Comparing pharmacologic mechanism of action for the vesicular monoamine transporter 2 (VMAT2) inhibitors valbenazine and deutetrabenazine in treating tardive dyskinesia: does one have advantages over the other?

Profiling deutetrabenazine extended-release tablets for tardive dyskinesia and chorea associated with Huntington's disease

INTRODUCTION

Tardive dyskinesia (TD) and Huntington's disease (HD)-associated chorea are persistent and disabling hyperkinetic disorders that can be treated with vesicular monoamine transporter type 2 (VMAT2) inhibitors, including the recently approved once-daily (QD) formulation of deutetrabenazine (DTBZ ER). While its efficacy and safety profile have not been directly investigated, currently available data confirms bioequivalence and similar bioavailability to the twice-daily formulation (DTBZ BID).

AREAS COVERED

The authors briefly review the pivotal trials establishing efficacy of DTBZ for TD and HD-associated chorea, the pharmacokinetic data for bioequivalence between QD and BID dosing of DTBZ, as well as dose proportionality evidence, titration recommendations, and safety profile for DTBZ ER.

EXPERT OPINION

Long-term data show that DTBZ is efficacious and well tolerated for the treatment of TD and HD-associated chorea. DTBZ ER likely demonstrates therapeutic equivalence with no new safety signals. Due to the lack of comparative clinical trial data, no evidence-based recommendation about choice of VMAT2 inhibitor or switching between VMAT2 inhibitors can be made about best practice. Ultimately, QD dosing may offer the chance of improved medication adherence, an important consideration in patients with complex treatment regimens and/or patients with cognitive decline.

Meta-analysis and systematic review of vesicular monoamine transporter (VMAT-2) inhibitors in schizophrenia and psychosis

RATIONALE

Dopamine antagonists induce dopamine receptor supersensitivity. This may manifest in late-appearing movement disorders (tardive dyskinesia (TD). VMAT-2 inhibitors reduce dopaminergic transmission but have limited activity at postsynaptic receptors and so may have antipsychotic activity with lower risk of tardive dyskinesia.

METHODS

We conducted a systematic database search from inception to September 2022 for articles describing the use of VMAT-2 inhibitors in psychosis. Inclusion criteria were as follows: Population: adults diagnosed with psychosis or schizophrenia; Intervention: treatment with tetrabenazine, deutetrabenazine or valbenazine; Comparison: comparison with placebo or/and antipsychotic drug; Outcomes: with efficacy outcomes (e.g. Brief Psychiatric Rating Scale (BPRS) change or clinician assessment) and adverse effects ratings (e.g. rating scale or clinician assessment or dropouts); and Studies: in randomised controlled trials and non-randomised studies.

RESULTS

We identified 4892 records relating to VMAT-2 inhibitor use of which 5 (173 participants) met our a priori meta-analysis inclusion criteria. VMAT-2 inhibitors were more effective than placebo for the outcome 'slight improvement' (risk ratio (RR) = 1.77 (95% CI 1.03, 3.04)) but not for 'moderate improvement' (RR 2.81 (95% CI 0.27, 29.17). VMAT-2 inhibitors were as effective as active comparators on both measures for-'slight improvement' (RR 1.05 (95% CI 0.6, 1.81)) and 'moderate improvement' (RR 1.11 (95% CI 0.51, 2.42). Antipsychotic efficacy was also suggested by a narrative review of 37 studies excluded from the meta-analysis.

CONCLUSIONS

VMAT-2 inhibitors may have antipsychotic activity and may offer promise for treatment of psychosis with the potential for a reduced risk of TD.

Pharmacokinetic and Pharmacologic Characterization of the Dihydrotetrabenazine Isomers of Deutetrabenazine and Valbenazine

Valbenazine and deutetrabenazine are vesicular monoamine transporter 2 (VMAT2) inhibitors approved for tardive dyskinesia. The clinical activity of valbenazine is primarily attributed to its only dihydrotetrabenazine (HTBZ) metabolite, [+]-α-HTBZ. Deutetrabenazine is a deuterated form of tetrabenazine and is metabolized to four deuterated HTBZ metabolites: [+]-α-deuHTBZ, [+]-β-deuHTBZ, [-]-α-deuHTBZ, and [-]-β-deuHTBZ. An open-label, crossover study characterized the pharmacokinetic profiles of the individual deuHBTZ metabolites, which have not been previously reported. VMAT2 inhibition and off-target interactions of the deuHTBZ metabolites were evaluated using radioligand binding. The only valbenazine HTBZ metabolite, [+]-α-HTBZ, was a potent VMAT2 inhibitor, with negligible affinity for off-target dopamine, serotonin, and adrenergic receptors. Following deutetrabenazine administration, [-]-α-deuHTBZ represented 66% of circulating deuHTBZ metabolites and was a relatively weak VMAT2 inhibitor with appreciable affinity for dopamine (D_2S , D₃ ) and serotonin (5-HT_1A , 5-HT_2B , 5-HT₇ ) receptors. [+]-β-deuHTBZ was the most abundant deuHTBZ metabolite that potently inhibited VMAT2, but it represented only 29% of total circulating deuHTBZ metabolites. The mean half-life of [+]-α-HTBZ (22.2 hours) was ∼3× longer than that of [+]-β-deuHTBZ (7.7 hours). These findings are similar to studies with tetrabenazine, in that deutetrabenazine is metabolized to four deuHTBZ stereoisomers, the most abundant of which has negligible interaction with VMAT2 in vitro and appreciable affinity for several off-target receptors. In contrast, valbenazine's single HTBZ metabolite is a potent VMAT2 inhibitor in vitro with no discernible off-target activity. Determination of the effects of intrinsic/extrinsic variables on deutetrabenazine's safety/efficacy profile should incorporate assessment of the effects on all deuHTBZ metabolites.

Efficacy and safety of valbenazine in Japanese patients with tardive dyskinesia: A multicenter, randomized, double-blind, placebo-controlled study (J-KINECT)

AIM

Valbenazine is approved in the US for treatment of tardive dyskinesia (TD); however, efficacy/safety data in Asian populations are lacking. We assessed the efficacy/safety of valbenazine in Japanese patients.

METHODS

This phase II/III, multicenter, randomized, double-blind, placebo-controlled study (NCT03176771) included adult psychiatric patients with TD, who were randomly allocated to receive placebo or valbenazine (once-daily 40- or 80-mg) for a 6-week, double-blind period, after which the placebo group was switched to valbenazine for a 42-week extension. The primary endpoint was change from baseline in Abnormal Involuntary Movement Scale (AIMS) total score at Week 6; clinical global impression of improvement of TD (CGI-TD) was also assessed.

RESULTS

Of 256 patients, 86, 85, and 85 were allocated to the 40-mg valbenazine, 80-mg valbenazine, and placebo groups, respectively. Least-squares mean (95% confidence interval) change from baseline in AIMS score at Week 6 was -2.3 (-3.0 to -1.7) in the valbenazine 40-mg group, -3.7 (-4.4 to -3.0) in the 80-mg group, and -0.1 (-0.8 to 0.5) in the placebo group; both treatment groups showed statistically significant improvements vs. placebo. Patients switched to valbenazine at Week 6 showed similar improvements in AIMS scores, which were maintained to Week 48. Improvements in CGI-TD scores were observed for both treatment groups vs. placebo. Incidence of adverse events was highest in the 80-mg group; common events included nasopharyngitis, somnolence, schizophrenia worsening, hypersalivation, insomnia, and tremor.

CONCLUSION

The efficacy/safety profile of valbenazine was similar to that of previous clinical trials, supporting its use for TD treatment in Japanese patients.

9-Cyclopropylmethoxy-dihydrotetrabenazine and its stereoisomers as vesicular monoamine transporter-2 inhibitors

Aim: To separate and evaluate 9-cyclopropylmethoxy-dihydrotetrabenazine (13a) and its stereoisomers for their high affinity for vesicular monoamine transporter-2 (VMAT2). Method: Stereoisomers of 13a were separated and configurations were ascertained by chiral chromatography and crystal diffraction combined with ¹H-¹H NOESY assay. Possible binding modes of eight stereoisomers and VMAT2 were explored by molecular docking assays. The VMAT2 affinity of the stereoisomers, inhibition in vivo and pharmacokinetics in rats were evaluated. Results: Three stereoisomers were obtained: P1, P2 and P3, and all had similar VMAT2 binding modes. P2 [(2R, 3R, 11bR)-13a] showed the highest potential VMAT2 binding activity (K_i = 0.75 nM), decreased locomotor activity in rats and had an oral absolute bioavailability of 92.0%. Conclusion: P2 has good efficacy and pharmacokinetic properties and warrants further development to treat tardive dyskinesia.

VMAT2 Inhibitors for the Treatment of Tardive Dyskinesia

Psychiatric nurses are at the forefront of optimizing psychiatric care, including educating patients and caregivers on the risks of antipsychotic-induced movement disorders such as tardive dyskinesia (TD). Nurses should be aware that all patients taking antipsychotics should be regularly monitored for the development of TD. Given the current pandemic and increase in telehealth, assessing for TD is challenging; however, evaluation can be successfully completed by implementing the best practices described in this paper. Once TD is diagnosed, nurses can reassure patients that safe and effective FDA-approved treatments for TD (e.g., valbenazine) are now available.

Pathophysiology, prognosis and treatment of tardive dyskinesia

Tardive dyskinesia (TD), a movement disorder associated with antipsychotics, most frequently affects the lower face and jaw muscles, but can also affect walking, breathing and use of the hands and limbs. Knowledge of TD among physicians may be limited, and the pathophysiology of TD is poorly understood. We conducted this review to summarise the current knowledge surrounding the pathophysiology of TD and present recommendations for prevention and treatment based on a literature search and roundtable discussion attended by psychiatrists in Japan. It has been suggested that dopamine hypersensitivity, damaged gamma-aminobutyric acidergic neurons and/or increased production of reactive oxygen species may contribute to development of TD. Symptoms can profoundly affect everyday life; patients who develop TD have poorer prognoses, worse health-related quality of life, greater social withdrawal and higher mortality than patients without TD. Traditional treatment options include dietary supplements, although evidence for their effectiveness is low. Among pharmaceutical interventions, there is moderate evidence that switching to the second-generation antipsychotic clozapine, which has a lower affinity for dopamine D₂ receptors than other antipsychotics, may improve symptoms. Vesicular monoamine transporter 2 (VMAT-2) inhibitors, which oppose the increased dopaminergic activity associated with prolonged antipsychotic use by interfering with dopamine uptake and storage, have the strongest evidence for efficacy. VMAT-2 inhibitors are approved in the United States for the treatment of TD, and the first VMAT-2 inhibitor was approved in Japan for this indication in March 2022. Most guidelines recommend treating TD by first reducing the dose of antipsychotics or switching to clozapine or other second-generation antipsychotics, which have a lower association with TD than first-generation antipsychotics. We recommend focusing on prevention and monitoring for TD when prescribing antipsychotics, given that TD is often irreversible. Physicians should treat with antipsychotics only when necessary and at the lowest effective dose, and frequently monitor for TD symptoms.

PLAIN LANGUAGE SUMMARY

Plain Language Summary (In Japanese).

VISUAL SUMMARY

Visual Summary (In Japanese).

(+)-9-Trifluoroethoxy-α-Dihydrotetrabenazine as a Highly Potent Vesicular Monoamine Transporter 2 Inhibitor for Tardive Dyskinesia

Valbenazine and deutetrabenazine are the only two therapeutic drugs approved for tardive dyskinesia based on blocking the action of vesicular monoamine transporter 2 (VMAT2). But there exist demethylated inactive metabolism at the nine position for both them resulting in low availability, and CYP2D6 plays a major role in this metabolism resulting in the genetic polymorphism issue. 9-trifluoroethoxy-dihydrotetrabenazine (13e) was identified as a promising lead compound for treating tardive dyskinesia. In this study, we separated 13e via chiral chromatography and acquired R,R,R-13e [(+)-13e] and S,S,S-13e [(−)-13e], and we investigated their VMAT2-inhibitory activity and examined the related pharmacodynamics and pharmacokinetics properties using in vitro and in vivo models (+)-13e displayed high affinity for VMAT2 (K_i = 1.48 nM) and strongly inhibited [³H]DA uptake (IC₅₀ = 6.11 nM) in striatal synaptosomes. Conversely, its enantiomer was inactive. In vivo, (+)-13e decreased locomotion in rats in a dose-dependent manner. The treatment had faster, stronger, and longer-lasting effects than valbenazine at an equivalent dose. Mono-oxidation was the main metabolic pathway in the liver microsomes and in dog plasma after oral administration, and glucuronide conjugation of mono-oxidized and/or demethylated products and direct glucuronide conjugation were also major metabolic pathways in dog plasma. O-detrifluoroethylation of (+)-13e did not occur. Furthermore, CYP3A4 was identified as the primary isoenzyme responsible for mono-oxidation and demethylation metabolism, and CYP2C8 was a secondary isoenzyme (+)-13e displayed high permeability across the Caco-2 cell monolayer, and it was not a P-glycoprotein substrate as demonstrated by its high oral absolute bioavailability (75.9%) in dogs. Thus, our study findings highlighted the potential efficacy and safety of (+)-13e in the treatment of tardive dyskinesia. These results should promote its clinical development.

Real-World Adherence to Tetrabenazine or Deutetrabenazine Among Patients With Huntington's Disease: A Retrospective Database Analysis

Introduction

Chorea, a common clinical manifestation of Huntington’s disease (HD), involves sudden, involuntary movements that interfere with daily functioning and contribute to the morbidity of HD. Tetrabenazine and deutetrabenazine are FDA-approved to treat chorea associated with HD. Compared to tetrabenazine, deutetrabenazine has a unique pharmacokinetic profile leading to more consistent systemic exposure, less frequent dosing, and a potentially more favorable safety/tolerability profile. Real-world adherence data for these medications are limited. Here, we evaluate real-world adherence patterns with the vesicular monoamine transporter 2 inhibitors, tetrabenazine and deutetrabenazine, among patients diagnosed with HD.

Methods

Insurance claims data from the Symphony Health Solutions Integrated Dataverse (05/2017–05/2019) were retrospectively analyzed for patients diagnosed with HD (ICD-10-CM code G10). Patients were categorized into cohorts based on treatment. Outcomes included adherence, which was measured by proportion of days covered (PDC), adherence rate (PDC > 80%), and discontinuation rates during the 6-month follow-up period (after a 30-day dose stabilization period).

Results

Patient demographic characteristics between the deutetrabenazine (N = 281) and tetrabenazine (N = 101) cohorts were comparable at baseline. Mean ± SD PDC was significantly higher in the deutetrabenazine versus tetrabenazine cohort (78.5% ± 26.7% vs. 69.3% ± 31.4%; P < 0.01). Similarly, a higher adherence rate was observed in the deutetrabenazine versus tetrabenazine cohort, though the difference was not statistically significant (64.1% vs. 55.4%; P = 0.1518). Discontinuation rates were significantly lower in the deutetrabenazine versus tetrabenazine cohort during the 6-month follow-up period (1 month, 3.5% vs. 9.2%; 3 months, 14.7% vs. 23.3%; 6 months, 25.4% vs. 37.2%; P < 0.05).

Conclusions

Results from this real-world analysis indicate that patients treated with deutetrabenazine are more adherent to treatment and have lower discontinuation rates compared with patients in the tetrabenazine cohort. However, a potential limitation is overestimated adherence, as claims for prescription fills may not capture actual use. Additional research is warranted to explore the differences in adherence patterns between treatments, which may inform treatment decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-021-00309-5.

Valbenazine for the Treatment of Adults with Tardive Dyskinesia

PURPOSE OF REVIEW

This a comprehensive review of the literature regarding the use of Valbenazine in treating tardive dyskinesia. A primarily oral movement disorder induced by chronic exposure to certain classes of medications, tardive dyskinesia is often resistant to many therapeutic approaches. This review presents the background, evidence, and indications for the use of Valbenazine as a treatment option for this condition.

RECENT FINDINGS

Tardive dyskinesia is a disorder arising from long-term exposure to medications that blocked dopamine receptors, primarily antipsychotics. It is characterized by abnormal movements of the oral-buccal-lingual structures as well as associated pain and hypertrophy. Simply stopping the use of the dopamine blocking agents effectively alleviates the symptoms but is not always reliable hence the need for another therapeutic approach.Valbenazine is thought to function as a highly selective inhibitor of the VMAT2 vesicular monoamine transporter resulting in decreased availability of dopamine in the presynaptic cleft. This leads to decreased dopaminergic activation of the striatal motor pathway. The FDA approved Valbenazine in 2017 to treat tardive dyskinesia in adults and needs to be evaluated with existing therapeutic approaches.

SUMMARY

The chronic use of dopamine receptor blocking agents, most commonly antipsychotics, can lead to a movement disorder called tardive dyskinesia. Once symptom onset has occurred, these movement abnormalities can persist for years to permanently, depending on the speed and effectiveness of treatment. Valbenazine is a relatively newer option for the treatment of tardive dyskinesia in adults. Compared to other pharmaceutical agents, it is more selective and has limited toxicities making it an effective treatment regimen. However, further research, including additional direct comparison studies, should be conducted to fully evaluate this drug's usefulness.

Deutetrabenazine for treatment of involuntary movements in patients with tardive dyskinesia

Introduction: Tardive dyskinesia (TD) is a hyperkinetic movement disorder that arises as a complication of exposure to dopamine receptor blocking agents. Vesicular monoamine transporter type 2 (VMAT2) inhibitors reduce dyskinesia by decreasing transport of monoamines, including dopamine, into presynaptic vesicles, leaving unpackaged dopamine to be metabolized by monoamine oxidase. Deutetrabenazine was adapted from an earlier VMAT2 inhibitor, tetrabenazine, by substituting three deuterium isotopes in place of three hydrogen isotopes at the site of metabolic degradation to improve upon the pharmacokinetics of the parent compound. Areas covered: The authors reviewed the pivotal trials examining the safety and efficacy of deutetrabenazine, as well as long-term data from an open-label extension. Also reviewed were posters and oral presentations, as well as information from the product label and the United States Food and Drug Administration. Expert opinion: Deutetrabenazine is effective at decreasing dyskinesia in TD, but drug selection and cost-effectiveness between existing VMAT2 inhibitors are evolving areas of study. Other areas of investigation include novel anti-dyskinetic agents and use of deep brain stimulation.

VMAT2 inhibitors for the treatment of hyperkinetic movement disorders

Hyperkinetic movement disorders comprise a variety of conditions characterized by involuntary movements, which include but are not limited to tardive dyskinesia, chorea associated with Huntington's Disease, and tic disorders. The class of medications that have been used to treat these conditions includes Vesicular Monoamine Transporter-2 (VMAT2) inhibitors. In 2008, the FDA approved tetrabenazine as a treatment for chorea associated with Huntington's Disease. Optimization of the pharmacology of tetrabenazine has since led to the approval of two new VMAT2 inhibitors, deutetrabenazine and valbenazine. The objective of this review is to provide background on the role of VMAT in monoamine neurotransmission, the mechanism of VMAT2 inhibition on the treatment of hyperkinetic disorders (specifically tardive dyskinesia and chorea associated with Huntington's Disease), the pharmacology and pharmacokinetics of the commercially available VMAT2 inhibitors, and a summary of the clinical data to support application of these medications.

Real-World Experience With VMAT2 Inhibitors

OBJECTIVES

The aim of this study was to review our "real-world" experience with the vesicular monoamine transporter 2 (VMAT2) inhibitors tetrabenazine (TBZ), deutetrabenazine (DTBZ), and valbenazine (VBZ) for treatment of hyperkinetic movement disorders. Access and adherence to VMAT2 inhibitors may be limited by insurance and regulatory issues, inexperience with their use by the prescribing physician, lack of efficacy, or side effects.

METHODS

We performed a retrospective chart review, supplemented with a questionnaire, of all our patients treated with a VMAT2 inhibitor between January 1, 2017, and August 30, 2018.

RESULTS

We identified 135 patients (57.8% male) and 178 prescriptions for VMAT2 inhibitors (TBZ, n = 45 [25.3%]; DTBZ, n = 104 [58.4%]; VBZ, n = 29 [16.3%]). Tourette syndrome/tics was the most common diagnosis (n = 67 [49.6%]) for which VMAT2 inhibitors were prescribed. The VMAT2 inhibitor mean treatment durations (range; SD) and daily dosages (range; SD) were as follows: TBZ (n = 31), 5.1 months (1-19; 3.9) at 48.8 mg (12.5-112.5; 29.6); DTBZ (n = 51), 8.0 months (0.25-16.5; 4.4) at 34.4 mg (6-96; 20.7); and VBZ (n = 20), 6.0 months (0.1-16; 5.6) at 64 mg (40-160; 35.3). The VMAT2 inhibitors effectively controlled hyperkinetic movement disorders as measured by a 1- to 4-point Likert scale (1 = normal or mildly ill, 4 = severely ill) comparing illness severity before starting and while on treatment (score of 1 in 13.0%-26.7% vs 60.9%-71.9% of patients). Side effects were mild and improved or resolved following dose reduction, drug cessation, or addition of adjunctive medications.

CONCLUSIONS

The VMAT2 inhibitors are effective and safe in a range of hyperkinetic movement disorders but are not readily accessible by patients in the United States for indications not approved by the Food and Drug Administration.

Tardive Dyskinesia: New Treatments Available

Tardive dyskinesia (TD), the choreoathetoid movements of fingers, arms, legs, and trunk and irregular stereotypical movements of the mouth, face, and tongue, has been the scourge of antipsychotic medications since the approval of chlorpromazine. TD tends to occur late in treatment and sometimes remains after discontinuation of the antipsychotic medication. With the recent approval of two medications, valbenazine (Ingrezza^®) and deutetrabenazine (Austedo^®), there are now treatments for this disfiguring consequence of dopamine-blocking medications. The current article distinguishes the movement disorder adverse effects of dopamine antagonists, explains the putative mechanism of action, and describes how best to treat TD with the new vesicular monamine transporter 2 (VMAT2) medications now approved by the U.S. Food and Drug Administration. [Journal of Psychosocial Nursing and Mental Health Services, 57(5), 11-14.].

Deutetrabenazine in the treatment of tardive dyskinesia

Tardive dyskinesia is a common movement disorder in the population of patients taking dopamine receptor blocking agents, such as antipsychotics and certain antiemetics, which likely lead to D2-receptor upregulation and hypersensitization. Efficacious and well-tolerated treatments are now available to reduce symptoms. Deutetrabenazine, a reversible inhibitor of vesicular monoamine transporter 2, was US FDA-approved for treatment of tardive dyskinesia in 2017. Two pivotal clinical trials, Aim to Reduce Movements in Tardive Dyskinesia (ARM-TD) and Addressing Involuntary Movements in Tardive Dyskinesia (AIM-TD), provide evidence that deutetrabenazine dosed 24-48 mg/day effectively controlled involuntary movements according to rating scales. Adverse events that occurred more frequently in the deutetrabenazine group (rate >2%) compared with placebo were nasopharyngitis and insomnia. Interim results of a long-term open-label study show continued efficacy and good tolerability, even in combination with baseline dopamine receptor blocking agents.

Current treatment of tardive dyskinesia

Tardive dyskinesia (TD) is a common, iatrogenic movement disorder affecting many individuals treated with dopamine-receptor blocking agents (DRBAs). Studying treatment of TD can be complex, as the symptoms can be affected by changes in either dosage or type of DRBA, as well as by the variable natural course of the disease. Historically many pharmacological therapies have been studied in TD, finding varying degrees of treatment success. Most recently, the VMAT2 inhibitors valbenazine and deutetrabenazine were rigorously studied in TD in large, phase III clinical trials, and were shown to be beneficial in this population. In this article, we will review various treatments of TD, including manipulation of the offending agent, VMAT2 inhibitors, other non-VMAT2-inhibiting medications, and non-pharmacological approaches.