Rexulti (Brexpiprazole) Should NOT Be Used in Patients with Parkinson's Disease
Brexpiprazole is contraindicated in Parkinson's disease patients due to its dopamine D2 receptor antagonism, which will worsen motor symptoms and potentially precipitate severe motor complications. While the FDA has approved Rexulti for agitation in Alzheimer's dementia, schizophrenia, and adjunctive treatment of major depression 1, none of these indications extend to patients with Parkinson's disease.
Why Rexulti Is Inappropriate for Parkinson's Disease
Dopaminergic Mechanism Conflict: Brexpiprazole functions as a partial D2 dopamine agonist with relatively low intrinsic activity 2. In Parkinson's disease, where dopaminergic transmission is already compromised, any D2 antagonism—even partial—will exacerbate motor symptoms including rigidity, bradykinesia, and tremor. This is fundamentally incompatible with the pathophysiology of PD.
Evidence-Based Alternatives Exist: Recent expert consensus specifically identifies which antipsychotics are appropriate for Parkinson's disease psychosis (PDP). The Movement Disorder Society found only pimavanserin and clozapine to be clinically useful for PDP, with quetiapine possibly useful 3, 4. All other antipsychotics, including brexpiprazole, should be avoided due to motor worsening 3.
Appropriate Treatment Algorithm for Parkinson's Disease Patients
If the Patient Has Psychosis:
First-line: Pimavanserin is recommended as the initial antipsychotic based on established safety and motor tolerability 4. It is the only FDA-approved medication specifically for PDP and does not worsen motor function 3.
Second-line alternatives:
- Clozapine: Demonstrated efficacy but requires blood monitoring for agranulocytosis 3
- Quetiapine: Commonly used off-label despite limited efficacy evidence, chosen because it doesn't worsen motor function, though it carries risks of somnolence, hypotension, and cognitive impairment 3, 4
If the Patient Has Depression:
Standard antidepressants (SSRIs, SNRIs) remain appropriate. Avoid atypical antipsychotics including brexpiprazole for depression in PD patients.
If the Patient Has Agitation:
Critical distinction: The agitation must be carefully characterized:
- If agitation occurs with dementia (Parkinson's disease dementia or Lewy body dementia), this still contraindicates brexpiprazole due to motor worsening risk
- Non-pharmacological interventions should be prioritized
- If antipsychotic treatment is absolutely necessary, use pimavanserin, quetiapine, or clozapine as above
Common Pitfall to Avoid
Do not extrapolate the FDA approval for "agitation in Alzheimer's dementia" to Parkinson's disease dementia or Lewy body dementia. These are distinct neurodegenerative conditions with different dopaminergic profiles. The FDA label explicitly states approval for agitation associated with dementia due to Alzheimer's disease 1, not Parkinson's disease dementia.
Monitoring If Brexpiprazole Was Inappropriately Started
If a patient with Parkinson's disease has already been started on brexpiprazole:
- Immediately assess motor function: Look for worsening rigidity, bradykinesia, tremor, gait disturbance, or falls
- Taper and discontinue: Cross-titrate to an appropriate alternative (pimavanserin preferred)
- Do not abruptly stop: Gradual cross-titration is necessary to avoid withdrawal effects and ensure continuous symptom management 5
The fundamental principle: In Parkinson's disease, motor tolerability is non-negotiable when selecting psychotropic medications, and brexpiprazole fails this requirement.