Patient factors associated with oral generic olanzapine initiation and substitution among Medicaid beneficiaries: a new user cohort study

Abstract

Objective

Generic drugs typically are less expensive than branded products; however, several factors can limit generic drug utilization. This study assesses the associations of patient factors with generic olanzapine initiation and substitution.

Methods

A retrospective new user cohort study was conducted using the 2011–2012 Medicaid administrative claims data. Beneficiaries continuously enrolled during the 6 month washout period prior to their initial oral brand or generic olanzapine prescription were included and followed up to 12 months. Among brand olanzapine new users, time to generic substitution and competing risk outcomes was estimated using the Fine–Gray cumulative incidence function. Patient demographic and health service utilization factors were assessed in the multivariate cause-specific hazards model.

Results

Among olanzapine new users, 70.7% patients initiated generic treatment. Beneficiaries aged ≥21, and living in the Midwest and West regions were more likely to initiate generic olanzapine. Among brand new users, 28.2% switched to generic olanzapine, 23.6% switched to an alternative atypical antipsychotic treatment and 38.0% discontinued within 12 months. Beneficiaries who resided in urban areas (adjusted hazard ratio [AHR) = 0.53, 95% CI = 0.37–0.75) and had prior hospitalizations (AHR = 0.85, 95% CI = 0.75–0.96) had lower rates of generic substitution, whereas those with emergency department (ED) visits (AHR = 1.06, 95% CI = 1.02–1.10) had a higher rate of generic substitution. In addition, beneficiaries in different age subgroups also had different rates of generic substitution in different regions.

Conclusion

Medicaid beneficiaries’ age, geographic region, prior hospitalization and ED utilization were associated with generic olanzapine initiation and substitution. Tailored educational outreach targeting these patient subgroups might improve generic olanzapine utilization.

Keywords:

• Brand
• generic substitution
• Medicaid
• competing risk

Transparency

Declaration of funding

Funding for this manuscript was made possible, in part, by the US Food and Drug Administration (FDA) grant # U01FD005875. Views expressed in written materials or publications and by speakers and moderators do not necessarily reflect the official policies of the Department of Health and Human Services; nor does any mention of trade names, commercial practices or organization imply endorsement by the United States Government.

Declaration of financial/other relationships

R.A.H. has disclosed that in the past 3 years he has provided expert testimony for Daiichi Sankyo and Takeda. No potential conflict of interest was reported by the other authors.

Author contributions

A.U.M. and J.Q. had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: J.Q., A.U.M., R.A.H., I.H. Acquisition, analysis or interpretation of data: J.Q., L.C., C.L., N.H. and A.U.M. Drafting of the manuscript: A.U.M. and J.Q. Critical revision of the manuscript for important intellectual content: all authors. Statistical analysis: C.L., N.H., A.U.M. Obtained funding: J.Q, R.A.H., I.H. and Z.K. Administrative, technical or material support: J.Q. and A.U.M. Study supervision: J.Q.

Notes

i Zyprexa is a registered trademark of Eli Lilly and Company, Indianapolis, IN, USA.