Effectiveness of different dosing regimens of risperidone and olanzapine in schizophrenia

The objective of this study was to evaluate the effectiveness and impact of once- versus twice-daily dosing of risperidone and olanzapine on clinical outcomes in patients with schizophrenia. Data from phase 1 of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) schizophrenia study were used. Patients with schizophrenia were randomly allocated to treatment with risperidone and olanzapine, and were also randomly assigned to once-daily (N=173 and 169, respectively) or twice-daily (N=168 and 167, respectively) dosing and followed for up to 18 months. Discontinuation rate and time to discontinuation were used as primary outcome measures to compare the two groups. The following outcome measures were also analyzed: efficacy, safety, medication adherence, adverse events, and concomitant psychotropic medications. No significant differences in discontinuation rates and time to discontinuation were observed between the once- and twice-daily dosing groups (P>0.05) in patients receiving risperidone or olanzapine. The once-daily dosing group demonstrated significantly lower mean daily doses of risperidone and olanzapine across phase 1, and lower rates of hospitalization for exacerbation of schizophrenia, sleepiness, and orthostatic faintness in patients receiving olanzapine (P<0.05) compared to the twice-daily dosing group. No significant differences were found in any other outcome measures between the two dosing groups. In conclusion, effectiveness and efficacy outcomes between once- and twice-daily dosing for risperidone and olanzapine were not significantly different. However, in view of the lower mean dose and better side effect profile, it is advisable to adhere to a once-daily dosing regimen, especially in the case of olanzapine.