12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
The exact mechanism of the antidepressant action of desvenlafaxine is unknown, but is thought to be related to the potentiation of serotonin and norepinephrine in the central nervous system, through inhibition of their reuptake. Non-clinical studies have shown that desvenlafaxine is a potent and selective serotonin and norepinephrine reuptake inhibitor (SNRI).
Desvenlafaxine lacked significant affinity for numerous receptors, including muscarinic-cholinergic, H1-histaminergic, or α1-adrenergic receptors in vitro. Desvenlafaxine also lacked monoamine oxidase (MAO) inhibitory activity.
Electrocardiograms were obtained from 1,492 desvenlafaxine treated patients with major depressive disorder and 984 placebo-treated patients in clinical studies lasting up to 8 weeks. No clinically relevant differences were observed between desvenlafaxine treated and placebo-treated patients for QT, QTc, PR, and QRS intervals. In a thorough QTc study with prospectively determined criteria, desvenlafaxine did not cause QT prolongation. No difference was observed between placebo and desvenlafaxine treatments for the QRS interval.
The single-dose pharmacokinetics of desvenlafaxine are linear and dose-proportional in a dose range of 50 to 600 mg (1 to 12 times the recommended approved dosage) per day. With once-daily dosing, steady-state plasma concentrations are achieved within approximately 4 to 5 days. At steady-state, multiple-dose accumulation of desvenlafaxine is linear and predictable from the single-dose pharmacokinetic profile.
The absolute oral bioavailability of PRISTIQ after oral administration is about 80%.
Steady-state volume of distribution of desvenlafaxine is 3.4 L/kg. Plasma protein binding of desvenlafaxine is 30% and is independent of drug concentration.
Desvenlafaxine is primarily metabolized by conjugation (mediated by UGT isoforms) and, to a minor extent, through oxidative metabolism. CYP3A4 mediates the oxidative metabolism (N-demethylation) of desvenlafaxine. The CYP2D6 metabolic pathway is not involved. The pharmacokinetics of desvenlafaxine was similar in subjects with CYP2D6 poor and extensive metabolizer phenotype.
No clinically significant differences in the exposures of desvenlafaxine were observed based on ethnicity (White, Black, Hispanic).
The effect of intrinsic patient factors on the pharmacokinetics of desvenlafaxine is presented in Figure 1.
|Figure 1 Impact of Intrinsic Factors (Renal, Hepatic Impairment and Population Description) on Desvenlafaxine Pharmacokinetics|
Drug Interaction Studies
Other Drugs on PRISTIQ
The effect of ketoconazole on the exposures of desvenlafaxine is summarized in Figure 2.
|Figure 2. Effect of Other Drugs on Desvenlafaxine Pharmacokinetics|
In Vitro Studies
Based on in vitro data, drugs that inhibit CYP isozymes 1A1, 1A2, 2A6, 2D6, 2C8, 2C9, 2C19, and 2E1 are not expected to have significant impact on the pharmacokinetic profile of desvenlafaxine.
Desvenlafaxine does not inhibit CYP1A2, 2A6, 2C8, 2C9, 2C19 CYP2D6, or CYP3A4 isozymes. Desvenlafaxine does not induce CYP3A4 either.
Desvenlafaxine is not a substrate or an inhibitor for the P-glycoprotein (P-gp) transporter.