Rationale. The implementation of Medicare Part D in January 2006 changed the source and management of insurance coverage for prescription drugs from state Medicaid programs to Medicare private drug plans (PDPs) for the six million beneficiaries enrolled in both programs (i.e., “dual beneficiaries”). This change in drug coverage affected the utilization management (UM) policies that dual beneficiaries faced when obtaining prescription drugs including prior authorization, tiered drugs, quantity limits and step therapy. Among publicly insured adults with bipolar disorder, UM policies are strongly associated with reduced use of recommended pharmacotherapy, reduced initiation of treatment with medication, and increased treatment discontinuation.  Discontinued or delayed use of anti-manic pharmacotherapy is in turn associated with the use of emergency department services and elevated health care costs.  Thus, while the originating legislation for Medicare Part D did not set out to alter the quality of medication treatment that dual beneficiaries with bipolar disorder received, the associated modifications to UM created the potential for such unintended effects.

Objectives. To assess if, and to what extent, the transition from Medicaid to Part D drug coverage changed the quality of pharmacotherapy for bipolar 1 disorder (BP1) and the quantity of emergency department (ED) use among beneficiaries with a diagnosis of BP1.

Data and Methods.    We merged Medicaid and Medicare enrollment and claims data to construct our analytic dataset of dual beneficiaries’ health care utilization. Specifically, we obtained Medicaid enrollment, Medicare enrollment and medical claims data for a five percent national random sample of fee-for-service (FFS) Medicare beneficiaries from 2004-2007.   From this sample, we identified a cohort of 1,975 adults, ages 20-64, continuously enrolled in Medicaid and Medicare from 2004-2007 with a diagnosis of BP1.   We use a quasi-experimental design, interrupted time series using monthly pharmaceutical and medical claims data, to examine the population-level effect of the transition to Part D on pharmacotherapy quality for BP1 and ED use (both all cause and behavioral health related).   Our pharmacotherapy indicators are derived from the American Psychiatric Association’s 2005 Practice Guideline for the Treatment of Patients with Bipolar Disorder and include the use of antimanic medication as an indicator of good quality and the use of antidepressant monotherapy as our indicator of poor quality.

Policy Implications. Medicaid beneficiaries with bipolar disorder and other serious mental illnesses continue to transition to dual enrollment and Part D drug coverage every day.  Understanding the effects of Part D coverage on medication treatment quality is instructive both for the ongoing design of Medicare PDPs and for Medicaid drug coverage.