This study aims to determine the optimal tolerability dose ranges of risperidone (RIS) and olanzapine (OLZ) administered during schizophrenia maintenance phase.Methods
Two-year continuation rates of prescription at discharge were examined using a retrospective cohort study method. Adult patients with schizophrenia and related psychotic disorders, receiving antipsychotic monotherapy with RIS or OLZ at discharge, were included. The primary outcome measures were the time to treatment discontinuation and 2-year continuation rates at 4 modal dose ranges of each drug. We estimated the optimal tolerability dose ranges by comparing the continuation rates at various modal doses.Results
Of 648 patients, 344 received RIS and 304 received OLZ. The RIS 2-year continuation rates at 4 daily modal dose ranges were significantly different (0.5–2.5 mg: 46.0%, 3.0–5.0 mg: 40.0%, 5.5–7.5 mg: 30.0%, and 8.0–10.0 mg: 28.0%), with the difference favoring RIS at lower doses (0.5–5.0 mg) more than higher doses (5.5–10.0 mg). In contrast, there were no significant differences among OLZ 4 modal dose ranges (2.5–7.5 mg: 49.1%, 10.0–15.0 mg: 42.6%, 17.5–22.5 mg: 40.9%, and 25.0–30.0 mg: 39.0%). The time to treatment discontinuation significantly favored OLZ over RIS. However, it did not significantly differ between RIS and OLZ at lower doses.Conclusions
It is suggested that the optimal tolerability dose range during maintenance treatment is 0.5 to 5.0 mg/d for RIS and 2.5 to 30 mg/d for OLZ, and that RIS at lower doses is comparable with OLZ at lower doses.