The primary objective of this study is to compare the incidence of hemorrhagic events in patients treated for non-valvular atrial fibrillation with DU-176b at each dose level versus warfarin potassium (warfarin). The secondary objective includes between-group comparisons with regard to incidence of thromboembolic events, pharmacodynamic parameters, and biomarkers for the efficacy evaluation, as well as incidence of adverse events and adverse reaction for the safety evaluation.

Inclusion Criteria:

• Patients with non-valvular atrial fibrillation who meet all of the following requirements will be considered for admission to the study:

  • Age≧20years
  • Atrial fibrillation confirmed by at least 2 electrocardiographic(ECG) tracings taken at an interval of ≧1week during the year before enrollment

• Presence of any (at least )one of the following risk factors for embolism:

  • Hypertension
  • Diabetes mellitus
  • Congestive heart failure
  • Previous transient ischemic attack (TIA) or cerebral infarction (more than 30 days before giving informed consent )
  • Age≧75 years
  • At time of giving informed consent.
  • To be confirmed on ECG charts, etc.

Exclusion Criteria:

• Presence of any of the following conditions with increased risk of hemorrhage:

  • History of intracranial, intraocular (excluding bleeding beneath the bulbar conjunctiva ), intrathecal, retroperitoneal, or non-traumatic intraarticular hemorrhage
  • History of gastrointestinal hemorrhage during the year before giving informed consent
  • History of peptic ulcers during the 90 days before giving informed consent
  • Surgical treatment or trauma requiring hospitalization during the 30 days before giving informed consent
  • Hemoglobin level <10 g/dL platelet count <10 ×10000 /μL at screening examinations
  • Active hemorrhage* present at giving informed consent or at enrollment
  • Any invasive therapeutic or diagnostic procedure (e.g., surgery, tissue, biopsy, and tooth extraction) scheduled during the period from the time of informed consent until completion of the trial treatment.
  • Any congenital hemorrhagic disease

• History of cerebral infarction or TIA within 30 days before giving informed consent

• Current treatment with any anticoagulant(other than warfarin)

• Concurrent rheumatic valvular disease

• History of valvular surgery

• Concurrent infectious endocarditis

• Concurrent cardiac myxoma

• Confirmed left ventricular or left atrial thrombosis

• Any congenital condition with a tendency toward thrombosis

• Electrical or pharmacological defibrillation scheduled during the trial treatment

• Uncontrolled hypertension (persistently high systolic ［>160mmHg］or diastolic [>100mmHg] pressure)

• Uncontrolled diabetes mellitus

• Renal or hepatic dysfunction (as defined below ), confirmed at screening examinations

  • Serum creatinine>1.5mg/dL
  • AST(GOT)or ALT(GPT)≧twice the upper limit of the reference range
  • Total bilirubin ≧twice the upper limit of the reference range

• Current antiplatelet therapy for any concomitant illness that may be aggravated after discontinuation of the therapy.

• Any concurrent severe cardiac disease

• Known allergy to warfarin or any condition contraindicating its use

• Inability to discontinue current treatment with vitamin K

• Confirmed or potential pregnancy, wish to become pregnant during the study period, or current breast feeding

• Previous treatment with DU-176b

• Participation in a trial of any other drug during the 6 month before giving informed consent

• Any other condition that disqualifies the patient for the study in the opinion of the investigator/subinvestigator *This includes ecchymosis identified as at least one hematoma sized ≧5 cm in longer diameter, macroscopic hematuria, and microscopic hematuria defined as a ≧2+test or a 1+ test for occult blood with a urine sediment containing ≧10 red cells per high-power field (except for a 2+ occult blood test persisting for 1 year before giving informed consent).

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.

Baseline Analysis Population is based on Full Analysis Set. FAS defined as all subjects enrolled in study, but excluded those who had GCP violations, who did not receive any dose of study drug, or who did not have atrial fibrillation confirmed by ECG performed at least twice within a 1-week or longer interval within 1 year before registration