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

Coronary heart disease (CHD) remains the leading cause of death in the United States, and the combined direct and indirect costs of CHD exceed $100 billion annually.1, 2 Patients who survive an initial myocardial infarction are at high risk for a successive event, and almost 500,000 Americans have a recurrent myocardial infarction each year.2 Many patients with CHD require coronary stent placement, and the initiation of dual antiplatelet therapy, such as aspirin and clopidogrel, after coronary stent placement is the standard of care in modern medicine.3 As with younger patients, the data from older adults indicate a clear benefit of revascularization in clinically appropriate settings.4,5 Unfortunately, many high-risk patients do not realize the full benefit of antiplatelet agents such as clopidogrel because of inadequate adherence. After coronary stent placement, 10–20% of patients inappropriately stop taking clopidogrel within the first 30 days after the procedure, and rates of nonadherence and/or complete discontinuation at 12 months are even greater.6–10 The risk of adverse events is particularly alarming for patients with drug-eluting stents who discontinue clopidogrel prematurely. These individuals have at least a 30-fold increased risk of stent thrombosis over 9 months of follow-up compared with similar patients with good adherence.11 Although nonadherence to clopidogrel is multifactorial in etiology, the burden of medication copayments has been consistently reported as an important underlying problem, particularly before the drug was available in generic form.9, 13–20 This relationship has been observed within low-income cohorts for whom an increase in medication out-of-pocket costs has been linked to decreased use of essential medications, including cardiovascular medications.21, 22 The Medicare Part D drug benefit includes a low-income cost subsidy (LIS) program designed to reduce medication copayments for beneficiaries with low income and limited assets, and also to eliminate the Part D “coverage gap.”23 Almost 10 million older adults are enrolled in the LIS program,23 and the program has been linked to better adherence and decreased use of cost-reducing behaviors such as borrowing money or going without necessities.24,25 The LIS benefit is associated with improved adherence to essential cardiovascular medications after a myocardial infarction26 and should also result in improved adherence among older adults who have had coronary revascularization with a stent, with or without a previous myocardial infarction. Using 2006 and 2007 claims data from a large, national Medicare Part D insurer, we investigated whether enrollment in the LIS program was associated with clopidogrel adherence and persistence after coronary stent placement. We hypothesized that enrollment in the LIS program would be associated with a higher likelihood of good fill adherence to clopidogrel. We also hypothesized that LIS-enrolled beneficiaries would be less likely to discontinue clopidogrel prematurely. Our data predate the availability of clopidogrel in generic form, but we believe that examining this research question remains applicable to newer antiplatelet medications that are still only available in branded form (e.g., ticagrelor, prasugrel).