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

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.