Do Restrictions on Antipsychotic Use Differ Between Medicare Part D Stand-Alone Versus Medicare Advantage Plans?

ABSTRACT

OBJECTIVE: The objective of this study was to describe the type of restrictions and differences among antipsychotic users enrolled in Medicare Part D Stand-Alone (PDPs) and Advantage (MAPDs) prescription drug plans. METHODS: This retrospective study used data from Chronic Condition Data Warehouse, comprising a random 5% sample of the Medicare population in 2008. This study used bivariate analyses and multivariate logistical regression models to study differences in formulary restrictions on antipsychotic use between PDP and MAPD enrollees, adjusting for enrollee characteristics. Dependent variables included type of restriction and antipsychotic therapeutic class. The study sample was restricted to continuous Part D enrollees (N = 1,346,978) stratified by plan type, MAPDs (N = 435,591), and PDPs (N = 911,387). RESULTS: According to the bivariate analysis, antipsychotic users enrolled in PDPs were more likely to encounter restrictions (39.8%), compared with those in MAPDs (30.3%). In the multivariate analyses, antipsychotic users in MAPDs were less likely to face any restriction (odds ratio [OR] = 0.75, 95% confidence interval [CI] 0.72-0.78). Furthermore, atypical antipsychotic users in MAPDs were less likely to face any restriction (OR = 0.76, 95% CI 0.73-0.79), while first-generation antipsychotic users in MAPDs were more likely to face any restriction (OR = 1.87, 95% CI 1.32-2.65). Low-income subsidy (LIS) beneficiaries using any antipsychotic were much more likely to face restrictions compared with non-LIS beneficiaries. CONCLUSION: PDP enrollees prescribed antipsychotics were more likely to face formulary restrictions, as opposed to those in MAPDs. LIS beneficiaries enrolled in PDPs faced much higher risk of restricted access to this "protected" drug class.