Absolute bioavailability and electroencephalographic effects of conventional and extended-release formulations of venlafaxine in healthy subjects

PBPK modeling to predict the pharmacokinetics of venlafaxine and its active metabolite in different CYP2D6 genotypes and drug-drug interactions with clarithromycin and paroxetine

Venlafaxine, a serotonin-norepinephrine reuptake inhibitor (SNRI), is indicated for the treatment of major depressive disorder, social anxiety disorder, generalized anxiety disorder, and panic disorder. Venlafaxine is metabolized to the active metabolite desvenlafaxine mainly by CYP2D6. Genetic polymorphism of CYP2D6 and coadministration with other medications can significantly affect the pharmacokinetics and/or pharmacodynamics of venlafaxine and its active metabolite. This study aimed to establish the PBPK models of venlafaxine and its active metabolite related to CYP2D6 genetic polymorphism and to predict drug-drug interactions (DDIs) with clarithromycin and paroxetine in different CYP2D6 genotypes. Clinical pharmacogenomic data for venlafaxine and desvenlafaxine were collected to build the PBPK model. Physicochemical and absorption, distribution, metabolism, and excretion (ADME) characteristics of respective compounds were obtained from previously reported data, predicted by the PK-Sim® software, or optimized to capture the plasma concentration-time profiles. Model evaluation was performed by comparing the predicted pharmacokinetic parameters and plasma concentration-time profiles to the observed data. Predicted plasma concentration-time profiles of venlafaxine and its active metabolite were visually similar to the observed profiles and all predicted AUC and Cmax values for respective compounds were included in the twofold error range of observed values in non-genotyped populations and different CYP2D6 genotypes. When clarithromycin or clarithromycin plus paroxetine was concomitantly administered, predicted plasma concentration-time profiles of venlafaxine properly captured the observed profiles in two different CYP2D6 genotypes and all predicted DDI ratios for AUC and Cmax were included within the acceptance range. Consequently, the present model successfully captured the pharmacokinetic alterations of venlafaxine and its active metabolite according to CYP2D6 genetic polymorphism as well as the DDIs between venlafaxine and two CYP inhibitors. The present model can be used to predict the pharmacokinetics of venlafaxine and its active metabolite considering different races, ages, coadministered drugs, and CYP2D6 activity of individuals and it can contribute to individualized pharmacotherapy of venlafaxine.

Differential inhibition of cardiac and neuronal Na(+) channels by the selective serotonin-norepinephrine reuptake inhibitors duloxetine and venlafaxine

Duloxetine and venlafaxine are selective serotonin-norepinephrine-reuptake-inhibitors used as antidepressants and co-analgesics. While venlafaxine rather than duloxetine induce cardiovascular side-effects, neither of the substances are regarded cardiotoxic. Inhibition of cardiac Na(+)-channels can be associated with cardiotoxicity, and duloxetine was demonstrated to block neuronal Na(+)-channels. The aim of this study was to investigate if the non-life threatening cardiotoxicities of duloxetine and venlafaxine correlate with a weak inhibition of cardiac Na(+)-channels. Effects of duloxetine, venlafaxine and amitriptyline were examined on endogenous Na(+)-channels in neuroblastoma ND7/23 cells and on the α-subunits Nav1.5, Nav1.7 and Nav1.8 with whole-cell patch clamp recordings. Tonic block of the cardiac Na(+)-channel Nav1.5 and rat-cardiomyocytes (CM) revealed a higher potency for duloxetine (Nav 1.5 IC50 14±1µM, CM IC50 27±3µM) as compared to venlafaxine (Nav 1.5 IC50 671±26µM, CM IC50 452±34µM). Duloxetine was as potent as the cardiotoxic antidepressant amitriptyline (IC50 13±1µM). While venlafaxine almost failed to induce use-dependent block on Nav1.5 and cardiomyocytes, low concentrations of duloxetine (1, 10µM) induced prominent use-dependent block similar to amitriptyline. Duloxetine, but not venlafaxine stabilized fast and slow inactivation and delayed recovery from inactivation. Duloxetine induced an unselective inhibition of neuronal Na(+)-channels (IC50 ND7/23 23±1µM, Nav1.7 19±2µM, Nav1.8 29±2). Duloxetine, but not venlafaxine inhibits cardiac Na(+)-channels with a potency similar to amitriptyline. These data indicate that an inhibition of Na(+)-channels does not predict a clinically relevant cardiotoxicity.

Preparation and characterisation of mucoadhesive nasal gel of venlafaxine hydrochloride for treatment of anxiety disorders

The aim of the present study is to prepare and evaluate mucoadhesive nasal gels of venlafaxine hydrochloride. Mucoadhesive nasal gels were prepared using polymers like carbopol 934 and sodium alginate and characterized in terms of viscosity, texture profile analysis, ex vivo drug permeation profiles and histopathological studies. The results show that values of viscosity, hardness and adhesiveness increase while those of cohesiveness decrease with corresponding increase in concentration of the polymers. Ex vivo drug permeation profiles showed that formulation containing 5% sodium alginate provided a better controlled release of the drug than the other formulations over a period of 12 h. Histopathological studies assured that gels containing different polymers did not produce any significant change in the nasal mucosae of goat even after 12 h permeation study. Mucoadhesive nasal gel of venlafaxine hydrochloride is a novel dosage form which delivers the drug directly into systemic circulation and provides controlled release of the drug.

Which metabolites circulate?

Characterization of the circulating metabolites for a new chemical entity in humans is essential for safety assessment, an understanding of their contributions to pharmacologic activities, and their potential involvement in drug-drug interactions. This review examines the abundance of metabolites relative to the total parent drug [metabolite-to-parent (M/P) ratio] from 125 drugs in relation to their structural and physicochemical characteristics, lipoidal permeability, protein binding, and fractional formation from parent (fm). Our analysis suggests that fm is the major determinant of total drug M/P ratio for amine, alcohol, N- and S-oxide, and carboxylic acid metabolites. Passage from the hepatocyte to systemic circulation does not appear to be limiting owing to the vast majority of metabolites formed being relatively lipid permeable. In some cases, active transport plays an important role in this process (e.g., carboxylic acid metabolites). Differences in total parent drug clearance and metabolite clearance are attenuated by the reduction in lipophilicity introduced by the metabolic step and resultant compensatory changes in unbound clearance and protein binding. A small subclass of these drugs (e.g., terfenadine) is unintentional prodrugs with very high parent drug clearance, resulting in very high M/P ratios. In contrast, arenol metabolites show a more complex relationship with fm due largely to the new metabolic routes (conjugation) available to the metabolite compared with the parent drug molecule. For these metabolites, a more thorough understanding of the elimination clearance of the metabolite is critical to discern the likelihood of whether the phenol will constitute a major circulating metabolite.

Bioequivalence of single and multiple doses of venlafaxine extended-release tablets and capsules in the fasted and fed states: four open-label, randomized crossover trials in healthy volunteers

BACKGROUND

Venlafaxine extended-release (ER) tablets use osmotic pressure to deliver venlafaxine hydrochloride at a controlled rate over approximately 24 hours.

OBJECTIVE

These studies were conducted to evaluate the bioequivalence of venlafaxine ER tablets and capsules based on the US Food and Drug Administration (FDA) definition.

METHODS

Four pharmacokinetic studies of the capsule (reference) and tablet (test) formulations were conducted in healthy adult volunteers. The first 2 were randomized, single-dose, 4-way crossover studies of either a 37.5-mg dose (study A) or a 75-mg dose (study B) of the reference and test products under fasting and fed conditions. The other 2 were randomized, 2-way crossover studies of either a single dose (study C) or multiple doses (study D) of venlafaxine ER 225 mg, delivered as one venlafaxine ER 225-mg tablet or one 150-mg + one 75-mg venlafaxine ER capsules under fed conditions. The primary outcome measures were the log-transformed C(max), AUC(0-t), and AUC(0-infinity). If the 90% CIs for the ratios of the least squares means of the primary outcome measures between the reference and test formulations fell within the regulatory range (80%-125%), the 2 formulations would be considered bioequivalent according to the FDA definition.

RESULTS

Thirty-six subjects (21 men, 15 women; mean [SD] age, 28.0 [8.7] years; mean weight, 161.0 [26.0] lb) were enrolled in study A and completed all treatment periods. Thirty-six subjects were enrolled in study B, of whom 30 (22 men, 8 women; mean age, 33.5 [9.6] years; mean weight, 172.7 [23.9] lb) completed all treatment periods. Thirty-six subjects were enrolled in study C, of whom 28 (16 men, 12 women; mean age, 33.1 [12.9] years; mean weight, 160.6 [29.6] lb) completed the study. Thirty-four subjects were enrolled in study D, of whom 33 (29 men, 4 women; mean age, 26.0 [8.1] years; mean weight, 178.0 [30.3] lb) completed the study. In study A, the 90% CIs for the log-transformed ratio (test vs reference) of C(max), AUC(0-t), and AUC(0-infinity) in the fasted state were 95.58 to 107.48, 97.58 to 111.09, and 100.31 to 112.85, respectively; in the fed state, the corresponding values were 84.26 to 94.86, 93.49 to 106.58, and 98.98 to 111.91. In study B, the respective values in the fasted state were 113.07 to 126.10, 111.11 to 124.57, and 106.86 and 120.71; in the fed state, the values were 90.50 to 100.90, 96.80 to 108.50, and 95.05 to 107.21. In study C, fed values were 94.15 to 109.37, 103.8 to 115.85, and 102.64 to 113.39. In study D, which involved multiple doses, fed values for C(max) and AUC(0-t) were 82.26 to 88.77 and 101.16 to 109.45, respectively. Adverse effects included nausea, vomiting, dizziness, syncope, and somnolence.

CONCLUSIONS

In these single- and multiple-dose studies, all doses of venlafaxine ER tablets tested met the FDA criterion for bioequivalence to the equivalent doses of venlafaxine ER capsules in the fed state. In the fasted state, the bioequivalence criterion was met for venlafaxine ER 37.5-mg tablets but not venlafaxine 75-mg tablets.

A fatal case of venlafaxine overdose

INTRODUCTION

Based on its primary action of serotonin reuptake inhibition, venlafaxine overdose would be expected to result in serotonergic effects.

CASE REPORT

A 40 year old male ingested venlafaxine without co-ingestants in a suicide attempt. The patient developed refractory ventricular fibrillation and expired approximately 9 hours post-ingestion. ECG monitoring revealed significant QRS and QTC interval prolongation prior to his demise.

DISCUSSION

A literature review of venlafaxine overdose cases and investigation into its mechanism of action was conducted. The potential for sodium channel blockade and implications for therapy are discussed.

Effect of terbinafine and voriconazole on the pharmacokinetics of the antidepressant venlafaxine

This study investigated the effect of terbinafine and voriconazole on the pharmacokinetics of venlafaxine in healthy volunteers. Plasma concentrations of venlafaxine and O-desmethylvenlafaxine (ODV) were measured after ingestion of 75 mg venlafaxine without pretreatment (control), after terbinafine pretreatment, or after voriconazole pretreatment. During the terbinafine phase, the area under the plasma concentration-time curve (AUC(0-infinity)) of venlafaxine was on average 490% (P<0.001) and that of ODV 57% (P<0.001) of the corresponding control value. Terbinafine decreased the AUC(0-infinity) ratio of ODV over venlafaxine by 82% (P<0.001). Voriconazole slightly increased the sum of AUC(0-infinity) of venlafaxine plus AUC(0-infinity) of ODV (active moiety) by 31% (P<0.001). The most likely mechanism for the interaction between terbinafine and venlafaxine is the inhibition of CYP2D6-mediated O-demethylation of venlafaxine, whereas the minor effects of voriconazole are probably due to the inhibition of CYP3A4-, CYP2C9-, or CYP2C19-mediated metabolism of venlafaxine.

Duloxetine and venlafaxine-XR in the treatment of major depressive disorder: a meta-analysis of randomized clinical trials

BACKGROUND

Duloxetine has joined venlafaxine on the antidepressant market as a second serotonin-norepinephrine reuptake inhibitor. No previous studies have directly compared these drugs.

OBJECTIVE

To compare indirectly the efficacy and safety of extended-release (XR) venlafaxine and duloxetine, the 2 currently available serotonin-norepinephrine reuptake inhibitors (SNRIs) in treating major depressive disorder.

METHODS

Outcomes from published, randomized, placebo-controlled trials reporting on moderately to severely depressed patients (Hamilton Rating Scale for Depression [HAM-D] > or =15 or Montgomery-Asberg Depression Rating Scale [MADRS] > or =18). A systematic literature search of Cochrane, EMBASE, and MEDLINE (1996-January 2005) was performed. Two independent reviewers judged the trials for acceptance, and last observation carried forward data were extracted. Differences in remission (8-week HAM-D score < or =7 or MADRS < or =10), response (50% decrease on either scale), and dropout rates from lack of efficacy and adverse events were meta-analyzed using a random effects model. Each rate was contrasted with placebo. Sensitivity analyses were performed to examine the robustness of the results.

RESULTS

Data were obtained from 8 trials evaluating 1754 patients for efficacy and 1791 patients for discontinuation/safety. Venlafaxine-XR rates were 17.8% (95% CI 9.0 to 26.5) and 24.4% (95% CI 15.0 to 37.7) greater than those with placebo for remission and response compared with 14.2% (95% CI 8.9 to 26.5) and 18.6% (95% CI 13.0 to 24.2) for duloxetine. Although numerically higher for venlafaxine-XR, no statistically significant differences were found between the drugs; however, both demonstrated overall remission and response rates significantly higher than the rates achieved with placebo (p < 0.001). Reported adverse events were comparable between drugs.

CONCLUSIONS

Venlafaxine-XR tends to have a favorable trend in remission and response rates compared with duloxetine. However, dropout rates and adverse events did not differ. A direct comparison is warranted to confirm this tendency.

Biomarkers for the effects of selective serotonin reuptake inhibitors (SSRIs) in healthy subjects

AIMS

Studies of novel centrally acting drugs in healthy volunteers are traditionally concerned with kinetics and tolerability, but useful information may also be obtained from biomarkers of clinical endpoints. This paper provides a systematic overview of CNS-tests used with SSRIs in healthy subjects. A useful biomarker should meet the following requirements: a consistent response across studies and drugs; a clear response of the biomarker to a therapeutic dose; a dose-response relationship; a plausible relationship between biomarker, pharmacology and pathogenesis.

METHODS

These criteria were applied to all individual tests found in studies of selective serotonin reuptake inhibitors (SSRIs), performed in healthy subjects since 1966, identified with a systematic MedLine search. Separate databases were created to evaluate the effects of single or multiple dose SSRI-studies, and for amitriptyline whenever the original report included this antidepressant as a positive control. Doses of the antidepressant were divided into high- and low-dose ranges, relative to a medium range of therapeutic doses. For each test, the drug effects were scored as statistically significant impairment/decrease (-), improvement/increase (+) or no change (=) relative to placebo.

RESULTS

56 single dose studies and 22 multiple dose studies were identified, investigating the effects of 13 different SSRIs on 171 variants of neuropsychological tests, which could be clustered into seven neuropsychological domains. Low single doses of SSRIs generally stimulated tests of attention and memory. High doses tended to impair visual/auditory and visuomotor systems and subjective performance, while showing an acceleration in motor function. The most pronounced effects were observed using tests that measure flicker discrimination (improvement at low doses: 75%, medium doses: 40%, high doses: 43% of studies); REM sleep (inconsistent decrease after medium doses, decrease in 83% of studies after high doses); and EEG recordings, predominantly in alpha (decrease in 60% and 43% of studies after low and medium doses, respectively) and in theta activity (increase in 43% and 33% of studies after medium and high doses, respectively). Amitriptyline generally impaired central nervous system (CNS) functions, which increased with doses. Multiple doses caused less pronounced effects on the reported tests. The most responsive tests to amitriptyline appeared to be EEG alpha and theta, and REM sleep duration.

CONCLUSIONS

SSRIs in healthy subjects appear to cause slight stimulating effects after low doses, which tend to diminish with dose. The most consistent effects were observed with flicker discrimination tests, EEG (alpha and beta bands), REM sleep duration, and subjective effects at higher doses. These effects are small compared with amitriptyline and other CNS-active drugs. Multiple dosing with SSRIs caused even fewer measurable differences from placebo, probably due to adaptive processes. SSRI-effects are best detected with a test battery that is sensitive to general CNS-stimulation, but such tests only comprise a very small portion of the close to 200 different methods that were found in current review.

'Atypical' antidepressants in overdose: clinical considerations with respect to safety

The 'atypical' antidepressants comprise a heterogenous class with wide variation in presentation and management during overdose, both when compared with each other and with more traditional agents.Further toxico-epidemiological data are required to make definitive predictions about the clinical effects of most of these agents in overdose. Here, however, we review the available information in a manner intended to benefit both prescribers and clinical toxicologists. Our conclusion is that there can be no generic response by medical practitioners as to the 'safety' of these new antidepressants. Though undoubtedly exhibiting fewer problems in specific areas than some of the older classes of agents (e.g. arrhythmias with tricyclic antidepressants) each nonetheless presents unique safety problems. We experienced great difficulty obtaining accurate information from the manufacturers about the animal toxicity data upon which their recommended human dose limits were set. This highlights the uncertainties involved with too readily making 'safety' claims about these agents. The decision to prescribe 'atypical' antidepressant medications alleged to be both efficacious and safe in overdose involves a medicolegal tension. This tension is between respecting patient autonomy through frank communication of the material risk of overdose and non-disclosure to avoid such harm.

Prediction of human pharmacokinetics from animal data and molecular structural parameters using multivariate regression analysis: volume of distribution at steady state

The aim of this study was to develop a regression equation for predicting volume of distribution at steady state (Vd(ss)) in humans to enable application to various types of drugs using animal experimental data for rats and dogs and some molecular structural parameters. The Vd(ss) data for rats, dogs and humans of 64 drugs were obtained from literature. The compounds have various structures, pharmacological activities and pharmacokinetic characteristics. In addition, the molecular weight, calculated partition coefficient (clogP), and the number of hydrogen bond acceptors were used as possible descriptors related to the Vd(ss) in humans. Multivariate regression analyses, multiple linear regression analysis and the partial least squares (PLS) method were used to predict Vd(ss) in humans. Interaction terms were also introduced into the regression analysis to evaluate the non-linear relationship. For the data set used in the present study, PLS with quadratic term descriptors gave the best predictive performance. The PLS model using Vd(ss) data for only two animal species and using easily calculated structural parameters could generally predict Vd(ss) in humans better than an allometric method. In addition, the PLS model with only animal data gave almost the same predictive performance as the PLS model with quadratic term descriptors. This model may be easier to use and be practical in a realistic situation, and could predict Vd(ss) in humans better than the allometric method.

Psychomotor and cognitive effects of piribedil, a dopamine agonist, in young healthy volunteers

Piribedil is a dopamine agonist acting on D2 and D3 central nervous system dopamine receptors. This drug has been administered to 12 young healthy male volunteers (age 22 +/- 2 years) according to a single center randomized, double-blind, two ways cross-over, placebo controlled trial, including a washout period of one week. Placebo and piribedil were administered by a single intravenous infusion over 2 h (3 mg). Psychomotor performance and cognitive functions were assessed through a standardized and computerized psychometric tests battery and a continuous electroencephalogram (EEG) mapping. Piribedil improved simple reaction time (P=0.02), immediate (P=0.045 and 0.004), and delayed free recall (P=0.05), dual coding test (P=0.02) and increased theta and fast beta waves on the EEG (P < 0.05 and 0.001, respectively). No deleterious effect was observed on the tests exploring attention and concentration via the other procedures. It is concluded that a single intravenous perfusion of piribedil 3 mg improves alertness and the information processing speed within the central nervous system, in healthy volunteers.

Review of the pharmacokinetics, pharmacogenetics, and drug interaction potential of antidepressants: focus on venlafaxine

Improving outcomes for patients with depression involves selecting the best possible drug therapy. Considerations relevant to drug product selection include: 1) pharmacokinetic issues such as half-life and time to steady-state, and protein binding; 2) pharmacodynamic drug-drug interactions; and 3) drug metabolism-related drug interactions. A comparison of selected antidepressants with an emphasis on venlafaxine's similarities and differences is presented. Based on these parameters, selecting an antidepressant medication, such as venlafaxine, that has a low potential for drug interactions at the Cytochrome P450 (CYP) enzyme system, and is easy to monitor and dose, facilitate successful treatment of patients. Venlafaxine has been evaluated in clinical studies that demonstrate low to negligible drug interaction potential at CYP2D6, CYP1A2, CYP2C19, and CYP3A4. Its short half-life and time to steady-state, when coupled with the extended release characteristics of the preferred dosage formulation allow for once daily dosing and rapid attainment of therapeutic effects. The CYP3A4 system is involved in both first-pass metabolism and systemic clearance of medications. Drug interactions at this isoenzyme have proven to be of high clinical relevance ranging from cardiovascular toxicity and death with commonly used drugs such as cisapride, to subtherapeutic levels of cyclosporine or protease inhibitors leading to transplant rejection or HIV relapse. Reasons for the under detection and reporting of drug interaction mediated adverse events include healthcare system structure, the poor return to follow up of non-adherent patients, the need for greater education and training of clinicians to recognize drug-related adverse events, and the reluctance of patients to spontaneously communicate about the unpleasant effects of their medication.

Clinical pharmacology of psychotropic drugs

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