Investigators are building an empirical evidence base for real world data through large-scale replication of randomized controlled trials. The investigators' goal is to understand for what types of clinical questions real world data analyses can be conducted with confidence and how to implement such studies.

This is a non-randomized, non-interventional study that is part of the RCT DUPLICATE initiative (www.rctduplicate.org) of the Brigham and Women's Hospital, Harvard Medical School. It is intended to replicate, as closely as possible in healthcare insurance claims data, the trial listed below/above. Although many features of the trial cannot be directly replicated in healthcare claims, key design features, including outcomes, exposures, and inclusion/exclusion criteria, were selected to proxy those features from the trial. Randomization is also not replicable in healthcare claims data but was proxied through a statistical balancing of measured covariates through standard practice. Investigators assume that the RCT provides the reference standard treatment effect estimate and that failure to replicate RCT findings is indicative of the inadequacy of the healthcare claims data for replication for a range of possible reasons and does not provide information on the validity of the original RCT finding.

Inclusion Criteria:

• Hospitalization for PE or Proximal DVT [Day -14, Day 0]
• At least 18 years of age

Exclusion Criteria:

• Prior use of a DOAC or warfarin [Day -180, Day 0]
• Stage 4 or 5 chronic kidney disease or end-stage renal disease [Day -180, Day 0]
• Dialysis or renal transplant [Day -180, Day 0]
• Recent major or clinically relevant non-major bleeding [Day -180, Day 0]
• Cancer [Day -180, Day 0]
• Bypass surgery, obesity, or the use of a weight loss or appetite suppressor [Day -180, Day 0]
• Significant liver disease and coagulopathy [Day -180, Day 0]
• Use of CYP3A4 or P-gp inhibitors or inducers [Day -180, Day 0]
• Other indications for anticoagulation (atrial fibrillation or prosthetic heart valve) [Day -180, Day 0]
• Pregnancy or breastfeeding [Day -180, Day 0]
• Use of an antiplatelet [Day -180, Day 0]

This study will involve a new user, parallel group, propensity score-matched, retrospective cohort study design comparing rivaroxaban to apixaban users. The patients will be required to have continuous enrollment during a baseline period of 180 days before initiation of rivaroxaban or apixaban (index date). Analysis is restricted to patients hospitalized with a VTE.