Presenter: Vicki Fung (Kaiser Permanente Division of Research. )
Discussant: Dan WaldoActuarial Research Corporation
Research Objectives: Many Medicare Part D prescription drug plans include a coverage gap when beneficiaries’ spending exceeds an annual threshold. Early evidence suggests that the gap is associated with reductions in drug adherence. An increasing number of plans offer supplemental coverage during the gap, including generic-only drug coverage; however, little is known about the impact of generic-only coverage during the gap or about how effects may differ for beneficiaries using brand versus generic drug regimens.
Study Design: We conducted a historical cohort study to examine chronic drug therapy adherence for three therapeutic classes (cholesterol, diabetes, blood thinners) in 2007. We measured drug use using the proportion of days covered (PDC) by any drug in the class, and defined adherence as PDC≥80%. To examine annual differences in adherence we used random-effects models adjusted for age, gender, and the Part D risk score (RxHCC). We also examined changes in adherence in the five months before and after beneficiaries entered the gap using within-person fixed effects models, and defined patients’ drug use as brand or generic based on use in the month prior to entering the gap.
Population Studied: The study population included Part D beneficiaries enrolled in stand-alone Prescription Drug Plans (PDPs) and Medicare Advantage Prescription Drug (MAPD) plans offered by a large national plan sponsor. Beneficiaries receiving employer sponsored benefits or low income subsidies were excluded.
Principal Findings: Among PDP beneficiaries, generic-only gap coverage was associated with higher PDC and adherence in each drug class compared with no gap coverage (e.g., OR=1.88, 95% CI: 1.85-1.92 for adherence to cholesterol drugs); among MAPD beneficiaries findings varied by drug class. Entering the gap was associated with significant reductions in drug supply for cholesterol and oral diabetes drugs for PDP and MAPD beneficiaries with a gap and generic-only gap coverage; however the magnitude of the reductions were larger for beneficiaries using brand versus generic drugs (p<0.05). Beneficiaries using generic drugs prior to entering the gap who were enrolled in plans providing generic-only gap coverage had the smallest reductions in use. Differences across groups were not significant for changes in use of blood thinners.
Conclusions: Patients reduced use of chronic drugs after entering the coverage gap. Brand drug users all experienced substantial reductions in adherence to cholesterol and oral diabetes drugs after reaching the gap. Generic-only gap coverage conferred modest benefits for generic drug users, compared to plans with the coverage gap, but was still associated with modest declines in drug use after reaching the gap.
Implications: Standard Part D drug plans with gaps in coverage are associated with poor adherence, particularly for beneficiaries taking brand drugs. Partial coverage plans that provide generic drug coverage during the gap offer only some coverage improvement. Additional efforts are needed to identify approaches for covering all necessary chronic drugs.
The 3rd Biennial Conference of the American Society of Health Economists took place at Cornell University.
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