CLINICAL PHARMACOLOGY
Mechanism of Action
The exact mechanism of the antidepressant action of levomilnacipran is unknown, but is thought to be related to the potentiation of serotonin and norepinephrine in the central nervous system, through inhibition of reuptake at serotonin and norepinephrine transporters. Non-clinical studies have shown that levomilnacipran is a potent and selective serotonin and norepinephrine reuptake inhibitor (SNRI).
Pharmacodynamics
Levomilnacipran binds with high affinity to the human serotonin (5-HT) and norepinephrine (NE) transporters (Ki = 11 and 91 nM, respectively) and potently inhibits 5-HT and NE reuptake (IC50 = 16-19 and 11 nM, respectively). Levomilnacipran lacks significant affinity for any other receptors, ion channels or transporters tested in vitro, including serotonergic (5HT1-7), α- and β- adrenergic, muscarinic, or histaminergic receptors and Ca2+, Na+, K+ or Cl- channels. Levomilnacipran did not inhibit monoamine oxidase (MAO).
Cardiovascular Electrophysiology
At a dose 2.5 times the maximum recommended dose, levomilnacipran does not prolong QTc to any clinically relevant extent.
Pharmacokinetics
The concentration of levomilnacipran at steady state is proportional to dose when administered from 25 to 300 mg once daily. Following an oral administration, the mean apparent total clearance of levomilnacipran is 21-29 L/h. Steady-state concentrations of levomilnacipran are predictable from single-dose data. The apparent terminal elimination half-life of levomilnacipran is approximately 12 hours. After daily dosing of FETZIMA 120 mg, the mean Cmax value is 341 ng/mL, and the mean steady-state AUC value is 5196 ng·h/mL. Interconversion between levomilnacipran and its stereoisomer does not occur in humans.
Absorption
The relative bioavailability of levomilnacipran after administration of FETZIMA ER was 92% when compared to oral solution. Levomilnacipran concentration was not significantly affected when FETZIMA was administered with food.
The median time to peak concentration (Tmax) of levomilnacipran is 6-8 hours after oral administration.
Distribution
Levomilnacipran is widely distributed with an apparent volume of distribution of 387-473 L; plasma protein binding is 22% over concentration range of 10 to 1000 ng/mL.
Metabolism
Levomilnacipran undergoes desethylation to form desethyl levomilnacipran and hydroxylation to form p-hydroxy-levomilnacipran. Both oxidative metabolites undergo further conjugation with glucuronide to form conjugates. The desethylation is catalyzed primarily by CYP3A4 with minor contribution by CYP2C8, 2C19, 2D6, and 2J2 [see Drug Interactions (7.4, 7.5)].
Elimination/Excretion
Levomilnacipran and its metabolites are eliminated primarily by renal excretion. Following oral administration of 14C-levomilnacipran solution, approximately 58% of the dose is excreted in urine as unchanged levomilnacipran. N-desethyl levomilnacipran is the major metabolite excreted in the urine and accounted for approximately 18% of the dose. Other identifiable metabolites excreted in the urine are levomilnacipran glucuronide (4%), desethyl levomilnacipran glucuronide (3%), p-hydroxy levomilnacipran glucuronide (1%), and p-hydroxy levomilnacipran (1%). The metabolites are inactive [see Dosage and Administration].
NONCLINICAL TOXICOLOGY
Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenesis
Levomilnacipran administered by oral gavage to rats for 2 years and Tg.rasH2 mice for 6 months did not increase the incidence of tumors in either study.
Rats received levomilnacipran at doses up to 90/70 mg/kg/day (the dose was lowered in males after 45 weeks of dosing). The 90 mg/kg/day dose is 7 times the maximum recommended human dose (MRHD) of 120 mg on a mg/m2 basis.
Tg.rasH2 mice received levomilnacipran at doses up to 150 mg/kg/day. This dose is 6 times the MRHD.
Mutagenesis
Levomilnacipran was not mutagenic in the in vitro bacterial mutation assay (Ames test) and was not clastogenic in an in vivo micronucleus assay in rats. Additionally, levomilnacipran was not genotoxic in the in vitro mouse lymphoma (L5178Y TK+/-) cell forward mutation assay.
Impairment of Fertility
When levomilnacipran was administered orally to male and female rats before mating, through mating and up to Day 7 of gestation at doses up to 100 mg/kg/day, no effects were observed on fertility. This dose is 8 times the MRHD.
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