Brexpiprazole

Indications

• Adjunctive treatment of major depressive disorder in adults with inadequate response to an antidepressant, at a usual dose of 2 mg/day.
• Schizophrenia in adults and in pediatric patients ages 13 and older, for acute treatment and for maintenance therapy.
• Agitation associated with dementia due to Alzheimer's disease, the first and so far only antipsychotic approved for this indication.
• The label explicitly states it is not indicated for as-needed treatment of agitation in Alzheimer's dementia, only scheduled dosing.
• Off-label use includes anxious depression and patients who responded to aripiprazole but could not tolerate its akathisia.

Mechanism of action

• Partial agonist at dopamine D2 and D3 receptors with lower intrinsic activity than aripiprazole, which reduces activation and akathisia.
• Potent partial agonism at serotonin 5-HT1A and strong antagonism at 5-HT2A support antidepressant and antipsychotic effects.
• High alpha-1B and alpha-2C adrenergic antagonism distinguishes it from aripiprazole and may add antidepressant activity.
• Low histamine H1 and negligible muscarinic affinity keep sedation and anticholinergic effects modest.
• Partial rather than full D2 blockade means prolactin generally falls or stays flat rather than rising.

Pharmacokinetics

• Oral bioavailability is about 95 percent and absorption is unaffected by food, so it may be taken at any time of day.
• Metabolized by CYP3A4 and CYP2D6 to DM-3411, a metabolite not considered to contribute meaningfully to clinical effect.
• Terminal half-life is about 91 hours, so steady state takes 10-14 days and dose changes cannot be judged sooner.
• CYP2D6 poor metabolizers have roughly double the exposure and require half the usual dose, as do patients on strong 2D6 inhibitors.
• Exposure rises with moderate to severe hepatic impairment and with creatinine clearance below 60 mL/min, both of which cap the dose.

Dosing

• Major depressive disorder adjunct: start 0.5-1 mg/day PO, increase weekly to 1 mg then to the target 2 mg/day, maximum 3 mg/day.
• Schizophrenia in adults: 1 mg/day on days 1-4, 2 mg/day on days 5-7, then 4 mg/day on day 8, targeting 2-4 mg/day with a 4 mg/day maximum.
• Agitation in Alzheimer's dementia: 0.5 mg/day for 7 days, 1 mg/day for 7 days, then 2 mg/day, with a maximum of 3 mg/day.
• Halve the dose with a strong CYP2D6 or strong CYP3A4 inhibitor, and reduce to a quarter when both are used together.
• With a strong CYP3A4 inducer such as carbamazepine, double the dose over 1-2 weeks and reverse the change when the inducer stops.
• Cap the dose at 2 mg/day for depression and 3 mg/day for schizophrenia in moderate to severe hepatic or renal impairment.

Adverse effects

• Weight gain averages 1.5-3 kg and increased appetite is common, placing brexpiprazole above aripiprazole but below olanzapine.
• Akathisia occurs in roughly 5-10 percent, distinctly less than with aripiprazole, and remains dose related.
• Somnolence, headache, fatigue, and restlessness are the other common effects, mostly early and often self-limited.
• Impulse control problems including gambling, compulsive shopping, binge eating, and hypersexuality are labeled and reversible on stopping.
• Serious risks include neuroleptic malignant syndrome, tardive dyskinesia, orthostatic hypotension, and rare leukopenia or neutropenia.
• In elderly patients with dementia, cerebrovascular events and increased mortality remain the dominant safety concern.

Monitoring

• Weight, BMI, blood pressure, fasting glucose or A1c, and lipids at baseline, at 12 weeks, and annually thereafter.
• Assess akathisia and restlessness at each early visit, since patients often describe it as anxiety or as the depression worsening.
• Ask directly about new gambling, spending, eating, or sexual urges at every follow-up, because patients rarely report them unprompted.
• Check renal and hepatic function at baseline to determine whether the reduced dose ceilings apply.
• In Alzheimer's agitation, reassess benefit at least every 3 months and document the rationale for continuing an antipsychotic.

Interactions

• Strong CYP2D6 inhibitors such as fluoxetine, paroxetine, and quinidine double exposure and require halving the dose.
• Strong CYP3A4 inhibitors including ketoconazole, itraconazole, and clarithromycin also call for a 50 percent dose reduction.
• Combined strong CYP2D6 and CYP3A4 inhibition requires reducing to one quarter of the usual dose.
• Strong inducers such as rifampin and carbamazepine roughly halve exposure and require doubling the dose over 1-2 weeks.
• Additive sedation with opioids, benzodiazepines, and alcohol; intrinsic QT liability is low.

Special populations

• Third-trimester exposure carries the class risk of neonatal extrapyramidal and withdrawal signs; human pregnancy data remain limited.
• Lactation data are lacking, so monitor breastfed infants for sedation and feeding difficulty or choose a better-characterized agent.
• Approved from age 13 for schizophrenia; safety and effectiveness in pediatric major depressive disorder have not been established.
• In older adults with Alzheimer's agitation, weigh the modest benefit against the boxed mortality and cerebrovascular risk in every case.
• Dose ceilings of 2-3 mg/day apply when creatinine clearance is under 60 mL/min or hepatic impairment is Child-Pugh class B or C.

Clinical pearls

• Less akathisia than aripiprazole, more weight gain; that trade-off drives most switches between them.
• A 91-hour half-life means waiting two weeks before calling a dose change ineffective.
• For Alzheimer's agitation, the approved dose is 2-3 mg/day scheduled, never as needed.