Acute kidney injury in patients with non-valvular atrial fibrillation treated with rivaroxaban or warfarin: a population-based study from the United Kingdom

Acute kidney injury (AKI) has been associated with use of oral anticoagulants (OACs) in patients with non-valvular atrial fibrillation (NVAF). We aimed to compare AKI risk among users of rivaroxaban vs. warfarin. We identified two cohorts of NVAF patients who initiated rivaroxaban (15/20 mg/day, N=6436) or warfarin (N=7129) excluding those without estimated glomerular filtration rate values recorded in the year before OAC initiation and those with a history of end-stage renal disease or AKI. We used two methods to define AKI during follow-up (mean 2.5 years): coded entries (method A), and the Aberdeen AKI phenotyping algorithm (method B), using recorded renal function laboratory values during the study period to identify a sudden renal deterioration event. Cox regression was used to calculate hazard ratios (HRs) for AKI with rivaroxaban vs. warfarin use, adjusted for confounders. The number of identified incident AKI cases was 249 (method) A and 723 (method B). Of the latter, 104 (14.4%) were also identified by method A. After adjusting for age, sex, baseline renal function and comorbidity, HRs (95% CIs) for AKI were 1.20 (0.93–1.55; p =0.16) using method A, and 0.80 (0.68–0.93; p <0.01) using method B. Estimates stratified by baseline level of chronic kidney disease were largely consistent with the main estimates. In conclusion, our results support a beneficial effect of rivaroxaban over warfarin in terms of AKI occurrence in patients with NVAF. More research into how best to define AKI using primary care records would be valuable for future studies.