Ambulatory Use of Olanzapine and Risperidone: A Population-Based Study on Persistence and the Use of Concomitant Therapy in the Treatment of Schizophrenia

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Abstract
Objective: To assess treatment discontinuation and concomitant use of other antipsychotics among individuals initiated on olanzapine or risperidone for the treatment of schizophrenia. Method: Using data from the Quebec health insurance plan and the Quebec database for hospitalization, we conducted a population-based cohort study of patients for whom a first claim for olanzapine or risperidone was submitted between 1 January 1997 and 31 August 1999. Included were 6405 patients with schizophrenia whom we followed from the date of the first claim for olanzapine or risperidone either to discontinuation date, end of eligibility for the drug plan, 365 days, date of moving out of the province, or date of death. We used Cox regression models to compute hazards ratios (HRs) of having the treatment discontinued and logistic regression models to compute odds ratios (ORs) among persisting patients of having any concomitant antipsychotic prescription. All models were adjusted for age, sex, schizophrenia disorder, comorbidity, region, beneficiary type, substance use disorder, and prior hospitalization for mental illness. Results: Compared with risperidone users ( n = 2718), discontinuation rates were lower for olanzapine users ( n = 3687; HR = 0.79; 95%CI, 0.74 to 0.84). The odds of receiving any concomitant antipsychotic prescription did not differ statistically between olanzapine and risperidone users (OR 0.85; 95%CI, 0.71 to 1.01). Conclusions: The study results suggest that new users of olanzapine were less likely to discontinue their initial treatment than were new users of risperidone, although discontinuation was high in both groups. Among those who persisted, concomitant use of other antipsychotics did not differ between olanzapine users and risperidone users.

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