A fatal case of desvenlafaxine and paroxetine poisoning

Desvenlafaxine (O-desmethylvenlafaxine) and paroxetine are antidepressants that inhibit serotonin reuptake. Despite their relatively safe profiles, several serious side effects, including serotonin syndrome, bleeding, mania, and high blood pressure, are observed. We report the confirmation of the death of a 41-year-old female, with an overdose of desvenlafaxine and paroxetine suspected as the main cause of death. To quantify the level of desvenlafaxine and paroxetine in whole blood and urine, solid phase extraction combined with liquid chromatography-tandem mass spectrometry was developed and validated. Calibration curves were linear with coefficients of determination (r2) >0.999 for desvenlafaxine and paroxetine. The limits of detection and the limits of quantification for both desvenlafaxine and paroxetine were 0.001 µg/mL and 0.02 µg/mL, respectively. Desvenlafaxine and paroxetine were detected in the postmortem samples, along with various psychiatric drugs, and the blood alcohol content level was below 0.010%. The concentrations of desvenlafaxine and paroxetine in the heart blood were 11.0 µg/mL and 2.1 µg/mL, respectively, indicating lethal concentrations. In the urine, the concentrations of desvenlafaxine and paroxetine were 87.7 µg/mL and 3.5 µg/mL, respectively. This is the first report to determine the blood concentration of desvenlafaxine in a fatal intoxication caused by an overdose of desvenlafaxine single formulation.

Impact of polymorphisms in CYP and UGT enzymes and ABC and SLCO1B1 transporters on the pharmacokinetics and safety of desvenlafaxine

Venlafaxine pharmacokinetic variability and pharmacotherapy outcomes are well known to be related to CYP2D6 pharmacogenetic phenotype. In contrast, scarce pharmacogenetic information is available nowadays concerning desvenlafaxine, its active metabolite first marketed in 2012. The aim of this study was to evaluate the impact of 29 alleles in 12 candidate genes (e.g., CYP enzymes like CYP2D6, CYP3A4, or CYP2C19; ABC transporters like ABCB1; SLCO1B1; and UGT enzymes like UGT1A1) on desvenlafaxine pharmacokinetic variability and tolerability. Pharmacokinetic parameters and adverse drug reaction (ADR) incidence obtained from six bioequivalence clinical trials (n = 98) evaluating desvenlafaxine formulations (five with single dose administration and one with multiple-dose administration) were analyzed. No genetic polymorphism was related to pharmacokinetic variability or ADR incidence. Volunteers enrolled in the multiple-dose clinical trial also showed a higher incidence of ADRs, e.g., xerostomia or appetite disorders. Volunteers experiencing any ADR showed a significantly higher area under the time-concentration curve (AUC) than those not experiencing any ADR (5115.35 vs. 4279.04 ng*h/mL, respectively, p = 0.034). In conclusion, the strong dose-dependent relationship with the occurrence of ADRs confirms that the mechanism of action of desvenlafaxine is essentially dose-dependent.

Effects of the Proton Pump Inhibitors Omeprazole and Pantoprazole on the Cytochrome P450-Mediated Metabolism of Venlafaxine

BACKGROUND AND OBJECTIVE: An increasing trend in prescribing proton pump inhibitors (PPIs) inevitably increases the risk of unwanted drug-drug interactions (DDIs). The aim of this study was to uncover pharmacokinetic interactions between two PPIs-omeprazole and pantoprazole-and venlafaxine.

METHODS

A therapeutic drug monitoring database contained plasma concentrations of venlafaxine and its active metabolite O-desmethylvenlafaxine. We considered three groups: a group of patients who received venlafaxine without confounding medications (non-PPI group, n = 906); a group of patients who were comedicated with omeprazole (n = 40); and a group of patients comedicated with pantoprazole (n = 40). Plasma concentrations of venlafaxine, O-desmethylvenlafaxine and active moiety (venlafaxine + O-desmethylvenlafaxine), as well as dose-adjusted plasma concentrations, were compared using non-parametrical tests.

RESULTS

Daily doses of venlafaxine did not differ between groups (p = 0.949). The Mann-Whitney U test showed significantly higher plasma concentrations of active moiety, as well as venlafaxine and O-desmethylvenlafaxine, in both PPI groups [p = 0.023, p = 0.011, p = 0.026, +29% active moiety, +27% venlafaxine, +36% O-desmethylvenlafaxine (pantoprazole); p = 0.003, p = 0.039 and p < 0.001, +36% active moiety, +27% venlafaxine, +55% O-desmethylvenlafaxine (omeprazole)]. Significantly higher concentration-by-dose (C/D) values for venlafaxine and active moiety were detected in the pantoprazole group (p = 0.013, p = 0.006, respectively), while in the omeprazole group, C/D ratios for all three parameters-venlafaxine, O-desmethylvenlafaxine and active moiety-were significantly higher (p = 0.021, p < 0.001 and p < 0.001, respectively).

CONCLUSIONS

Significantly higher plasma concentrations for all parameters (venlafaxine, O-desmethylvenlafaxine, active moiety) suggest clinically relevant inhibitory effects of both PPIs, most likely on the cytochrome P450 (CYP) 2C19-mediated metabolism of venlafaxine. The findings might be the result of different degrees of CYP2C19 involvement, therefore the inhibition of CYP2C19 by both PPIs may lead to an increased metabolism via CYP2D6 to O-desmethylvenlafaxine.

[Validation of interaction databases in psychopharmacotherapy]

BACKGROUND

Drug-drug interaction databases are an important tool to increase drug safety in polypharmacy. There are several drug interaction databases available but it is unclear which one shows the best results and therefore increases safety for the user of the databases and the patients. So far, there has been no validation of German drug interaction databases.

GOAL

Validation of German drug interaction databases regarding the number of hits, mechanisms of drug interaction, references, clinical advice, and severity of the interaction.

METHODS

A total of 36 drug interactions which were published in the last 3-5 years were checked in 5 different databases. Besides the number of hits, it was also documented if the mechanism was correct, clinical advice was given, primary literature was cited, and the severity level of the drug-drug interaction was given.

RESULTS

All databases showed weaknesses regarding the hit rate of the tested drug interactions, with a maximum of 67.7% hits. The highest score in this validation was achieved by MediQ with 104 out of 180 points. PsiacOnline achieved 83 points, arznei-telegramm® 58, ifap index® 54 and the ABDA-database 49 points. Based on this validation MediQ seems to be the most suitable databank for the field of psychopharmacotherapy.

DISCUSSION

The best results in this comparison were achieved by MediQ but this database also needs improvement with respect to the hit rate so that the users can rely on the results and therefore increase drug therapy safety.

Prediction of drug-drug interactions using physiologically-based pharmacokinetic models of CYP450 modulators included in Simcyp software

In recent years, physiologically based PharmacoKinetic (PBPK) modeling has received growing interest as a useful tool for the assessment of drug pharmacokinetics. It has been demonstrated to be informative and helpful to quantify the modification in drug exposure due to specific physio-pathological conditions, age, genetic polymorphisms, ethnicity and particularly drug-drug interactions (DDIs). In this paper, the prediction success of DDIs involving various cytochrome P450 isoenzyme (CYP) modulators namely ketoconazole (a competitive inhibitor of CYP3A), itraconazole (a competitive inhibitor of CYP3A), clarithromycin (a mechanism-based inhibitor of CYP3A), quinidine (a competitive inhibitor of CYP2D6), paroxetine (a mechanism-based inhibitor of CYP2D6), ciprofloxacin (a competitive inhibitor of CYP1A2), fluconazole (a competitive inhibitor of CYP2C9/2C19) and rifampicin (an inducer of CYP3A) were assessed using Simcyp^® software. The aim of this report was to establish confidence in each CYP-specific modulator file so they can be used in the future for the prediction of DDIs involving new victim compounds. Our evaluation of these PBPK models suggested that they can be successfully used to evaluate DDIs in untested scenarios. The only noticeable exception concerned a quinidine inhibitor model that requires further improvement. Additionally, other important aspects such as model validation criteria were discussed.

Pharmacokinetic Pharmacogenetic Prescribing Guidelines for Antidepressants: A Template for Psychiatric Precision Medicine

Antidepressants are commonly prescribed medications in the United States, and there is increasing interest in individualizing treatment selection for more than 20 US Food and Drug Administration-approved treatments for major depressive disorder. Providing greater precision to pharmacotherapeutic recommendations for individual patients beyond the large-scale clinical trials evidence base can potentially reduce adverse effect toxicity profiles and increase response rates and overall effectiveness. It is increasingly recognized that genetic variation may contribute to this differential risk to benefit ratio and thus provides a unique opportunity to develop pharmacogenetic guidelines for psychiatry. Key studies and concepts that review the rationale for cytochrome P450 2D6 (CYP2D6) and cytochrome P450 2C19 (CYP2C19) genetic testing can be delineated by serum levels, adverse events, and clinical outcome measures (eg, antidepressant response). In this article, we report the evidence that contributed to the implementation of pharmacokinetic pharmacogenetic guidelines for antidepressants primarily metabolized by CYP2D6 and CYP2C19.

How the Probability and Potential Clinical Significance of Pharmacokinetically Mediated Drug-Drug Interactions Are Assessed in Drug Development: Desvenlafaxine as an Example

OBJECTIVE

The avoidance of adverse drug-drug interactions (DDIs) is a high priority in terms of both the US Food and Drug Administration (FDA) and the individual prescriber. With this perspective in mind, this article illustrates the process for assessing the risk of a drug (example here being desvenlafaxine) causing or being the victim of DDIs, in accordance with FDA guidance.

DATA SOURCES/STUDY SELECTION

DDI studies for the serotonin-norepinephrine reuptake inhibitor desvenlafaxine conducted by the sponsor and published since 2009 are used as examples of the systematic way that the FDA requires drug developers to assess whether their new drug is either capable of causing clinically meaningful DDIs or being the victim of such DDIs. In total, 8 open-label studies tested the effects of steady-state treatment with desvenlafaxine (50-400 mg/d) on the pharmacokinetics of cytochrome (CYP) 2D6 and/or CYP 3A4 substrate drugs, or the effect of CYP 3A4 inhibition on desvenlafaxine pharmacokinetics. The potential for DDIs mediated by the P-glycoprotein (P-gp) transporter was assessed in in vitro studies using Caco-2 monolayers.

DATA EXTRACTION

Changes in area under the plasma concentration-time curve (AUC; CYP studies) and efflux (P-gp studies) were reviewed for potential DDIs in accordance with FDA criteria.

RESULTS

Desvenlafaxine coadministration had minimal effect on CYP 2D6 and/or 3A4 substrates per FDA criteria. Changes in AUC indicated either no interaction (90% confidence intervals for the ratio of AUC geometric least-squares means [GM] within 80%-125%) or weak inhibition (AUC GM ratio 125% to < 200%). Coadministration with ketoconazole resulted in a weak interaction with desvenlafaxine (AUC GM ratio of 143%). Desvenlafaxine was not a substrate (efflux ratio < 2) or inhibitor (50% inhibitory drug concentration values > 250 μM) of P-gp.

CONCLUSIONS

A 2-step process based on FDA guidance can be used first to determine whether a pharmacokinetically mediated interaction occurs and then to assess the potential clinical significance of the DDI. In the case of the drug tested in this series of studies, the potential for clinically meaningful DDIs mediated by CYP 2D6, CYP 3A4, or P-gp was found to be low.

Pharmacokinetic and pharmacodynamic interactions between almorexant, a dual orexin receptor antagonist, and desipramine

Almorexant is a dual orexin receptor antagonist (DORA) with sleep-enabling effects in humans. Insomnia is often associated with mental health problems, including depression. Hence, potential interactions with antidepressants deserve attention. Desipramine was selected as a model drug because it is mainly metabolized by CYP2D6, which is inhibited by almorexant in vitro. A single-center, randomized, placebo-controlled, two-way crossover study in 20 healthy male subjects was conducted to evaluate the pharmacokinetic and pharmacodynamic interactions between almorexant and desipramine. Almorexant 200mg or matching placebo (double-blind) was administered orally once daily in the morning for 10 days, and a single oral dose of 50mg desipramine (open-label) was administered on Day 5. Almorexant increased the exposure to desipramine 3.7-fold, suggesting that almorexant is a moderate inhibitor of desipramine metabolism through inhibition of CYP2D6. Conversely, desipramine showed no relevant effects on the pharmacokinetics of almorexant. Pharmacodynamic evaluations indicated that almorexant alone reduced visuomotor coordination, postural stability, and alertness, and slightly increased calmness. Desipramine induced a reduction in subjective alertness and an increase in pupil/iris ratio. Despite the increase in exposure to desipramine, almorexant and desipramine in combination showed the same pharmacodynamic profile as almorexant alone, except for prolonging reduced alertness and preventing the miotic effect of almorexant. Co-administration also prolonged the mydriatic effect of desipramine. Overall, repeated administration of almorexant alone or with single-dose desipramine was well tolerated. The lack of a relevant interaction with antidepressants, if confirmed for other DORAs, would be a key feature for a safer class of hypnotics.

Clinically significant drug interactions with atypical antipsychotics

Atypical antipsychotics [also known as second-generation antipsychotics (SGAs)] have become a mainstay therapeutic treatment intervention for patients with schizophrenia, bipolar disorders and other psychotic conditions. These agents are commonly used with other medications--most notably, antidepressants and antiepileptic drugs. Drug interactions can take place by various pharmacokinetic, pharmacodynamic and pharmaceutical mechanisms. The pharmacokinetic profile of each SGA, especially with phase I and phase II metabolism, can allow for potentially significant drug interactions. Pharmacodynamic interactions arise when agents have comparable receptor site activity, which can lead to additive or competitive effects without alterations in measured plasma drug concentrations. Additionally, the role of drug transporters in drug interactions continues to evolve and may effect both pharmacokinetic and pharmacodynamic interactions. Pharmaceutical interactions occur when physical incompatibilities take place between agents prior to drug absorption. Approximate therapeutic plasma concentration ranges have been suggested for a number of SGAs. Drug interactions that markedly increase or decrease the concentrations of these agents beyond their ranges can lead to adverse events or diminished clinical efficacy. Most clinically significant drug interactions with SGAs occur via the cytochrome P450 (CYP) system. Many but not all drug interactions with SGAs are identified during drug discovery and pre-clinical development by employing a series of standardized in vitro and in vivo studies with known CYP inducers and inhibitors. Later therapeutic drug monitoring programmes, clinical studies and case reports offer methods to identify additional clinically significant drug interactions. Some commonly co-administered drugs with a significant potential for drug-drug interactions with selected SGAs include some SSRIs. Antiepileptic mood stabilizers such as carbamazepine and valproate, as well as other antiepileptic drugs such as phenobarbital and phenytoin, may decrease plasma SGA concentrations. Some anti-infective agents such as protease inhibitors and fluoroquinolones are of concern as well. Two additional important factors that influence drug interactions with SGAs are dose and time dependence. Smoking is very common among psychiatric patients and can induce CYP1A2 enzymes, thereby lowering expected plasma levels of certain SGAs. It is recommended that ziprasidone and lurasidone are taken with food to promote drug absorption, otherwise their bioavailability can be reduced. Clinicians must be aware of the variety of factors that can increase the likelihood of clinically significant drug interactions with SGAs, and must carefully monitor patients to maximize treatment efficacy while minimizing adverse events.

The effect of mirabegron, a potent and selective β3-adrenoceptor agonist, on the pharmacokinetics of CYP2D6 substrates desipramine and metoprolol

Mirabegron is a potent and selective β3-adrenoceptor agonist developed for the treatment of overactive bladder. In vitro studies demonstrated that mirabegron partly acts as a (quasi-) irreversible, metabolism-dependent inhibitor of CYP2D6. The effect of steady-state mirabegron on single doses of the sensitive CYP2D6 substrates metoprolol (100 mg) and desipramine (50 mg) was assessed in two open-label, one-sequence crossover studies in healthy subjects (CYP2D6 extensive metabolizers). Mirabegron 160 mg/day increased metoprolol maximum plasma concentration (C max) 1.90-fold (90 % confidence interval [CI] 1.54; 2.33) and total exposure (AUC0-∞) 3.29-fold (90 % CI 2.70; 4.00) in 12 males (study 1). Mean metoprolol half-life increased from 2.96 to 4.11 h. α-Hydroxymetoprolol C max and AUC to last measurable concentration decreased 2.6-fold and 2.2-fold, respectively. In study 2, mirabegron 100 mg/day increased desipramine C max 1.79-fold (90 % CI 1.69; 1.90) and AUC0-∞ 3.41-fold (90 % CI 3.07; 3.80) in 14 males and 14 females. Mean desipramine half-life increased from 19.5 to 35.8 h. C max of 2-hydroxydesipramine decreased ~twofold, while AUC increased ~1.3-fold. Desipramine was administered again 2 weeks after the last mirabegron dose. Desipramine C max and AUC0-∞ were still ~1.13-fold increased; the 90 % CIs fell within the 0.80-1.25 interval. All treatments were well tolerated. In conclusion, mirabegron is a moderate CYP2D6 inhibitor (ratio and 90 % CI <5.0).

Desvenlafaxine in the treatment of major depressive disorder

Desvenlafaxine (DESV) is a newer antidepressant, which inhibits serotonin-norepinephrine reuptake neurotransmission, similarly to venlafaxine, milnacipran and duloxetine. It was approved in February 2008 by the FDA for the treatment of major depressive disorder (MDD), based on well-controlled and adequately powered, large clinical trials demonstrating efficacy and safety for patients with MDD. Currently available data show that DESV has proven efficacy, acceptable safety and tolerability profiles, convenient once-daily dosing and minimal impact on the cytochrome P450 enzyme system in patients with MDD. This mini-review summarizes the clinical data and practical use of DESV under this approved indication.

Clinically significant drug interactions with newer antidepressants

After the introduction of selective serotonin reuptake inhibitors (SSRIs), other newer antidepressants with different mechanisms of action have been introduced in clinical practice. Because antidepressants are commonly prescribed in combination with other medications used to treat co-morbid psychiatric or somatic disorders, they are likely to be involved in clinically significant drug interactions. This review examines the drug interaction profiles of the following newer antidepressants: escitalopram, venlafaxine, desvenlafaxine, duloxetine, milnacipran, mirtazapine, reboxetine, bupropion, agomelatine and vilazodone. In general, by virtue of a more selective mechanism of action and receptor profile, newer antidepressants carry a relatively low risk for pharmacodynamic drug interactions, at least as compared with first-generation antidepressants, i.e. monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants (TCAs). On the other hand, they are susceptible to pharmacokinetic drug interactions. All new antidepressants are extensively metabolized in the liver by cytochrome P450 (CYP) isoenzymes, and therefore may be the target of metabolically based drug interactions. Concomitant administration of inhibitors or inducers of the CYP isoenzymes involved in the biotransformation of specific antidepressants may cause changes in their plasma concentrations. However, due to their relatively wide margin of safety, the consequences of such kinetic modifications are usually not clinically relevant. Conversely, some newer antidepressants may cause pharmacokinetic interactions through their ability to inhibit specific CYPs. With regard to this, duloxetine and bupropion are moderate inhibitors of CYP2D6. Therefore, potentially harmful drug interactions may occur when they are coadministered with substrates of these isoforms, especially compounds with a narrow therapeutic index. The other new antidepressants are only weak inhibitors or are not inhibitors of CYP isoforms at usual therapeutic concentrations and are not expected to affect the disposition of concomitantly administered medications. Although drug interactions with newer antidepressants are potentially, but rarely, clinically significant, the use of antidepressants with a more favourable drug interaction profile is advisable. Knowledge of the interaction potential of individual antidepressants is essential for safe prescribing and may help clinicians to predict and eventually avoid certain drug combinations.

Prediction of CYP2D6 drug interactions from in vitro data: evidence for substrate-dependent inhibition

Predicting the magnitude of potential drug-drug interactions is important for underwriting patient safety in the clinical setting. Substrate-dependent inhibition of cytochrome P450 enzymes may confound extrapolation of in vitro results to the in vivo situation. However, the potential for substrate-dependent inhibition with CYP2D6 has not been well characterized. The inhibition profiles of 20 known inhibitors of CYP2D6 were characterized in vitro against four clinically relevant CYP2D6 substrates (desipramine, dextromethorphan, metoprolol, and thioridazine) and bufuralol. Dextromethorphan exhibited the highest sensitivity to in vitro inhibition, whereas metoprolol was the least sensitive. In addition, when metoprolol was the substrate, inhibitors with structurally constrained amino moieties (clozapine, debrisoquine, harmine, quinidine, and yohimbine) exhibited at least a 5-fold decrease in inhibition potency when results were compared with those for dextromethorphan. Atypical inhibition kinetics were observed for these and other inhibitor-substrate pairings. In silico docking studies suggested that interactions with Glu216 and an adjacent hydrophobic binding pocket may influence substrate sensitivity and inhibition potency for CYP2D6. The in vivo sensitivities of the clinically relevant CYP2D6 substrates desipramine, dextromethorphan, and metoprolol were determined on the basis of literature drug-drug interaction (DDI) outcomes. Similar to the in vitro results, dextromethorphan exhibited the highest sensitivity to CYP2D6 inhibition in vivo. Finally, the magnitude of in vivo CYP2D6 DDIs caused by quinidine was predicted using desipramine, dextromethorphan, and metoprolol. Comparisons of the predictions with literature results indicated that the marked decrease in inhibition potency observed for the metoprolol-quinidine interaction in vitro translated to the in vivo situation.

Antidepressant treatment and altered CYP2D6 activity: are pharmacokinetic variations clinically relevant?

BACKGROUND

Many currently used antidepressants are substrates of the cytochrome P450 (CYP) 2D6 enzyme. In patients who experience variations in the activity of this enzyme (e.g., CYP2D6 poor and ultrarapid metabolizers [PMs and UMs]), whether caused by genetic polymorphisms or concomitant administration of a CYP2D6 inhibitor (i.e., phenoconversion), the pharmacokinetics, and hence the effects, of CYP2D6 substrate antidepressants can be altered.

METHODS

This literature review describes the clinical and empirical evidence indicating that alterations in CYP2D6 activity can negatively affect treatment outcomes in patients receiving antidepressant pharmacotherapies that are CYP2D6 substrates.

RESULTS

Based on results from a small, prospective trial, a population analysis, and a pooled analysis, CYP2D6 PMs treated with agents dependent on CYP2D6 metabolism to form an active metabolite can experience a decline in antidepressant effect. Based on a population analysis and two case studies, CYP2D6 UMs treated with antidepressants that are CYP2D6 substrates and administered in a pharmacologically active form do not experience an antidepressant effect due to the agent being too rapidly eliminated from the body. Conversely, based on prospective trials, population analyses, and case studies, phenotypic and phenoconverted CYP2D6 PMs can experience an increase in concentration-dependent adverse events due to the agent being eliminated too slowly from the body.

CONCLUSIONS

Despite these examples, few large-scale, prospective trials exploring the effect of altered CYP2D6 metabolism on antidepressant outcomes have been conducted. Future clinical trials of CYP2D6-dependent antidepressants should be designed to allow for stratification of treatment outcomes by CYP2D6 metabolizer status.

Assessing risks and benefits of nonhormonal treatments for vasomotor symptoms in perimenopausal and postmenopausal women

BACKGROUND

Vasomotor symptoms (VMS); (hot flushes and night sweats) are the most common menopausal complaint for which women seek treatment. Several therapies can be considered to help manage these complaints. The objective of this review is to assess the risks and benefits of available and emerging therapeutic options for the management of menopausal VMS.

METHODS

A review of the literature was conducted based on relevant publications identified through a PubMed search for clinical trials of agents used in the treatment of VMS.

RESULTS

Hormone therapy (HT) remains the most effective treatment available, but there will always remain a need for nonhormonal options. Evidence does not support the efficacy of alternative or over-the-counter products, such as phytoestrogens and black cohosh, and their long-term safety is largely unknown. There is evidence supporting the efficacy of selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) for the management of VMS from clinical trials of paroxetine, venlafaxine, and desvenlafaxine. Gabapentin appears to be effective, but the doses required may cause poor tolerability and reduced patient adherence. Data also suggest that clonidine has a modest effect at the expense of considerable adverse effects.

CONCLUSIONS

Choosing an appropriate treatment approach for the management of VMS requires careful assessment of the riskbenefit ratio of each alternative, as well as individual patient preference.

Induction of drug efflux protein expression by venlafaxine but not desvenlafaxine

Venlafaxine and its metabolite desvenlafaxine are serotonin-norepinephrine reuptake inhibitors currently prescribed for the treatment of depression. Previously, it was reported that venlafaxine is an inducer of MDR1, the gene responsible for P-glycoprotein (P-gp). The present study expanded upon these findings by examining the effect of venlafaxine and desvenlafaxine on the expression of both P-gp and the breast cancer resistance protein (BCRP) in human brain endothelial cells (HBMEC), an in vitro model of the blood-brain barrier (BBB). The HBMEC were treated for 1 h with various concentrations (500 nM to 50 µM) of venlafaxine and desvenlafaxine. Western blot analysis revealed treatment with venlafaxine significantly induced the expression of P-gp (2-fold) and BCRP (1.75-fold) in a dose-dependent manner, while treatment with desvenlafaxine had no effect on drug efflux transporter expression. To determine the functional significance of this effect, the permeability of a known drug efflux probe, rhodamine 123, across the BBB model and Caco-2 cells, a model of intestinal absorption, were examined. Treatment with venlafaxine (1-50 µM) for 1 h significantly reduced the apical-to-basolateral permeability of R123 across the BBB model (30%) and Caco-2 cell monolayers (25%), indicative of increased drug efflux transporter expression at the apical membrane. Conversely, desvenlafaxine had no effect on R123 permeability in either cellular model. These studies indicate that venlafaxine, but not desvenlafaxine is an inducer of drug efflux transporter expression, which consequently increases the potential for clinical drug-drug interactions. Therefore, based on these preliminary results, caution should be taken when prescribing venlafaxine with other P-gp substrates.

A 10-month, open-label evaluation of desvenlafaxine in outpatients with major depressive disorder

BACKGROUND

The primary objective was to evaluate the long-term safety of desvenlafaxine (administered as desvenlafaxine succinate) during open-label treatment in adult outpatients with a primary DSM-IV diagnosis of major depressive disorder (MDD).

METHOD

Depressed adult outpatients (≥ 18 years) who had completed 8-week, double-blind therapy (desvenlafaxine, venlafaxine extended release, or placebo) in a phase 3 study of desvenlafaxine for MDD received up to 10 months of open-label treatment with flexible-dose desvenlafaxine (200 to 400 mg/d). Safety assessments included physical examination, measurement of weight and vital signs, laboratory determinations, and 12-lead electrocardiogram recordings. Adverse events (AEs) and discontinuations due to AEs were monitored throughout the trial. The primary efficacy outcome was mean change from baseline on 17-item Hamilton Depression Rating Scale (HDRS-17) total score. The trial was conducted from August 2003 to March 2006.

RESULTS

The safety population included 1,395 patients who took at least 1 dose of open-label desvenlafaxine. Treatment-emergent AEs were reported by 1,238 of 1,395 patients (89%) during the open-label, on-therapy period. Treatment-emergent AEs reported by 10% or more patients were headache, nausea, hyperhidrosis, dizziness, dry mouth, insomnia, upper respiratory infection, nasopharyngitis, and fatigue. Adverse events were the primary reason for study discontinuation in 296 of 1,395 patients (21%). Ten patients (< 1%) had serious AEs that were considered possibly, probably, or definitely related to the study drug during the on-therapy period. No deaths occurred during the study.

CONCLUSIONS

Desvenlafaxine can be safely administered for up to 12 months. No new safety findings were observed in this study.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01309542.

Pharmacological and clinical profile of newer antidepressants: implications for the treatment of elderly patients

The pharmacological treatment of older adults with major depressive disorder presents a variety of challenges, including a relative lack of high quality studies designed to measure the efficacy and safety of antidepressants specific to this patient population. Gaining a clear understanding of how to use antidepressants in elderly patients with depression, especially new and widely used agents, would provide valuable insight to clinicians. The purpose of the current article is to review the pharmacology, efficacy and safety of newer antidepressants (i.e. escitalopram, duloxetine and desvenlafaxine) in the treatment of late-life depression. To accomplish this goal, a MEDLINE and PubMed search (1966 - February 2010) was conducted for relevant articles. Animal and human studies have clearly demonstrated the effects of desvenlafaxine, duloxetine and escitalopram on monoamine reuptake transporters. The serotonergic and noradrenergic actions of desvenlafaxine and duloxetine may provide for a faster onset of antidepressant activity in the elderly, but more definitive data are needed and the clinical effects of the possible faster onset of action need to be elucidated. Duloxetine and escitalopram are extensively metabolized via cytochrome P450 (CYP) enzymes and the decreased hepatic metabolism present in many older adults should be taken into account when prescribing these medications. Duloxetine possesses the greatest likelihood of producing clinically relevant drug-drug interactions because of its inhibition of CYP2D6. All three agents must also be used cautiously in older adults with poor renal function. In terms of clinical efficacy, 14 prospective published trials involving escitalopram (n = 8) and duloxetine (n = 6) in the treatment of older adults with major depressive disorder were identified. No such studies involving desvenlafaxine were found. Of the five randomized, double-blind, controlled trials, 46% and 37% of antidepressant-treated patients were considered responders and remitters, respectively. In contrast to escitalopram, duloxetine-treated patients experienced improvements in depressive symptoms that more consistently differentiated themselves from the symptoms of placebo-treated patients. Escitalopram and duloxetine were generally well tolerated, but 5-20% and 10-27% of patients, respectively, dropped out because of medication-related adverse effects. Adverse effects experienced by older adults were generally similar to those experienced by younger adults, although indirect comparisons suggest that older adults are more likely to experience dry mouth and constipation with duloxetine and escitalopram, while orthostasis may be more common in older adults prescribed desvenlafaxine. Overall, duloxetine and escitalopram represent modestly effective treatments for late-life depression that are generally well tolerated but do produce a variety of adverse effects. Conclusions regarding desvenlafaxine cannot be made at this time because of a lack of geriatric-specific data.

Desvenlafaxine succinate: a newer antidepressant for the treatment of depression and somatic symptoms

Desvenlafaxine succinate (DVS) is one of several serotonin-norepinephrine reuptake inhibitors (SNRIs). Others are venlafaxine hydrochloride, milnacipran, and duloxetine. Desvenlafaxine has been approved by the US Food and Drug Administration (FDA) for the treatment of major depressive disorder (MDD) based on a number of randomized, placebo-controlled clinical trials. Clinical studies have investigated the efficacy of DVS in doses ranging from 50 to 400 mg/day for the treatment of MDD in adult outpatients. The effects of DVS 50 mg/day have been clearly distinguished from placebo in the reduction of MDD symptoms in such clinical trials. No additional therapeutic benefits were found at doses > 50 mg/day. The recommended dose of DVS ranges from 50 to 100 mg. Desvenlafaxine is currently the third SNRI approved by the FDA for this indication. Preliminary evidence also suggests the clinical usefulness of DVS in the treatment of vasomotor symptoms of menopause, anxiety symptoms, and painful physical symptoms. The modified pharmacokinetic and pharmacodynamic profiles of DVS differentiate this drug from the original product, venlafaxine. Significant points of difference, compared with venlafaxine, are once-daily dosing and the achievement of steady-state plasma concentrations within 4 to 5 days. To summarize, current evidence indicates that DVS has proven efficacy, acceptable safety and tolerability profiles, convenient dosing, and minimal impact on the cytochrome P450 enzyme system. A reduced risk for pharmacokinetic drug interactions is a potential advantage over other selective serotonin noradrenaline reuptake inhibitors. Desvenlafaxine succinate has demonstrated its efficacy for treating MDD but its variable efficacy, as shown in individual studies, limited long-term data, and its different risk-to-benefit ratio compared with earlier antidepressants, means that further investigation of this drug is necessary.

Factors that impact choice of antidepressant treatment in medically complex patients

In medically complex patients with multiple comorbid illnesses who require concomitant medications, selecting the optimal antidepressant (ie, low risk of adverse effects and/or pharmacokinetic interactions) for an individual patient is critical for positive long-term patient outcomes. The serotonin-norepinephrine reuptake inhibitors (SNRls) are increasingly being used as first-line treatment for major depressive disorder (MDD) and may prove beneficial for treatment of medically complex patients.Thus, it is key for clinicians to evaluate the differences in the pharmacokinetic and tolerability profiles of the SNRI class of antidepressants, evaluating differences both within the class and compared with other antidepressants used to treat MDD.