Leslie Citrome, MD, MPH Clinical Professor Department of Psychiatry and Behavioral Sciences New York Medical College Valhalla, New York
Disclosure In the past 12 months, Dr. Citrome has served as a consultant to Acadia, Alkermes, Allergan, Intra-Cellular Therapeutics, Janssen, Lundbeck, Merck, Neurocrine, Noven, Otsuka, Pfizer, Shire, Sunovion, Takeda, Teva, and Vanda; and a speaker for Acadia, Alkermes, Allergan, Janssen, Lundbeck, Merck, Neurocrine, Otsuka, Pfizer, Shire, Sunovion, Takeda, Teva, and Vanda.
However, binding affinities differ substantially among the agents (for example, cariprazine has only moderate binding affinity at serotonin 5-HT2A receptors [18.8 nM]), and differences also exist in terms of intrinsic activity at the receptors where partial agonism is operative. Compared with aripiprazole, brexpiprazole has lower intrinsic activity at the dopamine D2 receptor (and thus is expected to cause less akathisia), and has an approximately 10-fold higher affinity for serotonin 5-HT1A and 5-HT2A receptors, also potentially enhancing tolerability and perhaps anxiolytic activity.32,33 When cariprazine was compared with aripiprazole in functional assays for dopamine D2 and D3 receptors, similar D2 and higher D3 antagonist-partial agonist affinity and a 3- to 10-fold greater D3 vs D2 selectivity was observed for cariprazine.34 Whether specifically targeting the dopamine D3 receptor over the dopamine D2 receptor is clinically advantageous remains unknown, but in preclinical studies, dopamine D3–preferring agents may exert pro-cognitive effects.35-37 All 3 agents have only moderate binding affinities to histamine H1 receptors, thus sedation should not be prominent for any of them. None of the 3 agents have appreciable binding at muscarinic receptors, thus adverse effects related to antimuscarinic activity should not be present as well.
Schizophrenia is a heterogenous disorder. We know from clinical practice that patients respond differently to specific antipsychotics. Having different pharmacodynamic “fingerprints” to choose from allows for flexibility in treatment. Moreover, dopamine receptor partial agonists provide an alternative to the array of dopamine receptor antagonists, such as the other second-generation antipsychotics and all first-generation antipsychotics.
Dosing.Although all 3 agents are dosed once daily, only for aripiprazole is the recommended starting dose the same as the recommended maintenance dose in adults with schizophrenia or bipolar mania. Although the starting dose for cariprazine for schizophrenia can be therapeutic (1.5 mg/d), for the treatment of bipolar mania, cariprazine will need to be titrated from the starting dose of 1.5 mg/d to the recommended target dose range of 3 to 6 mg/d.
Half-life.Aripiprazole and brexpiprazole share a similar elimination half-life: approximately 75 hours and 94 hours for aripiprazole and its active metabolite dehydro-aripiprazole, respectively, and 91 hours and 86 hours for brexpiprazole and its major metabolite, DM-3411 (inactive), respectively. Cariprazine is strikingly different, with an elimination half-life of 2 to 4 days, and approximately 1 to 3 weeks for its active metabolite didesmethyl cariprazine.
Drug interactions.Both aripiprazole and brexpiprazole are metabolized via cytochrome P450 (CYP) 2D6 and CYP3A4, and thus the dose may need to be adjusted in the presence of CYP2D6 inhibitors or CYP3A4 inhibitors/inducers; with inhibitors, the dose is decreased by half or more, and with inducers, the dose is doubled. In contrast, cariprazine is primarily metabolized by CYP3A4 and thus potential drug–drug interactions are primarily focused on CYP3A4 inhibitors (decrease cariprazine dose by half) and inducers (co-prescribing of cariprazine with a CYP3A4 inducer is not recommended).
