Weight decline in patients switching from olanzapine to quetiapine

This open-label study investigated the strategy of switching patients who had gained excessive weight on olanzapine to quetiapine, with assessments of safety and continued efficacy as well as weight change. Patients who were psychiatrically stable on olanzapine but had gained >20% in weight and had body mass index >25 mg/kg² were switched to quetiapine over a 4-week period and followed for 6 weeks, the total study duration being 10 weeks. Assessments included weight change, antipsychotic efficacy using the Positive and Negative Symptom Syndrome Scale (PANSS), extrapyramidal adverse events using the Simpson-Angus Scale (SAS), and laboratory studies for metabolic measures. Of 16 enrolled patients, 12 completed the study. Mean weight loss was 2.25 kg (Cohen's d=0.12; P=0.03). There were no significant changes in PANSS total scores, SAS scores, or metabolic parameters. Switching patients to quetiapine, appears to be a viable strategy for managing olanzapine-induced weight gain as indicated by this 10-week open-label study. Prospective controlled trials of longer duration and larger number of subjects are needed.