Association between warfarin and direct oral anticoagulants users and risk of mortality: cohort studies in England and Hong Kong

Abstract Background The evidence of the association between warfarin and risk of mortality compared with direct oral anticoagulants (DOACs) has been mixed in current literature. Purpose To investigate the association between all-cause mortality and warfarin, compared with DOACs. Methods Population-based cohort studies were conducted using the data from the Hong Kong Clinical Data Analysis and Reporting System (CDARS) and United Kingdom Clinical Practice Research Datalink (CPRD) Aurum. People with atrial fibrillation aged ≥18 years who initiated warfarin or a DOAC during the study period (1st Jan 2014 - 31st Dec 2019) were identified. Follow-up started from the first date of oral anticoagulant prescription and ended at earliest of the date of death, the day before drug switching (between warfarin and DOACs), transferring out of the practice (CPRD Aurum only), last data collection date for the practice (CPRD Aurum only) or the end of study period. We estimated propensity score (PS) based on the list of potential confounders including demographics, co-morbidities, co-medications and polypharmacy. Cox proportional hazards regression model with PS-weighting was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results Among 227,190 new oral anticoagulant users, 54,367 (23.93%) died. The median follow-up was 2.96 and 2.45 years in CPRD and CDARS, respectively. Compared with DOAC use, a lower hazard of all-cause mortality was found in warfarin use (PS-weighted hazard ratio [HR]=0.94, 95% confidence interval [CI]=0.89-0.99) in CPRD; while a higher hazard was observed in warfarin users (PS-weighted HR=1.31, 95% CI=1.24-1.39) in CDARS, versus DOAC users. Consistent results were seen in both databases when stratified warfarin users by Time in Therapeutic Range (TTR). We observed a lower hazard of all-cause mortality in warfarin users with TTR≥65% (PS-weighted HR=0.90, 95% CI=0.85-0.94 in CPRD; 0.87, 0.79-0.96 in CDARS) and increased hazard in warfarin users with TTR