New antipsychotics and schizophrenia: a review on efficacy and side effects

The first compounds showing efficacy in the treatment of schizophrenia and other psychotic disorders was chlorpromazine, an anti-histaminic compound casually observed to possess antipsychotic effects. The discovery of the real mechanism of action of antipsychotic substances dates back to the 1960s, when researchers found that these compounds act as dopamine receptor antagonists. Unfortunately, this type of drugs cannot block the D2 receptors only in the mesolimbic dopaminergic pathway (which mediates their therapeutic effects), because of their non-selective D2 receptor blockage in both the mesolimbic and striatal regions, and the consequent appearance of side effects related to striatal interaction in the same dosage range as is needed for the therapeutical effects. Clozapine, discovered in the early 1970s, seemed to represent the solution to contrast these side effects, as it possesses antipsychotic activity without inducing extrapyramidal disorders in humans or catalepsy in rats; for this reason, it was defined as an "atypical" antipsychotic drug. Later, other beneficial properties, such as improvement of negative symptoms and of cognitive dysfunction and efficacy in neuroleptic-resistant schizophrenia, were included in the definition of "atypical". In recent years, the appearance of new atypical antipsychotics (risperidone, olanzapine, quetiapine, ziprasidone) has opened new ways to therapy. The aim of this paper is to review literature about newer antipsychotics, focusing on their advantages in terms of efficacy and side effect profiles when compared to classical and older atypical antipsychotics, and to evaluate the efficacy of the different new antipsychotics when compared to one another.