OBJECTIVES: This study was undertaken to examine if patients exhibit more pronounced metabolic abnormalities after 8-year treatment with clozapine or olanzapine than before, and also to investigate whether there exist any differences between long-term clozapine and olanzapine therapies regarding metabolic side- effects.
METHODS: Fifty psychiatric outpatients diagnosed with schizophrenia or schizoaffective disorder and on treatment with clozapine or olanzapine were studied during 8 years. Fasting blood or serum samples for glucose, lipids, prolactin and antipsychotic drug concentrations were analyzed. In addition, body mass index was calculated.
RESULTS: More patients treated with olanzapine compared with those treated with clozapine ended with their medication, in most cases because of diabetes mellitus and/or hyperlipidemia, during the 8-year follow-up. Also more patients treated with olanzapine compared with those treated with clozapine developed manifest diabetes mellitus during the 8-year period. Prolactin levels were higher in the patients treated with olanzapine compared with in those treated with clozapine at study start, but there were no differences in the other parameters between the treatment groups at study start. In the patients remaining on their medication all 8 years, the glucose level increased over time in the clozapine group, but not in the olanzapine group, whereas body mass index and lipids were unchanged over time in both treatment groups.
CONCLUSIONS: Our findings point to that both olanzapine and clozapine long-term treatments cause development of hyperglycemia and/or hyperlipidemia. Furthermore, olanzapine long-term treatment seems to more often lead to development of manifest diabetes mellitus than long-term treatment with clozapine.