Trade Names:Xenazine- Tablets, oral 12.5 mg- Tablets, oral 25 mg
Precise mechanism of action is unknown; however, reversible depletion of monoamines, such as dopamine, serotonin, norepinephrine, and histamine, from nerve terminals may be involved.
Following oral administration, absorption is at least 75%. T max is approximately 1 to 1.5 h.
Protein binding ranges from 82% to 85%.
At least 19 metabolites have been identified. The 2 major metabolites are formed by carbonyl reductase in the liver.
Elimination half-life of the major circulating metabolites is 2 to 8 h. Elimination is primarily by the kidney (approximately 75%) and about 7% to 16% in the feces.
Pharmacokinetics have not be studied.Hepatic Function Impairment
Metabolism of tetrabenazine is decreased in patients with hepatic function impairment and the C max is 7- to 190-fold higher compared with healthy subjects. The elimination half-life in patients with hepatic function impairment is 17.5 h.
Treatment of chorea associated with Huntington disease.
Patients who are actively suicidal; untreated or inadequately treated depression; hepatic function impairment; MAOI therapy, reserpine therapy, and for at least 20 days after stopping reserpine.
The daily dose of tetrabenazine should be reduced by 50%.Patients stabilized on a strong CYP2D6 inhibitor
Initiate tetrabenazine using the dosing recommendations for CYP2D6 poor metabolizers.Huntington DiseaseAdults
PO Start with 12.5 mg once daily in the morning. Increase the dosage to 12.5 mg twice daily after 1 wk. Titrate the dose slowly at weekly intervals by increments of 12.5 mg daily. If akathisia, anxiety, insomnia, depression, intolerable sedation, parkinsonism, or restlessness occur, stop titration and reduce the dose. If the adverse reaction does not resolve, consider discontinuing tetrabenazine or administering another treatment (eg, antidepressants).CYP2D6 extensive and intermediate metabolizers
May require doses higher than 50 mg/day. Titrate doses higher than 50 mg/day slowly at weekly intervals by increments of 12.5 mg daily to a max of 100 mg daily. If akathisia, anxiety, depression, insomnia, intolerable sedation, parkinsonism, or restlessness occur, stop titration and reduce the dose. If the adverse reaction does not resolve, consider discontinuing tetrabenazine or administering another treatment (eg, antidepressants).CYP2D6 poor metabolizers
Dosing is similar to extensive metabolizers, except the max single dose is 25 mg and max daily dose is 50 mg.
Store at 59° to 86°F.
CNS depressant effects may be enhanced.Drugs that prolong the QTc interval (eg, class 1A [eg, procainamide] or class III [eg, amiodarone] antiarrhythmic agents, chlorpromazine, moxifloxacin, thioridazine, ziprasidone)
Risk of life-threatening cardiac arrhythmias may be increased; avoid coadministration with tetrabenazine.Moderate or weak CYP2D6 inhibitors (eg, amiodarone, duloxetine, sertraline, terbinafine)
Use with caution; effects have not been evaluated.Neuroleptic agents (eg, chlorpromazine, haloperidol, risperidone)
Tetrabenazine adverse reactions (eg, extrapyramidal effects, NMS, QTc prolongation) may be exaggerated.Reserpine
To avoid overdosage and major depletion of serotonin and norepinephrine in the CNS when switching a patient from reserpine to tetrabenazine, allow chorea to reemerge before starting tetrabenazine. Allow at least 20 days to elapse after stopping reserpine before starting tetrabenazine.Strong CYP2D6 inhibitors (eg, fluoxetine, paroxetine, quinidine)
Tetrabenazine plasma levels may be elevated; reduce tetrabenazine dosage by half.
None well documented.
Any extrapyramidal event (33%); sedation/somnolence (31%); fatigue, insomnia (22%); akathisia, depression (19%); anxiety or aggravated anxiety (15%); balance difficulty, bradykinesia/parkinsonism, irritability (9%); decreased appetite, dizziness, dysarthria, headache, obsessive reaction, unsteady gait (4%).
Nausea (13%); dysphagia (10%); vomiting (6%).
Upper respiratory tract infection (11%); bronchitis, shortness of breath (4%).
Falling (15%); head laceration (6%).
Depression and suicidal thoughts and behavior (suicidality) can be increased in patients with Huntington disease. Closely observe patients for emergence or worsening of depression, suicidality, or unusual changes in behavior. Exercise particular caution in treating patients with a history of depression or suicide attempts or ideation, which are increased in frequency in patients with Huntington disease.
Periodically evaluate the need for continued tetrabenazine therapy by assessing the beneficial effect on choreiform movements and possible adverse reactions. Monitor patients for the presence of akathisia and for signs and symptoms of restlessness and agitation. Before administering daily doses of tetrabenazine higher than 50 mg, genotype patients to determine if they are poor, extensive, or intermediate CYP2D6 metabolizers.
Category C .
Safety and efficacy not established.
Use with caution in patients with a history of depression or suicidality, or with conditions, diseases, or treatments that could cause depression or suicidality.
Dysphagia is a component of Huntington disease and has been associated with drugs that reduce dopaminergic transmission, such as tetrabenazine; therefore, use with caution in patients at risk of aspiration pneumonia.
Elevated serum prolactin concentrations may occur.
Has been reported.
Since tetrabenazine or its metabolites bind to melanin-containing tissue, toxicity in these tissues over time is a possibility.
Potentially life-threatening NMS has been reported.
Small increases in the QTc interval may occur, increasing the risk of life-threatening arrhythmias, including torsades de pointes. Avoid use in patients with congenital long QT syndrome and in patients with a history of cardiac arrhythmias.
Caution patients about operating potentially hazardous machinery (eg, driving) until they know whether the drug impairs their ability.
A potentially irreversible syndrome of involuntary, dyskinetic movements may occur in patients receiving neuroleptic agents.
Acute dystonia, confusion, diarrhea, hallucinations, hypotension, nausea, oculogyric crisis, rubor, sedation, sweating, tremor, vomiting.
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