Our study is the first to examine the impact of the new Medicare drug benefit on likelihood of antidepressant treatment, medication choice and refill adherence for older adults with depression who previously lacked or had minimal drug coverage.
Part D was associated with an increased likelihood of antidepressant treatment among older adults diagnosed with depression who previously lacked drug coverage. This result is consistent with a major goal of Part D -- to reduce financial barriers to medication access among the elderly – and is important given the significant morbidity and mortality associated with under-treatment of depression in elderly patients.(2
) We did not see an increase in likelihood of antidepressant treatment, however, among those who transitioned from limited benefits to Part D benefits suggesting that Part D’s effect on overall rates of depression treatment will be concentrated among seniors who lacked drug coverage prior to Part D who went on to enroll in the new benefit.
Part D was also associated with increased rates of refill adherence in the group that previously lacked coverage and also among those who experienced improvements in drug coverage (i.e., those with capped benefits). We estimated that older adults enrolled in Part D had more than twice the relative odds of good adherence in the first six months of treatment compared to those enrolled in the same plan who had limited ($150 caps) or no drug coverage prior to Part D. Experiments with value-based insurance design, whereby insurers reduce cost-sharing for medications shown to reduce morbidity and mortality, have yielded similar improvements in adherence.(28
) Our findings have important clinical implications because improved antidepressant use and adherence reduces rates of relapse and recurrence of depression.(29
) The fact that Part D was associated with a change in adherence but not likelihood of treatment in the group who transitioned from capped benefits suggests that an older adult with limited drug coverage may be willing to start antidepressant treatment but, when faced with gaps in coverage, may forgo refills and be non-adherent over a longer time period.
In spite of the significant improvements in adherence associated with Part D, however, only half of individuals in our study sample were adherent to antidepressant pharmacotherapy. These findings suggest that reductions in cost-sharing should be combined with other interventions, such as depression care management, to improve antidepressant adherence among older adults.(2
We did not detect the hypothesized reduction in the use of TCAs and MAOIs, which have been available as less expensive generics for several years, after the implementation of Part D. Use of these medications increases the risk of interactions with other drugs and/or exacerbations of other diseases in older adults(22
) although recent evidence suggests that rates of adverse effects such as falls are similar between SSRIs and TCAs.(31
) One possible explanation for this finding is that a number of newer antidepressants (e.g., SSRIs) also became available as less expensive generics before Part D’s implementation so the pharmacy copayments, which differ for brand name and generic drugs, were similar across pharmacologic classes in the antidepressant category. Thus, out-of-pocket costs were just as low for many of the most commonly used SSRIs as they were for older agents.
There are some potential limitations to our study. First, selection bias may be introduced if individuals with poorer health status were more likely to enroll in plans with more generous drug coverage. Because the level of coverage pre-Part D depended on where beneficiaries lived or whether they were eligible for retiree drug coverage, we believe the degree of selection bias across study groups to be small. Second, as is typical of analyses of claims data, we lack information on socioeconomic status and other variables (e.g., marital status). We used census block-level data on race, education and income which has been found to yield similar estimates of the associations between socioeconomic status and health outcomes as individual-level data although these effects are sometimes underestimated.(32
). Third, depression is often undercoded in claims data. To check the robustness of our estimates we conducted analyses (except for the treatment initiation model) using all individuals who filled antidepressant prescriptions (regardless of depression diagnosis). The results were qualitatively similar to the more conservative approach of requiring a diagnosis which has higher specificity.(21
) We do not expect the degree of diagnosis coding to vary across benefit groups or over time so as to bias our estimates of the effect of Part D. Fourth, to the degree those without benefits filled prescriptions in non-network pharmacies in 2004 and 2005, we may overestimate the effect of Part D on antidepressant use. We believe this bias is small because we limited our analyses to individuals who filled prescriptions in network pharmacies; plan members received a 15% discount when doing so. Finally, this study of community-dwelling elders living in Pennsylvania may not be representative of older adults nationally. However, our study sample spans the range in generosity of pharmacy benefits in existence nationally at the time of Part D’s implementation. Moreover, national Part D data do not contain pre-Part D utilization data required for our analyses.
This is the first study to show that Medicare Part D was associated with an increase in the likelihood of antidepressant treatment and refill adherence for antidepressants in older adults with depression. Our results indicate that Medicare Part D may have helped to address a major barrier to achieving optimal quality of care for depressed elders. Additional interventions may be necessary to further improve selection of antidepressant agent and adherence.