Rexulti (Brexpiprazole): Pharmacokinetics and FDA Indications
FDA-Approved Indications
Rexulti is FDA-approved for three specific indications: adjunctive treatment of major depressive disorder (MDD) in adults, treatment of schizophrenia in adults and adolescents (13-17 years), and treatment of agitation associated with dementia due to Alzheimer's disease 1.
Specific Dosing by Indication
- Major Depressive Disorder (adjunctive): Start 0.5-1 mg/day, target 2 mg/day, maximum 3 mg/day 1
- Schizophrenia (adults): Start 1 mg/day, target 2-4 mg/day, maximum 4 mg/day 1
- Schizophrenia (adolescents 13-17 years): Start 0.5 mg/day, target 2-4 mg/day, maximum 4 mg/day 1
- Agitation in Alzheimer's dementia: Start 0.5 mg/day, target 2 mg/day, maximum 3 mg/day 1
Pharmacokinetics
Absorption
Brexpiprazole demonstrates excellent oral bioavailability at 95% and can be taken without regard to meals 1. Peak plasma concentrations (Tmax) occur within 4 hours after administration. High-fat meals do not significantly affect Cmax or AUC, making food timing irrelevant for dosing 1. The drug exhibits dose-proportional increases in exposure (Cmax and AUC) across the therapeutic range 1.
Distribution
The volume of distribution is high (1.56 ± 0.42 L/kg), indicating extensive extravascular distribution 1. Brexpiprazole is greater than 99% protein-bound to serum albumin and α1-acid glycoprotein, and this binding is not affected by renal or hepatic impairment, warfarin, diazepam, or digitoxin 1.
Metabolism
Metabolism occurs primarily via CYP3A4 and CYP2D6 enzymes 1. The major metabolite DM-3411 represents 23-48% of brexpiprazole exposure at steady-state but does not contribute to therapeutic effects 1. This dual metabolic pathway necessitates dose adjustments when CYP2D6 poor metabolizers are identified or when strong CYP3A4/CYP2D6 inhibitors or inducers are co-administered 1.
Elimination
The terminal elimination half-life is 91 hours for brexpiprazole and 86 hours for its major metabolite DM-3411 1. Steady-state concentrations are achieved within 10-12 days of once-daily dosing 1. Following oral administration, approximately 25% of radioactivity is recovered in urine and 46% in feces. Less than 1% of unchanged drug appears in urine, while approximately 14% is recovered unchanged in feces 1. Apparent oral clearance is 19.8 (±11.4) mL/h/kg 1.
Critical Dosing Adjustments
Renal Impairment
For patients with CrCl <60 mL/minute, the maximum recommended dose is 2 mg/day for MDD or Alzheimer's agitation and 3 mg/day for schizophrenia 1. Population pharmacokinetic analysis demonstrated higher brexpiprazole exposure in patients with moderate renal impairment compared to those with normal renal function 1.
Hepatic Impairment
For moderate to severe hepatic impairment, maximum doses are identical to renal impairment: 2 mg/day for MDD or Alzheimer's agitation and 3 mg/day for schizophrenia 1.
CYP2D6 Poor Metabolizers
A 50% dose reduction is required for known CYP2D6 poor metabolizers 1. However, recent PBPK modeling suggests this may overcompensate for decreased clearance, with simulations showing PMs consistently achieve lower minimum concentrations than extensive metabolizers despite dose reduction 2.
Mechanism of Action
While the precise mechanism remains unknown, efficacy is thought to result from partial agonist activity at serotonin 5-HT1A and dopamine D2 receptors combined with antagonist activity at serotonin 5-HT2A receptors 1. Brexpiprazole exhibits high affinity (Ki values) for multiple monoaminergic receptors: 5-HT1A (0.12 nM), 5-HT2A (0.47 nM), D2 (0.30 nM), and various adrenergic receptors 1.
Clinical Considerations
Pediatric Use
Population PK analysis in adolescents (13-17 years) demonstrated comparable systemic exposure to adults across the 0.5-4 mg dose range, supporting the same target doses in this population 1, 3.
Cardiac Safety
At doses 3-4 times the maximum recommended human dose, brexpiprazole does not prolong the QTc interval to any clinically relevant extent 1.
Black Box Warning
Like all antipsychotics used in dementia-related psychosis, brexpiprazole carries a black box warning for increased mortality risk in elderly patients with dementia-related psychosis 4.