Comparative Effectiveness of Non-Vitamin K Antagonist Oral Anticoagulants (NOACS) And Warfarin In The Scottish Atrial Fibrillation Population: The Value of Real World Evidence

OBJECTIVES: Real world data, compared to randomised controlled trial (RCT) data, provides evidence from real world scenarios. However, the absence of randomisation does not allow for an unbiased comparison between the treatment and the comparator. The objective of this study was to assess the effectiveness and safety of NOACs, and whether RCTs findings are generalizable to clinical practice in Scotland. METHODS: National data on prescribing, hospitalisations and death for newly anticoagulated patients, with a diagnosis of atrial fibrillation (AF) were linked. Patients 50 years or older were followed from first oral anticoagulant prescription to first clinical event or death. Censoring was applied to treatment switching. AF related outcomes observed with NOACs were compared with warfarin at 2 and 6 years. Observed confounding was adjusted for with the inverse probability of treatment weighting propensity score method. Using a continuous treatment approach, hazard ratios were estimated, adjusting for age, sex and comorbidities. RESULTS: At 2-year follow-up there were no differences in risk of ischaemic stroke for apixaban (HR 0.91; 95%CI 0.70-1.18), dabigatran (HR 0.82; 95%CI 0.44-1.53) and rivaroxaban (HR 1.15; 95%CI 0.92-1.42) compared with warfarin. However, when comparing rivaroxaban with warfarin, increased risks of the composite endpoint of stroke or systemic embolism or all-cause mortality (HR 1.19; 95%CI 1.08-1.32), major bleeding (HR 1.28; 95%CI 1.11-1.46) and all-cause mortality (HR 1.23; 95%CI 1.10-1.37); and reduced risk of myocardial infarction (HR 0.66; 95%CI: 0.47-0.95) was observed. For all comparisons, results at 6-year were consistent with those observed at 2-year follow up. CONCLUSIONS: At 2 and 6-year follow up, no risk differences were found for apixaban and dabigatran compared to warfarin. However, this was not the case for rivaroxaban. These results of longer-term follow-up diverge from those reported in RCTs, and may have implications on the cost-effectiveness of these treatments in a Scottish setting.