Tecarfarin Anti-Coagulation Trial (TACT)

General Screening Inclusion Criteria 1. Is male or female and at least 18 years of age. 2. Is able and willing to sign an IRB-approved written informed consent. 3. Is able and willing to follow instructions, to comply with protocol requirements, and to attend required study visits. 4. Is taking a CYP2C9-interacting medication (inhibitor, substrate, or inducer; see list in Appendix A) at the time of randomization and is expected to receive this medication chronically for the duration of the trial. 5. Has either 1. Chronic kidney disease stage 3 or 4 (eGFR ≥ 15 to \<60 mL/min/1.73 m2 at Screening based on central laboratory) and/or 2. A CYP2C9 genotype variant allele 6. (Only for warfarin experienced patients) Patient is considered poorly controlled on warfarin therapy as judged by the investigator, e.g. has at least 2 INR values out of target range within previous 12 months Anticoagulation-Related Inclusion Criteria 7. Requires chronic anticoagulation therapy. 8. Is willing to receive chronic anticoagulation investigational therapy for the duration of the study or, for warfarin-naïve DVT subjects, treating physician prescribed at least a 6-month treatment period with an oral anticoagulation agent. 9. Has one or more of the following indications for chronic oral anticoagulation: 1. Atrial fibrillation/flutter (paroxysmal, persistent or permanent), not due to a reversible cause, documented by electrocardiography (ECG) 2. Aortic and/or mitral prosthetic HV 3. History of venous thromboembolic disease 4. History of myocardial infarction or cardiomyopathy 5. Any another indication for which warfarin is approved or recommended, with Sponsor approval 10. Conforms to the following restrictions regarding vitamin-K containing dietary supplements: 1. If taking at Baseline (Visit 2), is willing to continue with consistent doses throughout the study 2. If not taking at Baseline (Visit 2), is willing to abstain from such supplements throughout the study General Exclusion Criteria 1. Is pregnant, nursing, or a woman of childbearing potential who cannot assure that they will not become pregnant for the duration of the study. 2. Has been treated with an investigational drug within 30 days or 5 half-lives, whichever is longer, at time of screening. Safety-Related Exclusion Criteria 3. Has a life expectancy \<1 year 4. Is age \>85 years 5. Has severe end-organ disease, such as: 1. Estimated GFR (eGFR) \< 15 mL/min/1.73 m2 at Screening per the central laboratory 2. Is on dialysis 3. Is expected to be on dialysis or receive kidney transplant within 6 months of screening 4. Advanced pulmonary disease requiring home oxygen 5. NYHA class IV heart failure 6. Severe psychiatric disorder such as advanced dementia 6. Has a history of ischemic stroke without residual neurologic deficit within the last 3 months, prior major ischemic stroke with residual neurologic deficit, or any history of intracranial bleeding 7. Is an ongoing alcohol or substance abuser 8. Has anemia (screening hemoglobin \<9 g/dL) For subjects who have received a MHV within 4 weeks of Screening, who have no active bleeding, and whose hemoglobin is stable, a Screening hemoglobin as low as 8 g/dL is allowed. For subjects with severe CKD (eGFR ≥ 15 to \<30 mL/min/1.73 m2), who have no active bleeding, and whose hemoglobin is stable, a Screening hemoglobin as low as 8 g/dL is allowed. 9. Has thrombocytopenia (screening platelet count \<90,000 x 103/microL) 10. Has a history of or presence of any illness or condition, which, in the judgment of the Investigator, may compromise the safety of the subject during Study Drug administration. Anticoagulation-related Exclusion Criteria 11. Has active bleeding or lesions at risk of bleeding such as gastric ulceration, colonic or cerebral arterio-venous malformations, cerebral or aortic aneurysms, pericarditis or endocarditis 12. Except for MHV replacement surgery and related or concurrent procedures, has recently (\<14 days from Screening) undergone non-thromboembolic surgery or other invasive procedures such as lumbar puncture. 13. Has blood dyscrasias or inherited disorders of hemostasis. 14. Has a history of hemorrhagic tendencies or prior serious hemorrhagic events such as hemorrhage within the cranium, eye, spinal cord, retroperitoneum. 15. Has active gross hematuria or gastrointestinal bleeding 16. Has a history of gross hematuria or gastrointestinal bleeding within the past 6 months prior to Screening. (Note: Investigators may enroll patients with such bleeding episodes if they are resolved at least 4 weeks prior to screening and if the benefits of anticoagulation outweigh the risks using accepted risk stratification methods such as HASBLED.) 17. Has received concomitant therapy with other anticoagulant or antiplatelet agents, such as clopidogrel, prasugrel, ticlopidine, dipyridamole, heparin or low molecular weight heparin (LMWH), or nonsteroidal anti-inflammatory drugs (NSAIDs) that cannot be discontinued prior to initiating tecarfarin/warfarin dosing, unless use of such drugs is necessary as part of bridging/transitioning during the first several days of Study Drug administration. Daily use of 81 - 100 mg aspirin and intermittent or chronic use of the selective COX-2 inhibitors celecoxib and valdecoxib is allowed. 18. Has congenital or acquired coagulant inhibitors present which would interfere with the use of the INR, eg: 1. Antiphospholipid antibody syndrome or positive lupus anticoagulant 2. Abnormally prolonged prothrombin time, in the absence of therapeutic anticoagulation, due to an endogenous inhibitor