CLINICAL PHARMACOLOGY
Mechanism Of Action
The mechanism of action of valbenazine in the treatment
of tardive dyskinesia is unknown, but is thought to be mediated through the
reversible inhibition of vesicular monoamine transporter 2 (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 [+]-αHTBZ have no appreciable
binding affinity (Ki > 5000 nM) for dopaminergic (including D2),
serotonergic (including 5HT2B), adrenergic, histaminergic or muscarinic receptors.
Cardiac Electrophysiology
INGREZZA 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 two healthy volunteer studies revealed increased QTc interval with
higher plasma concentrations of the active metabolite. Based on this model,
patients taking an INGREZZA 80 mg dose with increased exposure to the
metabolite (e.g., being a CYP2D6 poor metabolizer) may have a mean QT
prolongation of 11.7 msec (14.7 msec upper bound of double-sided 90% CI) as
compared to otherwise healthy volunteers given INGREZZA, who had a mean QT
prolongation of 6.7 msec (8.4 msec) [see WARNINGS AND PRECAUTIONS].
Pharmacokinetics
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 INGREZZA.
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 INGREZZA 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.
Studies In Specific Populations
Exposures of valbenazine in patients with hepatic
impairment are summarized in Figure 1.
Figure 1: Effects of Hepatic Impairment on Valbenazine
Pharmacokinetics
AUCinf=area under the plasma concentration versus time
curve from 0 hours extrapolated to infinity
[+]-α-HTBZ=[+]-α-dihydrotetrabenazine (active metabolite)
Drug Interaction Studies
The effects of ketoconazole and rifampin on the exposure
of valbenazine are summarized in Figure 2.
Figure 2: Effects of Strong CYP3A4 Inducers and
Inhibitors on Valbenazine Pharmacokinetics
AUCinf=area under the plasma concentration versus time
curve from 0 hours extrapolated to infinity
[+]-α-HTBZ=[+]-α-dihydrotetrabenazine (active metabolite)
The effects of valbenazine on the exposure of other
coadministered drugs are summarized in Figure 3.
Figure 3: Effects of Valbenazine on Pharmacokinetics
of Other Drugs
AUC inf=area under the plasma concentration versus time
curve from 0 hours extrapolated to infinity
Clinical Studies
A randomized, double-blind, placebo-controlled trial of
INGREZZA 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 INGREZZA (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 INGREZZA 40 mg or 80 mg. Subjects originally
randomized to INGREZZA continued INGREZZA 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 3, with the distribution
of responses shown in Figure 4. The change from baseline in the AIMS total
dyskinesia score in the 80 mg INGREZZA 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 5. Among subjects remaining in the study at the end
of the 48-week treatment (N=123 [52.6%]), following discontinuation of
INGREZZA, the mean AIMS dyskinesia total score appeared to return toward
baseline (there was no formal hypothesis testing for the change following
discontinuation).
Table 3: Primary Efficacy Endpoint – Severity of Tardive
Dyskinesia at Baseline and the End of Week 6
Endpoint |
Treatment Group |
Mean Baseline Score (SD) |
LS Mean Change from Baseline (SEM)** |
Placebo-subtracted Difference (95% CI) |
AIMS Dyskinesia Total Score |
INGREZZA 40 mg |
9.8 (4.1) |
-1.9 (0.4) |
-1.8 (-3.0, -0.7) |
INGREZZA 80 mg* |
10.4 (3.6) |
-3.2 (0.4) |
-3.1 (-4.2, -2.0) |
Placebo |
9.9 (4.3) |
-0.1 (0.4) |
|
LS Mean=least-squares mean; SD=standard deviation;
SEM=standard error of the mean; CI=2-sided 95% confidence interval *Dose that
was statistically significantly different from placebo after adjusting for
multiplicity.
**A negative change from baseline indicates improvement. |
Figure 4: Percent of Patients with Specified Magnitude
of AIMS Total Score Improvement at the End of Week 6
ITT=Intent to Treat; This analysis set includes all
randomized patients who had a baseline and at least one post-baseline AIMS
dyskinesia total score value reported.
Figure 5: AIMS Dyskinesia Total Score Mean Change from
Baseline – Entire Study Duration (Arithmetic Mean)
DB=Double-Blind; After Week 6, subjects initially
receiving placebo were re-randomized to receive INGREZZA 40 mg or 80 mg until
the end of Week 48. Error bars represent ±1 Standard Error of the Mean (SEM).