Milnacipran is well absorbed after oral administration with an absolute bioavailability of approximately 85% to 90%. The exposure to milnacipran increased proportionally within the therapeutic dose range. It is excreted predominantly unchanged in urine (55%) and has a terminal elimination half-life of about 6 to 8 hours. Steady-state levels are reached within 36 to 48 hours and can be predicted from single-dose data. The active enantiomer, d-milnacipran, has a longer elimination half-life (8 to 10 hours) than the l-enantiomer (4 to 6 hours). There is no interconversion between the enantiomers.
Absorption and Distribution
Milnacipran HCl is absorbed following oral administration with maximum concentrations (Cmax) reached within 2 to 4 hours post dose. Absorption of milnacipran HCl is not affected by food. The absolute bioavailability is approximately 85% to 90%. The mean volume of distribution of milnacipran following a single intravenous dose to healthy subjects is approximately 400 L.
Plasma protein binding is 13%.
Metabolism and Elimination
Milnacipran and its metabolites are eliminated primarily by renal excretion. Following oral administration of 14C-milnacipran hydrochloride, approximately 55% of the dose was excreted in urine as unchanged milnacipran (24% as l-milnacipran and 31% as d-milnacipran). The l-milnacipran carbamoyl-O-glucuronide was the major metabolite excreted in urine and accounted for approximately 17% of the dose; approximately 2% of the dose was excreted in urine as d-milnacipran carbamoyl-O-glucuronide. Approximately 8% of the dose was excreted in urine as the N-desethyl milnacipran metabolite.
Pharmacokinetics in Special Populations
Renal Impairment - Milnacipran pharmacokinetics were evaluated following single oral administration of 50 mg milnacipran HCl to subjects with mild (creatinine clearance [CLcr] 50 to 80 mL/min), moderate (CLcr 30 to 49 mL/min), and severe (CLcr 5 to 29 mL/min) renal impairment and to healthy subjects (CLcr > 80 mL/min). The mean AUC0-∞ increased by 16%, 52%, and 199%, and terminal elimination half-life increased by 38%, 41%, and 122% in subjects with mild, moderate, and severe renal impairment, respectively, compared with healthy subjects.
No dosage adjustment is necessary for patients with mild renal impairment. Caution should be exercised in patients with moderate renal impairment. Dose adjustment is necessary in severe renal impairment patients [see Dosage and Administration (2.2)].
Hepatic Impairment - Milnacipran pharmacokinetics were evaluated following single oral administration of 50 mg milnacipran HCl to subjects with mild (Child-Pugh A), moderate (Child-Pugh B), and severe (Child-Pugh C) hepatic impairment and to healthy subjects. AUC0-∞ and T½ were similar in healthy subjects and subjects with mild and moderate hepatic impairment. However, subjects with severe hepatic impairment had a 31% higher AUC0-∞ and a 55% higher T½ than healthy subjects. Caution should be exercised in patients with severe hepatic impairment.
Elderly - Cmax and AUC parameters of milnacipran were about 30% higher in elderly (> 65 years) subjects compared with young subjects due to age-related decreases in renal function.
No dosage adjustment is necessary based on age unless renal function is severely impaired [see Dosage and Administration (2.2)].
Gender - Cmax and AUC parameters of milnacipran were about 20% higher in female subjects compared with male subjects. Dosage adjustment based on gender is not necessary.
Lactation study - In a pharmacokinetic study, a single, oral dose of 50 mg milnacipran HCl tablet was administered to 8 lactating women who were at least 12 weeks postpartum and weaning their infants. The maximum estimated daily infant dose for milnacipran from breast milk (assuming mean milk consumption of 150 mL/kg/day) was 5% of the maternal dose based on peak plasma concentrations. In most patients, peak concentrations of milnacipran in breast milk were seen within 4 hours after the maternal dose. Because of the limited data regarding infant exposure to milnacipran HCl, caution should be exercised when milnacipran HCl is administered to a nursing woman.
Drug-Drug Interactions
In Vitro Studies
In general, milnacipran, at concentrations that were at least 25 times those attained in clinical trials, did not inhibit human CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 or induce human CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP3A4/5 enzyme systems, indicating a low potential of interactions with drugs metabolized by these enzymes.
In vitro studies have shown that the biotransformation rate of milnacipran by human hepatic microsomes and hepatocytes was low. A low biotransformation was also observed following incubation of milnacipran with cDNA-expressed human CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 isozymes.
In Vivo Studies
The drug interaction studies described in this section were conducted in healthy adult subjects.
Carbamazepine - There were no clinically significant changes in the pharmacokinetics of milnacipran following co-administration of milnacipran HCl (100 mg/day) and carbamazepine (200 mg twice a day). No changes were observed in the pharmacokinetics of carbamazepine or its epoxide metabolite due to co-administration with milnacipran HCl.
Clomipramine - Switching from clomipramine (75 mg once a day) to milnacipran (100 mg/day) without a washout period did not lead to clinically significant changes in the pharmacokinetics of milnacipran. Because an increase in adverse events (e.g., euphoria and postural hypotension) was observed after switching from clomipramine to milnacipran, monitoring of patients during treatment switch is recommended.
Digoxin - There was no pharmacokinetic interaction between milnacipran HCl (200 mg/day) and digoxin (0.2 mg/day Lanoxicaps) following multiple-dose administration to healthy subjects.
Fluoxetine - Switching from fluoxetine (20 mg once a day), a strong inhibitor of CYP2D6 and a moderate inhibitor of CYP2C19, to milnacipran (100 mg/day) without a washout period did not affect the pharmacokinetics of milnacipran.
Lithium - Multiple doses of milnacipran HCl (100 mg/day) did not affect the pharmacokinetics of lithium.
Lorazepam - There was no pharmacokinetic interaction between a single dose of milnacipran HCl (50 mg) and lorazepam (1.5 mg).
Pregabalin - There were no clinically significant changes in the steady-state pharmacokinetics of milnacipran or pregabalin following twice a day co-administration of 50 mg milnacipran and 150 mg pregabalin.
Warfarin - Steady-state milnacipran (200 mg/day) did not affect the pharmacokinetics of R-warfarin and S-warfarin or the pharmacodynamics (as assessed by measurement of prothrombin INR) of a single dose of 25 mg warfarin. The pharmacokinetics of milnacipran HCl was not altered by warfarin.