Mechanism of Action
Non-clinical studies have shown that desvenlafaxine succinate is a potent and selective serotonin and norepinephrine reuptake inhibitor (SNRI). The clinical efficacy of desvenlafaxine succinate is thought to be related to the potentiation of these neurotransmitters in the central nervous system.
Desvenlafaxine lacked significant affinity for numerous receptors, including muscarinic-cholinergic, H1-histaminergic, or α1-adrenergic receptors in vitro. Pristiq also lacked monoamine oxidase (MAO) inhibitory activity.
The single-dose pharmacokinetics of desvenlafaxine are linear and dose-proportional in a dose range of 100 to 600 mg/day. The mean terminal half-life, t1/2, is approximately 11 hours. With once-daily dosing, steady-state plasma concentrations are achieved within approximately 4-5 days. At steady-state, multiple-dose accumulation of desvenlafaxine is linear and predictable from the single-dose pharmacokinetic profile.
Absorption and Distribution
The absolute oral bioavailability of Pristiq after oral administration is about 80%. Mean time to peak plasma concentrations (Tmax) is about 7.5 hours after oral administration.
A food-effect study involving administration of Pristiq to healthy subjects under fasting and fed conditions (high-fat meal) indicated that the Cmax was increased about 16% in the fed state, while the AUCs were similar. This difference is not clinically significant; therefore, Pristiq can be taken without regard to meals [ see Dosage and Administration (2.1) ].
The plasma protein binding of desvenlafaxine is low (30%) and is independent of drug concentration. The desvenlafaxine volume of distribution at steady-state following intravenous administration is 3.4 L/kg, indicating distribution into nonvascular compartments.
Metabolism and Elimination
Desvenlafaxine is primarily metabolized by conjugation (mediated by UGT isoforms) and, to a minor extent, through oxidative metabolism. CYP3A4 is the cytochrome P450 isozyme mediating the oxidative metabolism (N-demethylation) of desvenlafaxine. The CYP2D6 metabolic pathway is not involved, and after administration of 100 mg, the pharmacokinetics of desvenlafaxine was similar in subjects with CYP2D6 poor and extensive metabolizer phenotype. Approximately 45% of desvenlafaxine is excreted unchanged in urine at 72 hours after oral administration. Approximately 19% of the administered dose is excreted as the glucuronide metabolite and < 5% as the oxidative metabolite (N,O-didesmethylvenlafaxine) in urine.
In a study of healthy subjects administered doses of up to 300 mg, there was an approximate 32% increase in Cmax and a 55% increase in AUC in subjects older than 75 years of age (n = 17), compared with subjects 18 to 45 years of age (n = 16). Subjects 65 to 75 years of age (n = 15) had no change in Cmax, but an approximately 32% increase in AUC, compared to subjects 18 to 45 years of age [ see Dosage and Administration (2.2) ].
In a study of healthy subjects administered doses of up to 300 mg, women had an approximately 25% higher Cmax and an approximately 10% higher AUC than age-matched men. No adjustment of dosage on the basis of gender is needed.
Pharmacokinetic analysis showed that race (White, n = 466; Black, n = 97; Hispanic, n = 39; Other, n = 33) had no apparent effect on the pharmacokinetics of Pristiq. No adjustment of dosage on the basis of race is needed.
The disposition of desvenlafaxine succinate after administration of 100 mg was studied in subjects with mild (Child‑Pugh A, n = 8), moderate (Child‑Pugh B, n = 8), and severe (Child‑Pugh C, n = 8) hepatic impairment and to healthy subjects (n = 12).
Average AUC was increased by approximately 31% and 35% in patients with moderate and severe hepatic impairment, respectively, as compared to healthy subjects. Average AUC values were similar in subjects with mild hepatic impairment and healthy subjects (< 5% difference).
Systemic clearance (CL/F) was decreased by approximately 20% and 36% in patients with moderate and severe hepatic impairment, respectively, as compared to healthy subjects. CL/F values were comparable in mild hepatic impairment and healthy subjects (< 5% difference).
The mean t1/2 changed from approximately 10 hours in healthy subjects and subjects with mild hepatic impairment to 13 and 14 hours in moderate and severe hepatic impairment, respectively. No adjustment in starting dosage is necessary for patients with hepatic impairment.
The disposition of desvenlafaxine after administration of 100 mg was studied in subjects with mild (n = 9), moderate (n = 8), severe (n = 7) and end-stage renal disease [ESRD] (n = 9) requiring dialysis and in healthy, age-matched control subjects (n = 8). Elimination was significantly correlated with creatinine clearance. Increases in AUCs of about 42% in mild renal impairment (24‑hr CrCl = 50‑80 mL/min), about 46% in moderate renal impairment (24‑hr CrCl = 30‑50 mL/min), about 108% in severe renal impairment (24‑hr CrCl ≤ 30 mL/min), and about 116% in ESRD subjects were observed, compared with healthy, age-matched control subjects.
The mean terminal half-life (t1/2) was prolonged from 11.1 hours in the control subjects to approximately 13.5, 15.5, 17.6, and 22.8 hours in mild, moderate, severe renal impairment and ESRD subjects, respectively. Less than 5% of the drug in the body was cleared during a standard 4-hour hemodialysis procedure.
Dosage adjustment (every other day dosing) is recommended in patients with significant impairment of renal function [ see Dosage and Administration (2.2) and Use in Specific Populations (8.6) ].
Carcinogenesis, Mutagenesis, Impairment of Fertility
Desvenlafaxine succinate administered by oral gavage to mice and rats for 2 years did not increase the incidence of tumors in either study.
Mice received desvenlafaxine succinate at dosages up to 500/300 mg/kg/day (dosage lowered after 45 weeks of dosing). The 300 mg/kg/day dose is 15 times a human dose of 100 mg/day on a mg/m2 basis.
Rats received desvenlafaxine succinate at dosages up to 300 mg/kg/day (males) or 500 mg/kg/day (females). The highest dose is 29 (males) or 48 (females) times a human dose of 100 mg/day on a mg/m2 basis.
Desvenlafaxine was not mutagenic in the in vitro bacterial mutation assay (Ames test) and was not clastogenic in an in vitro chromosome aberration assay in cultured CHO cells, an in vivo mouse micronucleus assay, or an in vivo chromosome aberration assay in rats. Additionally, desvenlafaxine was not genotoxic in the in vitro CHO mammalian cell forward mutation assay and was negative in the in vitro BALB/c-3T3 mouse embryo cell transformation assay.
Impairment of fertility
Reduced fertility was observed in a study in which both male and female rats received desvenlafaxine succinate. This effect was noted at oral doses approximately 10 times a human dose of 100 mg/day on a mg/m2 basis. There was no effect on fertility at oral doses approximately 3 times a human dose of 100 mg/day on a mg/m2 basis.