Aripiprazole lauroxil

The pharmacological activity of aripiprazole lauroxil is thought to be mainly mediated by its metabolite aripiprazole, and to a lesser extent, dehydro-aripiprazole. Aripiprazole functions as a partial agonist at the dopamine D2 and the serotonin 5-HT1A receptors, and as an antagonist at the serotonin 5-HT2A receptor. The desired outcome of antipsuchotic agents in schizophrenia is to inhibit dopaminergic transmission in the limbic system and enhance dopaminergic transmission in the prefrontal cortex. As a partial agonist at D2 receptors in the mesolimbic dopaminergic pathway, aripiprazole acts as a functional antagonist in the mesolimbic dopamine pathway and reduces the extent of dopaminergic pathway activity. This results in reduced positive symptoms in schizophrenia and extrapyramidal motor side effects. In contrast, aripiprazole is thought to act as a functional agonist in the mesocortical pathway, where reduced dopamine activity is seen in association with negative symptoms and cognitive impairment. Antagonism at 5-HT2A receptors by aripiprazole alleviates the negative symptoms and cognitive impairment of schizophrenia. 5-HT2A receptors are Gi/Go-coupled that upon activation, produce neuronal inhibition via decreased neuronal excitability and decreased transmitter release at the nerve terminals. In the nigrostriatal pathway, 5-HT2A regulates the release of dopamine. Through antagonism of 5-HT2A receptors, aripiprazole disinhibits the release of dopamine in the striatum and enhance the levels of the transmitters at the nerve terminals. The combined effects of D2 and 5-HT2A antagonism are thought to counteract the increased dopamine function causing increased extrapyramidal side effects. Blocking 5-HT2A receptors may also lead to the modulation of glutamate release in the mesocortical circuit, which is a transmitter that plays a role in schizophrenia. 5-HT1A receptors are autoreceptors that inhibit 5-HT release upon activation. Aripiprazole is a partial agonist at theses receptors and reduces 5-HT release; this results in potentiated dopamine release in the striatum and prefrontal cortex. It is reported that therapeutic doses of aripiprazole occupies up to 90% of brain D2 receptors in a dose-dependent manner.

Apripiprazole targets different receptors that lead to drug-related adverse reactions; for example, the antagonist activity at the alpha-1 adrenergic receptors results in orthostatic hypotension. Aripiprazole's antagonism of histamine H1 receptors may explain the somnolence observed with this drug.