Medicare coverage gap status, adherence to oral anticoagulation, and stroke rates in patients with atrial...

Prior to 2025, Medicare Part D included a coverage gap during which beneficiaries were responsible for substantially higher portions of medication costs. The impact of this on oral anticoagulant (OAC) prescription fills and subsequent stroke in patients with atrial fibrillation (AF) is not known.

Using Centers for Medicare and Medicaid Services claims data from 2016 to 2018, we evaluated OAC prescription fills in patients with AF by assessing their proportion of days covered on OAC before, during, and after their coverage gap. Hazard of stroke was assessed for patients who entered the coverage gap before entering, while in, and after exiting, the gap.

Patients who entered the coverage gap had a 16% decrease in median proportion of days covered from pregap (0.92 [interquartile range 0.80, 0.97]) to in-gap (0.76 [0.41, 0.98]). Proportion of days covered continued to drop for patients who entered and then left the coverage gap, despite regaining coverage (pregap: 0.95 [0.85, 0.98]; in-gap: 0.88 [0.55, 0.97]; postgap: 0.70 [0.00, 1.00]). Patients who entered the gap were at significantly higher risk for stroke while in the gap (HR 2.21, 95% CI 1.91-2.54) and during the combined in-gap and postgap periods (HR 3.13, 95% CI 2.71-3.62).

OAC use decreased upon entering the coverage gap and was associated with an increased stroke risk, that persisted for the rest of the calendar year. Health policy decisions regarding Medicare can have unintended adverse public health consequences, highlighting the importance of assessing the impact of such policy changes.