Plasma concentrations of fluvoxamine and maprotiline in major depression: implications on therapeutic efficacy and side effects

Serum Concentration-Dose Relationship and Modulation Factors in Children and Adolescents Treated with Fluvoxamine

INTRODUCTION

Fluvoxamine is used in children and adolescents ('youths') for treating obsessive compulsive disorder (OCD) but also off-label for depressive and anxiety disorders. This study aimed to investigate the relationship between fluvoxamine dose and serum concentrations, independent correlates of fluvoxamine concentrations, and a preliminary therapeutic reference range (TRR) for youths with OCD and treatment response.

METHODS

Multicenter naturalistic data of a therapeutic drug monitoring service, as well as prospective data of the 'TDM Vigil study' (EudraCT 2013-004881-33), were analyzed. Patient and treatment characteristics were assessed by standardized measures, including Clinical Global Impressions-Severity (CGI-S) and -Change (CGI-I), with CGI-I of much or very much improved defining treatment response and adverse drug reactions using the Udvalg for Kliniske Undersogelser (UKU) Side Effect Rating Scale. Multivariable regression analysis was used to evaluate the influence of sex, age, body weight, body mass index (BMI), and fluvoxamine dose on fluvoxamine serum concentrations.

RESULTS

The study included 70 youths (age = 6.7-19.6 years, OCD = 78%, mean fluvoxamine dose = 140.4 (range = 25-300) mg/d). A weak positive correlation between daily dose and steady-state trough serum concentrations was found (rs = 0.34, p = 0.004), with dose variation explaining 16.2% of serum concentration variability. Multivariable correlates explaining 25.3% of the variance of fluvoxamine concentrations included higher fluvoxamine dose and lower BMI. Considering responders with OCD, the estimated TRR for youths was 55-371 ng/mL, exceeding the TRR for adults with depression of 60-230 ng/mL.

DISCUSSION

These preliminary data contribute to the definition of a TRR in youth with OCD treated with fluvoxamine and identify higher BMI as a moderator of lower fluvoxamine concentrations.

Antidepressant-induced membrane trafficking regulates blood-brain barrier permeability

As the most prescribed psychotropic drugs in current medical practice, antidepressant drugs (ADs) of the selective serotonin reuptake inhibitor (SSRI) class represent prime candidates for drug repurposing. The mechanisms underlying their mode of action, however, remain unclear. Here, we show that common SSRIs and selected representatives of other AD classes bidirectionally regulate fluid-phase uptake at therapeutic concentrations and below. We further characterize membrane trafficking induced by a canonical SSRI fluvoxamine to show that it involves enhancement of clathrin-mediated endocytosis, endosomal system, and exocytosis. RNA sequencing analysis showed few fluvoxamine-associated differences, consistent with the effect being independent of gene expression. Fluvoxamine-induced increase in membrane trafficking boosted transcytosis in cell-based blood-brain barrier models, while a single injection of fluvoxamine was sufficient to enable brain accumulation of a fluid-phase fluorescent tracer in vivo. These findings reveal modulation of membrane trafficking by ADs as a possible cellular mechanism of action and indicate their clinical repositioning potential for regulating drug delivery to the brain.

Update Lessons from PET Imaging Part II: A Systematic Critical Review on Therapeutic Plasma Concentrations of Antidepressants

BACKGROUND

Compared with antipsychotics, the relationship between antidepressant blood (plasma or serum) concentrations and target engagement is less well-established.

METHODS

We have discussed the literature on the relationship between plasma concentrations of antidepressant drugs and their target occupancy. Antidepressants reviewed in this work are citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, venlafaxine, duloxetine, milnacipran, tricyclic antidepressants (amitriptyline, nortriptyline, and clomipramine), bupropion, tranylcypromine, moclobemide, and vortioxetine. Four electronic databases were systematically searched.

RESULTS

We included 32 articles published 1996-2022. A strong relationship between serotonin transporter (SERT) occupancy and drug concentration is well established for selective serotonin reuptake inhibitors. Lower limits of recommended therapeutic reference ranges largely corroborate with the findings from positron emission tomography studies (80% SERT occupancy). Only a few novel studies have investigated alternative targets, that is, norepinephrine transporters (NETs), dopamine transporters (DATs), or monoamine oxidase A (MAO-A). For certain classes of drugs, positron emission tomography study data are inconclusive. Low DAT occupancy after bupropion treatment speculates its discussed mechanism of action. For MAO inhibitors, a correlation between drug concentration and MAO-A occupancy could not be established.

CONCLUSIONS

Neuroimaging studies are critical in TDM-guided therapy for certain antidepressants, whereas for bupropion and MAO inhibitors, the available evidence offers no further insight. Evidence for selective serotonin reuptake inhibitors is strong and justifies a titration toward suggested ranges. For SNRIs, duloxetine, and venlafaxine, NETs are sufficiently occupied, well above the SERT efficacy threshold. For these drugs, a titration toward higher concentrations (within the recommended range) should be considered in case of no response at lower concentrations.

Selective serotonin reuptake inhibitors: New hope in the fight against COVID-19

The emerging COVID-19 pandemic led to a dramatic increase in global mortality and morbidity rates. As in most infections, fatal complications of coronavirus affliction are triggered by an untrammeled host inflammatory response. Cytokine storms created by high levels of interleukin and other cytokines elucidate the pathology of severe COVID-19. In this respect, repurposing drugs that are already available and might exhibit anti-inflammatory effects have received significant attention. With the in vitro and clinical investigation of several studies on the effect of antidepressants on COVID-19 prognosis, previous data suggest that selective serotonin reuptake inhibitors (SSRIs) might be the new hope for the early treatment of severely afflicted patients. SSRIs' low cost and availability make them potentially eligible for COVID-19 repurposing. This review summarizes current achievements and literature about the connection between SSRIs administration and COVID-19 prognosis.

Use of Human Lung Tissue Models for Screening of Drugs against SARS-CoV-2 Infection

The repurposing of licenced drugs for use against COVID-19 is one of the most rapid ways to develop new and alternative therapeutic options to manage the ongoing pandemic. Given circa 7817 licenced compounds available from Compounds Australia that can be screened, this paper demonstrates the utility of commercially available ex vivo/3D airway and alveolar tissue models. These models are a closer representation of in vivo studies than in vitro models, but retain the benefits of rapid in vitro screening for drug efficacy. We demonstrate that several existing drugs appear to show anti-SARS-CoV-2 activity against both SARS-CoV-2 Delta and Omicron Variants of Concern in the airway model. In particular, fluvoxamine, as well as aprepitant, everolimus, and sirolimus, has virus reduction efficacy comparable to the current standard of care (remdesivir, molnupiravir, nirmatrelvir). Whilst these results are encouraging, further testing and efficacy studies are required before clinical use can be considered.

Low-Dose Fluvoxamine Modulates Endocytic Trafficking of SARS-CoV-2 Spike Protein: A Potential Mechanism for Anti-COVID-19 Protection by Antidepressants

Commonly prescribed antidepressants may be associated with protection against severe COVID-19. The mechanism of their action in this context, however, remains unknown. Here, I investigated the effect of an antidepressant drug fluvoxamine on membrane trafficking of the SARS-CoV-2 spike protein and its cell host receptor ACE2 in HEK293T cells. A sub-therapeutic concentration (80 nM) of fluvoxamine rapidly upregulated fluid-phase endocytosis, resulting in enhanced accumulation of the spike-ACE2 complex in enlarged early endosomes. Diversion of endosomal trafficking provides a simple cell biological mechanism consistent with the protective effect of antidepressants against COVID-19, highlighting their therapeutic and prophylactic potential.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Effect of catechol-O-methyltransferase Val(108/158)Met polymorphism on antidepressant efficacy of fluvoxamine

Rationale

The catechol-O-methyltransferase (COMT) enzyme inactivates catecholamines, and the COMT Val(108/158)Met polymorphism (rs4680) influences the enzyme activity. Recent clinical studies found a significant effect of rs4680 on antidepressant response to fluoxetine and paroxetine, but several other studies were negative. No study considered drug plasma levels as possible nuisance covariate.

Objectives

We studied the effect of rs4680 on response to fluvoxamine antidepressant monotherapy.

Patients and methods

Forty-one consecutively admitted inpatients affected by a major depressive episode in course of major depressive disorder were administered fluvoxamine for 6 weeks. Changes in severity of depression were assessed with weekly Hamilton Depression ratings and analyzed with repeated measures ANOVA in the context of General Linear Model, with rs4680 and fluvoxamine plasma levels as factors.

Results

rs4680 significantly interacted with time in affecting antidepressant response to fluvoxamine, with outcome being inversely proportional to the enzyme activity: better effects in Met-carriers, worse effects in Val/Val homozygotes. The effect became significant at the fourth week of treatment, and influence final response rates. Fluvoxamine plasma levels had marginal effects on outcome.

Conclusions

This is the first study that reports a positive effect of rs4680 on response to fluvoxamine, and the third independent report of its influence on response to selective 5-HT reuptake inhibitors (SSRIs). Our findings support the hypothesis that factors affecting catecholaminergic neurotransmission might contribute to shape the individual response to antidepressants irrespective of their primary molecular target.

Concentration-Effect Relationships of Psychoactive Drugs and the Problem to Calculate Therapeutic Reference Ranges

BACKGROUND

Despite the obvious potential of Therapeutic Drug Monitoring (TDM) as a tool to optimize psychopharmacotherapy, especially treatment with mood-stabilizing, antidepressant and antipsychotic drugs, acceptance of TDM as a routine tool is still limited. A serious scientific argument against the regular use of TDM is the lack of evidence for a concentration-dependent clinical effect. The aim of this review was to highlight methodological problems leading to poor or even negative concentration-effect relationships and to show how therapeutically effective concentrations of psychoactive drugs can be determined using routine TDM databases.

METHODS

Reports on concentration-effect relationships of psychoactive drugs were analyzed with regard to applied methods. From routine TDM databases of patients who had been treated with antidepressant or antipsychotic drugs and whose improvement was measured by the clinical global impressions scale, mean and median drug concentrations were calculated and compared with reference ranges recommended by TDM guidelines.

RESULTS

Few fixed-dose studies with adequate design and data analysis demonstrated a correlation between drug concentration and clinical effect for psychoactive drugs. Most studies, however, mostly retrospective analyses of TDM databases, failed to find significant concentration-effect relationships because of flexible dosing. They were not suitable for the determination of therapeutically effective drug concentrations. Using TDM databases of antidepressant and antipsychotic drug concentrations in blood of patients who were categorized as responders by the clinical global impressions score, the interquartile ranges of drug concentrations (25th-75th percent range) can be shown to be very close to the therapeutic reference ranges recommended in guidelines for TDM in psychiatry.

CONCLUSIONS

This review provides a discussion on why simple correlation analyses of psychoactive drug concentrations in blood and clinical effects are obsolete for flexible-dose studies or TDM databases. TDM databases, however, can and should be used to calculate drug concentrations in blood of patients who had responded to the drugs. Interquartile ranges can be regarded and used as preliminary therapeutic reference ranges.

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.

5-HTR1A and 5-HTR2A genetic polymorphisms and SSRI antidepressant response in depressive Chinese patients

OBJECTIVE

Genetic variabilities within the serotoninergic system may predict response or remission to antidepressant drugs. Several serotonin receptor (5-HTR) gene polymorphisms have been associated with susceptibility to psychiatric diseases. In this study, we analyzed the correlation between 5-HTR1A and 5-HTR2A polymorphisms and response or remission to selective serotonin reuptake inhibitors (SSRIs) drugs.

METHODS

Two hundred and ninety patients who met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for major depressive disorder were involved in this study. SSRIs (fluoxetine, paroxetine, citalopram, or sertraline) were selected randomly for treatment. The Hamilton Rating Scale for Depression was used to evaluate the antidepressant effect. To assess 5-HTR gene variabilities, two single-nucleotide polymorphisms in 5-HTR1A (rs1364043 and rs10042486) and three in 5-HTR2A (rs6311, rs6313, and rs17289304) were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using the Sequenom MassARRAY Analyzer 4 system.

RESULTS

There were 220 responders and 70 nonresponders (120 remissioners and 170 nonremissioners) after 6 weeks of treatment. We found no association between any of the five 5-HTR1A and 5-HTR2A gene polymorphisms and antidepressant drug response or remission (P>0.05). It is worth mentioning that TT genotype frequency of rs10042486 was significantly different from the CT genotype frequency between responders and nonresponders, although the significance was not maintained after correcting for multiple testing.

CONCLUSION

Thus, 5-HTR1A and 5-HTR2A gene polymorphisms may not play an important role in antidepressant drug response or remission.

Selective serotonin reuptake inhibitors facilitate ANO6 (TMEM16F) current activation and phosphatidylserine exposure

Anoctamin 6 (ANO6) is a member of the recently identified TMEM16/anoctamin protein family comprising Ca(2+)-activated Cl(-) channels that generate outward-rectifying ionic currents in response to intracellular Ca(2+) increase. ANO6 is also essential for Ca(2+)-dependent phospholipid scrambling required for blood coagulation. Selective serotonin reuptake inhibitors (SSRIs)--fluoxetine, sertraline, and paroxetine-that are used for the treatment of major depressive disorders can increase the risk of upper gastrointestinal bleeding after chronic treatment. However, at the earlier stage of intake, which is 1-7 days after the treatment, the possibility of blood coagulation might also increase, but transiently. Therefore, in this study, we investigated whether therapeutic SSRI concentrations affected the Cl(-) current or phospholipid scrambling activity of ANO6 by assessing ANO6 currents (I ANO6), phosphatidylserine (PS) exposure, and platelet aggregation. In the whole-cell patch mode, SSRIs facilitated Ca(2+)-dependent activation of IANO6 in ANO6-transfected cells, as evidenced by a significant decrease in the delay of IANO6 generation. On the other hand, in the inside-out patch clamp configuration, SSRIs showed an inhibitory effect on ANO6 currents, suggesting that SSRIs activate ANO6 via an indirect mechanism in intact cells. SSRIs also facilitated Ca(2+)-dependent PS exposure and α-thrombin-induced platelet aggregation. These results indicate that SSRIs at clinically relevant concentrations promote Ca(2+)-dependent activation of ANO6, which may have potential clinical implications such as the underlying mechanism of SSRI-induced adverse drug reactions.

Aging and Clinical Pharmacology: Implications for Antidepressants

The elderly frequently have changes in pharmacokinetics, sensitivity to medications, homeostatic reserve (ability to tolerate physiological challenges), exposure to multiple medications, and adherence. All of these age-associated factors can potentially influence total exposure to medication, adverse effects, and subsequent treatment outcome. Most clinical trials are performed with healthy, younger adults. Extrapolating the results of these trials to the elderly may be inappropriate, particularly for the antidepressant treatment of depression. The authors review these age-associated differences and discuss their implications for antidepressant use in older adults.

GTP cyclohydrolase 1 gene haplotypes as predictors of SSRI response in Japanese patients with major depressive disorder

BACKGROUND

Tetrahydrobiopterin (BH4) plays an important role in the biosynthesis of serotonin, melatonin and catecholamines, all of which are implicated in the pathophysiology of mood disorders (MDs), including major depressive disorder (MDD) and bipolar disorder (BP). Production of BH4 is regulated by GTP cyclohydrolase transcription and activity. Thus, we considered the GTP cyclohydrolase gene (GCH1) to be a good candidate gene in the pathophysiology of MDs and of the serotonin selective reuptake inhibitors (SSRIs) response in MDD, and conducted a case-control study utilizing three SNPs (rs8007267, rs3783641 and rs841) and moderate sample sizes (405 MDD patients, including 262 patients treated by SSRIs, 1022 BP patients and 1805 controls).

METHOD

A multiple logistic regression analysis was carried out to compare the frequencies of each SNP genotype for the target phenotype across patients and controls in several genetic models, while adjusting for possible confounding factors. A clinical response was defined as a decrease of more than 50% from the baseline score on the Structured Interview Guide for Hamilton Rating Scale for Depression (SIGH-D) within 8 weeks, and clinical remission as a SIGH-D score of less than 7 at 8 weeks.

RESULT

No associations between three SNPs in GCH1 and MDD or BP were observed; however, GCH1 was associated with SSRI therapeutic response in MDD in all the marker's haplotype analysis (Global P value=0.0379).

CONCLUSIONS

Results suggest that GCH1 may predict response to SSRI in MDD in the Japanese population. Nevertheless, a replication study using larger samples may be required for conclusive results, since our sample size was small.

Plasma fluvoxamine levels and OCD symptoms/response in adult patients

OBJECTIVE

In this study, we explored the possible relationships between plasma fluvoxamine levels and clinical features and/or response in adult obsessive-compulsive disorder (OCD) patients treated with this drug for 6 months.

METHODS

Twenty OCD outpatients of both sexes who were already taking fluvoxamine (mean dose ± SD: 216.7 ± 86.2) for at least 4 weeks were included in the study. The severity of OCD was assessed by means of the Yale-Brown obsessive-compulsive scale (Y-BOCS). The fluvoxamine plasma levels were measured by high-performance liquid chromatography analysis. All evaluations were performed after 4 weeks (t1) and 6 months (t2) of fluvoxamine intake.

RESULTS

The plasma levels of fluvoxamine remained stable at the two assessment times, with no sex-related differences. Sixteen (80%) patients responded to treatment as shown by the significant (>35%) decrease of the Y-BOCS total score. Men's compulsions improved more than those of women. Significant and positive correlations were detected between fluvoxamine plasma levels at t1 and t2 and the difference (delta) of the Y-BOCS total and compulsion subscale scores between t1 and t2. Another significant, albeit negative, correlation was measured between the difference of the compulsion subscale score and the difference of fluvoxamine levels at t1 and t2.

CONCLUSIONS

These findings underline the potential importance of evaluating fluvoxamine plasma levels in OCD and their relationships with the clinical response that may be gender-related on specific symptoms.

Onset of clinical effects and plasma concentration of fluvoxamine in Japanese patients

It is widely accepted that selective serotonin reuptake inhibitors (SSRIs) require 2 to 4 weeks of administration before improvements in emotional symptoms of depression are seen. We evaluated whether early monitoring of Hamilton Rating Scale for Depression (HAMD) scores in patients treated with the SSRI fluvoxamine could predict antidepressant response, and also assessed the relationship between the onset of clinical response following the start of fluvoxamine administration and its plasma concentration. Twelve depressed patients (baseline HAMD score ≥15) received an initial dose of fluvoxamine (50 mg/d) followed by an optimized maintenance dose according to their clinical symptoms after 7 d. HAMD scores and plasma drug concentrations were determined at 7 and 28 d after the first administration. There were 7 responders and 5 non-responders on day 28, as evaluated by HAMD scores. The HAMD score for the responders was significantly lower than that for the non-responders on day 7 (mean±S.D., 11.6±6.1 vs. 26.6±6.5, p=0.006). Thus, the reduction in HAMD score on day 7 was clearly divided between responders and non-responders. On day 28, the plasma concentration of fluvoxamine in responders was lower than that in non-responders (14.2±10.5 ng/ml vs. 44.2±28.1 ng/ml, p=0.051). Furthermore, receiver operating characteristic curve analysis conducted on day 28 revealed an upper concentration threshold of 28.2 ng/ml (p=0.042), with none in the responder group above that level. Our results suggest that HAMD score after the first week of treatment with fluvoxamine and the upper threshold of plasma drug concentration could predict whether a patient is a non-responder.

CYP2D6 genotype and smoking influence fluvoxamine steady-state concentration in Japanese psychiatric patients: lessons for genotype-phenotype association study design in translational pharmacogenetics

The CYP2D6 enzyme is a capacity-limited high-affinity drug elimination pathway that metabolizes numerous psychiatric medicines. The capacity-limited nature of this enzyme suggests that drug dose may serve as an important factor that influence genotype-phenotype associations. However, dose dependency of CYP2D6 genotype contributions to drug elimination, and its interaction with environmental factors (e.g., smoking) did not receive adequate attention in translational study designs. Fluvoxamine is a selective serotonin reuptake inhibitor antidepressant. Fluvoxamine concentration is one of the factors previously linked to clinical remission in moderate to severe depression. We investigated the joint effect of smoking (an inducer of CYP1A2) and CYP2D6 genotype on interindividual variability in fluvoxamine steady-state concentration. Fluvoxamine concentration was measured in 87 patients treated with 50, 100, 150 or 200 mg/d. While CYP2D6 genotype significantly influenced fluvoxamine concentration in all four dose groups (p < 0.05), the percentage variance explained (R²) by CYP2D6 decreased as the dose of fluvoxamine increased. Smoking status (nonsmokers vs. smoking 20 or more cigarettes/d) significantly affected fluvoxamine concentration in the 50 mg/d group only (p = 0.005). Together, CYP2D6 genotype and smoking status explained 23% of the variance in fluvoxamine concentration but only at the low 50 mg/d dose group. These findings contribute to evidence-based and personalized choice of fluvoxamine dose using smoking status and CYP2D6 genetic variation. Additionally, these data lend evidence for drug dose as an important variable in translational pharmacogenetic study design and pharmaceutical phenotype associations with capacity-limited drug metabolism pathways such as CYP2D6.

Classification of drugs based on properties of sodium channel inhibition: a comparative automated patch-clamp study

Background

There is only one established drug binding site on sodium channels. However, drug binding of sodium channels shows extreme promiscuity: ∼25% of investigated drugs have been found to potently inhibit sodium channels. The structural diversity of these molecules suggests that they may not share the binding site, and/or the mode of action. Our goal was to attempt classification of sodium channel inhibitors by measuring multiple properties of inhibition in electrophysiology experiments. We also aimed to investigate if different properties of inhibition correlate with specific chemical properties of the compounds.

Methodology/Principal Findings

A comparative electrophysiological study of 35 compounds, including classic sodium channel inhibitors (anticonvulsants, antiarrhythmics and local anesthetics), as well as antidepressants, antipsychotics and neuroprotective agents, was carried out using rNav1.2 expressing HEK-293 cells and the QPatch automatic patch-clamp instrument. In the multi-dimensional space defined by the eight properties of inhibition (resting and inactivated affinity, potency, reversibility, time constants of onset and offset, use-dependence and state-dependence), at least three distinct types of inhibition could be identified; these probably reflect distinct modes of action. The compounds were clustered similarly in the multi-dimensional space defined by relevant chemical properties, including measures of lipophilicity, aromaticity, molecular size, polarity and electric charge. Drugs of the same therapeutic indication typically belonged to the same type. We identified chemical properties, which were important in determining specific properties of inhibition. State-dependence correlated with lipophilicity, the ratio of the neutral form of molecules, and aromaticity: We noticed that the highly state dependent inhibitors had at least two aromatic rings, logP>4.0, and pKa<8.0.

Conclusions/Significance

The correlations of inhibition properties both with chemical properties and therapeutic profiles would not have been evident through the sole determination of IC₅₀; therefore, recording multiple properties of inhibition may allow improved prediction of therapeutic usefulness.

Fluvoxamine versus other anti-depressive agents for depression

BACKGROUND

Fluvoxamine, one of the oldest selective serotonin reuptake inhibitors (SSRIs), is prescribed to patients with major depression in many countries. Several studies have previously reviewed the efficacy and tolerability of fluvoxamine for the treatment of major depression. However, these reviews are now outdated.

OBJECTIVES

Our objective is to evaluate the effectiveness, tolerability and side effect profile of fluvoxamine for major depression in comparison with other anti-depressive agents, including tricyclics (TCAs), heterocyclics, other SSRIs, SNRIs, other newer agents and other conventional psychotropic drugs.

SEARCH STRATEGY

We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Register. Trial databases and ongoing trial registers in North America, Europe, Japan and Australia, were handsearched for randomised controlled trials. We checked reference lists of the articles included in the review, previous systematic reviews and major textbooks of affective disorder for published reports and citations of unpublished research. The date of last search was 31 August 2008.

SELECTION CRITERIA

We included all randomised controlled trials, published in any language, that compared fluvoxamine with any other active antidepressants in the acute phase treatment of major depression.

DATA COLLECTION AND ANALYSIS

Two independent review authors inspected citations and abstracts, obtained papers, extracted data and assessed the risk of bias of included studies. We analysed dichotomous data using odds ratios (ORs) and continuous data using the standardised mean difference (SMD). A random effects model was used to combine studies.

MAIN RESULTS

A total of 54 randomised controlled trials (n = 5122) were included. No strong evidence was found to indicate that fluvoxamine was either superior or inferior to other antidepressants regarding response, remission and tolerability. However, differing side effect profiles were evident, especially with regard to gastrointestinal side effects of fluvoxamine when compared to other antidepressants. For example, fluvoxamine was generally associated with a higher incidence of vomiting/nausea (versus imipramine, OR 2.23, CI 1.59 to 3.14; versus clomipramine, OR 2.13, CI 1.06 to 4.27; versus amitriptyline, OR 2.86, CI 1.31 to 2.63).

AUTHORS' CONCLUSIONS

We found no strong evidence that fluvoxamine was either superior or inferior to any other antidepressants in terms of efficacy and tolerability in the acute phase treatment of depression. However, differing side effect profiles were evident. Based on these findings, we conclude that clinicians should focus on practical or clinically relevant considerations, including these differences in side effect profiles.

A case with occurring adverse effects when cross-over titration from fluvoxamine to paroxetine associated with increasing the plasma fluvoxamine level in major depressive disorder

Selective serotonin reuptake inhibitors (SSRIs) are first line drugs for treating not only depressive disorder but also anxiety disorder. Fluvoxamine, a SSRI, is mainly metabolized by cytochrome P450 (CYP) 2D6 and 1A2. However, paroxetine, an another SSRI is potent inhibitor for CYP 2D6. We report a case with depression whose plasma fluvoxamine level rapidly increased after the addition of paroxetine while switching from fluvoxamine to paroxetine. The case indicates that emerging adverse effects via the pharmacokinetic interaction of these drugs when switching patients from fluvoxamine to paroxetine can occur.

HTR2A is associated with SSRI response in major depressive disorder in a Japanese cohort

Several recent investigations reported that the serotonin 2A receptor gene (HTR2A) was associated with selective serotonin reuptake inhibitors (SSRIs) in major depressive disorder. There have also been two reported association analyses of HTR2A with SSRI response in Japanese MDD patients, but the results were rather inconsistent and both studies had the problem of small sample sizes. Therefore, we conducted a replication association study using a sample larger than those in the two original Japanese studies (265 MDD patients), and found that four SNPs, two functional SNPs (-A1438G: rs6311 and T102C: rs6313) and two SNPs (rs7997012 and rs1928040) in HTR2A, were associated with the therapeutic response to SSRIs. HTR2A was associated with the therapeutic response SSRIs in Japanese MDD patients in a haplotype-wise analysis (P(all markers) = 0.0136), and a significant association between rs1928040 in HTR2A and SSRI response was detected in MDD (P(allele-wise analysis) = 0.0252). However, this significance disappeared after Bonferroni correction (P(allele-wise analysis) = 0.101). In conclusion, we suggest that HTR2A may play an important role in the pathophysiology of the therapeutic response to SSRIs in Japanese MDD patients. However, it will be important to replicate and confirm these findings in other independent studies using large samples.

Concentration-response relationship for fluvoxamine using remission as an endpoint: a receiver operating characteristics curve analysis in major depression

Therapeutic drug monitoring studies of selective serotonin reuptake inhibitor (SSRI) antidepressants thus far failed to identify a clear concentration-response relationship in major depression. Majority of the previous studies defined clinical response as 50% or greater reduction from baseline in depression rating scale scores. Because many patients who meet these criteria still present symptoms associated with functional impairment, there is a need to consider "remission" as an alternative end point in concentration-response analyses of SSRIs. The present 12-week prospective study investigated the relationship between fluvoxamine (an SSRI) plasma concentration and remission in outpatients with depression. We used a flexible dose titration study designed to mimic clinical practice within the therapeutic dose range of fluvoxamine (25-200 mg/d). Receiver operating characteristics (ROC) curve was computed to determine the optimal fluvoxamine plasma concentration for remission using 269 concentration data obtained from 80 patients. Analysis of the ROC curve from the entire study sample did not reveal a fluvoxamine concentration significantly predicting remission. By contrast, ROC analysis specifically in patients with moderate to severe depression (N = 51; baseline 17-item Hamilton Rating Scale for Depression score > or = 20) found a fluvoxamine concentration of 61.4 ng/mL as a significant predictor of remission. In conclusion, therapeutic drug monitoring may be useful for rational titration and individualization of fluvoxamine dose and predicting remission in patients with moderate to severe depression, who may presumably display lesser placebo component in pharmacodynamic response.

Association study between vesicle-associated membrane protein 2 gene polymorphisms and fluvoxamine response in Japanese major depressive patients

BACKGROUND

Vesicle-associated membrane protein 2 (VAMP2) is a key component of the synaptic vesicle docking/fusion machinery and its mRNA reportedly increases in the frontal cortex of rats following chronic antidepressant and electroconvulsive treatment. VAMP2 is therefore thought to be involved in the mechanism of action of antidepressants and may alter their efficacy. The purpose of this study was to investigate whether the VAMP2 gene is associated with clinical responses to a specific antidepressant, fluvoxamine.

METHODS

A total of 106 patients with major depressive disorder were given fluvoxamine (50-200 mg/day) for 8 weeks and assessed for severity of depression using the Semi-Structured Interview Guide of the Hamilton Depressive Scale (SIGH-D; 17 items) at 0 and 8 weeks. We defined a clinical response as more than a 50% reduction in baseline SIGH-D within 8 weeks, and defined clinical remission as a SIGH-D score of less than 7 at 8 weeks. Genotyping was performed by PCR-RFLP.

RESULTS

Analysis of haplotype tagging single nucleotide polymorphisms as well as haplotype analysis did not reveal any significant associations.

CONCLUSION

Our results suggest that the VAMP2 gene is unlikely to play a major role in the efficacy of fluvoxamine.

Sodium channel blockade may contribute to the analgesic efficacy of antidepressants

Sodium channel blockers such as lidocaine, lamotrigine, and carbamazepine can be effective in the treatment of neuropathic pain. Though not approved for neuropathic pain indications, tricyclic antidepressants are often considered first-line treatment for conditions such as post-herpetic neuralgia and diabetic neuropathy. Several tricyclic antidepressants have been shown to block peripheral nerve sodium channels, which may contribute to their antihyperalgesic efficacy. In this study, we compared the sodium channel-blocking potency of a number of antidepressants, including tricyclic antidepressants and selective serotonin reuptake inhibitors. All compounds tested inhibited Na(V)1.7 in a state- and use-dependent manner, with affinities for the inactivated state ranging from 0.24 micromol/L for amitriptyline to 11.6 micromol/L for zimelidine. The tricyclic antidepressants were more potent blockers of Na(V)1.7. Moreover, IC(50)s for block of the inactivated state for amitriptyline, nortriptyline, imipramine, desipramine, and maprotiline were in the range of therapeutic plasma concentrations for both the treatment of depression as well as neuropathic pain. By contrast, fluoxetine, paroxetine, mianserine, and zimelidine had IC(50)s for Na(V)1.7 outside their therapeutic concentration ranges and generally were not efficacious against post-herpetic neuralgia or diabetic neuropathy. These results suggest that block of peripheral nerve sodium channels may contribute to the antihyperalgesic efficacy of certain antidepressants.

PERSPECTIVE

Tricyclic antidepressants are often considered first-line treatment for neuropathic pain. Some tricyclic antidepressants block sodium channels, which may contribute to their antihyperalgesic efficacy. In the current study, we compared the potency of peripheral sodium channel blockade for several tricyclic antidepressants and selective serotonin reuptake inhibitors with their therapeutic efficacy.

Atypical tetracyclic antidepressant maprotiline is an antagonist at cardiac hERG potassium channels

Maprotiline is an antidepressant compound with an atypical tetracyclic structure that is widely used in elderly patients due to its favourable side-effect profile. However, there have been reports of proarrhythmia associated with maprotiline and in vitro studies of its electrophysiological properties have been lacking. Therefore, we characterised the effects of maprotiline on cardiac hERG channels. hERG channels were expressed in HEK cells and in the Xenopus oocyte expression system. Currents were measured using a whole-cell patch clamp and a two-microelectrode voltage-clamp. Maprotiline inhibited hERG currents with an IC(50) of 8.2 micromol/l in HEK cells and 29.2 micromol/l in Xenopus oocytes. Onset of the effect was rather slow and took several minutes. No wash-out of effect was observed. Maprotiline blocked hERG channels in the open and inactivated states, but not in the closed states. In mutant hERG channels Y652A and F656A, the effect was markedly attenuated (hERG-F656A) or completely abolished (hERG-Y652A). Voltage dependence of hERG current activation and inactivation was not affected by maprotiline. hERG inactivation was accelerated at positive potentials. The effect of maprotiline on hERG currents was voltage-dependent with a marked reduction at a more positive potential. hERG blockade by maprotiline was not frequency-dependent. Maprotiline is an antagonist of cardiac hERG potassium channels that preferably accesses the putative pore binding site Y652/F656. Although the affinity of maprotiline to hERG channels is low, its use in patients with risk factors for acquired long QT syndrome should be monitored appropriately.

The AGNP-TDM Expert Group Consensus Guidelines: focus on therapeutic monitoring of antidepressants

Therapeutic drug monitoring (TDM) of psychotropic drugs such as antidepressants has been widely introduced for optimization of pharmacotherapy in psychiatric patients. The interdisciplinary TDM group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) has worked out consensus guidelines with the aim of providing psychiatrists and TDM laboratories with a tool to optimize the use of TDM. Five research-based levels of recommendation were defined with regard to routine monitoring of drug plasma concentrations: (i) strongly recommended; (ii) recommended; (iii) useful; (iv) probably useful; and (v) not recommended. In addition, a list of indications that justify the use of TDM is presented, eg, control of compliance, lack of clinical response or adverse effects at recommended doses, drug interactions, pharmacovigilance programs, presence of a genetic particularity concerning drug metabolism, and children, adolescents, and elderly patients. For some drugs, studies on therapeutic ranges are lacking, but target ranges for clinically relevant plasma concentrations are presented for most drugs, based on pharmacokinetic studies reported in the literature. For many antidepressants, a thorough analysis of the literature on studies dealing with the plasma concentration-clinical effectiveness relationship allowed inclusion of therapeutic ranges of plasma concentrations. In addition, recommendations are made with regard to the combination of pharmacogenetic (phenotyping or genotyping) tests with TDM. Finally, practical instructions are given for the laboratory practitioners and the treating physicians how to use TDM: preparation of TDM, drug analysis, reporting and interpretation of results, and adequate use of information for patient treatment TDM is a complex process that needs optimal interdisciplinary coordination of a procedure implicating patients, treating physicians, clinical pharmacologists, and clinical laboratory specialists. These consensus guidelines should be helpful for optimizing TDM of antidepressants.

Relationship between clinical effects of fluvoxamine and the steady-state plasma concentrations of fluvoxamine and its major metabolite fluvoxamino acid in Japanese depressed patients

OBJECTIVES

The relationship between clinical effects of fluvoxamine (FLV) and the steady-state plasma concentrations (Css) of FLV and its major metabolite fluvoxamino acid (FLA) was studied.

METHODS

The subjects were 49 Japanese patients with major depressive disorder receiving FLV 200 mg/day for 6 weeks. Depressive symptoms and side effects were evaluated by the Montgomery Asberg Depression Rating Scale (MADRS), and the UKU Side Effect Rating Scale, respectively. The Css of FLV and FLA were measured by HPLC, and the CYP2D6 genotyping was performed by PCR methods.

RESULTS

The Css of FLV and FLV+FLA showed significant negative correlations with the final MADRS score. The Css of FLV, FLA and FLV+FLA were significantly higher in the responders (final MADRS score < or =10) than in non-responders. The proportion of responders was significantly higher in the patients with the Css of FLV, FLA and FLV+FLA above 150, 55 and 180 ng/ml, respectively. In the multiple regression, the Css of FLV+FLA showed a significant negative correlation with the final MADRS score. In the logistic regression, the Css of FLA had a significant effect on the differentiation of responders from non-responders. The incidence of side effects was low, and the development of nausea, the most frequent one, was not dependent on any Css. The number of mutated CYP2D6 alleles causing absent or decreased enzyme activity was not related to the therapeutic response or development of nausea.

CONCLUSIONS

The present study suggests that there is a therapeutic threshold for the Css of FLV and probably also for the Css of FLA, and the Css of FLV+FLA above 180 ng/ml best predicts a good therapeutic response.

Suitable dose and duration of fluvoxamine administration to treat depression

The purpose of the present paper was to determine the suitable dose and appropriate trial duration of fluvoxamine to treat for depression. A retrospective cohort analysis was performed among depression patients who were treated in the Department of Psychiatry, Kawasaki Medical School Hospital, Kurashiki, Japan, in 2000. A total of 72 patients received fluvoxamine to treat depression. The dose-response was compared and the initial significant clinical action was examined. The percentage showing improvement after receiving a high daily dose (100-150 mg) of fluvoxamine was 73.7%, but that showing improvement on a low daily dose (50-75 mg) was 47.1%. A significant difference between the two groups was seen on Kaplan-Meier analysis and log-rank test (chi2 = 4.814; d.f. = 1; P = 0.0282). The cumulative percentage of responder patients was more than 80% at the end of a 6-week period. Fluvoxamine is recommended at a daily dose of 100 mg or 150 mg as the initial dose. If a patient does not show improvement by the end of 6 weeks the treatment regimen of fluvoxamine should be altered.

Association between -1438G/A promoter polymorphism in the 5-HT(2A) receptor gene and fluvoxamine response in Japanese patients with major depressive disorder

Genetic polymorphism of the serotonin 5-HT(2A) receptor seems to be associated with therapeutic response to selective serotonin reuptake inhibitors (SSRIs). The present study investigated whether a novel -1438G/A polymorphism in the promoter region of the 5-HT(2A )receptor gene is associated with therapeutic response to fluvoxamine (an SSRI) in 66 Japanese patients with major depressive disorder. Fluvoxamine (50 to 200 mg) was administered twice daily for 6 weeks. Fifty-four patients completed this study. The genotype distribution and the allele frequencies showed no significant difference between responders and non-responders. The time-course of the Montgomery-Asberg Depression Rating Scale scores showed no significant difference among -1438G/G, -1438G/A, and -1438A/A genotype groups. The results demonstrated that the -1438G/A promoter polymorphism in the 5-HT(2A) receptor gene was unlikely to have a major role in therapeutic response to fluvoxamine in Japanese patients with major depressive disorder.

Role of selective serotonin reuptake inhibitors in psychiatric disorders: a comprehensive review

The selective serotonin reuptake inhibitors (SSRIs) have emerged as a major therapeutic advance in psychopharmacology. As a result, the discovery of these agents marks a milestone in neuropsychopharmacology and rational drug design, and has launched a new era in psychotropic drug development. Prior to the SSRIs, all psychotropic medications were the result of chance observation. In an attempt to develop a SSRI, researchers discovered a number of nontricyclic agents with amine-uptake inhibitory properties, acting on both noradrenergic and serotonergic neurons with considerable differences in potency. A given drug may affect one or more sites over its clinically relevant dosing range and may produce multiple and different clinical effects. The enhanced safety profile includes a reduced likelihood of pharmacodynamically mediated adverse drug-drug interactions by avoiding affects on sites that are not essential to the intended outcome. SSRIs were developed for inhibition of the neuronal uptake pump for serotonin (5-HT), a property shared with the TCAs, but without affecting the other various neuroreceptors or fast sodium channels. The therapeutic mechanism of action of SSRIs involves alteration in the 5-HT system. The plethora of biological substrates, receptors and pathways for 5-HT are candidates to mediate not only the therapeutic actions of SSRIs, but also their side effects. A hypothesis to explain these immediate side effects is that 5-HT is increased at specific 5-HT receptor subtypes in discrete regions of the body where the relevant physiologic processes are regulated. Marked differences exist between the SSRIs with regard to effects on specific cytochrome P450 (CYP) enzymes, and thus the likelihood of clinically important pharmacokinetic drug-drug interactions. Although no clear relationship exists between the clinical efficacy, plasma concentration of SSRIs, nor any threshold that defines toxic concentrations, but therapeutic drug monitoring (TDM) may be useful in special populations, such as in elderly patients, poor metabolizers (PM) of sparteine (CYP2D6) or mephenytoin (CYP2C19), and patients with liver and kidney impairment. Several meta-analyses have reviewed the comparative efficacy of TCAs and SSRIs, and concluded that both TCAs and SSRIs have similar efficacy in the treatment of depression. SSRIs have demonstrated better efficacy and tolerability in the treatment of obsessive compulsive disorder (OCD). They have also been found to be effective in the treatment for social anxiety disorder both in reducing total levels of social anxiety and in improving overall clinical condition. The benefit of SSRIs in anorexia nervosa (AN) is apparently short-term unless medication is given in the context of nutritional or behavioral therapy. No single antidepressant can ever be recommended for every patient, but in a vast majority of patients, SSRIs should be considered as one of the first-line drugs in the treatment of depression.

Monoamine oxidase: A gene polymorphism, tryptophan hydroxylase gene polymorphism and antidepressant response to fluvoxamine in Japanese patients with major depressive disorder

Monoamine oxidase A (MAOA) and tryptophan hydroxylase (TPH) are the staple enzymes in the metabolism of serotonin (5-HT). The genetic polymorphisms of these two enzymes might individually alter the production, release, reuptake or degradation of 5-HT during the treatment of selective serotonin reuptake inhibitors (SSRIs), leading to the individual differences in the antidepressant effects of SSRIs. The authors investigated whether a functional polymorphism in the MAOA gene promoter (MAOA-VNTR) and a TPH gene polymorphism in intron 7 (TPH-A218C) were associated with the antidepressant response to fluvoxamine in 66 Japanese patients with major depressive disorder during a 6-week study with a specific dosage plan. Fifty-four patients completed the study. The present study fails to demonstrate that the genetic polymorphisms of MAOA-VNTR and TPH-A218C affect the antidepressant effect of fluvoxamine in Japanese patients with major depressive disorder.

A variable number of tandem repeats in the serotonin transporter gene does not affect the antidepressant response to fluvoxamine

A variable number of tandem repeats (VNTR) in the second intron of the serotonin transporter gene (STin2) has been studied in association with the susceptibility to affective disorders. Recently, it was reported that selective serotonin reuptake inhibitors were more effective in patients with major depressive disorder having the homozygous allele pair (12-copy/12-copy) of VNTR in the STin2 than in ones having other allele combinations. As the study had methodological problems, further studies are needed to confirm the above finding. Therefore, the authors investigated whether the allelic variation of VNTR in the STin2 was associated with the antidepressant response to fluvoxamine in 66 patients with major depressive disorder. Fluvoxamine was prescribed up to 200 mg/day in the dosing protocol for 6 weeks. The present study showed no significant association between the polymorphism of VNTR in the STin2 and the treatment response to fluvoxamine.

Fluvoxamine treatment of mixed anxiety and depression: evidence for serotonergically mediated anxiolysis

Although increasing evidence suggests that selective serotonin reuptake inhibitor (SSRI) treatment may be effective for anxiety in addition to depression, SSRI anxiolysis has not been definitively related to the inhibition of serotonin (5-HT) transport. The gene that encodes for the human serotonin transporter (5-HTT) expresses its protein in neurons and in blood platelets, and both tissues respond to transport inhibition similarly in response to SSRI treatment. This study examined the relationship between the change in the 5-HTT's apparent affinity for 5-HT and the anxiolytic response in a group of 18 fluvoxamine-treated patients meeting Structured Clinical Interview for DSM-IV criteria for both generalized anxiety disorder and major depression. Significant decreases were found in both Hamilton anxiety and Hamilton depression scores over a 2-month treatment period. Robust increases were found in the apparent affinity constant (Km) for platelet 5-HT transport with treatment, and the increases covaried significantly with the decrease in anxiety (F = 4.97, p < 0.03). The pretreatment 5-HTT Km significantly correlated with the improvement in depression scores (r = 0.53, p < 0.03), consistent with the Hypothesis of Initial Conditions. These results suggest that the therapeutic effect of SSRI treatment can be linked to the magnitude and time-course of 5-HT transport inhibition effected with fluvoxamine, a drug that seems to have an antianxiety effect of the same magnitude as its effect on depression.

Fluvoxamine as an adjunctive agent in schizophrenia

Schizophrenia is a common mental disorder that has an early onset and rates high as a cause of medical disability. Antipsychotic agents are the mainstay of treatment but response is often inadequate. Negative symptoms (disturbances in volition, social interaction and affective functions) are particularly difficult to treat and form a major obstacle to rehabilitation. A promising approach to improve response of negative symptoms has been to add a selective serotonin reuptake inhibitor (SSRI) antidepressant to antipsychotic treatment. This review examines evidence pertaining to the efficacy, tolerability, and safety of the SSRI fluvoxamine, combined with antipsychotic agents, in the treatment of negative symptoms in schizophrenia. Important methodological issues, such as differentiating primary and secondary negative symptoms, are discussed. The balance of available evidence indicates that fluvoxamine can improve primary negative symptoms in chronic schizophrenia patients treated with typical antipsychotics and suggests that it may also do so in some patients treated with clozapine. This combination is generally safe and well tolerated although, as antipsychotic drug concentrations may be elevated, attention to dose and drug monitoring should be considered appropriately. Combination with clozapine may require particular caution because of potential toxicity if serum clozapine levels rise steeply. The fluvoxamine doses effective in augmentation are lower than those usually used to treat depression. Evidence regarding the use of fluvoxamine augmentation to treat phenomena, such as obsessions and aggression, which may be associated with schizophrenia, is also examined. An important goal of future studies will be to define which patient groups can benefit from combined treatment.

Is therapeutic drug monitoring a case for optimizing clinical outcome and avoiding interactions of the selective serotonin reuptake inhibitors?

The selective serotonin reuptake inhibitors (SSRIs) comprise citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline and they differ from each other in chemical structure, by pharmacokinetic properties and, most importantly, with respect to enzyme-specific metabolism and interactions. Citalopram is administered as a racemic mixture. The drug is oxidated to desmethylcitalopram in the liver, partially by CYP2C19 and partially by CYP3A4. Fluoxetine is administered as a racemate of R- and S-fluoxetine. Both R- and S-fluoxetine are metabolized by CYP2D6 to the active metabolites R- and S-norfluoxetine. Fluvoxamine is metabolized to inactive metabolites by CYP1A2 and CYP2D6. Paroxetine is metabolized to inactive metabolites partially by CYP2D6, and accordingly the metabolism of paroxetine is dependent on the genetic polymorphism of CYP2D6. Sertraline is metabolized to desmethylsertraline, probably by CYP3A4. Several analytical methods have been described for all SSRIs. Most assays are based on separation by high-performance liquid chromatography or gas chromatography. Stereoselective methods for the analysis of racemic citalopram and fluoxetine have been published. The SSRIs are generally well tolerated and their therapeutic indices are large. In several studies there has not been found a clear relationship between clinical efficacy and plasma concentration, nor any threshold that defines toxic concentrations. The available data do not suggest that any benefit be obtained from routine monitoring of SSRI plasma levels. Therefore therapeutic drug monitoring (TDM) of the SSRIs may be useful mainly in situations where poor compliance is suspected and when therapeutic failure or toxic events are experienced at clinically relevant dosages. Further, in special populations, such as in elderly patients, poor metabolizers of sparteine (CYP2D6) or mephenytoin (CYP2C19), and patients with liver impairment, the measurement of plasma concentrations may be useful.

Pharmacokinetics of selective serotonin reuptake inhibitors

The five selective serotonin reuptake inhibitors (SSRIs), fluoxetine, fluvoxamine, paroxetine, sertraline, and citalopram, have similar antidepressant efficacy and a similar side effect profile. They differ, however, in their pharmacokinetic properties. Under steady-state concentrations, their half-lives range between 1 and 4 days for fluoxetine (7 and 15 days for norfluoxetine) and between 21 (paroxetine) and 36 (citalopram) hr for the other SSRIs. Sertraline and citalopram show linear and fluoxetine, fluvoxamine, and paroxetine nonlinear pharmacokinetics. SSRIs underlie an extensive metabolism with high interindividual variability, whereby cytochrome P450 (CYP) isoenzymes play a major role. Therefore, resulting blood concentrations are highly variable between individuals. Except for N-demethylated fluoxetine, metabolites of SSRIs do not contribute to clinical actions. Therapeutically effective blood concentrations are unclear so far, although there is evidence for minimal effective and upper-threshold concentrations that should not be exceeded. Paroxetine and, to a lesser degree, fluoxetine and norfluoxetine are potent inhibitors of CYP2D6 and fluvoxamine of CYP1A2 and CYP2C19. This can give rise to drug-drug interactions that may have no effect, lead to intoxication, or improve the therapeutic response. These different pharmacokinetic properties of the five SSRIs, especially their drug-drug interaction potential, should be considered when selecting a distinct SSRI for treatment of depression or other disorders with a suggested dysfunction of the serotonergic system in the brain.

Metabolism and pharmacokinetics of selective serotonin reuptake inhibitors

1. Five drugs with the predominant pharmacologic effect of inhibiting the neuronal reuptake of serotonin are available worldwide for clinical use. This class of psychoactive drugs, known as selective serotonin reuptake inhibitors (SSRIs), is comprised of fluoxetine, sertraline, paroxetine, fluvoxamine, and citalopram. 2. The SSRIs appear to share similar pharmacodynamic properties which translate to efficacy in the treatment of depression and anxiety syndromes. The drugs are differentiated by their pharmacokinetic properties with regard to stereochemistry, metabolism, inhibition of cytochrome enzymes, and participation in drug-drug interactions. Studies focusing on the relationship of plasma drug concentration to therapeutic and adverse effects have not confirmed the value of plasma concentration monitoring. 3. This review summarizes the metabolism and relevant pharmacokinetic properties of the SSRIs.

Effect of fluvoxamine therapy on the activities of CYP1A2, CYP2D6, and CYP3A as determined by phenotyping

OBJECTIVE

To determine the effect of 150 mg/day fluvoxamine on the activities of CYP1A2, CYP2D6, CYP3A, N-acetyltransferase-2 (NAT2), and xanthine oxidase (XO) by phenotyping with caffeine, dextromethorphan, and midazolam.

METHODS

Oral caffeine (2 mg/kg), oral dextromethorphan (30 mg), and intravenous midazolam (0.025 mg/kg) were administered to 10 white male volunteers every 14 days for 4 months and to 10 white premenopausal female volunteers during the midfollicular and midluteal phases of the menstrual cycle for 4 complete cycles (8 total phenotyping measures). The first 6 phenotyping measures were used to establish baseline activity. Subjects were given 150 mg/day fluvoxamine for the fourth month or cycle of the study. Enzyme activity for CYP1A2, CYP2D6, NAT2, and XO was expressed as urinary metabolite ratios. Midazolam plasma clearance was used to express CYP3A activity.

RESULTS

No difference between baseline and weeks 2 and 4 of fluvoxamine therapy was observed for NAT2 or XO metabolite ratios. For CYP1A2, CYP2D6, and CYP3A phenotypes, significant differences existed between baseline and fluvoxamine therapy. For CYP1A2, the mean urinary metabolite ratio (+/-SD) was 7.53 +/- 7.44 at baseline and 4.30 +/- 2.82 with fluvoxamine ( P = .012). Mean CYP2D6 molar urinary dextromethorphan ratios before and after fluvoxamine therapy were 0.00780 +/- 0.00694 and 0.0153 +/- 0.0127, respectively (P = .011). Midazolam clearance decreased from 0.0081 +/ 0.0024 L/min/kg at baseline to 0.0054 +/- 0.0021 L/min/kg with therapy (P = .0091). For CYP1A2, CYP2D6, and CYP3A, fluvoxamine therapy changed the phenotyping measures by a median of -44.4%, 123.5%, and -34.4%, respectively.

CONCLUSIONS

We concluded that fluvoxamine may cause significant inhibition of CYP1A2, CYP2D6, and CYP3A activity. This metabolic inhibition may have serious implications for a variety medications.

Nonlinear pharmacokinetics of fluvoxamine and gender differences

This prospective study assessed fluvoxamine serum concentrations under two different fixed doses. The study included 15 male and female patients who met the DSM-III-R criteria for major depression. They were prescribed 50 mg fluvoxamine twice a day for 2 weeks and 100 mg twice a day thereafter. Drug monitoring was carried out on days 14 and 28. Fluvoxamine serum concentrations were highly variable between patients. After the dose was doubled, the serum concentrations of fluvoxamine increased disproportionately (mean, 3.4-fold), and there was a significantly (p < 0.05) more pronounced increase in men (4.6-fold) than in women (2.4-fold). These results provide evidence of nonlinear, sex-dependent pharmacokinetics of fluvoxamine.

Non-linear fluvoxamine disposition

AIMS

To study the pharmacokinetics of fluvoxamine when given in increasing doses to healthy volunteers.

METHODS

Ten healthy, non-smoking men were given maintenance treatment with fluvoxamine for 4 weeks. Eight subjects were CYP2D6 extensive metabolisers (EMs) and two were CYP2D6 poor metabolisers (PMs). As a measure of the CYP1A2 phenotype, the paraxanthine/caffeine ratio in saliva after intake of caffeine was studied. The fluvoxamine doses given were 25 mg day(-1) the first week, 50 mg day(-1) the second week, 100 mg day(-1) the third week and 200 mg day(-1) the fourth week, divided in two daily doses. On the seventh day every week, serum concentrations of fluvoxamine were followed for a dose interval of 12 h. After discontinuation of treatment, fluvoxamine concentrations were followed for 1 week.

RESULTS

For each of the three two-fold increases in given dose, the mean AUC increased 3.25-fold, 3.17-fold and 3.14-fold, respectively (P < 0.0001), indicating a decrease in oral clearance with increasing dose. The elimination half-life based upon the serum concentrations 12-48 h after discontinuation of fluvoxamine was 32.1 +/- 11.0 h whereas the half-life based upon the concentrations 3-7 days after discontinuation was significantly shorter, 15.8 +/- 4.2h (means +/- s.d.; P < 0.001). There were no significant correlations between the CYP1A2 phenotype and fluvoxamine AUCs at different doses (r = -0.56; P = 0.095 for the correlation between the paraxanthine/caffeine ratio in saliva and fluvoxamine AUC at a dose of 50 mg day[-1]). The two CYP2D6 PMs had AUC values in the same range as the EMs.

CONCLUSIONS

The present study conclusively demonstrates that fluvoxamine exhibits non-linear kinetics within the therapeutic dose interval. The reason for non-linearity is not Michaelis-Menten saturation kinetics of a single metabolic pathway, but rather a complex involvement of multiple parallel pathways.

Dose escalation vs. continued doses of paroxetine and maprotiline: a prospective study in depressed out-patients with inadequate treatment response

In view of the fact that controlled prospective studies on the benefits of dose escalation of the selective serotonin re-uptake inhibitor (SSRI) paroxetine are lacking, we conducted a double-blind, randomized, parallel-group multicentre study designed to compare the possible benefits of dose escalation of paroxetine and maprotiline in patients suffering from major or minor depression according to modified Research Diagnostic Criteria (RDC) with inadequate treatment response. The study sample consisted of 544 out-patients with different degrees of severity of depression. Patients received either 20 mg paroxetine (n = 271) or 100 mg maprotiline (n = 273) for the first 3 weeks in a double-blind manner. Response after 3 weeks was defined using explicit operationalized criteria. Patients with inadequate treatment response (paroxetine group, n = 86; maprotiline group, n = 88) were again randomized to either continuation of the previous dosage (paroxetine, n = 36; maprotiline, n = 48) or increased doses, i.e. 40 mg paroxetine (n = 50) or 150 mg maprotiline (n = 40), respectively. Intention-to-treat and completer analyses were performed. Defining response as a reduction in Hamilton Depression Rating Scale (17-item version) (HAMD-17) score of at least 50% from baseline, no significant benefits of dose escalation were found for either paroxetine or maprotiline. Stratification according to baseline severity of depression also revealed no significant benefits of dose escalation. After dose escalation, new adverse events that had not been present during treatment with lower doses rarely occurred. Our results support the view that a dose of 20 mg paroxetine is optimal for the acute treatment of depression in the majority of patients.

Clinically relevant pharmacology of selective serotonin reuptake inhibitors. An overview with emphasis on pharmacokinetics and effects on oxidative drug metabolism

This paper presents an overview of the clinically relevant pharmacology of selective serotonin reuptake inhibitors (SSRIs) with an emphasis on their pharmacokinetics and effects on cytochrome P450 (CYP) enzymes. The SSRIs are potent inhibitors of the neuronal reuptake pump for serotonin (5-hydroxytryptamine; 5-HT) and have minimal effects on a number of other sites of actions (e.g. neuroreceptors and fast sodium channels). For this reason, drugs in this class have remarkable similarity as regards acute and maintenance antidepressant efficacy and tolerability profile. However, individual members of this class differ substantially in their pharmacokinetics and effects on CYP enzymes. Most SSRIs have a half-life (t1/2) of approximately 1 day. Fluoxetine, however, has a longer t1/2 of 2 to 4 days, and its active metabolite, norfluoxetine, has an extended t1/2 of 7 to 15 days. Fluoxetine, paroxetine and, to a lesser extent, fluvoxamine inhibit their own metabolism. That is not the case for citalopram or sertraline. There are nonlinear increases in paroxetine plasma concentrations with dosage increases, but proportional changes with citalopram and sertraline. Indirect data suggest that fluoxetine and fluvoxamine also have nonlinear pharmacokinetics over their usual dosage range. Age-related increases in plasma drug concentrations for citalopram (approximately 130%) and paroxetine (approximately 50 to 100%) have been observed in healthy elderly (65 to 75 years) persons versus those who are younger. There is an age-gender interaction for sertraline, with its plasma concentrations being 35 to 40% lower in young men than in elderly or young females or elderly males. While there is no apparent change in fluvoxamine plasma levels as a function of age, plasma drug concentrations are 40 to 50% lower in males than in females. Limited data from clinical trials suggest that age-related differences with fluoxetine may be comparable to those of citalopram and paroxetine. Marked differences exist between the SSRIs with regard to effects on specific CYP enzymes and, thus, the likelihood of clinically important pharmacokinetic drug-drug interactions. The most extensive in vitro and in vivo research has been done with fluoxetine, fluvoxamine and sertraline; there has been less with paroxetine and citalopram. The available in vivo data at each drug's usually effective antidepressant dose are summarised below. Citalopram produces mild inhibition of CYP2D6. Fluvoxamine produces inhibition (which would be expected to be clinically meaningful) of two CYP enzymes. CYP1A2 and CYP2C19, and probably a third, CYP3A3/4. Fluoxetine substantially inhibits CYP2D6 and probably CYP2C9/10, moderately inhibits CYP2C19 and mildly inhibits CYP3A3/4. Paroxetine substantially inhibits CYP2D6 but doses not appear to inhibit any other CYP enzyme. Sertraline produces mild inhibition of CYP2D6 but has little, if any, effect on CYP1A2, CYP2C9/10, CYP2C19 or CYP3A3/4. Understanding the similarities and differences in the pharmacology of SSRIs can aid the clinician in optimal use of this important class of antidepressants.

Pharmacokinetic-pharmacodynamic relationship of the selective serotonin reuptake inhibitors

The recently introduced antidepressants, the selective serotonin reuptake inhibitors (SSRIs) [citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline], are known for their clinical efficacy, good tolerability and relative safety. They differ from each other in chemical structure, metabolism and pharmacokinetic properties. Therapeutic drug monitoring of these compounds is not widely used, as the plasma concentration ranges within which clinical response with minimal adverse effects appears to be optimal are not clearly defined. Almost all recent assays developed for the quantitative determination of SSRIs and their metabolites in blood are based either on the separation of SSRIs by high performance liquid chromatography (HPLC) or gas chromatography (GC). Citalopram and fluoxetine have been introduced as racemic compounds. There are some differences in the pharmacological profile, metabolism and pharmacokinetics between the enantiomers of the parent compounds and their demethylated metabolites. Stereoselective chromatographic methods for their analysis in blood are now available. With regard to the SSRIs presently available, no clearcut plasma concentration-clinical effectiveness relationship in patients with depression has been shown, nor any threshold which defines toxic concentrations. This may be explained by their low toxicity and use at dosages where serious adverse effects do not appear. SSRIs vary widely in their qualitative and quantitative interaction with cytochrome P450 (CYP) isozymes in the liver. CYP2D6 is inhibited by SSRIs, in order of decreasing potency paroxetine, norfluoxetine, fluoxetine, sertraline, citalopram and fluvoxamine. This may have clinical consequences with some but not all SSRIs, when they are taken with tricyclic antidepressants. Except for citalopram and paroxetine, little is known about the enzymes which control the biotransformation of the SSRIs. There have been many reports on marked pharmacokinetic interactions between fluoxetine and tricyclic antidepressants. Fluoxetine has a stronger effect on their hydroxylation than on their demethylation. Interactions observed between fluoxetine and alprazolam, midazolam and carbamazepine seem to occur on the level of CYP3A. Fluvoxamine strongly inhibits the N-demethylation of some tricyclic antidepressants of the tertiary amine type and of clozapine. This may lead to adverse effects but augmentation with fluvoxamine can also improve response in very rapid metabolisers, as it increases the bioavailability of the comedication. Fluvoxamine inhibits with decreasing potency, CYP1A2, CYP2C19, CYP2D6 and CYP1A1, but it is also an inhibitor of CYP3A. Fluoxetine and fluvoxamine have shown to increase methadone plasma concentrations in dependent patients. Some authors warn about a combination of monoamine oxidase (MAO) inhibitors with SSRIs, as this could lead to a serotonergic syndrome. Studies with healthy volunteers suggest, however, that a combination of moclobemide and SSRIs, such as fluvoxamine, should not present serious risks in promoting a serotonin syndrome. A combination of moclobemide and fluvoxamine has successfully been used in refractory depression, but more studies are needed, including plasma-concentration monitoring, before this combined treatment can be recommended. Paroxetine is a substrate of CYP2D6, but other enzyme(s) could also be involved. Its pharmacokinetics are linear in poor metabolisers of sparteine, and non-linear in extensive metabolisers. Due to its potent CYP2D6 inhibiting properties, comedication with this SSRI can lead to an increase of tricyclic antidepressants in plasma, as shown with amitriptyline and trimipramine. CYP3A has been claimed to be involved in the biotransformation of sertraline to norsertraline. Clinical investigations (with desipramine) confirmed in vitro findings that CYP2D6 inhibition by sertraline is only moderate. (ABSTRACT TRUNCATED)

Overview of the pharmacokinetics of fluvoxamine

The pharmacokinetics of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) with antidepressant properties, are well established. After oral administration, the drug is almost completely absorbed from the gastrointestinal tract, and the extent of absorption is unaffected by the presence of food. Despite complete absorption, oral bioavailability in man is approximately 50% on account of first-pass hepatic metabolism. Peak plasma fluvoxamine concentrations are reached 4 to 12 hours (enteric-coated tablets) or 2 to 8 hours (capsules, film-coated tablets) after administration. Steady-state plasma concentrations are achieved within 5 to 10 days after initiation of therapy and are 30 to 50% higher than those predicted from single dose data. Fluvoxamine displays nonlinear steady-state pharmacokinetics over the therapeutic dose range, with disproportionally higher plasma concentrations with higher dosages. Plasma fluvoxamine concentrations show no clear relationship with antidepressant response or severity of adverse effects. Fluvoxamine undergoes extensive oxidative metabolism, most probably in the liver. Nine metabolites have been identified, none of which are known to be pharmacologically active. The specific cytochrome P450 (CYP) isoenzymes involved in the metabolism of fluvoxamine are unknown. CYP2D6, which is crucially involved in the metabolism of paroxetine and fluoxetine, appears to play a clinically insignificant role in the metabolism of fluvoxamine. The drug is excreted in the urine, predominantly as metabolites, with only negligible amounts ( < 4%) of the parent compound. Fluvoxamine shows a biphasic pattern of elimination with a mean terminal elimination half-life of 12 to 15 hours after a single oral dose; this is prolonged by 30 to 50% at steady-state. Plasma protein binding of fluvoxamine (77%) is low compared with that of other SSRIs. Fluvoxamine pharmacokinetics are substantially unaltered by increased age or renal impairment. However, its elimination is prolonged in patients with hepatic cirrhosis. Fluvoxamine inhibits oxidative drug metabolising enzymes (particularly CYP1A2, and less potently and much less potently CYP3A4 and CYP2D6, respectively) and has the potential for clinically significant drug interactions. Drugs whose metabolic elimination is impaired by fluvoxamine include tricyclic antidepressants (tertiary, but not secondary, amines), alprazolam, bromazepam, diazepam, theophylline, propranolol, warfarin and, possibly, carbamazepine. Fluvoxamine is a second generation antidepressant that selectively inhibits neuronal reuptake of serotonin (5-hydroxytryptamine; 5-HT). Fluvoxamine exhibits antidepressant activity similar to that of the tricyclic antidepressants, but has a somewhat improved tolerability profile, particularly with respect to a lower incidence of anticholinergic effects and reduced cardiotoxic potential. However, gastrointestinal adverse effects, especially nausea, are seen more frequently with fluvoxamine than with the tricyclic antidepressants. Fluvoxamine does not have an asymmetric carbon in its structure (fig. 1) and therefore does not exist as optical isomers. For this reason, the potentially confounding problem of stereoisomerism does not arise with fluvoxamine.

Pharmacokinetic optimisation of therapy with newer antidepressants

Since the early 1950s, when imipramine was first introduced, a whole series of antidepressants with differences in structures, neurochemical effects and pharmacokinetics have been developed. Structurally or functionally, they have been classified as tricyclic antidepressants (TCAs), tetracyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs). In addition, there is a series of antidepressants with unique structures. Many of the newer TCAs appear to have shorter half-lives than the standard TCAs (e.g. imipramine), allowing for the possibility of a more rapid response, but requiring the drugs to be given in multiple daily doses, which may reduce patient compliance. The short time to peak plasma concentration (tmax) can also lead to rapid onset of adverse effects. The tetracyclic antidepressants have longer elimination half-lives (t1/2) than the TCAs, but there is only very minimal evidence for a relationship between drug concentrations in the blood and clinical response. The triazolopyridines, like the newer TCAs, show pharmacokinetic evidence for rapid onset of adverse effects and the need for multiple daily doses due to short tmax and t1/2. The newer MAOIs are a significant addition to therapy, as the rapid binding action of these medications increases their safety margin with regard to tyramine interactions. Further information in this area is required. In addition, moclobemide has pharmacokinetic features that are clinically beneficial (e.g. aging and renal dysfunction have little effect on the elimination of the drug), but also features that are not beneficial (e.g. nonlinear pharmacokinetics). Among the SSRIs, there are a range of t1/2 values for the parent drugs, from relatively short t1/2 values of less than 24 hours (paroxetine, fluvoxamine) to among the longest found (e.g. 2 days for fluoxetine). Only 2 of the agents (sertraline and citalopram) have linear pharmacokinetics, and 1 drug has nonlinear pharmacokinetics within the usual therapeutic range (fluvoxamine). Once a therapeutic blood concentration is established, linearity is helpful in avoiding the small dose changes and repeated rechecking of concentrations of medications that would be required for those agents with nonlinear pharmacokinetics. Sertraline stands out as having the best effects on behaviour among all antidepressants. However, fluoxetine and fluvoxamine are least likely to penetrate into breast milk. All 3 of the structurally unique newer antidepressants [amfebutamone (bupropion), viloxazine venlafaxine] have relatively short tmax values (1 to 2 hours), which may relate to the early onset of adverse effects. Amfebutamone has the benefits of linear pharmacokinetics with potential for defined therapeutic blood concentrations, lack of effect of liver enzymes on metabolism of the drug, and lack of significant effects of either aging or hepatic dysfunction on elimination of the drug. Thus, the antidepressants best suited for pharmacokinetic optimisation of therapy are the following: desipramine, sertraline, fluvoxamine, citalopram and amfebutamone.

Assay for maprotiline in human serum with improved sensitivity and selectivity

The use of a photoreactor and fluorescence detection enables measurement of the tetracyclic antidepressant drug 3-(9,10-dihydro-9,10-ethanoanthracene-9-yl)-N-methylpropylamine (maprotiline) with a sensitivity of 100 pg/ml serum. This detection system is highly specific and enables the measurement of very low concentrations in the presence of high concentrations of other drugs that are often found in patient samples. The mean free portions of maprotiline and desmethylmaprotiline were found to be 2.2% and 1.5%, respectively.