The effect of the US Medicare Part D coverage gaps on medication use among patients with depression and heart failure

Abstract

Background: Medication use among Medicare beneficiaries has increased and adherence has improved since the implementation of the Medicare Part D prescription drug benefit in 2006. However, the structure of the benefit, particularly, the coverage gap, is still problematic. It is critical to understand how beneficiaries with coexisting conditions respond to the coverage gap and whether their response differs by type of medications.

Aims of the study: The paper aims to evaluate the effects of Medicare Part D's coverage gap on drug regimens among beneficiaries with coexisting depression and heart failure (HF).

Methods: Drug utilization patterns and medication adherence of a 5% random sample of Medicare Part D beneficiaries with depression and HF in 2007 were observed. Drug utilization patterns were measured on the basis of reported drug claims and medication adherence was defined as the proportion of days of medication possession in a given period. We compared pre-post drug use patterns and medication adherence across three groups: no coverage, generic coverage, and full coverage due to low-income subsidies (LIS) and used propensity score weighting to adjust for difference across groups.

Results: Beneficiaries with some drug coverage in the gap were more likely to enter the gap: 82% for LIS, 79% for generic-only and 58% for no coverage. Beneficiaries without drug coverage reduced their use of antidepressants by 5.0% (95% CI 1.7%-8.2%), and HF drugs by 9.4% (95% CI 7.2%-11.5%) after they entered the coverage gap. Those with generic coverage cut their brand-name drugs more than generic drugs but did not shift to generic drugs. However, adherence to antidepressants did not change; adherence to HF drugs reduced slightly, 2.5% (95% CI 1.2%-3.7%) in the no-coverage group and 2.6% (95% CI 1.3%-3.9%) in the generic-coverage group.

Conclusions: The coverage gap was associated with a modest reduction in number of prescriptions filled for depression and HF but it was not associated with a significant effect on adherence.

Implications for health policy: We found that beneficiaries with coexisting depression and HF were less likely to reduce their drug use than beneficiaries in general. In addition, the gap was not associated with a large reduction in adherence. It suggests that concerns about the coverage gap's harmful effects on medication adherence, or comorbidities might be overstated.

Implications for further research: Further studies on how people make medication use decisions in the face of changes in benefits and how the coverage affects non-drug medical outcomes are warranted.

Figure 1

Histograms of the Time Spent in the Gap by Group Abbreviations: LIS = low-income-subsidies; this is the comparison group.