In patients with cirrhosis of the liver, the clearances of venlafaxine and its active metabolite (ODV) were decreased, thus prolonging the elimination half-lives of these substances. A large degree of intersubject variability was noted. [ See Clinical Pharmacology (12.3). ] A lower dose and individualization of dosing may be necessary [ see Dosage and Administration (2.3) ]. Venlafaxine extended-release tablets, like all drugs effective in the treatment of major depressive disorder, should be used with caution in such patients.
In patients with renal impairment (GFR = 10 to 70 mL/min), the clearances of venlafaxine and its active metabolites were decreased, thus prolonging the elimination half-lives of these substances [ see Clinical Pharmacology (12.3) ]. It is recommended that the total daily dose be reduced by 25% to 50% in patients with renal impairment. Because there was much individual variability in clearance between patients with renal impairment, individualization of dosage may be desirable in some patients. In patients undergoing hemodialysis, it is recommended that the total daily dose be reduced by 50%. [S ee Dosage and Administration (2.3). ] Venlafaxine extended-release tablets, like all drugs effective in the treatment of major depressive disorder, should be used with caution in such patients.
Venlafaxine extended-release tablets (Venlafaxine hydrochloride) are not a controlled substance.
While venlafaxine has not been systematically studied in clinical trials for its potential for abuse, there was no indication of drug-seeking behavior in the clinical trials. However, it is not possible to predict on the basis of premarketing experience the extent to which a CNS active drug will be misused, diverted, and/or abused once marketed. Consequently, physicians should carefully evaluate patients for history of drug abuse and follow such patients closely, observing them for signs of misuse or abuse of venlafaxine (e.g., development of tolerance, incrementations of dose, drug-seeking behavior).
In vitro studies revealed that venlafaxine has virtually no affinity for opiate, benzodiazepine, phencyclidine (PCP), or N-methyl-D-aspartic acid (NMDA) receptors.
Venlafaxine was not found to have any significant CNS stimulant activity in rodents. In primate drug discrimination studies, venlafaxine showed no significant stimulant or depressant abuse liability.
Discontinuation effects have been reported in patients receiving venlafaxine [see Dosage and Administration (2.4) and Warnings and Precautions (5.5)].
Among the patients included in the premarketing evaluation of venlafaxine hydrochloride extended-release capsules, there were 2 reports of acute overdosage with venlafaxine hydrochloride extended-release capsules in major depressive disorder trials, either alone or in combination with other drugs. One patient took a combination of 6 g of venlafaxine hydrochloride extended-release capsules and 2.5 mg of lorazepam. This patient was hospitalized, treated symptomatically, and recovered without any untoward effects. The other patient took 2.85 g of venlafaxine hydrochloride extended-release capsules. This patient reported paresthesia of all four limbs but recovered without sequelae.
There were no reports of acute overdose with venlafaxine hydrochloride extended-release capsules in Social Anxiety Disorder trials.
Among the patients included in the premarketing evaluation with venlafaxine hydrochloride immediate-release tablets, there were 14 reports of acute overdose with venlafaxine, either alone or in combination with other drugs and/or alcohol. The majority of the reports involved ingestion in which the total dose of venlafaxine taken was estimated to be no more than several-fold higher than the usual therapeutic dose. The 3 patients who took the highest doses were estimated to have ingested approximately 6.75 g, 2.75 g, and 2.5 g. The resultant peak plasma levels of venlafaxine for the latter 2 patients were 6.24 and 2.35 μg/mL, respectively, and the peak plasma levels of O-desmethylvenlafaxine were 3.37 and 1.30 μg/mL, respectively. Plasma venlafaxine levels were not obtained for the patient who ingested 6.75 g of venlafaxine. All 14 patients recovered without sequelae. Most patients reported no symptoms. Among the remaining patients, somnolence was the most commonly reported symptom. The patient who ingested 2.75 g of venlafaxine was observed to have 2 generalized convulsions and a prolongation of QTc to 500 msec, compared with 405 msec at baseline. Mild sinus tachycardia was reported in 2 of the other patients.
In postmarketing experience, overdose with venlafaxine has occurred predominantly in combination with alcohol and/or other drugs. The most commonly reported reactions in overdosage include tachycardia, changes in level of consciousness (ranging from somnolence to coma), mydriasis, seizures, and vomiting. Electrocardiogram changes (e.g., prolongation of QT interval, bundle branch block, QRS prolongation), ventricular tachycardia, bradycardia, hypotension, rhabdomyolysis, vertigo, liver necrosis, serotonin syndrome, and death have been reported.
Published retrospective studies report that venlafaxine overdosage may be associated with an increased risk of fatal outcomes compared to that observed with SSRI antidepressant products, but lower than that for tricyclic antidepressants. Epidemiological studies have shown that venlafaxine-treated patients have a higher pre-existing burden of suicide risk factors than SSRI-treated patients. The extent to which the finding of an increased risk of fatal outcomes can be attributed to the toxicity of venlafaxine in overdosage as opposed to some characteristic(s) of venlafaxine-treated patients is not clear. Prescriptions for venlafaxine extended-release tablets should be written for the smallest quantity of tablets consistent with good patient management, in order to reduce the risk of overdose.
Treatment should consist of those general measures employed in the management of overdosage with any antidepressant.
Ensure an adequate airway, oxygenation, and ventilation. Monitor cardiac rhythm and vital signs. General supportive and symptomatic measures are also recommended. Induction of emesis is not recommended. Gastric lavage with a large bore orogastric tube with appropriate airway protection, if needed, may be indicated if performed soon after ingestion or in symptomatic patients.
Activated charcoal should be administered. Due to the large volume of distribution of this drug, forced diuresis, dialysis, hemoperfusion, and exchange transfusion are unlikely to be of benefit. No specific antidotes for venlafaxine are known.
In managing overdosage, consider the possibility of multiple drug involvement. The physician should consider contacting a poison control center for additional information on the treatment of any overdose. Telephone numbers for certified poison control centers are listed in the Physicians’ Desk Reference ® (PDR).
Venlafaxine extended-release tablets (venlafaxine hydrochloride) are extended-release tablets for oral administration that contain venlafaxine hydrochloride, a structurally novel antidepressant. Venlafaxine hydrochloride is a selective serotonin and norepinephrine reuptake inhibitor (SNRI). It is designated (R/S)-1-[2-(dimethylamino)-1-(4-methoxyphenyl)ethyl] cyclohexanol hydrochloride or (±)-1-[α-[(dimethylamino)methyl]-p-methoxybenzyl] cyclohexanol hydrochloride and has the empirical formula of C 17 H 27 NO 2 HCl. Its molecular weight is 313.87. The structural formula is shown below.
Venlafaxine hydrochloride is a off-white to white crystalline solid with a solubility of 572 mg/mL in water (adjusted to ionic strength of 0.2 M with sodium chloride). Its octanol:water (0.2 M sodium chloride) partition coefficient is 0.43.
Venlafaxine extended-release tablets are formulated as extended-release tablet for once-a-day oral administration. Venlafaxine extended-release tablets use osmotic pressure to deliver venlafaxine hydrochloride at a controlled rate over approximately 24 hours. The system, which resembles a conventional tablet in appearance, comprises an osmotically active core surrounded by a semipermeable membrane. The unitary tablet core is composed of the drug and excipients (including the osmotically active components). There is a precision-laser drilled orifice in the semipermeable membrane on the side of the tablet. In an aqueous environment, such as the gastrointestinal tract, water permeates through the membrane into the tablet core, causing the drug to dissolve and the osmotic components to expand. This expansion pushes the drug out through the orifice. The semipermeable membrane controls the rate at which water permeates into the tablet core, which in turn controls the rate of drug delivery. The controlled rate of drug delivery into the gastrointestinal lumen is thus independent of pH or gastrointestinal motility. The function of venlafaxine extended-release tablets depends on the existence of an osmotic gradient between the contents of the core and the fluid in the gastrointestinal tract. Since the osmotic gradient remains constant, drug delivery remains essentially constant.
The biologically inert components of the tablet remain intact during gastrointestinal transit and are eliminated in the feces as an insoluble shell.
Tablets contain Venlafaxine hydrochloride, USP equivalent to 37.5 mg, 75 mg, 150 mg, or 225 mg venlafaxine. Inactive ingredients consist of mannitol, microcrystalline cellulose, povidone, polyethylene glycol, colloidal silicon dioxide, magnesium stearate, cellulose acetate, hypromellose, titanium dioxide and talc.
Each tablet strength also contains black iron oxide, hypromellose and propylene glycol as imprinting ink.
The mechanism of the antidepressant action of venlafaxine in humans is believed to be associated with its potentiation of neurotransmitter activity in the CNS. Preclinical studies have shown that venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV), are potent inhibitors of neuronal serotonin and norepinephrine reuptake and weak inhibitors of dopamine reuptake.
Venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV) have no significant affinity for muscarinic cholinergic, H 1 -histaminergic, or α 1 -adrenergic receptors in vitro. Pharmacologic activity at these receptors is hypothesized to be associated with the various anticholinergic, sedative, and cardiovascular effects seen with other psychotropic drugs. Venlafaxine and ODV do not possess monoamine oxidase (MAO) inhibitory activity.
Steady-state concentrations of venlafaxine and O-desmethylvenlafaxine (ODV) in plasma are attained within 3 days of oral multiple dose therapy. Venlafaxine and ODV exhibited linear kinetics over the dose range of 75 to 450 mg/day. The mean ± SD apparent elimination half-life for venlafaxine and ODV after administration of 75 mg venlafaxine extended-release tablets under fed conditions were 10.7±3.2 hours and 12.5±3.0 hours respectively. Venlafaxine and ODV are minimally bound at therapeutic concentrations to plasma proteins (27% and 30%, respectively).
Absorption and Distribution
Venlafaxine is well absorbed and extensively metabolized in the liver. ODV is the only major active metabolite. On the basis of mass balance studies, at least 92% of a single oral dose of venlafaxine is absorbed. The absolute bioavailability of venlafaxine is about 45%. Administration of 75 mg venlafaxine extended-release tablets under fed conditions resulted in mean ± SD venlafaxine C max of 26.9 ± 13.4 ng/mL and AUC of 1536.3 ± 496.8 ng·hr/mL. T max was 6.3 ± 2.3 hours. ODV mean ± SD C max , AUC, T max after administration of 75 mg venlafaxine extended-release tablets under fed conditions were 97.9 ± 29.4 ng/mL, 2926.0 ± 746.1 ng·hr/mL, and 11.6 ± 2.9 hours, respectively.
Administration of venlafaxine hydrochloride extended-release capsules (150 mg q24 hours)
generally resulted in lower C max (150 ng/mL for Venlafaxine and 260 ng/mL for ODV) and later T max (5.5 hours for Venlafaxine and 9 hours for ODV) than for immediate release venlafaxine tablets (C max ‘s for immediate release 75 mg q12 hours were 225 ng/mL for venlafaxine and 290 ng/mL for ODV; T max ‘s were 2 hours for venlafaxine and 3 hours for ODV). When equal daily doses of venlafaxine were administered as either an immediate release tablet or the extended-release form of venlafaxine, the exposure to both venlafaxine and ODV would be similar for the two treatments. Venlafaxine extended-release tablets would, therefore, provide a slower rate of absorption, but the same extent of absorption compared with the immediate release tablet.
Food did not affect the pharmacokinetic parameters AUC, C max , and T max of venlafaxine or its active metabolite, ODV, after administration of venlafaxine extended-release tablets. Time of administration (AM vs PM) would not affect the pharmacokinetics of venlafaxine and ODV.
Equal doses of venlafaxine hydrochloride extended-release tablets are bioequivalent to Effexor XR capsules when administered under fed conditions.
Metabolism and Excretion
Following absorption, venlafaxine undergoes extensive presystemic metabolism in the liver, primarily to ODV, but also to N-desmethylvenlafaxine, N,O-didesmethylvenlafaxine, and other minor metabolites. In vitro studies indicate that the formation of ODV is catalyzed by CYP2D6; this has been confirmed in a clinical study showing that patients with low CYP2D6 levels (“poor metabolizers”) had increased levels of venlafaxine and reduced levels of ODV compared to people with normal CYP2D6 (“extensive metabolizers”). The differences between the CYP2D6 poor and extensive metabolizers, however, are not expected to be clinically important because the sum of venlafaxine and ODV is similar in the two groups and venlafaxine and ODV are pharmacologically approximately equiactive and equipotent.
Approximately 87% of a venlafaxine dose is recovered in the urine within 48 hours as unchanged venlafaxine (5%), unconjugated ODV (29%), conjugated ODV (26%), or other minor inactive metabolites (27%). Renal elimination of venlafaxine and its metabolites is thus the primary route of excretion.
Age and Gender: A population pharmacokinetic analysis of 404 Venlafaxine-treated patients from two studies involving both b.i.d. and t.i.d. regimens showed that dose-normalized trough plasma levels of either venlafaxine or ODV were unaltered by age or gender differences. Dosage adjustment based on the age or gender of a patient is generally not necessary [ see Dosage and Administration (2) ].
Extensive/Poor Metabolizers: Plasma concentrations of venlafaxine were higher in CYP2D6 poor metabolizers than extensive metabolizers. Because the total exposure (AUC) of venlafaxine and ODV was similar in poor and extensive metabolizer groups, however, there is no need for different venlafaxine dosing regimens for these two groups.
Liver Disease: In 9 subjects with hepatic cirrhosis, the pharmacokinetic disposition of both venlafaxine and ODV was significantly altered after oral administration of venlafaxine. Venlafaxine elimination half-life was prolonged by about 30%, and clearance decreased by about 50% in cirrhotic subjects compared to normal subjects. ODV elimination half-life was prolonged by about 60%, and clearance decreased by about 30% in cirrhotic subjects compared to normal subjects. A large degree of intersubject variability was noted. Three patients with more severe cirrhosis had a more substantial decrease in venlafaxine clearance (about 90%) compared to normal subjects.
In a second study, venlafaxine was administered orally and intravenously in normal (n = 21) subjects, and in Child-Pugh A (n = 8) and Child-Pugh B (n = 11) subjects (mildly and moderately impaired, respectively). Venlafaxine oral bioavailability was increased 2-3 fold, oral elimination half-life was approximately twice as long and oral clearance was reduced by more than half, compared to normal subjects. In hepatically impaired subjects, ODV oral elimination half-life was prolonged by about 40%, while oral clearance for ODV was similar to that for normal subjects. A large degree of intersubject variability was noted.
Dosage adjustment is necessary in these hepatically impaired patients [see Dosage and Administration (2.3) and Use in Specific Populations (8.6) ].
Renal Disease: In a renal impairment study, venlafaxine elimination half-life after oral administration was prolonged by about 50% and clearance was reduced by about 24% in renally impaired patients (GFR=10 to 70 mL/min), compared to normal subjects. In dialysis patients, venlafaxine elimination half-life was prolonged by about 180% and clearance was reduced by about 57% compared to normal subjects. Similarly, ODV elimination half-life was prolonged by about 40% although clearance was unchanged in patients with renal impairment (GFR=10 to 70 mL/min) compared to normal subjects. In dialysis patients, ODV elimination half-life was prolonged by about 142% and clearance was reduced by about 56% compared to normal subjects. A large degree of intersubject variability was noted. Dosage adjustment is necessary in these patients [ see Dosage and Administration (2.3) and Use in Specific Populations (8.7) ].
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