New antipsychotics: classification, efficacy, and adverse effects.

Compared to traditional neuroleptics, most of the new antipsychotics are characterized by a low extrapyramidal side effect (EPS) liability and varying antipsychotic efficacy. This topic is reviewed for four principal classes of new, established, and potential antipsychotics: (1) Antipsychotics such as sulpiride and remoxipride that block a subgroup of dopamine (DA) D2/D3 receptors produce a relatively low level of side effects, including EPS, and have an antipsychotic effect equal to or slightly weaker than traditional neuroleptics. D1 antagonists demonstrate a low level of EPS in primates and may prove to be a valuable new type of antipsychotic drug. (2) Theoretically, partial D2 agonists have the advantage of producing few or no EPS and a specific beneficial effect in negative symptoms, but as yet the expectations have not been fulfilled. (3) Nondopamine drugs such as serotonin (5HT1) agonists, 5HT2 antagonists, 5HT3 antagonists, and gamma-amino-butyric-acid-A (GABA-A) benzodiazepine agonists have anxiolytic, antidepressant, antiaggressive, and maybe antiparkinsonian effects and may play an adjunctive role in the treatment of schizophrenia. 5HT3 antagonists (e.g., ondansetron), partial benzodiazepine agonists, and partial glutamate agonists may prove to be effective antipsychotics. (4) Antipsychotics such as clozapine and risperidone, which affect D2/D3 receptors as well as 5HT, alpha 1, and/or D1 receptors appear to have the most pronounced antipsychotic effect.