In this review, we identified 26 studies evaluating the effect of Medicare Part D implementation on drug utilization and out-of-pocket costs. As expected, Part D's inception was associated with a consistent overall increase in drug utilization and a decrease in out-of-pocket costs for enrollees. The transition to Part D went smoothly for many elderly dual-eligible patients, but other vulnerable populations appear to have experienced difficulties. Finally, the Part D coverage gap was associated with decreased drug utilization and increased out-of-pocket costs.
There was little variation in effect estimates among studies evaluating the effect of Part D implementation: a 6-13% increase in drug utilization and a 13-18% decrease in out-of-pocket drug costs. Changes in utilization and costs varied by drugs, disease and/or population studied, underscoring the need to consider such factors when assessing Part D's impact. However, there was little indication that Part D selectively led to increased use of essential, underused drugs as compared to overused medications.13
In studies of the Part D transition period, elderly dual-eligible beneficiaries generally fared well, while other populations seemed to experience problems. Two hypotheses may explain these disparate experiences. Due to concerns about the Part D transition for dual-eligibles, many of whom are elderly, both the Centers for Medicaid Services and the states instituted a variety of mechanisms to ease the change, including auto-enrollment and temporary continuation of Medicaid drug coverage during early 2006.29
In contrast, vulnerable populations, such as those with HIV or mental illness, may have had difficulties with the transition due to factors associated with their illnesses.
A second hypothesis is that studies using claims data were unable to identify medication access problems because claims reflected only successfully filled prescriptions, not attempted fills, whereas the survey-based studies were able to tease out these problems. Using claims data, no changes were seen in medication continuity for benzodiazepines.26
Similar methodology might be used to examine continuity of other medications during the transition period, shedding light on the ability of drug claims versus survey-based data to expose medication access problems.
Finally, across all studies, Part D beneficiaries' entry into the coverage gap was associated with decreased drug utilization of 9-16% (an amount similar in magnitude to the increases seen after Part D implementation) and increased out-of-pocket costs with changes as high as 89%. Patients who entered the coverage gap were 5-11% more likely to report discontinuing, switching and/or failing to initiate a medication than were patients who did not enter the coverage gap. Use of generic drugs increased 20% during the coverage gap. These studies suggest that when patients enter the coverage gap, the cost burden dramatically and immediately affects drug utilization and moves patients towards more affordable generic drugs.
The consistency of these findings has important implications. Similarly structured benefit gaps (e.g., drug caps) have been associated with adverse outcomes such as death and increased non-elective healthcare use.30
As Part D reforms are contemplated, policymakers must consider whether drug cost savings during the gap offset the benefits of drug coverage, with the gap potentially leading to adverse health outcomes and even greater spending on healthcare services.
The conclusions drawn from studies in this systematic review must be interpreted with caution. Even though research has found that elderly patients fill 97% of prescriptions within a single pharmacy chain, 31
studies that rely on retail prescription claims may miss prescriptions for patients who use more than one pharmacy chain. Studies evaluating patients without prior drug insurance did not have Part D enrollment files for patients but rather estimated Part D coverage using cost algorithms, so there is likely some misclassification. Finally, these studies offer little or no evidence regarding the impact of Part D on health outcomes. Because the primary goal of Part D was to improve the health of Medicare beneficiaries, such studies are desperately needed.
Using different data sources, designs, and analytic approaches, the studies included in this systematic review showed consistent estimates of Part D's impact in the initial year(s) of the benefit as well as during the coverage gap period. Conflicting results regarding the Part D transition period can be further examined using existing data and methodologies applied to specific drug classes and populations. While we look forward to studies that employ public-use Part D claims, we believe that the currently available evidence documents Part D's role in improving medication access for Medicare beneficiaries and highlights Part D benefit features such as the coverage gap that merit reconsideration and potential improvement. As the fate of the Part D benefit and the coverage gap are pondered, data about effects on health outcomes are urgently needed.