Metabolic Effects of Olanzapine and Quetiapine: A Six-Week Random- ized, Single Blind, Controlled Study

The objective of this study is to compare the course of metabolic effects of olanzapine and quetiapine, two atypical antipsychotics with similar structure and receptor binding affinities but clinically observed different metabolic effects. This 6 week, single blind, randomized, controlled study was carried out during a structured treatment protocol in a female inpatient service, thus enabled to control effects of energy expenditure and other life style related factors. Subjects were randomly assigned into olanzapine (n=15) and quetiapine (n=15) groups. Weight and calorie intake (CI) were measured daily. Symptom severity and serum leptin levels (SLL) were measured biweekly. Serum lipids were measured at baseline and 6th week. Olanzapine treatment was associated with more severe weight gain (F=11.2, p<0.01), increase in CI (F=8.1, p<0.01) and a more disturbed lipid profile than quetiapine. The course of SLL were similar between the groups (F=1.39, p=0.26). Weight, CI and SLL changed in a similar pattern within the groups but the patterns were different for each drug, suggesting that the two drugs have different mechanisms for weight change. The explanation probably involves different affinities for 5HT2C receptors leading to different patterns of CI which we propose as possible targets of intervention to manage antipsychotic induced weight gain.