Table of Contents
Introduction
Ingrezza is the brand name of valbenazine, an oral drug used for movement disorders caused by abnormal monoamine signaling in the brain. Pharmacologically, valbenazine is a vesicular monoamine transporter 2 inhibitor, commonly called a VMAT2 inhibitor.
VMAT2 is a transporter present on synaptic vesicles inside presynaptic neurons. Its normal role is to move monoamine neurotransmitters such as dopamine, norepinephrine, serotonin, and histamine from the neuronal cytoplasm into synaptic vesicles for storage and later release.
Ingrezza is indicated for the treatment of adults with tardive dyskinesia and adults with chorea associated with Huntington’s disease. The current label also includes Ingrezza Sprinkle, an oral sprinkle capsule formulation of valbenazine.
The exact mechanism by which valbenazine improves tardive dyskinesia and Huntington’s chorea is not fully understood. However, its therapeutic effect is thought to occur through reversible inhibition of VMAT2. By inhibiting VMAT2, valbenazine decreases packaging of monoamines, especially dopamine, into presynaptic vesicles. This reduces dopamine release into synapses and helps reduce hyperkinetic involuntary movements.
For exam purposes, Ingrezza should be remembered as an oral VMAT2 inhibitor used in tardive dyskinesia and Huntington’s disease chorea. Its key concept is reduction of presynaptic dopamine storage and release, leading to decreased abnormal involuntary movement signaling.
Mechanism of Action (Step-wise)
Step 1: Monoamines are stored in synaptic vesicles
Monoamine neurotransmitters such as dopamine, norepinephrine, serotonin, and histamine are synthesized in presynaptic neurons. Before release, they must be transported into synaptic vesicles.
Step 2: VMAT2 transports monoamines into vesicles
VMAT2 is responsible for moving monoamines from the cytoplasm into synaptic vesicles. Once stored in vesicles, neurotransmitters can be released into the synaptic cleft during neuronal signaling.
Step 3: Dopamine signaling controls movement pathways
Dopamine is especially important in basal ganglia motor circuits. These circuits regulate voluntary movement, motor inhibition, motor initiation, and suppression of unwanted movements.
Step 4: Excess dopaminergic signaling contributes to hyperkinetic movements
Tardive dyskinesia and Huntington’s chorea involve abnormal involuntary movements. Although their causes are different, excessive or dysregulated dopaminergic signaling in motor pathways can contribute to abnormal movement expression.
Step 5: Tardive dyskinesia is often linked to long-term dopamine receptor blockade
Tardive dyskinesia commonly develops after chronic exposure to dopamine receptor-blocking drugs such as antipsychotics or certain antiemetics. Long-term D2 receptor blockade may lead to dopamine receptor hypersensitivity and abnormal basal ganglia motor output.
Step 6: Huntington’s chorea involves basal ganglia degeneration
In Huntington’s disease, degeneration of striatal neurons disrupts the balance of basal ganglia pathways. This produces chorea, which consists of irregular, unpredictable, involuntary movements.
Step 7: Ingrezza inhibits VMAT2
Valbenazine reversibly inhibits VMAT2. This is the central molecular mechanism of Ingrezza. The label states that valbenazine’s effect is thought to be mediated through reversible inhibition of VMAT2, which regulates monoamine uptake from cytoplasm into synaptic vesicles for storage and release.
Step 8: Dopamine packaging into vesicles decreases
When VMAT2 is inhibited, less dopamine is transported into synaptic vesicles. This reduces the amount of dopamine available for vesicular release.
Step 9: Synaptic dopamine release decreases
Because vesicular dopamine storage is reduced, less dopamine is released into the synaptic cleft during neuronal firing. This lowers dopaminergic stimulation in movement-related brain circuits.
Step 10: Abnormal involuntary movement signaling decreases
Reduced presynaptic dopamine release helps decrease excessive motor pathway activity. In tardive dyskinesia, this can reduce repetitive involuntary movements such as lip smacking, tongue movements, facial grimacing, chewing movements, trunk movements, and limb movements.
Step 11: Choreiform movements may decrease
In Huntington’s disease, lowering dopaminergic signaling can reduce chorea severity. This may improve uncontrolled movements of the face, trunk, and limbs, although it does not stop the neurodegenerative process itself.
Step 12: Active metabolite contributes to VMAT2 inhibition
Valbenazine is converted to the active metabolite [+]-alpha-dihydrotetrabenazine, also called [+]-α-HTBZ. The label states that valbenazine inhibits human VMAT2 and is converted to [+]-α-HTBZ, which also binds human VMAT2 with relatively high affinity.
Step 13: Ingrezza is not a direct dopamine receptor blocker
Valbenazine and its active metabolite do not have appreciable binding affinity for dopamine receptors, including D2 receptors, or for serotonergic, adrenergic, histaminergic, or muscarinic receptors. This means Ingrezza reduces dopamine release upstream rather than directly blocking postsynaptic dopamine receptors.
Step 14: Dopamine reduction can also cause adverse effects
Because dopamine is required for normal movement and alertness, excessive VMAT2 inhibition can cause somnolence, sedation, parkinsonism, tremor, gait disturbance, rigidity, or mood-related effects in susceptible patients.
Step 15: Final therapeutic outcome
The final therapeutic effect of Ingrezza is reduction of abnormal involuntary movements by decreasing VMAT2-mediated monoamine storage and dopamine release in motor circuits. It treats movement symptoms but does not cure tardive dyskinesia or Huntington’s disease.
Pharmacokinetics
Ingrezza is administered orally once daily and may be taken with or without food. For tardive dyskinesia, the initial dosage is 40 mg once daily. After one week, the dose is increased to the recommended dosage of 80 mg once daily. A dosage of 40 mg or 60 mg once daily may be considered depending on response and tolerability.
For chorea associated with Huntington’s disease, the initial dosage is also 40 mg once daily. The dose may be increased in 20 mg increments every two weeks to the recommended dosage of 80 mg once daily. A dosage of 40 mg or 60 mg once daily may be considered depending on response and tolerability.
Ingrezza capsules are available in 40 mg, 60 mg, and 80 mg strengths. Ingrezza Sprinkle is also available in 40 mg, 60 mg, and 80 mg strengths. Ingrezza Sprinkle may be swallowed whole with water or opened and sprinkled over soft food such as applesauce, yogurt, or pudding. It should not be sprinkled into milk or drinking water.
After oral administration of Ingrezza, valbenazine reaches maximum plasma concentration in about 0.5 to 1 hour. Steady-state plasma concentrations are reached within approximately one week. The absolute oral bioavailability of valbenazine is about 49%.
Valbenazine is converted to the active metabolite [+]-α-HTBZ. This active metabolite reaches peak concentration more gradually, about 4 to 8 hours after Ingrezza administration.
Food does not prevent administration, so Ingrezza can be taken with or without meals. A high-fat meal decreases valbenazine peak concentration and slightly decreases overall exposure, but the active metabolite exposure is not meaningfully affected.
Valbenazine and its active metabolite are protein bound. Valbenazine is more than 99% bound to plasma proteins, while [+]-α-HTBZ is approximately 64% protein bound. The mean steady-state volume of distribution of valbenazine is about 92 L.
Valbenazine is extensively metabolized after oral administration. It is hydrolyzed to form the active metabolite [+]-α-HTBZ and is also metabolized by oxidative pathways, mainly CYP3A4/5. The active metabolite is further metabolized partly by CYP2D6.
The half-lives of valbenazine and [+]-α-HTBZ are approximately 15 to 22 hours, supporting once-daily dosing. Less than 2% is excreted unchanged as valbenazine or active metabolite in urine or feces.
Dose adjustment is important in several situations. The recommended dosage is 40 mg once daily in patients with moderate or severe hepatic impairment, known CYP2D6 poor metabolizers, patients receiving strong CYP3A4 inhibitors, and patients receiving strong CYP2D6 inhibitors. Strong CYP3A4 inducers are not recommended because they may reduce exposure and efficacy.
Clinical Uses
Ingrezza is used for the treatment of tardive dyskinesia in adults. Tardive dyskinesia is a movement disorder characterized by involuntary, repetitive movements, often involving the face, mouth, tongue, jaw, trunk, or limbs.
Tardive dyskinesia commonly occurs after long-term use of dopamine receptor-blocking drugs, especially antipsychotics. It may persist even after the causative drug is reduced or stopped. Ingrezza helps reduce abnormal movements by reducing presynaptic dopamine release rather than directly reversing dopamine receptor hypersensitivity.
Ingrezza is also used for chorea associated with Huntington’s disease in adults. Huntington’s disease is a hereditary neurodegenerative disorder that can cause chorea, psychiatric symptoms, cognitive decline, and progressive functional impairment.
In Huntington’s chorea, Ingrezza helps reduce excessive involuntary movements. However, it does not cure Huntington’s disease, stop disease progression, or reverse neuronal degeneration.
Ingrezza is not an antipsychotic, antidepressant, antiepileptic, benzodiazepine, dopamine agonist, or muscle relaxant. It is a targeted VMAT2 inhibitor used to control specific hyperkinetic movement symptoms.
Ingrezza is not approved for pediatric patients. The label states that safety and effectiveness have not been established in pediatric patients.
Adverse Effects
The most important boxed warning for Ingrezza is depression and suicidal ideation and behavior in patients with Huntington’s disease. VMAT2 inhibitors, including Ingrezza, can increase this risk in patients treated for chorea associated with Huntington’s disease. Patients should be monitored for new or worsening depression, suicidal thoughts, unusual behavior changes, or mood deterioration.
This warning is especially important because Huntington’s disease itself is associated with a higher frequency of depression and suicidal ideation. The risk of psychiatric worsening must be balanced against the clinical need to control chorea.
Hypersensitivity reactions can occur. Ingrezza is contraindicated in patients with a history of hypersensitivity to valbenazine or any component. Rash, urticaria, and reactions consistent with angioedema, including swelling of the face, lips, mouth, larynx, or glottis, have been reported.
Somnolence and sedation are important adverse effects. The label states that Ingrezza can cause somnolence and sedation, which was the most common adverse reaction in placebo-controlled trials. Patients should avoid driving or operating hazardous machinery until they know how the drug affects them.
QT prolongation is an important safety issue. Ingrezza may prolong the QT interval, especially when drug exposure is increased, such as in CYP2D6 poor metabolizers or patients taking strong CYP2D6 or CYP3A4 inhibitors. It should be avoided in patients with congenital long QT syndrome or arrhythmias associated with prolonged QT interval.
Neuroleptic malignant syndrome, or NMS, has been reported with VMAT2 inhibitors. NMS is a rare but serious condition that may include hyperpyrexia, muscle rigidity, altered mental status, autonomic instability, elevated creatine kinase, and possible renal injury.
Parkinsonism can occur with Ingrezza. Symptoms may include tremor, rigidity, bradykinesia, drooling, gait disturbance, reduced arm swing, balance problems, or falls. Dose reduction or discontinuation may be needed if clinically significant parkinson-like symptoms develop.
Common adverse reactions in tardive dyskinesia studies include somnolence, anticholinergic effects, balance disorder or falls, headache, akathisia, vomiting, nausea, and arthralgia. In Huntington’s chorea studies, common adverse reactions included somnolence, fatigue, rash, and urticaria.
Drug interactions are clinically important. MAO inhibitors should be avoided because combined effects on monoamine neurotransmitters may increase adverse reaction risk or reduce treatment effect. Strong CYP3A4 inducers are not recommended because they can lower valbenazine and active metabolite exposure. Strong CYP3A4 inhibitors and strong CYP2D6 inhibitors require dose reduction.
Ingrezza can increase digoxin levels due to inhibition of intestinal P-glycoprotein. Digoxin concentrations should be monitored when the drugs are used together, and digoxin dose adjustment may be needed.
Pregnancy data are limited. Animal studies showed increased stillbirths and postnatal pup mortality at certain exposures, so pregnant patients should be advised of potential fetal risk. Breastfeeding is not recommended during treatment and for 5 days after the final dose.
Comparative Analysis
Ingrezza is commonly compared with deutetrabenazine, tetrabenazine, antipsychotic dose adjustment, benzodiazepines, amantadine, botulinum toxin, and symptomatic chorea treatments.
Compared with tetrabenazine, Ingrezza has the same broad target class because both inhibit VMAT2. Tetrabenazine is older and is strongly associated with depression, suicidality, parkinsonism, akathisia, and multiple daily dosing. Ingrezza is given once daily and has a different pharmacokinetic profile.
Compared with deutetrabenazine, Ingrezza is also a VMAT2 inhibitor. Deutetrabenazine is a deuterated form of tetrabenazine designed to alter metabolism and exposure. Both reduce abnormal movements by decreasing monoamine storage and dopamine release, but they differ in dosing schedules, titration, formulations, interactions, and adverse-effect profiles.
Compared with antipsychotic dose reduction in tardive dyskinesia, Ingrezza directly targets the movement disorder mechanism through VMAT2 inhibition. Dose reduction or discontinuation of the causative dopamine-blocking drug may help some patients, but psychiatric stability can limit that approach.
Compared with anticholinergic drugs, Ingrezza has a different role. Anticholinergics can help drug-induced parkinsonism but may worsen tardive dyskinesia in some patients. Ingrezza reduces involuntary movements by decreasing presynaptic dopamine release.
Compared with benzodiazepines, Ingrezza is more mechanism-targeted for tardive dyskinesia and Huntington’s chorea. Benzodiazepines may reduce anxiety or movement intensity through CNS depressant effects but do not specifically inhibit VMAT2.
Compared with dopamine receptor-blocking antipsychotics, Ingrezza does not directly block D2 receptors. It decreases dopamine release presynaptically, which can reduce hyperkinetic movements while avoiding direct postsynaptic dopamine receptor antagonism.
Compared with dopamine agonists used in Parkinson’s disease, Ingrezza has the opposite functional direction. Dopamine agonists increase dopaminergic stimulation, while VMAT2 inhibitors reduce monoamine storage and dopamine release. Therefore, VMAT2 inhibition can worsen or cause parkinsonian symptoms in susceptible patients.
Compared with botulinum toxin, Ingrezza works centrally in brain neurotransmitter pathways. Botulinum toxin works peripherally at the neuromuscular junction and may be used for focal dystonia or focal abnormal movements, but it does not treat generalized basal ganglia-driven dyskinesia in the same way.
MCQs
- Ingrezza contains which active drug?
a) Deutetrabenazine
b) Valbenazine
c) Tetrabenazine
d) Haloperidol
Answer: b) Valbenazine
- Ingrezza belongs to which pharmacological class?
a) VMAT2 inhibitor
b) Dopamine D2 receptor antagonist
c) SSRI antidepressant
d) Cholinesterase inhibitor
Answer: a) VMAT2 inhibitor
- VMAT2 normally transports monoamines into:
a) Synaptic vesicles
b) Mitochondria
c) Cell nucleus
d) Lysosomes only
Answer: a) Synaptic vesicles
- The exact therapeutic mechanism of valbenazine is:
a) Unknown, but thought to involve reversible VMAT2 inhibition
b) Fully explained by direct dopamine D2 receptor blockade
c) Due to irreversible MAO inhibition
d) Due to direct GABA-A receptor activation
Answer: a) Unknown, but thought to involve reversible VMAT2 inhibition
- Ingrezza decreases abnormal movements mainly by reducing:
a) Presynaptic dopamine storage and release
b) Insulin secretion
c) Acetylcholine breakdown
d) Thyroid hormone production
Answer: a) Presynaptic dopamine storage and release
- Ingrezza is indicated for adults with:
a) Tardive dyskinesia
b) Parkinson’s disease tremor only
c) Epilepsy
d) Alzheimer’s dementia
Answer: a) Tardive dyskinesia
- Ingrezza is also indicated for adults with:
a) Chorea associated with Huntington’s disease
b) Acute migraine aura
c) Myasthenia gravis
d) Multiple sclerosis relapse
Answer: a) Chorea associated with Huntington’s disease
- The active metabolite of valbenazine is:
a) [+]-alpha-dihydrotetrabenazine
b) Morphine-6-glucuronide
c) Norfluoxetine
d) Desmethylclozapine
Answer: a) [+]-alpha-dihydrotetrabenazine
- Valbenazine and its active metabolite have no appreciable binding affinity for:
a) Dopamine D2 receptors
b) VMAT2
c) Synaptic vesicle transporters
d) Monoamine storage pathways
Answer: a) Dopamine D2 receptors
- The usual initial dose of Ingrezza for tardive dyskinesia is:
a) 40 mg once daily
b) 500 mg twice daily
c) 5 mg every month
d) 1 mg three times daily
Answer: a) 40 mg once daily
- The usual recommended dose after titration is:
a) 80 mg once daily
b) 10 mg once weekly
c) 300 mg every 4 weeks
d) 1,000 mg daily
Answer: a) 80 mg once daily
- The boxed warning of Ingrezza is mainly related to:
a) Depression and suicidal ideation and behavior in patients with Huntington’s disease
b) Thyroid C-cell tumors
c) Severe hypoglycemia
d) Pulmonary fibrosis in every patient
Answer: a) Depression and suicidal ideation and behavior in patients with Huntington’s disease
- Which adverse effect is common with Ingrezza?
a) Somnolence and sedation
b) Severe ototoxicity
c) Gingival hyperplasia
d) Mandatory hypoglycemia
Answer: a) Somnolence and sedation
- Which ECG-related adverse effect is important with Ingrezza?
a) QT prolongation
b) Complete AV block in every patient
c) Permanent QT shortening
d) Ventricular hypertrophy cure
Answer: a) QT prolongation
- Which statement best describes Ingrezza?
a) It reversibly inhibits VMAT2, reducing monoamine vesicular storage and dopamine release
b) It directly blocks dopamine D2 receptors like haloperidol
c) It stimulates dopamine receptors like pramipexole
d) It blocks acetylcholinesterase like donepezil
Answer: a) It reversibly inhibits VMAT2, reducing monoamine vesicular storage and dopamine release
FAQs
What is the mechanism of action of Ingrezza?
Ingrezza, or valbenazine, reversibly inhibits VMAT2. This decreases transport of monoamines, especially dopamine, into synaptic vesicles, reducing presynaptic dopamine release and helping control abnormal involuntary movements.
What is the generic name of Ingrezza?
The generic name of Ingrezza is valbenazine.
What is Ingrezza used for?
Ingrezza is used in adults for tardive dyskinesia and chorea associated with Huntington’s disease.
Is Ingrezza a dopamine blocker?
No. Ingrezza does not directly block dopamine D2 receptors. It reduces dopamine release presynaptically by inhibiting VMAT2-mediated vesicular storage.
Does Ingrezza cure tardive dyskinesia?
No. Ingrezza helps reduce abnormal involuntary movements, but it does not cure the underlying cause of tardive dyskinesia. Symptoms may return or worsen after discontinuation in some patients.
Why does Ingrezza cause sleepiness?
Ingrezza reduces monoamine neurotransmitter storage and release. Because monoamines are involved in alertness and arousal, VMAT2 inhibition can cause somnolence, sedation, tiredness, and slower reaction time.
What is the boxed warning for Ingrezza?
The boxed warning is depression and suicidal ideation and behavior in patients with Huntington’s disease. Patients treated for Huntington’s chorea should be monitored closely for mood worsening, suicidal thoughts, and unusual behavior changes.
How is Ingrezza different from tetrabenazine?
Both are VMAT2 inhibitors, but Ingrezza contains valbenazine and is taken once daily. Tetrabenazine is an older VMAT2 inhibitor with different dosing, pharmacokinetics, and safety considerations.
References
Goodman & Gilman’s The Pharmacological Basis of Therapeutics
Katzung Basic & Clinical Pharmacology
