Adverse clinical events among medicare beneficiaries using antipsychotic drugs: linking health insurance benefits and clinical needs

Abstract

Objective: Medicare Part D provides formulary protections for antipsychotics but does not exempt these drugs from cost-sharing. We investigated the impact of Part D coverage on antipsychotic drug spending, adherence, and clinical outcomes among beneficiaries with varying indications for use.

Methods: We conducted a historical cohort study of Medicare Advantage beneficiaries who received antipsychotic drugs, with diagnoses of schizophrenia or bipolar disorder or with no mental health diagnoses (N=10,190). Half had a coverage gap; half had no gap because of low-income subsidies. Using fixed effects regression models, we examined changes in spending and adherence as beneficiaries experienced cost-sharing increases after reaching the gap. We examined changes in hospitalizations and emergency department visits using proportional hazard models.

Results: Across all diagnostic groups, total monthly expenditure on antipsychotic drugs decreased with cost-sharing increases in the gap compared with those with no gap (eg, schizophrenia: -$123 95% confidence interval [-$138, -$108]), and out-of-pocket spending increased (eg, schizophrenia: $104 [$98, $110]). Adherence similarly decreased, with the largest declines among those with schizophrenia (-20.6 percentage points [-22.3, -18.9] in proportion of days covered). Among beneficiaries with schizophrenia and bipolar disorder, hospitalizations and emergency department visit rates increased with cost-sharing increases (eg, schizophrenia: hazard ratio=1.32 [1.06, 1.65] for all hospitalizations), but did not among subjects without mental health diagnoses. Clinical event rates did not change among beneficiaries with low-income subsidies without gaps.

Conclusions: There is evidence of interruptions in antipsychotic use attributable to Part D cost-sharing. Adverse events increased among beneficiaries with approved indications for use, but not among beneficiaries without such indications.

Figure 1. Changes in Adherence to Antipsychotics Before and After Reaching the Gap Threshold

Notes: We used linear fixed effects regression models (xtreg, fe in Stata 10) to examine changes in the monthly PDC (proportion of days covered) by any antipsychotic in the five months before and after reaching the coverage gap threshold ($2,400 in total drug spending); changes are relative to the month prior to reaching the coverage gap (month -1). Beneficiaries with no gap receive the low income subsidy (LIS) that reduces cost-sharing and eliminates the gap.