Quetiapine has a direct effect on the negative symptoms of schizophrenia

Second-generation 'atypical' antipsychotics appear to be more effective than first-generation 'typical' antipsychotics in improving negative symptoms in schizophrenia; it is unclear, however, if this greater improvement represents a direct beneficial effect or is mediated indirectly by an antidepressant effect or the absence of extrapyramidal symptoms (EPS). To address this issue with reference to quetiapine ('Seroquel'), data were evaluated from four randomized, controlled clinical studies involving 1106 patients employing a path analysis model. The total effect of quetiapine on negative symptoms was measured using the Scale for Assessment of Negative Symptoms (SANS) total score. Indirect effects on negative symptoms via positive, depressive and EPS were assessed using appropriate instruments. Effect sizes were calculated by path analysis for the difference between treatment groups in change from baseline to endpoint in SANS total score. Analysis confirmed that quetiapine produced a greater overall improvement in negative symptoms than placebo (effect size 1.96); this was explained by a significant direct effect (p = 0.001; 44.2% of total improvement), and a secondary effect of improved positive symptoms (p < 0.001; 47.5% of total improvement), but was not a consequence of changes in depressive symptoms or EPS. Within the constraints of the path analysis methodology, these results indicate that quetiapine has a substantial direct effect on improving the negative symptoms of schizophrenia.