Aripiprazole

Aripiprazole (produced by Bristol-Myers Squibb and sold as Abilify®) is the sixth and most recent of the atypical antipsychotic medications to be approved by the FDA for the treatment of schizophrenia. It has also recently received FDA approval for the treatment of acute manic and mixed episodes associated with bipolar disorder. more...

Pharmacology

Aripirazole possesses a novel mechanism of action when compared to the other FDA approved atypical antipsychotics (i.e. clozapine, olanzapine, quetiapine, ziprasidone, and risperidone). Aripiprazole appears to mediate its antipsychotic effects primarily by partial agonism at the D2 receptor. Partial agonism at D2 receptors has been shown to modulate dopaminergic activity in areas where dopamine activity may be high or low, such as the mesolimbic and mesocortical areas of the schizophrenic brain, respectively. In addition to partial agonist activity at the D2 receptor, aripirazole is also a partial agonist at the 5-HT1A receptor, and like the other atypical antipsychotics, aripiprazole displays an antagonist profile at the 5-HT2A receptor. Aripiprazole has moderate affinity for histamine and alpha adrenergic receptors, and no appreciable affinity for cholinergic muscarinic receptors.

Pharmacokinetics

Aripiprazole displays linear kinetics with an elimination half-life of approximately 75 hours. Accordingly, steady state plasma concentrations are achieved in about 14 days. Cmax (maximum plasma concentration) is achieved in 3-5 hours after oral dosing. The bioavailabilty of the oral tablets is about 90%. The drug undergoes extensive hepatic metabolization (dehydrogenation, hydroxylation, and N-dealkylation). The active major metabolite is dehydro-aripiprazole with an elemination half-life of about 94 hours. The parent drug is excreted only in traces and the metabolites, whether active or not, are excreted via feces and urine.

Metabolism

Aripiprazole is metabolized by the Cytochrome P450 isoenzymes 3A4 and 2D6. Accordingly, coadministration of aripiprazole with medications that may inhibit (e.g. paroxetine, fluoxetine) or induce (e.g. carbamazepine) these metabolic enzymes may increase or decrease, respectively, plasma concentrations of aripiprazole.

Adverse Events

Adverse events reported in the package insert for aripiprazole include headache, nausea, vomiting, somnolence, insomnia, and akathisia. It appears that aripirazole has a low incidence of EPS (extrapyramidal side effects). The risk of tardive dyskinesia with prolonged aripirazole use is unclear.

Dosage Forms

Aripirazole is available in 5mg, 10mg, 15mg, 20mg, and 30mg tablets.

Warnings About Medications with Similar Names

A warning has gone out recently because of this drug's name. The '-prazole' ending of this drug name makes this drug sound like it is one of the proton pump inhibitors (such as omeprazole, pantoprazole, lansoprazole) which are used in treating peptic ulcer disease. However, aripiprazole and these drugs are in an entirely different class of drugs altogether and confusing the two can lead to some unnecessary side effects.

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