A Pharmacogenetic Study of Warfarin Dosing, "The COUMA-GEN Study"

Anticoagulation with warfarin is a common and potentially hazardous therapeutic intervention. It is a leading cause of iatrogenic bleeding events and, hence, of malpractice claims. There are no good alternatives presently for warfarin anticoagulation, and even when alternatives become available (i.e., ximelagatran), cost, labeling, and experience (outcomes-related) issues will continue to favor an extensive and ongoing use of warfarin. If the present study is able to confirm an advantage for a genotype-driven algorithm, in terms of improved efficiency, therapeutic efficacy, and, especially, safety, then a pharmacogenetics approach to warfarin dosing can be recommended as the basis for an Intermountain Health Care (IHC)-wide quality improvement initiative that should improve patient outcomes, reduce resource use (costs of achieving safe and therapeutic anticoagulation), and reduce adverse clinical events. COUMA-GEN is a prospective, randomized study of patients who are to begin chronic warfarin therapy for specific, qualifying clinical reasons (i.e., atrial fibrillation (AF), deep vein thrombosis (DVT), or post-orthopedic surgery prophylaxis). Qualifying patients will be consented and randomized to an individualized, genotype-based warfarin-dosing regimen or to standard care (without knowledge of genotype). In each study arm, a predicted maintenance dose will be determined. All patients will receive a baseline International Normalized Ratio (INR). For patients in all 3 entry strata, a starting dose of warfarin that is twice the assigned daily maintenance dose (according to the specific treatment arm) will be prescribed on the first and second days, and then the dose will revert to the assigned maintenance dose.