Deutetrabenazine

Indications

• FDA-approved for chorea associated with Huntington disease in adults, the indication that carries the boxed warning.
• FDA-approved for tardive dyskinesia in adults, with efficacy established in the ARM-TD and AIM-TD randomized trials.
• Recommended alongside valbenazine as first-line pharmacotherapy for moderate to severe tardive dyskinesia in current guidance.
• Deuteration allows lower and less frequent dosing than tetrabenazine, with lower rates of depression, akathisia, and sedation.
• Off-label use for other hyperkinetic movement disorders such as tardive dystonia and tics has limited controlled support.
• Not indicated for acute extrapyramidal symptoms, drug-induced parkinsonism, or dementia-related agitation.

Mechanism of action

• Reversibly inhibits vesicular monoamine transporter 2, depleting presynaptic vesicular dopamine and reducing striatal dopamine release.
• Lower dopamine tone attenuates the postsynaptic receptor supersensitivity that underlies tardive dyskinesia and dampens Huntington chorea.
• Deuterium substitution at the methoxy groups slows CYP2D6-mediated cleavage, roughly doubling the half-life of the active metabolites.
• Slower metabolism lowers peak concentrations for a given exposure, which reduces peak-related sedation, depression, and akathisia.
• Serotonin and norepinephrine stores are also depleted, contributing to the depression risk that defines the boxed warning.

Pharmacokinetics

• Absorption is rapid, and administration with food increases exposure of the active metabolites substantially, so it is taken with meals.
• Carbonyl reductase converts the parent drug to active alpha- and beta-dihydrotetrabenazine, which are then cleared by CYP2D6.
• The active metabolites have half-lives of about 9 to 10 hours, allowing twice-daily immediate-release or once-daily extended-release dosing.
• CYP2D6 poor metabolizers and patients on strong CYP2D6 inhibitors reach higher exposures and require lower maximum doses.
• Hepatic impairment increases active metabolite exposure several-fold, which is why any degree of hepatic impairment is a contraindication.

Dosing

• For tardive dyskinesia start 12 mg/day as 6 mg twice daily, then increase by 6 mg per day at weekly intervals as tolerated.
• For Huntington chorea start 6 mg once daily and increase by 6 mg per day weekly, guided by chorea control and tolerability.
• The maximum for both indications is 48 mg/day, and single immediate-release doses should not exceed 24 mg.
• Cap the total at 36 mg/day with strong CYP2D6 inhibitors or in known poor metabolizers, with a single-dose limit of 18 mg.
• Immediate-release doses of 12 mg or more per day are divided twice daily and taken with food; the extended-release tablet is once daily.
• Doses may be stopped without taper for short interruptions, but restart titration if therapy has lapsed for more than a week.

Adverse effects

• Somnolence, fatigue, and insomnia are the most frequent effects and cluster around dose increases in the first weeks.
• Depression and suicidal ideation are the critical risks in Huntington disease and require systematic screening at each visit.
• Akathisia, restlessness, and drug-induced parkinsonism reflect excessive dopamine depletion and generally improve with dose reduction.
• Diarrhea, dry mouth, nausea, and constipation are common gastrointestinal complaints, usually mild and dose-related.
• Mean QT prolongation is small at about 4 milliseconds at therapeutic doses but rises with CYP2D6 inhibition or poor metabolizer status.
• Neuroleptic malignant syndrome and akathisia severe enough to stop therapy have been reported with VMAT2 inhibitors as a class.

Monitoring

• Screen for depression and suicidality at baseline and at every visit in Huntington disease, and enlist caregivers to report changes.
• Use the AIMS at baseline and every 3 to 6 months in tardive dyskinesia to track response and justify continued dosing.
• Consider CYP2D6 genotyping or careful medication review before exceeding 36 mg per day, since exposure varies widely.
• Obtain an ECG at baseline and after escalation in patients with congenital long QT, bradycardia, or other QT-prolonging drugs.
• Watch for emergent parkinsonism, sedation, and gait instability at each visit, all of which respond to lowering the dose.

Interactions

• Strong CYP2D6 inhibitors including paroxetine, fluoxetine, bupropion, and quinidine raise exposure and cap the dose at 36 mg/day.
• Concomitant MAO inhibitors are contraindicated, and deutetrabenazine should not be started within 14 days of stopping an MAOI.
• Reserpine must be stopped at least 20 days before starting, and tetrabenazine or valbenazine must not be given concurrently.
• Additive sedation with alcohol, benzodiazepines, and opioids, and additive parkinsonism with antipsychotics and metoclopramide.
• Any degree of hepatic impairment is a contraindication because active metabolite exposure rises severalfold.

Special populations

• Pregnancy data in humans are lacking and animal studies show developmental effects, so use only if clearly needed.
• It is unknown whether deutetrabenazine passes into human milk; weigh the benefit of nursing against potential infant exposure.
• Safety and efficacy in patients under 18 years have not been established for either approved indication.
• Older adults tolerate it reasonably well, but sedation, falls, and parkinsonism argue for slower titration and lower targets.
• Hepatic impairment of any severity is a contraindication; formal renal impairment data are not available.

Clinical pearls

• Contraindicated in untreated depression or active suicidality; screen mood before every dose increase.
• Take it with food; fasting administration meaningfully lowers active metabolite exposure.
• Adding paroxetine or fluoxetine caps the total daily dose at 36 mg through CYP2D6 inhibition.