Abstract

With the use of chlorpromazine and other traditional antipsychotics for psychosis, it was soon discovered that the antipsychotic efficacy of this class of medications was closely associated with their ability to block dopamine D2 receptors in the brain. This prompted the hypothesis that the etiology of schizophrenia and other psychotic illnesses might be caused by a dysregulation of dopamine. This hypothesis, that the dopamine system explains schizophrenia symptoms, however, is far from complete and the treatment with conventional antipsychotic medications is far from ideal. There has been a great deal of speculation regarding the role of serotonin receptor antagonism in regards to antipsychotic effects. The second-generation antipsychotics (SGAs), clozapine, risperidone, olanzapine, quetiapine, ziprasidone and aripiprazole generally have relatively high serotonin to dopamine binding ratios. Serotonin receptor binding may be important to these drugs actions, possibly by stimulating dopamine activity in mesocortical pathways. Yet, while the mechanism of action of SGAs as a group remain unsolved, it is important to note that the SGAs offer many clinical benefits to treatment as compared to traditional antipsychotics and are quickly emerging as first-line therapy for schizophrenia. In addition to lower rates of EPS and tardive dyskinesia, other benefits to treatment with this class of antipsychotics include better treatment of negative symptoms, better compliance, possible benefits for cognitive impairments, lower rates of relapse and rehospitalization, and more cost-effective therapy. Within the class of SGAs, however, differences exist both in efficacy and side effects and these will be described. Optimization of treatment and understanding the exact mechanism of action of current antipsychotic medications will help pave the way for new drug targets in the future.

Keywords: schizophrenia, antipsychotics, clozapine, risperidone, mechanism of action, quetiapine, ziprasidone, olanzapine, aripiprazole