The Effects of Risperidone on the Five Dimensions of Schizophrenia Derived by Factor Analysis: Combined Results of the North American Trials

Background: In two double-blind trials conducted in North America, 513 patients with chronic schizophrenia received risperidone, haloperidol, or placebo. In the present study, combined data from the two trials were analyzed.

Method: Patients were randomly assigned to receive placebo, fixed doses of risperidone (2, 6, 10, and 16 mg/day), or 20 mg/day of haloperidol for 8 weeks. Factor analysis of scores on the Positive and Negative Syndrome Scale (PANSS) produced five dimensions (negative symptoms, positive symptoms, disorganized thought, uncontrolled hostility/excitement, and anxiety/depression), similar to the five dimensions of previous factor-analytic studies of PANSS data.

Results: Mean changes (symptom reductions) in PANSS factor scores from baseline to treatment Weeks 6 and 8 were significantly greater in patients receiving 6_16 mg/day of risperidone than in patients receiving placebo or haloperidol. The advantages of risperidone were greatest for negative symptoms, uncontrolled hostility/excitement, and anxiety/depression. Even at the lowest dose, 2 mg/day, risperidone was significantly (pÐ.05) superior to haloperidol in reducing negative symptoms. The differences in outcomes between risperidone and haloperidol on PANSS scores were not related to extrapyramidal symptoms.

Conclusion: Risperidone produced significantly (pÐ.05) greater improvements than haloperidol on all five dimensions. The large between-group differences on negative symptoms, hostility/excitement, and anxiety/depression suggest that risperidone and other serotonin/dopamine antagonists have qualitatively different effects from those of conventional antipsychotic agents.