XENAZINE TABLETS 25MG 112`S

Tetrabenazine is a VMAT2 (vesicular monoamine transporter 2) inhibitor. It works by depleting monoamine neurotransmitters — primarily dopamine — from presynaptic nerve terminals in the brain.

Reducing dopamine activity in the striatum, it suppresses the involuntary, purposeless movements (hyperkinesias) that characterise certain neurological movement disorders.

Xenazine is used to treat:

•       Hyperkinetic movement disorders — including chorea associated with Huntington's disease (HD), which is its primary licensed indication in most countries.

•       Hemiballismus, senile chorea, Tourette syndrome, and tardive dyskinesia (in some countries / specialist use).

Doses above 50 mg/day require CYP2D6 genotyping — dosing strategy differs for poor metabolisers vs extensive/intermediate metabolisers. Start at 12.5 mg (half tablet) once daily. Increase by 12.5 mg per week to a clinical response. Usual maintenance: 25 mg two to three times daily. Maximum dose: 100 mg/day (extensive metabolisers); 50 mg/day (poor metabolisers). Take with or without food.

Tetrabenazine is contraindicated in: untreated or inadequately controlled depression; suicidality; concomitant reserpine (at least 20 days washout required); concomitant MAO inhibitors; concomitant deutetrabenazine or valbenazine (same mechanism); hepatic impairment; and patients who are breastfeeding.

•       MAO inhibitors (selegiline, rasagiline, phenelzine): CONTRAINDICATED — risk of severe hypertensive crisis, hyperthermia, and death.

•       Reserpine: synergistic monoamine depletion — contraindicated; 20-day washout required.

•       Strong CYP2D6 inhibitors (fluoxetine, paroxetine, quinidine): double tetrabenazine exposure — reduce dose by 50%.

•       Dopamine agonists / levodopa: opposing mechanism — avoid.

•       QT-prolonging agents: additive risk — avoid.

•       Alcohol / CNS depressants: additive sedation.

Store at room temperature below 25°C. Keep in original packaging. Keep out of reach of children. Do not use after expiry date.

Tetrabenazine can be a very effective medicine for reducing the involuntary movements of Huntington's disease and other choreas. However, its effects on mood must be taken very seriously. The risk of depression and suicidal thoughts is real and significant. Caregivers should actively monitor for changes in mood, withdrawal, expressions of hopelessness, or any talk of self-harm, and communicate these immediately to the neurologist.

Sedation can be significant, especially at higher doses or during dose increases. It is very important not to drive or operate heavy machinery until the effect of any dose change on alertness has been fully assessed.

The involuntary movements of Huntington's disease can cause difficulties swallowing — this risk continues and may be worsened by high tetrabenazine doses. Work with a speech and language therapist if swallowing difficulties develop.

The 112-tablet pack covers approximately 4 weeks at a dose of 25 mg four times daily (100 mg/day) — the maximum dose for extensive CYP2D6 metabolisers.

Tetrabenazine is rapidly metabolised to alpha- and beta-dihydrotetrabenazine (HTBZ), which are the active VMAT2-inhibiting metabolites. Alpha-HTBZ is further metabolised by CYP2D6 — making poor metabolisers (approximately 7–10% of white Europeans) susceptible to accumulation.

Strong CYP2D6 inhibitors (fluoxetine, paroxetine) should be avoided or dose halved. The newer VMAT2 inhibitors deutetrabenazine and valbenazine have longer half-lives and improved pharmacokinetic profiles with potentially better tolerability but are not interchangeable — do not co-administer.

Will this medicine cure Huntington's disease?

No — tetrabenazine treats the involuntary movements (chorea) but does not affect the underlying genetic progression of Huntington's disease. The cognitive and psychiatric features of HD require separate assessment and management.

My family member seems more confused on this medicine — what should I do?

Increased confusion or sedation can occur with tetrabenazine, particularly when doses are increased. Contact your neurologist promptly — a dose reduction may be appropriate.

Can I drive while taking tetrabenazine?

Tetrabenazine commonly causes sedation and cognitive slowing, especially during dose adjustments. Driving should be assessed carefully by the neurologist. Do not drive if you feel sedated or unsteady.

What is CYP2D6 testing, and why is it done?

CYP2D6 is a liver enzyme that breaks down tetrabenazine. Poor metabolisers of CYP2D6 break down the drug more slowly, causing it to accumulate to higher levels at the same dose. Testing identifies these patients so the maximum dose is appropriately limited to 50 mg/day to avoid toxicity.