Formulary Restrictions and Stroke Risk in Patients With Atrial Fibrillation

OBJECTIVES: To determine the use of formulary restrictions (prior authorization and step therapy) on the use of non-vitamin K antagonist oral anticoagulants (NOACs) and their effect on health outcomes. STUDY DESIGN: Longitudinal cohort study. We identified a sample of Medicare beneficiaries with an incident diagnosis of atrial fibrillation (AF) in 2011 to 2015 and followed them until the end of 2016 or death. We compared anticoagulant use and health outcomes associated with Medicare Part D plan coverage of NOACs. METHODS: The primary outcomes were composite rates of death, stroke, transient ischemic attack, and systemic embolism. We used Cox proportional hazards models to estimate the association between formulary restrictions and adverse health outcomes. RESULTS: Beneficiaries enrolled in Part D plans that restricted access to NOACs had a lower probability of NOAC use (30.2% vs 32.2%), worse adherence conditional on NOAC use (32.1% vs 34.3% adherent), and longer delays in filling an initial prescription (46% vs 55% filled within 30 days of AF diagnosis). Beneficiaries in restricted plans had higher aggregate risk of mortality/stroke/transient ischemic attack (adjusted HR, 1.098; 95% CI, 1.079-1.118). CONCLUSIONS: Limiting access to NOACs may exacerbate current underuse of anticoagulants and increase the risk of stroke among patients with newly diagnosed AF. Pharmacy benefit managers and Part D plans need to continuously review the appropriateness of formulary policies to ensure patient access to effective medications.