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Mechanism of action
The mechanism of the antidepressant effect of vilazodone is not fully understood but is thought to be related to its enhancement of serotonergic activity in the CNS through selective inhibition of serotonin reuptake. Vilazodone is also a partial agonist at serotonergic 5-HT1A receptors; however, the net result of this action on serotonergic transmission and its role in vilazodone's antidepressant effect are unknown.
Vilazodone binds with high affinity to the serotonin reuptake site (Ki= 0.1 nM), but not to the norepinephrine (Ki=56 nM) or dopamine (Ki=37 nM) reuptake sites. Vilazodone potently and selectively inhibits reuptake of serotonin (IC50= 1.6 nM). Vilazodone also binds selectively with high affinity to 5-HT1A receptors (IC50=2.1 nM) and is a 5-HT1A receptor partial agonist.
Thorough QT Study: Treatment with VIIBRYD did not prolong the QTc interval. The effect of vilazodone (20, 40, 60, and 80 mg) on the QTc interval was evaluated in a randomized, placebo-, and active-controlled (moxifloxacin 400 mg), parallel-group, thorough QTc study in 157 healthy subjects. The study demonstrated an ability to detect small effects. The upper bound of the 90% confidence interval for the largest placebo-adjusted, baseline-corrected QTc interval was below 10 msec, based on the individual correction method (QTcI). This is below the threshold for clinical concern. However, it is unknown whether 80 mg is adequate to represent a high clinical exposure condition.
Vilazodone activity is due primarily to the parent drug. The pharmacokinetics of vilazodone (5 mg – 80 mg) are dose-proportional. Accumulation of vilazodone is predictable from single dose data, does not vary with dose, and steady-state is achieved in about 3 days. Elimination of vilazodone is primarily by hepatic metabolism with a terminal half-life of approximately 25 hours. At steady-state, after daily dosing of VIIBRYD 40 mg under fed conditions, the mean Cmax value is 156 ng/mL, and the mean AUC (0-24 hours) value is 1645 ng·h/mL.
Vilazodone concentrations peak at a median of 4-5 hours (Tmax) after administration and decline with a terminal half-life of approximately 25 hours. The absolute bioavailability of vilazodone is 72% with food. Administration of VIIBRYD with food (high fat or light meal) increases oral bioavailability (Cmax increased by approximately 147-160%, and AUC increased by approximately 64-85%).
Coadministration of VIIBRYD with ethanol or with a proton pump inhibitor (pantoprazole) did not affect the rate or extent of vilazodone absorption [see DRUG INTERACTIONS, Figure 1)]. In addition, neither the Tmax nor terminal elimination rate of vilazodone was altered by coadministration with either pantoprazole or ethanol.
Absorption is decreased by approximately 25% if vomiting occurs within 7 hours of ingestion; no replacement dose is needed.
Vilazodone is widely distributed and approximately 96-99% protein-bound
Metabolism and Elimination
VIIBRYD is extensively metabolized through CYP and non- CYP pathways (possibly by carboxylesterase), with only 1% of the dose recovered in the urine and 2% of the dose recovered in the feces as unchanged vilazodone. CYP3A4 is primarily responsible for its metabolism among CYP pathways, with minor contributions from CYP2C19 and CYP2D6. In vitro studies with human microsomes and human hepatocytes indicate that vilazodone is unlikely to inhibit or induce the metabolism of other CYP (except for CYP2C8) substrates; and an in vivo study with probe substrates for CYP2C19, 2D6 and 3A4 showed vilazodone did not alter the pharmacokinetics of the probe substrates. However, an in vivo study with probe substrate for CYP2C19 demonstrated a minor induction of CYP2C19. Strong inhibitors of CYP3A4 (e.g., ketoconazole) can reduce the metabolism of vilazodone in vivo and increase exposure. Conversely, inducers of CYP3A4 can decrease vilazodone exposure [see DRUG INTERACTIONS].
The presence of mild or moderate renal impairment, or mild or moderate hepatic impairment did not affect the apparent clearance of vilazodone.
The efficacy of VIIBRYD as a treatment for major depressive disorder was established in two 8-week, multicenter, randomized, double-blind, placebo-controlled studies in adult (18-70 years of age) outpatients who met the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criteria for MDD. In these studies, patients were titrated over 2 weeks to a dose of 40 mg of VIIBRYD with food (n=436) or placebo (n = 433) once daily. VIIBRYD was superior to placebo in the improvement of depressive symptoms as measured by the mean change from baseline to Week 8 in the Montgomery-Asberg Depression Rating Scale (MADRS) total score. Examination of population subgroups based on age (there were few patients over 65), gender, and race did not reveal any clear evidence of differential responsiveness.
Table 4: Summary of Results for the Primary Efficacy
|Study Number||Primary Endpoint||LS Mean (95% CI)a difference from placebo in change from baseline|
|1||MADRS||-3.2 (-5.2, -1.3)|
|2||MADRS||-2.5 (-4.4, -0.6)|
|a Least Squares Mean (95% Confidence Interval)|
Last reviewed on RxList: 1/10/2013
This monograph has been modified to include the generic and brand name in many instances.
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