tetrabenazine

(redirected from Xenazine)

tetrabenazine

(te-tra-ben-a-zeen) ,

Xenazine

(trade name)

Classification

Therapeutic: antichoreas
Pharmacologic: reversible monoamine depleters
Pregnancy Category: C

Indications

Treatment of chorea due to Huntington's Disease.

Action

Acts as a reversible inhibitor of the vesicle monoamine transporter type 2 (VMAT-2); which inhibits the reuptake of serotonin, norepinephrine and dopamine into vesicles in presynaptic neurons.

Therapeutic effects

Decreased chorea due to Huntington's Disease.

Pharmacokinetics

Absorption: At least 75% absorbed following oral administration.
Distribution: Crosses the blood-brain barrier.
Metabolism and Excretion: genetic implication Rapidly and extensively metabolized by the liver; CYP2D6 plays a large role in the metabolic process (the CYP2D6 enzyme system exhibits genetic polymorphism; 7% of population may be poor metabolizers and may have significantly ↑ concentrations and an ↑ risk of adverse effects). Metabolites are renally excreted. Two metabolites α-dihydrotetrabenazine (α-HTBZ) and β-HTBZ bind to VMAT-2 and are pharmacologically active.
Half-life: α-HTBZ—4-8 hrs; β-HTBZ—2-4 hr.

Time/action profile (blood levels)

ROUTEONSETPEAKDURATION
POunknown1.0–1.5 hr12–18 hr*
*Return of symptoms following discontinuation.

Contraindications/Precautions

Contraindicated in: Hepatic impairment;Concurrent use of reserpine or MAO inhibitors;Patients who are actively suicidal or have untreated depression; Lactation: Lactation.
Use Cautiously in: History of/propensity for depression or history of psychiatric illness; history of suicidality;genetic implication Poor CYP2D6 metabolizers; initial dose reduction required;Concurrent use of CYP2D6 inhibitors; dose modification required;Recent history of myocardial infarction or unstable heart disease; Obstetric: Use only when potential benefit justifies potential risk to the fetus; Pediatric: Safety and effectiveness not established.

Adverse Reactions/Side Effects

Central nervous system

  • anxiety (most frequent)
  • fatigue (most frequent)
  • insomnia (most frequent)
  • depression (most frequent)
  • sedation/somnolence (most frequent)
  • cognitive defects
  • dizziness
  • headache

Respiratory

  • shortness of breath

Cardiovascular

  • hypotension
  • QTc interval prolongation

Gastrointestinal

  • nausea (most frequent)
  • dysphagia

Neurologic

  • akathisia (most frequent)
  • balance difficulty
  • dysarthria
  • parkinsonism
  • unsteady gait

Miscellaneous

  • neuroleptic malignant syndrome (life-threatening)

Interactions

Drug-Drug interaction

Blood levels are ↑ by drugs that inhibit the CYP2D6 enzyme system including fluoxetine, paroxetine, and quinidine ; initial dose ↓ of tetrabenazine recommended.Reserpine binds to VMAT-2 and depletes monoamines in the CNS; avoid concurrent use; wait 3 wk after discontinuing to initiate tetrabenazine.Concurrent use of MAO inhibitors ↑ risk of serious adverse reactions and is contraindicated.Concurrent use with neurolpetic drugs or dopamine antagonists including haloperidol, chlorpromazine, risperidone, and olanzapine may ↑ risk of QTc interval prolongation, neuroleptic malignant syndrome and extrapyramidal disorders.Concurrent use of alcohol or other CNS depressants may ↑ risk of CNS depression.

Route/Dosage

Oral (Adults) 12.5 mg/day for one wk initially, ↑ by 12.5 weekly up to 37.5–50 mg/day in 3 divided doses; genetic implicationConcurrent use of strong inhibitors of CYP2D6 or poor CYP2D6 metabolizers—start with initial dose of 6.25 mg, titrate carefully.

Availability

Tablets: 12.5 mg, 25 mg

Nursing implications

Nursing assessment

  • Assess signs of Huntington's disease (changes in mood, cognition, chorea, rigidity, and functional capacity) periodically during therapy. Re-evaluate need for tetrabenazine periodically by assessing beneficial effect and side effects; determination may require dose reduction or discontinuation. Underlying chorea may improve over time, decreasing need for tetrabenazine.
  • Monitor closely for new or worsening depression or suicidality. If depression or suicidality occurs ↓ dose and may initiate or ↑ dose of antidepressants.
  • Monitor for signs of neuroleptic malignant syndrome (hyperpyrexia, muscle rigidity, altered mental status, irregular pulse or BP, tachycardia, diaphoresis, cardiac dysrhythmia) periodically during therapy. If symptoms occur discontinue tetrabenazine and manage symptomatically. If re-introduction of tetrabenazine is considered monitor carefully; recurrences of neuroleptic malignant syndrome have occurred.
  • Monitor patient for onset of akathisia (restlessness or desire to keep moving) and parkinsonian (difficulty speaking or swallowing, loss of balance control, pill rolling of hands, mask-like face, shuffling gait, rigidity, tremors). Notify health care professional if these symptoms occur; reduction in dose or discontinuation may be necessary.
  • Assess BP sitting and standing. May cause orthostatic hypotension.
  • Lab Test Considerations: genetic implication Test for the CYP2D6 gene in patients requiring doses of >50 mg/day to determine if they are poor, intermediate, or extensive metabolizers. Limit dose to 50 mg in patients who are poor metabolizers.

Potential Nursing Diagnoses

Risk for suicide (Adverse Reactions)

Implementation

  • Dose should be titrated slowly and individualized.
  • Oral: May be administered without regard to food.

Patient/Family Teaching

  • Instruct patient to take tetrabenazine as directed. Do not take more or stop taking tetrabenazine without consulting health care professional. Dose adjustment may take several wk. Discuss procedure for missed doses with health care professional before beginning therapy; do not double doses. If a dose is missed or medication discontinued, involuntary movements will return or worsen in 12–18 hrs. If tetrabenazine is stopped for more than 5 days, consult health care professional before taking another dose; lower dose may be required.
  • Advise patient and family to monitor for changes, especially sudden changes, in mood, behaviors, thoughts or feelings. If new or worse feelings of sadness or crying spells, lack of interest in friends or activities, sleeping a lot more or less, feelings of unimportance, guilt, hopelessness or helplessness, irritability or aggression, more or less hungry, difficulty paying attention, or thoughts of hurting self or ending life occur, notify health care professional promptly.
  • Causes sedation. Caution patient to avoid driving and other activities requiring alertness until response to medication is known.
  • Advise patient to avoid alcohol and other CNS depressants during therapy; ↑ sedation.
  • Inform patient of potential side effects and instruct to notify health care professional if side effects occur.
  • Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and consult health care professional before taking any new medications.
  • Advise female patients to notify health care professional if pregnancy is planned or suspected or if breast feeding.

Evaluation/Desired Outcomes

  • ↓ in chorea due to Huntington's disease.

Tetrabenazine

A drug given to control chorea that appears to benefit HD patients.
Mentioned in: Huntington Disease
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