Can Rexulti (Brexpiprazole) 1 mg Cause Muscle Twitching?
Yes, brexpiprazole 1 mg can cause muscle twitching and other extrapyramidal symptoms (EPS), though the incidence appears relatively low compared to placebo in clinical trials.
Mechanism and Clinical Evidence
Brexpiprazole, like other antipsychotics, acts as a dopamine D2 receptor partial agonist, which can lead to extrapyramidal side effects including tremors, muscle rigidity, and involuntary movements 1. The FDA label specifically lists tremor as an adverse reaction occurring in ≥2% of patients treated with brexpiprazole 1.
Incidence in Clinical Trials
In adult schizophrenia studies, tremor occurred in 2-3% of patients taking brexpiprazole 1-4 mg/day compared to 1% on placebo 1. The overall incidence of EPS-related adverse reactions (excluding akathisia) was 5% for brexpiprazole versus 4% for placebo 1.
In pediatric patients (13-17 years), extrapyramidal symptoms were more prominent, with 36% experiencing EPS-related effects (including tremor, muscle rigidity, and eye movement disorders) compared to 3% on placebo 1. This suggests adolescents may be at higher risk for movement-related side effects 2, 3.
Types of Movement Disorders to Monitor
Acute Extrapyramidal Symptoms
Several movement-related side effects can occur with brexpiprazole 2, 3:
- Tremor: Rhythmic shaking movements, typically of the hands 2, 1
- Dystonia: Sudden spastic muscle contractions, often affecting the neck, eyes, or torso 2, 3
- Akathisia: Severe restlessness with an urge to move, occurring in 4-9% of patients on brexpiprazole 1, 4
- Drug-induced Parkinsonism: Bradykinesia, tremors, and rigidity 2, 3
Tardive Dyskinesia Risk
Tardive dyskinesia (TD) is a serious concern with all antipsychotics, characterized by involuntary movements typically affecting the face, tongue, and extremities 2, 3, 1. The FDA label warns that TD may not resolve even after stopping brexpiprazole and may start after discontinuation 1. Children and adolescents may be at higher risk for EPS than adults 2.
Clinical Monitoring Recommendations
Objective assessment tools should be used regularly 1:
- Simpson-Angus Scale (SAS) for general EPS
- Barnes Akathisia Rating Scale (BARS) for akathisia
- Abnormal Involuntary Movement Scale (AIMS) for dyskinesia
In clinical trials, 4% of brexpiprazole-treated patients shifted from normal to abnormal on the SAS compared to 3% on placebo 1.
Dose-Related Considerations
The 1 mg dose of brexpiprazole appears to have a lower incidence of movement disorders than higher doses 1, 5. In schizophrenia trials, brexpiprazole 1 mg showed numerical improvements in efficacy with potentially fewer side effects than the 2-4 mg doses 5.
However, brexpiprazole requires proper titration: starting at 1 mg/day, increasing to 2 mg on days 5-7, then to 4 mg on day 8 if needed 4, 6. Abrupt dose changes may increase the risk of side effects 2.
Important Clinical Caveats
Children and adolescents require especially careful monitoring because they may have greater difficulty communicating concerns about side effects and may be at higher risk for EPS than adults 2, 7. In the long-term adolescent study, most treatment-emergent adverse events were mild to moderate 7.
Distinguish between different movement disorders: Akathisia (restlessness) is often misinterpreted as psychotic agitation or anxiety and is a common reason for medication noncompliance 2. True muscle twitching may represent early dystonia, tremor, or myoclonus 2, 3.
Consider neuroleptic malignant syndrome (NMS) if muscle rigidity occurs with fever, altered mental status, and autonomic instability—this is a medical emergency requiring immediate discontinuation of the antipsychotic 3, 1.