Xenazine Dosage

Generic name: TETRABENAZINE 12.5mg
Dosage form: tablet
Drug class: VMAT2 inhibitors

Medically reviewed by Drugs.com. Last updated on Oct 23, 2023.

General Dosing Considerations

The chronic daily dose of XENAZINE used to treat chorea associated with Huntington’s disease (HD) is determined individually for each patient. When first prescribed, XENAZINE therapy should be titrated slowly over several weeks to identify a dose of XENAZINE that reduces chorea and is tolerated. XENAZINE can be administered without regard to food [see Clinical Pharmacology (12.3)].

Individualization of Dose

The dose of XENAZINE should be individualized.

Dosing Recommendations Up to 50 mg/day

The starting dose should be 12.5 mg/day given once in the morning. After 1 week, the dose should be increased to 25 mg/day given as 12.5 mg twice a day. XENAZINE should be titrated up slowly at weekly intervals by 12.5 mg daily, to allow the identification of a tolerated dose that reduces chorea. If a dose of 37.5 to 50 mg/day is needed, it should be given in a three times a day regimen. The maximum recommended single dose is 25 mg. If adverse reactions such as akathisia, restlessness, parkinsonism, depression, insomnia, anxiety or sedation occur, titration should be stopped and the dose should be reduced. If the adverse reaction does not resolve, consideration should be given to withdrawing XENAZINE treatment or initiating other specific treatment (e.g., antidepressants) [see Adverse Reactions (6.1)].

Dosing Recommendations Above 50 mg/day

Patients who require doses of XENAZINE greater than 50 mg/day should be first tested and genotyped to determine if they are poor metabolizers (PMs) or extensive metabolizers (EMs) by their ability to express the drug metabolizing enzyme, CYP2D6. The dose of XENAZINE should then be individualized accordingly to their status as PMs or EMs [see Warnings and Precautions (5.3), Use in Specific Populations (8.7), Clinical Pharmacology (12.3)].

Extensive and Intermediate CYP2D6 Metabolizers

Genotyped patients who are identified as extensive (EMs) or intermediate metabolizers (IMs) of CYP2D6, who need doses of XENAZINE above 50 mg/day, should be titrated up slowly at weekly intervals by 12.5 mg daily, to allow the identification of a tolerated dose that reduces chorea. Doses above 50 mg/day should be given in a three times a day regimen. The maximum recommended daily dose is 100 mg and the maximum recommended single dose is 37.5 mg. If adverse reactions such as akathisia, parkinsonism, depression, insomnia, anxiety or sedation occur, titration should be stopped and the dose should be reduced. If the adverse reaction does not resolve, consideration should be given to withdrawing XENAZINE treatment or initiating other specific treatment (e.g., antidepressants) [see Warnings and Precautions (5.3), Use in Specific Populations (8.7), Clinical Pharmacology (12.3)].

Poor CYP2D6 Metabolizers

In PMs, the initial dose and titration is similar to EMs except that the recommended maximum single dose is 25 mg, and the recommended daily dose should not exceed a maximum of 50 mg [see Use in Specific Populations (8.7), Clinical Pharmacology (12.3)].

Dosage Adjustment with CYP2D6 Inhibitors

Strong CYP2D6 Inhibitors

Medications that are strong CYP2D6 inhibitors such as quinidine or antidepressants (e.g., fluoxetine, paroxetine) significantly increase the exposure to α-HTBZ and β-HTBZ; therefore, the total dose of XENAZINE should not exceed a maximum of 50 mg and the maximum single dose should not exceed 25 mg [see Warnings and Precautions (5.3), Drug Interactions (7.1), Use in Specific Populations (8.7), Clinical Pharmacology (12.3)].

Discontinuation of Treatment

Treatment with XENAZINE can be discontinued without tapering. Re-emergence of chorea may occur within 12 to 18 hours after the last dose of XENAZINE [see Drug Abuse and Dependence (9.2)].

Resumption of Treatment

Following treatment interruption of greater than 5 days, XENAZINE therapy should be re-titrated when resumed. For short-term treatment interruption of less than 5 days, treatment can be resumed at the previous maintenance dose without titration.