Drug Use Patterns in Severely Mentally Ill Medicare Beneficiaries: Impact of Discontinuities in Drug Coverage

ABSTRACT

Objective. To describe the extent of drug coverage among severely mentally ill Medicare beneficiaries and to determine whether and to what extent discontinuities in prescription drug coverage influence the use of medications used to treat serious mental health conditions.

Data Source. 1997–2001 Medicare Current Beneficiary Surveys.

Study Design. We use a zero-inflated negative binomial model to estimate: (1) the probability of not receiving any mental health drug and (2) the number of medications received, adjusting for age, race, income, census region, health status, and comorbidity. Severe mental illness is defined using inpatient and outpatient claims with ICD-9 codes of schizophrenia, other psychotic disorders, bipolar disorders, and major depression. Mental health medications include antidepressants, antipsychotics, mood stabilizers, anxiolytic/sedative-hypnotics, and stimulants. Prescription drug coverage is assessed as full coverage (0 percent discontinuities), no coverage (100 percent discontinuities), or as discontinuous coverage, measured as 1–25, 26–50, and 51–99 percent of time without coverage.

Data Collection/Extraction Methods. We constructed three 3-year longitudinal cohorts of severely mentally ill Medicare beneficiaries residing in the community (n=901).

Principal Findings. Severely mentally ill Medicare beneficiaries with drug coverage discontinuities are more likely than their continuously insured peers not to receive medications used to treat mental health disorders, with the most significant impact seen in the probability of receiving any psychiatric medications. Analysis of two therapeutic classes—antidepressants and antipsychotics—revealed varying impacts of drug gaps on both probability of any drug use, as well as number of medications received among users.

Conclusions. Severely mentally ill Medicare beneficiaries may be particularly vulnerable to the Medicare Part D drug benefit design and, as such, warrant close evaluation and monitoring to insure adequate access to and utilization of medications used to manage mental illness.