. The VKORC1 polymorphisms had a significant effect on the time to first INR in therapeutic range.4. The CYP2C9 polymorphisms are associated with warfarin total dose of the first 5 days after operation.5. The CYP2C9 polymorphisms had no effect on the time to first INR in therapeutic range and weather the INR within the therapeutic window in day 6 after operation.Part 3: Create a dose algorithm and validationObjectives1. To create a dose algorithm that based on genetic information, demographic characteristics and clinical variables of the Chinese patients with prosthetic heart valves.2. Validate the dose algorithm.Subjects and methods1. Derivation cohort: 132 patients taking prosthetic heart valve replacement and been administrated with warfarin after operation in Fuwai Hospital2. Validation cohort: 40 patients taking prosthetic heart valve replacement and been administrated with warfarin after operation in Fuwai Hospital3. Analysis with VKORC1 polymorphisms, CYP2C9 polymorphisms, demographic characteristics and clinical information, create a a dose algorithm.4. Validation: Calculating the predicted dose and compare to the real dose.Results1. Dose=1.837-2.268×VKORC1 haplotype - 1.632×CYP2C9 genotype -0.649×Gender -0.041×Year+0.045×Height+0.147×Weight-0.608×Heart function + 4.436×INR + 0.008×Cr-0.021×ALT + -1.865×Amiodarone - 0.84×Digoxin2. No difference had been found between the real dose and the predicted dose (p>0.05).Conclusion1. Both VKORC1 and CYP2C9 polymorphisms have effect on the warfarin initial reponse.2. Initial variability in the reponse to warfarin was more strongly associated with genetic variability in the VKORC1 than with CYP2C9.3. The use of pharmacogenetic algorithm for estimating the appropriate iniatial dose are significant closer to the real dose.