Antipsychotic switching: results from a one-year prospective, observational study of patients with schizophrenia

The Health Outcomes of a Canadian Community Cohort (HOCCC) study is a 1-year prospective observational study of outpatients with schizophrenia or related psychotic disorders. The purpose of the study was to compare effectiveness of antipsychotic treatment as measured by 1-year treatment completion rates.

Patients (N = 929) were enrolled if in the course of usual clinical practice they switched to a second-generation antipsychotic (SGA). Observational data were collected for up to 1 year. The primary analysis compared 1-year treatment-completion rates for the olanzapine cohort with the other SGA cohort (quetiapine, risperidone, clozapine), using a chi-squared test.

Of 929 patients enrolled, 64.8% (516/796) of evaluable patients completed 1 year of treatment. There was no statistically significant difference in the proportion of treatment completers between the olanzapine cohort (67.4%, 256/380) and the other SGA cohort (62.5%, 260/416). Treatment-completion rates were risperidone 62.0% (127/205), quetiapine 63.7% (123/193) and clozapine 55.6% (10/18). Antipsychotic polypharmacy was common. Patients treated with olanzapine or risperidone had significantly higher increases in BMI than quetiapine-treated patients. There were no major differences between olanzapine monotherapy and pooled other SGA monotherapy groups in status of extrapyramidal symptoms from baseline to endpoint.

Olanzapine and other SGAs exhibited similar rates of 1-year treatment completion. Further study of medication combinations is needed, given their perceived clinical value, and the high frequency of antipsychotic polypharmacy in clinical practice.

As most patients received several psychotropics and power was reduced in monotherapy analyses, comparisons between cohorts must be interpreted cautiously. Comparisons between individual antipsychotics were post hoc and not powered a priori. Accuracy and completeness of adverse event information for drugs other than olanzapine is limited.