Diruixin Tetrabenazine Tablets

1. Indications and Usage
Tetrabenazine tablets are indicated for the treatment of chorea associated with Huntington’s disease.
2. Dosage and Administration
Initial Dosage: The recommended starting dosage is 12.5 mg once daily in the morning.
Titration: After one week, the daily dosage can be increased to 25 mg (12.5 mg twice daily). Dosage should be titrated slowly, typically by increasing the daily dosage by 12.5 mg per week, until chorea is controlled or intolerable side effects occur.
Maximum Dosage: The maximum recommended daily dosage is 50 mg. If the daily dosage reaches 37.5–50 mg, it should be administered in three divided doses (e.g., morning, afternoon, and before bedtime).
Administration: Tablets can be taken with or without food.
3. Mechanism of Action
Tetrabenazine is a reversible inhibitor of the vesicular monoamine transporter 2 (VMAT2). It depletes presynaptic stores of monoamine neurotransmitters, including dopamine, serotonin, and norepinephrine. By reducing dopaminergic neurotransmission, it alleviates the hyperkinetic movements characteristic of Huntington’s disease.
4. Safety and Warnings
Depression and Suicidality: Tetrabenazine can cause or worsen depression and increase the risk of suicidal ideation and behavior. It is contraindicated in patients with active suicidal ideation or untreated/uncontrolled depression.
Neuroleptic Malignant Syndrome (NMS): Rare cases of NMS have been reported, which can be fatal.
Sedation and Somnolence: The drug can cause significant sedation and sleepiness, affecting the ability to drive or operate machinery.
Parkinsonism: Tetrabenazine can cause or worsen parkinsonian symptoms due to dopamine depletion.
QTc Prolongation: Tetrabenazine can prolong the QTc interval, increasing the risk of arrhythmias.
5. Adverse Reactions and Clinical Research
Common Adverse Reactions: The most frequent adverse reactions include somnolence/sedation, fatigue, insomnia, depression, akathisia, anxiety, and nausea.
Extrapyramidal Symptoms: Parkinsonism, dystonia, and rigidity are common due to the drug’s dopaminergic effects.
6. Drug Interactions
CYP2D6 Inhibitors: Co-administration with strong CYP2D6 inhibitors (e.g., fluoxetine, paroxetine, quinidine) significantly increases tetrabenazine exposure. In patients taking strong inhibitors, the maximum recommended daily dosage is 50 mg.
CYP2D6 Genotyping: Patients requiring a daily dosage greater than 50 mg must be genotyped for CYP2D6.
Antipsychotics and Dopamine Depleters: Concomitant use with other drugs that deplete dopamine or block dopamine receptors increases the risk of extrapyramidal symptoms and NMS.
7. Pharmaceutical Information
Composition: The active ingredient is tetrabenazine.
Appearance: 12.5 mg tablets are white and unscored. 25 mg tablets are pale yellow to yellow and scored on one side.
Storage: Store at or below 25°C in a tightly closed container, protected from light.