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Pharmacology: Mechanism of action: The mechanism of action of valbenazine in the treatment of tardive dyskinesia is unclear, but is thought to be mediated through the reversible inhibition of VMAT2, a transporter that regulates monoamine uptake from the cytoplasm to the synaptic vesicle for storage and release.
Pharmacodynamics: Valbenazine inhibits human VMAT2 (Ki~150 nM) with no appreciable binding affinity for VMAT1 (Ki>10 μM). Valbenazine is converted to the active metabolite [+]-α-dihydrotetrabenazine ([+]-α-HTBZ). [+]-α-HTBZ also binds with relatively high affinity to human VMAT2 (Ki~3 nM). Valbenazine and [+]-α- HTBZ have no appreciable binding affinity (Ki>5000 nM) for dopaminergic (including D2), serotonergic (including 5HT2B), adrenergic, histaminergic or muscarinic receptors.
Cardiac Electrophysiology: REMLEAS may cause an increase in the corrected QT interval in patients who are CYP2D6 poor metabolizers or who are taking a strong CYP2D6 or CYP3A4 inhibitor. An exposure-response analysis of clinical data from the healthy volunteer studies revealed increased QTc interval with higher plasma concentrations of the active metabolite [see Precautions].
Efficacy/Clinical studies: A randomized, double-blind, placebo-controlled trial of REMLEAS was conducted in patients with moderate to severe tardive dyskinesia as determined by clinical observation. Patients had underlying schizophrenia, schizoaffective disorder, or a mood disorder. Individuals at significant risk for suicidal or violent behavior and individuals with unstable psychiatric symptoms were excluded.
The Abnormal Involuntary Movement Scale (AIMS) was the primary efficacy measure for the assessment of tardive dyskinesia severity. The AIMS is a 12-item scale; items 1 to 7 assess the severity of involuntary movements across body regions and these items were used in this study. Each of the 7 items was scored on a 0 to 4 scale, rated as: 0=no dyskinesia; 1=low amplitude, present during some but not most of the exam; 2=low amplitude and present during most of the exam (or moderate amplitude and present during some of the exam); 3=moderate amplitude and present during most of exam; or 4=maximal amplitude and present during most of exam. The AIMS dyskinesia total score (sum of items 1 to 7) could thus range from 0 to 28, with a decrease in score indicating improvement. The AIMS was scored by central raters who interpreted the videos blinded to subject identification, treatment assignment, and visit number.
The primary efficacy endpoint was the mean change from baseline in the AIMS dyskinesia total score at the end of Week 6. The change from baseline for two fixed doses of REMLEAS (40 mg or 80 mg) was compared to placebo. At the end of Week 6, subjects initially assigned to placebo were re-randomized to receive REMLEAS 40 mg or 80 mg. Subjects originally randomized to REMLEAS continued REMLEAS at their randomized dose. Follow-up was continued through Week 48 on the assigned drug, followed by a 4-week period off-drug (subjects were not blind to withdrawal).
A total of 234 subjects were enrolled, with 29 (12%) discontinuing prior to completion of the placebo-controlled period. Mean age was 56 (range 26 to 84). Patients were 54% male and 46% female. Patients were 57% Caucasian, 38% African-American, and 5% other. Concurrent diagnoses included schizophrenia/schizoaffective disorder (66%) and mood disorder (34%). With respect to concurrent antipsychotic use, 70% of subjects were receiving atypical antipsychotics, 14% were receiving typical or combination antipsychotics, and 16% were not receiving antipsychotics.
Results are presented in Table 1, with the distribution of responses shown in Figure 1. The change from baseline in the AIMS total dyskinesia score in the 80 mg REMLEAS group was statistically significantly different from the change in the placebo group. Subgroup analyses by gender, age, racial subgroup, underlying psychiatric diagnostic category, and concomitant antipsychotic medication did not suggest any clear evidence of differential responsiveness.
The mean changes in the AIMS dyskinesia total score by visit are shown in Figure 2. Among subjects remaining in the study at the end of the 48-week treatment (N=123 [52.6%]), following discontinuation of REMLEAS, the mean AIMS dyskinesia total score appeared to return toward baseline (there was no formal hypothesis testing for the change following discontinuation). (See Table 1 and Figures 1 and 2.)
Click on icon to see table/diagram/image
Click on icon to see table/diagram/image
Click on icon to see table/diagram/imagePharmacokinetics: Valbenazine and its active metabolite ([+]-α-HTBZ) demonstrate approximate proportional increases for the area under the plasma concentration versus time curve (AUC) and maximum plasma concentration (Cmax) after single oral doses from 40 mg to 300 mg (i.e., 50% to 375% of the recommended treatment dose).
Absorption: Following oral administration, the time to reach maximum valbenazine plasma concentration (tmax) ranges from 0.5 to 1.0 hours. Valbenazine reaches steady state plasma concentrations within 1 week. The absolute oral bioavailability of valbenazine is approximately 49%. [+]-α-HTBZ gradually forms and reaches Cmax 4 to 8 hours after administration of REMLEAS.
Ingestion of a high-fat meal decreases valbenazine Cmax by approximately 47% and AUC by approximately 13%. [+]-α-HTBZ Cmax and AUC are unaffected.
Distribution: The plasma protein binding of valbenazine and [+]-α-HTBZ are greater than 99% and approximately 64%, respectively. The mean steady state volume of distribution of valbenazine is 92 L.
Nonclinical data in Long-Evans rats show that valbenazine can bind to melanin-containing structures of the eye such as the uveal tract. The relevance of this observation to clinical use of REMLEAS is unknown.
Elimination: Valbenazine has a mean total plasma systemic clearance value of 7.2 L/hr. Valbenazine and [+]-α-HTBZ have half-lives of 15 to 22 hours.
Metabolism: Valbenazine is extensively metabolized after oral administration by hydrolysis of the valine ester to form the active metabolite ([+]-α-HTBZ) and by oxidative metabolism, primarily by CYP3A4/5, to form mono-oxidized valbenazine and other minor metabolites. [+]-α-HTBZ appears to be further metabolized in part by CYP2D6.
The results of in vitro studies suggest that valbenazine and [+]-α-HTBZ are unlikely to inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2E1 or CYP3A4/5, or induce CYP1A2, CYP2B6 or CYP3A4/5 at clinically relevant concentrations.
The results of in vitro studies suggest that valbenazine and [+]-α-HTBZ are unlikely to inhibit the transporters (BCRP, OAT1, OAT3, OCT2, OATP1B1, or OATP1B3) at clinically relevant concentrations.
Excretion: Following the administration of a single 50-mg oral dose of radiolabeled C-valbenazine (i.e., ~63% of the recommended treatment dose), approximately 60% and 30% of the administered radioactivity was recovered in the urine and feces, respectively. Less than 2% was excreted as unchanged valbenazine or [+]-α-HTBZ in either urine or feces.
Specific Populations: Exposures of valbenazine in patients with hepatic and Severe Renal impairment are summarized in Figure 3. (See Figure 3.)
Click on icon to see table/diagram/imageAfter administration of valbenazine 50 mg, subjects with mild hepatic impairment had little or no effect on Cmax of valbenazine or NBI-98782 (Metabolite formed from hydrolysis of valbenazine). Administration in subjects with hepatic impairment resulted in valbenazine and NBI-98782 Cmax and AUC0-∞ of approximately 2- to 3-fold greater in subjects with moderate and severe hepatic impairment than in subjects with normal hepatic function.
Administration of valbenazine 40 mg to subjects with severe renal impairment had little or no effect on Cmax or AUC0-∞ of valbenazine or NBI-98782 compared to subjects with normal renal function.
Drug Interaction Studies: The effects of paroxetine, ketoconazole and rifampin on the exposure of valbenazine are summarized in Figure 4. (See Figure 4.)
Click on icon to see table/diagram/imageCoadministration with rifampin (strong CYP3A4/5 inducer): Coadministration of valbenazine and rifampin led to an approximate 30% decrease in Cmax and an approximate 70% decrease in AUC0-∞ of valbenazine compared with administration of valbenazine alone. Concomitant administration of valbenazine and rifampin also led to an approximate 50% decrease in Cmax and an approximate 80% decrease in AUC0-∞ of the active metabolite NBI-98782 compared with administration of valbenazine alone.
Coadministration with ketoconazole (strong CYP3A4/5 inhibitor): Coadministration of valbenazine and ketoconazole led to a Cmax and AUC0-∞ of valbenazine 1.5-fold and 2.1-fold, respectively, compared with administration of valbenazine alone. Administration of valbenazine plus ketoconazole also led to a Cmax and AUC0-∞ of the active metabolite NBI-98782 1.6-fold and 2.1-fold, compared with administration of valbenazine alone.
Coadministration with paroxetine (strong CYP2D6 inhibitor): Coadministration of valbenazine and paroxetine led to a 24% and 9% reduction in Cmax and AUC0-∞, respectively, of valbenazine compared with administration of valbenazine alone. Coadministration of valbenazine and paroxetine led to a Cmax and AUC0-∞ of the active metabolite NBI-98782 of 1.4-fold and 1.9-fold, respectively, compared with administration of valbenazine alone.
The effects of valbenazine on the exposure of other coadministered drugs are summarized in Figure 5. (See Figure 5.)
Click on icon to see table/diagram/imageCoadministration with digoxin (sensitive P-gp substrate): Coadministration of valbenazine 80 mg and 0.5 mg digoxin resulted in an approximate 1.9-fold increase in the Cmax of digoxin. The effect of valbenazine on digoxin AUC0-∞ was modest (1.4-fold increase) and the mean t½ of digoxin was similar with and without valbenazine administration.
Coadministration with midazolam (CYP3A4 substrate): Midazolam Cmax and AUC0-∞ were similar with and without valbenazine administration. Median midazolam tmax was the same (0.50 hours) with and without valbenazine administration. The mean t½ of midazolam was similar with and without valbenazine administration (4.7 and 4.5 hours, respectively).
Toxicology: Preclinical safety data: Carcinogenesis: Valbenazine did not increase tumors in rats treated orally for 91 weeks at 0.5, 1, and 2 mg/kg/day. These doses are <1 times (0.06, 0.1, and 0.24 times, respectively) the MRHD of 80 mg/day based on mg/m2.
Valbenazine did not increase tumors in hemizygous Tg.rasH2 mice treated orally for 26 weeks at 10, 30 and 75 mg/kg/day, which are 0.6, 1.9 and 4.6 times the MRHD of 80 mg/day based on mg/m2.
Mutagenesis: Valbenazine was not mutagenic in the in vitro bacterial reverse mutation test (Ames) or clastogenic in the in vitro mammalian chromosomal aberrations assay in human peripheral blood lymphocytes or in the in vivo rat bone marrow micronucleus assay.
Impairment of Fertility: In a fertility study, rats were treated orally with valbenazine at 1, 3, and 10 mg/kg/day prior to mating and through mating, for a minimum of 10 weeks (males) or through Day 7 of gestation (females). These doses are 0.1, 0.4, and 1.2 times the MRHD of 80 mg/day based on mg/m2, respectively. Valbenazine delayed mating in both sexes, which led to lower number of pregnancies and disrupted estrous cyclicity at the high dose, 1.2 times the MRHD of 80 mg/day based on mg/m2. Valbenazine had no effects on sperm parameters (motility, count, density) or on uterine parameters (corpora lutea, number of implants, viable implants, pre-implantation loss, early resorptions and post-implantation loss) at any dose.
