[A new approach to antischizophrenic therapeutics: D2 dopamine receptor partial agonists]

Since chlorpromazine was described, antischizophrenic therapeutics have been enriched with various other D2 dopamine receptors antagonists, either neuroleptics (which develop extrapyramidal side effects) or non neuroleptic antipsychotics (devoid of extrapyramidal side effects when used at effective doses against psychotic expressions). The latter drugs display such properties on account of several associated pharmacological activities (D3 receptors antagonism more efficient than D2 antagonism; antagonism at cholinergic muscarinic receptors; antagonism at 5HT2 serotonin receptors). All these antipsychotic drugs are not, as initially described, neutral antagonists of D2 receptors, but are in fact inverse agonists (alpha<0), because they suppress the constitutive activity of these receptors (i.e. their spontaneous activity in the absence of dopamine stimulation). Thus they induce effects which are opposite to those of dopamine. Partial agonists, also called agonists-antagonists, induce intermediate effects between those of full agonists and neutral antagonists. Their intrinsic activity is the following (1>alpha>0>- 1) in the hierarchy: full agonist>partial agonist>neutral antagonist>inverse agonist. These partial agonists moderate the activity of hyperactive dopaminergic neurons (reducing positive expressions: delusion, hallucinations, agitation). They activate deficient dopaminergic transmissions, alleviating at least partly negative expressions. This approach is presently illustrated by aripiprazole: OP 4597. Many other molecules are candidates for such a therapeutic promotion, justified by the search for both antiproductive and antideficit activities, with a low incidence of adverse side effects such as extrapyramidal effects, thermoregulation effects, induction of late dyskinesias, sedation, bulimia, excessive weight, depressive symptoms, incitation to consume addictive drugs, hyperprolactinemia....