Effects of olanzapine and other antipsychotics on cognitive function in chronic schizophrenia: a longitudinal study

This study aimed to determine the effect of olanzapine and other antipsychotic drugs on cognitive functions after 6months of treatment. Baseline, 3month and 6month psychopathological and cognitive evaluations were made. Thirty-eight partially responsive outpatients with DSM-IV chronic schizophrenia diagnosis were included in the study. On the indication of their attending psychiatrists, 21 patients initiated treatment with olanzapine, and 17 remained on their previous treatment with other antipsychotic drugs. Cognitive assessments were blind to medication and psychopathological status. The olanzapine group presented a significantly greater improvement in negative symptomatology and verbal memory than the comparison group in repeated-measures of MANOVAs between baseline, 3month and 6month assessments. These differences remained statistically significant after covarying out gender, treatment with other atypical antipsychotics, biperidene doses and changes in positive and negative symptoms. In order to match previous differences between groups, cognitive baseline scores for each test were introduced as covariates, resulting in a significant improvement for the olanzapine group in negative symptomatology and the interference task of the Stroop test.We then re-analyzed the data, dividing the comparison group into two groups: risperidone-treated patients (n=9) and patients receiving conventional antipsychotic drugs (n=8). Post-hoc analyses between groups were carried out with baseline cognitive assessment as covariate. The olanzapine group improved significantly more than the risperidone group in negative symptomatology and in the interference task of Stroop test. The improvement in the number of categories of the Wisconsin Card Sorting Test was higher in risperidone patients than in those receiving olanzapine or conventional antipsychotic treatment. Conventional antipsychotic drugs did not present a significant improvement over atypical antipsychotic drugs in any cognitive function. In summary, in patients suffering from chronic schizophrenia, atypical antipsychotic agents were associated with slight differential improvements over time in attentional, verbal memory and executive functions compared with conventional neuroleptic drugs. No differential improvements were found in social functioning, verbal fluency, non-verbal domains of memory or visuo-motor abilities.