Cost analysis in a Medicaid program for patients with bipolar disorder who initiated atypical antipsychotic monotherapy^*

ABSTRACT

Background: Use of atypical antipsychotics in treatment of patients with bipolar disorder is increasingly common, yet few studies have systematically investigated or compared medical costs associated with use of specific atypical antipsychotics.

Objective: To evaluate the direct healthcare costs associated with olanzapine, risperidone, or quetiapine monotherapy among Medicaid patients diagnosed with bipolar disorder (ICD-9: 296.4x-296.8x).

Methods: North Carolina Medicaid patients with bipolar disorder were followed for 12 months after initiation of atypical antipsychotic monotherapy (index date). They had no bipolar-related medical visit, hospitalization, or use of atypical antipsychotics 90-days prior to the treatment initiation. Costs of index drug, all bipolar-related medical care, and all health-related costs were examined. A two-stage sample selection model was employed to account for potential confounders and sample selection bias. Medication adherence measures using cumulative medication acquisition and cumulative medication gap were calculated as separate outcomes.

Results: Inclusion criteria were met by 838 continuously eligible patients (393 olanzapine, 262 risperidone, 183 quetiapine). Drug-taking adherence was similar across the drug cohorts. After adjusting for potential confounders, patients taking olanzapine incurred $863 (p < 0.001) and $449 higher (p < 0.01) index drug costs than patients taking risperidone and quetiapine, respectively. Bipolar-related medical costs for patients taking olanzapine were higher ($616; p = 0.06) than for patients taking risperidone at 10% significance level, while such costs for patients taking olanzapine and quetiapine were similar. Total health-related costs did not differ across patient cohorts, including or excluding the index drug costs.

Limitations: The final study sample is a highly selected one based on the study design. This sample may not represent the entire bipolar population. The criteria used to guard against omitting bipolar disorder patients misdiagnosed with major depression need further validation.

Conclusions: No evidence was identified that there is any difference for total health-related costs in using olanzapine, risperidone, or quetiapine monotherapy to treat bipolar disorder, from a Medicaid payer's perspective. The clinical difference between these atypical antipsychotic drugs for the treatment of bipolar disorder could be of more interest than the economic difference.

Key words: :

• Atypical antipsychotic
• Bipolar disorder
• Cost analysis
• Olanzapine
• Quetiapine
• Risperidone

Acknowledgments

Declaration of interest: The authors gratefully acknowledge the financial support of Eli Lilly and Company in the form of an unrestricted research and educational grant to conduct this study. No outside help was enlisted for the preparation of this manuscript. At the time of the study Y.Q. was a Post Doctoral Research Fellow and G.L. was Associate Professor at the University of North Carolina School of Pharmacy, Chapel Hill, North Carolina.

Notes

* Data from this paper were presented in part at the 11th Annual International Meeting of the International Society for Pharmacoeconomics and Outcomes Research, Philadelphia, PA, USA, May 20–24, 2006