Introduction: Dabigatran and Rivaroxaban have shown better or similar efficacy to lower stroke risk compared to warfarin in clinical trials. Evidence suggests adherence to cardiac drugs tend to reduce outcomes and cost. Our study is the first to examine the impact of atleast 6 to 12 month adherence to NOACs on ischemic stroke, major bleeding, Deep Vein Thrombosis and Pulmonary Embolism (DVTPE) risk in a propensity score based matched sample.
Methods: A retrospective cohort study utilized de-identified data from Optum® Clinformatics™ Data Mart database (OptumInsight, Eden Prairie, MN) (Jan 1, 2010 and Dec 31, 2012). Adult patients with ≥ 1 diagnosis of atrial fibrillation or flutter (ICD9 427.31/32), >1 prescription of NOACs, 6 months pre-index continuous enrollment and CHA2DS2VASC score >1 were included. Adherence was calculated using Proportion of Days Covered (PDC ≥80%) for atleast 6 and 12 months of NOAC use and cohorts (adherent vs. non adherent) were matched on propensity score using Inverse Probability Treatment Weighting (IPTW) controlling for demographic and clinical characteristics at baseline. The risk of ischemic stroke, major bleeding (primary outcomes) and DVTPE (exploratory outcome) was evaluated for the matched cohorts post adherence assessment using Cox regression.
Results: Out of 25,150 NOAC patients, a total of 3,629 and 1,946 patients with atleast 6 and 12 months of NOAC use were included. Across 2 cohorts, the mean age of the sample was 65 years, 65% were males and >60% had a moderate-high risk of stroke (CHA2DS2VASC>2). Adherence (PDC ≥80%) was 77% and 76% for patients with 6 and 12 month drug use. Post 12 months of drug use, the overall incidence of bleeding, stroke, and DVTPE in the follow-up period was 4.42%, 1.80%, and 0.82% respectively. Each outcome was analyzed separately to avoid calculation of competing risks. Using Cox models with IPTW balanced cohorts, non-adherence was significantly (p ≤0.05) associated with an increase in stroke (≥ 1.5 fold) and DVTPE (≥ 2 fold) risk in both 6 and 12 month users. The risk of bleeding was not significantly different across adherent vs. non adherent users (Table).
Conclusion: In our sample, adherence to NOACs was associated with a reduction in stroke and DVTPE risk but did not substantially increase bleeding risk. Further studies with newer NOACs are warranted.