Cognitive effects of olanzapine and clozapine treatment in chronic schizophrenia

Rationale. Schizophrenia patients are known to manifest widespread, multifaceted cognitive deficits. There is now an increasing emphasis on the critical importance of cognitive deficits for the functional outcome in schizophrenia. Typical antipsychotics, although effective in reducing positive symptoms of the illness, have not shown much effect on cognitive functions. Atypical antipsychotics have shown promise of improving some cognitive functions. Objectives. This naturalistic study aimed to determine whether olanzapine and clozapine improve cognitive functioning in a sample of 48 patients with chronic schizophrenia who had either failed to show sufficient clinical improvements or suffered from distressing side effects with conventional antipsychotics and were switched to either olanzapine or clozapine for clinical reasons and, if so, whether the two drugs produce similar or different cognitive effects. Methods. All patients completed a comprehensive battery of neuropsychological tests designed to index executive functioning, verbal learning, verbal and visual and memory, attention, working memory, and psychomotor speed at: (i) baseline, (ii) after 6 weeks and (iii) after 6 months of treatment with olanzapine or clozapine. Results. From the initial 48 patients who remained on olanzapine (n=16) or clozapine (n=14) for the entire duration with continuous participation, 30 provided data for this study. There were improvements over time (i.e. from baseline through 6 weeks to 6 months) in both treatment groups on verbal fluency, verbal learning and verbal and visual memory measures. Conclusions. The findings indicate similar beneficial effects of olanzapine and clozapine on verbal learning and memory measures in patients showing a favourable clinical response to these drugs.