Background: Some, but not all, previous studies have indicated that weight gain is associated with greater improvement in psychopathology during clozapine treatment. Possible reasons for the inconsistent results include failure to adjust for initial body weight and level of psychopathology, differences in trial duration, outcome measures, reliability of assessment, concomitant medications and clozapine dosage. The purpose of this study was to test the hypothesis that clozapine-induced weight gain is related to antipsychotic efficacy at 6 weeks and 6 months after adjusting for initial body weight and severity of illness.
Methods: Weight and psychopathology were determined in 74 patients with schizophrenia or schizoaffective disorder at baseline and after 6 weeks and 6 months of open treatment with clozapine monotherapy. The primary measures of psychopathology were the Brief Psychiatric Rating Scale (BPRS) Total and Positive symptoms subscales, Schedule for Assessment of Negative Symptoms (SANS), Schedule for Assessment of Positive Symptoms (SAPS) and Global Assessment of Function Scale (GAFS).
Results: Significant improvement in the key measures of psychopathology was noted at 6 weeks and 6 months. Mean weight gains at 6 weeks and 6 months were 3.7+/-5.7 S.D. and 7.3+/-7.9 S.D. kg, respectively, with the increase between 6 weeks and 6 months being significant. Age, but not gender, initial body weight, clozapine dosage or plasma levels predicted weight gain at both time points. At 6 weeks and 6 months, after adjustment for age, initial weight and level of psychopathology, the percentage change in weight significantly predicted the improvement in the BPRS Total and Positive symptoms subscale, the SANS Global score, as well as other measures of psychopathology.
Conclusions: Increase in weight with clozapine predicted improvement in psychopathology. This suggests that effects of clozapine on neurotransmitters which influence weight gain, e.g. 5-HT(2C) and 5-HT(1a) antagonism, in association with individual variations in these receptors and others molecules, e.g. peptides and transporters, due to polymorphisms or post-translational editing of mRNAs, may also contribute to the improvement in psychopathology.