Association of Medicare Part D Low‐Income Cost Subsidy Program Enrollment with Increased Fill Adherence to Clopidogrel After Coronary Stent Placement

Study Objective To determine the association between enrollment in the Medicare Part D low‐income subsidy ( LIS ) program, which reduces out‐of‐pocket medication costs, and fill adherence to the antiplatelet drug clopidogrel after coronary stent placement. Design Retrospective cohort study. Data Source Pharmacy claims database of a large national Medicare Part D insurer. Patients We selected a total of 2967 beneficiaries of a national Medicare Part D plan who had a coronary stent placed between April and December 2006 and were prescribed clopidogrel but were not preexisting users of clopidogrel. Of these patients, 504 were enrolled in the LIS program and 2463 were not. Measurements and Main Results We defined LIS status as enrollment in the LIS program at any point during the 12 months after the procedure. We examined the association between LIS status and good medication fill adherence to clopidogrel, defined as proportion of days covered of 80% or more, or discontinuation of clopidogrel over the 12‐month window starting from the date of their stent placement. We also identified patients with claims‐based diagnoses of major bleeding events while taking clopidogrel. For those patients, we calculated fill adherence only for the period between medication initiation and the onset of major bleeding and/or did not classify them as having inappropriately discontinued the medication. We created a propensity score predicting the propensity of being eligible for the LIS benefit and used inverse propensity score weighting with regression adjustment to generate estimates of the effect parameters. LIS enrollment was associated with a higher predicted likelihood of good clopidogrel fill adherence after stent placement (54.8% for LIS enrollees vs 47.6% for nonenrollees; p=0.008). No significant difference was noted between the two groups in predicted risk of discontinuing clopidogrel after stent placement (18.3% for LIS enrollees vs 21.0% for nonenrollees; p=0.21). Conclusion The LIS benefit was associated with better clopidogrel fill adherence after stent placement. Although clopidogrel is now available in generic form, our work underscores the need for efforts to identify and enroll patients in the LIS benefit who require costly antiplatelet medications for coronary heart disease.