Warfarin Pharmacogenetics: Pharmacogenetic Optimization of Anticoagulant Response (POAT) and Genetic and Environmental Determinants of Warfarin Response (GEDWR)

Although the efficacy of warfarin in the treatment and prevention of thromboembolic disorders is proven, it is vastly underutilized with difficulties in management and risk of complications being the main deterrents. Recognition of genetic regulation of warfarin response has fueled efforts to quantify this influence, but the focus has been restricted to select genes and outcomes mainly in European Americans. Race appears to influence warfarin dose requirements with African Americans requiring larger and Asians requiring lower doses compared to Europeans. This variation in dose requirement by race may at least partially be explained by genetic differences. The Genetic and Environmental Determinants of Warfarin Response (GEDWR) and the Pharmacogenetic Optimization of Anticoagulation Therapy (POAT) are prospective cohort study aimed at defining the influence of CYP2C9, VKORC1 and other genes. All patients were followed at monthly intervals from initiation of therapy. At each visit factors influencing warfarin response such as warfarin dose, INR, concurrent medications, etc. were documented. Information on concurrent medications was updated at every clinic visit by self-report and verified by medical record review. Concomitant use of drugs such as drugs that alter warfarin pharmacokinetics, including CYP2C9 inhibitors (e.g., amiodarone), and pharmacodynamics such as antiplatelet agents (e.g. aspirin). Although the a priori hypothesis focused on the candidate-gene approach, with the recognition that the candidate-gene approach is bound by the assumption that our knowledge of genetic influences on warfarin response is complete. Among African Americans known variation in candidate genes (CYP2C9 and VKORC1) explain substantially less variability in warfarin dose requirements. Therefore a genome-wide association study (GWAS) was conducted on African American patients to identify novel variants associated with warfarin dose requirements.]]> The Genetic and Environmental Determinants of Warfarin Response (GEDWR) and the Pharmacogenetic Optimization of Anticoagulation Therapy (POAT) are prospective cohort study aimed at defining the influence of CYP2C9, VKORC1 and other genes. The outcome variable we analyzed is stable warfarin dose (mg/week) that was defined as the dose (with up to a 10% change) that resulted in a therapeutic INR between 1.8 and 3.2 for at least 3 consecutive clinic visits at least two weeks apart. the number of subjects were 200.Patients ≥20 years of age were identified at the initiation of chronic warfarin therapy. Patients were considered eligible if the target INR range was 2-3 and are managed at an anticoagulation clinic. Patients with short duration of therapy (e.g. 4 weeks post-knee replacement) were excluded as were patients who required anticoagulation with a higher target INR range (INR 2.5 to 3.5).]]>