Risk of discontinuation of atypical antipsychotic agents in the treatment of schizophrenia

OBJECTIVES: To compare discontinuation rates of atypical antipsychotic agents in patients with schizophrenia. METHOD: Adult Maryland Medicaid patients with schizophrenia were categorized based on initial atypical antipsychotic drug received: aripiprazole (n=446); olanzapine (n=1705); quetiapine (n=1467); risperidone (n=1580); and ziprasidone (n=700). Discontinuation was measured using refill patterns, allowing 14-day gaps between refill dates. Using olanzapine as the reference drug, the hazard of discontinuation within the first year of follow-up was compared across atypicals using Cox proportional hazard models adjusted for demographic and clinical covariates. Sensitivity analysis tested the robustness of results by using different definitions of the index date. RESULTS: At one-year follow-up, most patients discontinued their antipsychotic medication (90.4% adjusted mean discontinuation). The hazard ratio (HR) for discontinuing therapy in patients starting treatment on aripiprazole, risperidone, or ziprasidone was not significantly different from olanzapine HR 1.047, 0.973 and 0.990, respectively]. Quetiapine was associated with significantly higher hazard of discontinuation HR 1.130] than olanzapine. Covariates associated with significantly lower discontinuation were being male HR 0.899], older age HR 0.997] and being on concurrent medication when initiating therapy HR 0.225]; having a previous hospitalization was associated with significantly higher discontinuation hazard HR 1.276]. Results were robust in the sensitivity analysis. CONCLUSIONS: Discontinuation rates were high at one-year follow-up and did not differ significantly for patients on aripiprazole, olanzapine, risperidone, or ziprasidone. The higher hazard of discontinuation associated with quetiapine when compared to olanzapine is consistent with that observed in Phase I of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE).