The major fluvoxamine metabolite in urine is formed by CYP2D6

Metabolic bioactivation of antidepressants: advance and underlying hepatotoxicity

Many drugs that serve as first-line medications for the treatment of depression are associated with severe side effects, including liver injury. Of the 34 antidepressants discussed in this review, four have been withdrawn from the market due to severe hepatotoxicity, and others carry boxed warnings for idiosyncratic liver toxicity. The clinical and economic implications of antidepressant-induced liver injury are substantial, but the underlying mechanisms remain elusive. Drug-induced liver injury may involve the host immune system, the parent drug, or its metabolites, and reactive drug metabolites are one of the most commonly referenced risk factors. Although the precise mechanism by which toxicity is induced may be difficult to determine, identifying reactive metabolites that cause toxicity can offer valuable insights for decreasing the bioactivation potential of candidates during the drug discovery process. A comprehensive understanding of drug metabolic pathways can mitigate adverse drug-drug interactions that may be caused by elevated formation of reactive metabolites. This review provides a comprehensive overview of the current state of knowledge on antidepressant bioactivation, the metabolizing enzymes responsible for the formation of reactive metabolites, and their potential implication in hepatotoxicity. This information can be a valuable resource for medicinal chemists, toxicologists, and clinicians engaged in the fields of antidepressant development, toxicity, and depression treatment.

[The relationship of cytochrome P450 isoforms with the efficacy and safety of antipsychotic and antidepressant therapy]

Cytochrome P450 (CYP450) is the leading enzyme in the biotransformation of most psychotropic drugs. CYP450 gene polymorphisms determine a patient's endophenotype with respect to the activity of enzymes of the family and affect the metabolism of prescribed antipsychotics and antidepressants. Categorizing patients by endophenotype during genotyping is likely to help simplify the selection of therapy in clinical practice. Co-prescribing drugs that may be inhibitors or inducers of CYP450 isoforms, in turn, may lead to adverse reactions or no effect of therapy. The article presents a compilation of known pharmacogenetic recommendations regarding the four major endophenotypes of metabolizers.

Optimising Fluvoxamine Maternal/Fetal Exposure during Gestation: A Pharmacokinetic Virtual Clinical Trials Study

Fluvoxamine plasma concentrations have been shown to decrease throughout pregnancy. CYP2D6 polymorphisms significantly influence these changes. However, knowledge of an optimum dose adjustment according to the CYP2D6 phenotype is still limited. This study implemented a physiologically based pharmacokinetic modelling approach to assess the gestational changes in fluvoxamine maternal and umbilical cord concentrations. The optimal dosing strategies during pregnancy were simulated, and the impact of CYP2D6 phenotypes on fluvoxamine maternal and fetal concentrations was considered. A significant decrease in fluvoxamine maternal plasma concentrations was noted during gestation. As for the fetal concentration, a substantial increase was noted for the poor metabolisers (PM), with a constant level in the ultrarapid (UM) and extensive (EM) metabolisers commencing from gestation week 20 to term. The optimum dosing regimen suggested for UM and EM reached a maximum dose of 300 mg daily at gestational weeks (GW) 15 and 35, respectively. In contrast, a stable dose of 100 mg daily throughout gestation for the PM is sufficient to maintain the fluvoxamine plasma concentration within the therapeutic window (60-230 ng/mL). Dose adjustment during pregnancy is required for fluvoxamine, particularly for UM and EM, to maintain efficacy throughout the gestational period.

The role of cytochromes P450 in metabolism of selected antidepressants and anxiolytics under psychological stress

In today's modern society, it seems to be more and more challenging to cope with life stresses. The effect of psychological stress on emotional and physical health can be devastating, and increased stress is associated with increased rates of heart attack, hypertension, obesity, addiction, anxiety and depression. This review focuses on the possibility of an influence of psychological stress on the metabolism of selected antidepressants (TCAs, SSRIs, SNRIs, SARIs, NDRIs a MMAs) and anxiolytics (benzodiazepines and azapirone), as patients treated with antidepressants and/or anxiolytics can still suffer from psychological stress. Emphasis is placed on the drug metabolism mediated by the enzymes of Phase I, typically cytochromes P450 (CYPs), which are the major enzymes involved in drug metabolism, as the majority of psychoactive substances are metabolized by numerous CYPs (such as CYP1A2, CYP2B6, CYP2C19, CYP2C9, CYP2A6, CYP2D6, CYP3A4). As the data on the effect of stress on human enzymes are extremely rare, modulation of the efficacy and even regulation of the biotransformation pathways of drugs by psychological stress can be expected to play a significant role, as there is increasing evidence that stress can alter drug metabolism, hence there is a risk of less effective drug metabolism and increased side effects.

Effect of Genetic Polymorphism of the CYP2D6 Gene on the Efficacy and Safety of Fluvoxamine in Major Depressive Disorder

BACKGROUND

Previous studies have shown that cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of fluvoxamine, the activity of which is highly dependent, inter alia, on the polymorphism of the gene encoding it. The objective of our study was to investigate the effect of 1846G>A polymorphism of the CYP2D6 gene on the efficacy and safety of fluvoxamine, using findings on CYP2D6 enzymatic activity and on CYP2D6 expression level in patients with depressive disorders comorbid with alcohol use disorder.

STUDY QUESTION

Efficacy and safety of fluvoxamine depend on the polymorphism of CYP2D6 gene in patients with major depressive disorder.

STUDY DESIGN

Our study enrolled 96 male patients with depressive disorders comorbid with alcohol use disorder. Patients were examined on days 1, 9, and 16 of fluvoxamine therapy.

MEASURES AND OUTCOMES

Treatment efficacy was evaluated using the validated psychometric scales. Therapy safety was assessed using the UKU Side-Effect Rating Scale. For genotyping and estimation of the microRNA (miRNA) plasma levels, we performed the real-time polymerase chain reaction. The activity of CYP2D6 was evaluated using the HPLC-MS/MS method by the content of the endogenous substrate of given isoenzyme and its metabolite in urine (6-hydroxy-1,2,3,4-tetrahydro-β-carboline/pinoline ratio).

RESULTS

Our study revealed the statistically significant results for the treatment efficacy evaluation [the Hamilton Depression Rating Scale scores at the end of the treatment course: (GG) 2.0 (1.0-4.0) and (GA) 5.0 (4.0-7.0), P < 0.001]. Analysis of the results of the pharmacotranscriptomic part of the study did not show the statistically significant difference in the hsa-miR-370-3p plasma levels in patients with different genotypes: (GG) 26.9 (15.0-32.2), (GA) 31.8 (22.7-33.7), P = 0.247. In addition, we evaluated the relationship between the CYP2D6 enzymatic activity (as evaluated by 6-hydroxy-1,2,3,4-tetrahydro-β-carboline/pinoline ratio measurement) and the hsa-miR-370-3p plasma concentration: rs = -0.243, P = 0.017.

CONCLUSIONS

The effect of genetic polymorphism of the CYP2D6 gene on the efficacy and safety profiles of fluvoxamine was demonstrated in a group of 96 patients with depressive disorders comorbid with alcohol use disorder.

Distribution of Fluvoxamine and Identification of the Main Metabolite in a Fatal Intoxication

Fluvoxamine is a selective serotonin reuptake inhibitor, with a half-life of about 30 hours, that is commonly prescribed in the treatment of depression and obsessive and compulsive disorders. Though its more favorable adverse effect profile in comparison to tricyclic antidepressants, overdosages could lead to severe central nervous system depression. We hereby report the case of a 48-year-old woman with psychiatric disorders, who died in the Protected Community where she lived. An autopsy, during which multiorgan congestion and aspiration of gastric content were found, was performed 9 days after the death. Femoral and cardiac blood, urine and bile were collected for toxicological analysis. GC-MS, LC-MS-MS and LC-HRMS screenings were performed on blood samples. The analysis allowed to identify the following drugs: fluvoxamine, clotiapine, 7-aminoclonazepam, propranolol, gabapentin and haloperidol. Quantification of the detected drugs in blood was performed by means of a validated LC-MS-MS analytical procedure, and the following results were achieved: fluvoxamine (2.20 mg/L), gabapentin (41.00 mg/L), 7-aminoclonazepam (0.24 mg/L), clotiapine (0.07 mg/L), haloperidol (<0.01 mg/L) and propranolol (0.24 mg/L). Fluvoxamine concentration in blood exceeded ~10 times the upper limit of therapeutic blood levels (0.23 mg/L). Contributory causes of death, such as due to multiple drug use, however, cannot be excluded. The distribution of fluvoxamine in all biological fluids was evaluated and a postmortem redistribution effect was observed (C/P blood ratio: 1.86). Fluvoxamine acid metabolite was identified in urine, bile and in cardiac blood, through an LC-QTOF analytical procedure.

Physiologically-Based Pharmacokinetic Models for CYP1A2 Drug-Drug Interaction Prediction: A Modeling Network of Fluvoxamine, Theophylline, Caffeine, Rifampicin, and Midazolam

This study provides whole‐body physiologically‐based pharmacokinetic models of the strong index cytochrome P450 (CYP)1A2 inhibitor and moderate CYP3A4 inhibitor fluvoxamine and of the sensitive CYP1A2 substrate theophylline. Both models were built and thoroughly evaluated for their application in drug–drug interaction (DDI) prediction in a network of perpetrator and victim drugs, combining them with previously developed models of caffeine (sensitive index CYP1A2 substrate), rifampicin (moderate CYP1A2 inducer), and midazolam (sensitive index CYP3A4 substrate). Simulation of all reported clinical DDI studies for combinations of these five drugs shows that the presented models reliably predict the observed drug concentrations, resulting in seven of eight of the predicted DDI area under the plasma curve (AUC) ratios (AUC during DDI/AUC control) and seven of seven of the predicted DDI peak plasma concentration (C_max) ratios (C_max during DDI/C_max control) within twofold of the observed values. Therefore, the models are considered qualified for DDI prediction. All models are comprehensively documented and publicly available, as tools to support the drug development and clinical research community.

Pharmacokinetics of serotonergic drugs: focus on OCD

INTRODUCTION

Although the treatment of obsessive-compulsive disorder (OCD), a common, chronic, and disabling psychiatric condition, has significantly improved in the last decades, with the demonstration of the specific effectiveness of serotonin reuptake inhibitors (SRIs), a large proportion of patients still show high relapse rates. In addition, pharmacological treatments should be maintained for years, so that the clinicians should take into account the pharmacokinetic changes in the long-term, which may be responsible for dangerous side effects or interactions. Areas covered: The aim of this paper was to review the literature on the pharmacokinetics of SSRIs and clomipramine, and on their pharmacokinetic parameters in OCD patients. Expert opinion: Although the literature on the pharmacokinetics of both clomipramine and SSRIs is consistent, data on pharmacokinetic parameters in OCD patients are very few. Given the impact of OCD, its chronicity requiring long-term treatments, together with the need to increase the clinical response rate, more studies in this field are urgently required.

Genetic Polymorphisms of Cytochrome P450 Enzymes and the Effect on Interindividual, Pharmacokinetic Variability in Extensive Metabolizers

Genetic polymorphisms of cytochrome P450 (CYP) enzymes are one of the factors that contribute to the pharmacokinetic (PK) variability of drugs. PK variability is observed in the bimodal distribution between extensive metabolizers (EMs) and poor metabolizers (PMs). PK variability may also exist between individuals genotyped as homozygous EMs and heterozygous EMs. This may carry implications for drug dosing and drug response (e.g., risk of therapeutic failure or drug toxicity). Studies have reported significant PK differences between homozygous and heterozygous EMs. Some literature suggests that this distinction may be of clinical relevance. Due to study design limitations and data that are either sparse or conflicting, generalizations regarding the potential impact of the CYP genotype, within EMs, are difficult. Optimally designed clinical trials are needed. This review evaluates the potential impact of CYP genetic polymorphisms on interindividual PK variability of drugs within an EM population.

In silico and intuitive predictions of CYP46A1 inhibition by marketed drugs with subsequent enzyme crystallization in complex with fluvoxamine

Cytochrome P450 46A1 (cholesterol 24-hydroxylase) is an important brain enzyme that may be inhibited by structurally distinct pharmaceutical agents both in vitro and in vivo. To identify additional inhibitors of CYP46A1 among U.S. Food and Drug Administration-approved therapeutic agents, we used in silico and intuitive predictions and evaluated some of the predicted binders in the enzyme and spectral binding assays. We tested a total of 298 marketed drugs for the inhibition of CYP46A1-mediated cholesterol hydroxylation in vitro and found that 13 of them reduce CYP46A1 activity by >50%. Of these 13 inhibitors, 7 elicited a spectral response in CYP46A1 with apparent spectral K(d) values in a low micromolar range. One of the identified tight binders, the widely used antidepressant fluvoxamine, was cocrystallized with CYP46A1. The structure of this complex was determined at a 2.5 Å resolution and revealed the details of drug binding to the CYP46A1 active site. The NH(2)-containing arm of the Y-shaped fluvoxamine coordinates the CYP46A1 heme iron, whereas the methoxy-containing arm points away from the heme group and has multiple hydrophobic interactions with aliphatic amino acid residues. The CF(3)-phenyl ring faces the entrance to the substrate access channel and has contacts with the aromatic side chains. The crystal structure suggests that only certain drug conformers can enter the P450 substrate access channel and reach the active site. Once inside the active site, the conformer probably further adjusts its configuration and elicits the movement of the protein side chains.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Identification of human cytochrome P450 enzymes involved in the major metabolic pathway of fluvoxamine

The metabolism of fluvoxamine to fluvoxamino acid is known to involve a two-step oxidation process via an alcohol intermediate, fluvoxamino alcohol. The present study was carried out to identify the cytochrome P450 (CYP) enzyme(s) involved in the metabolism offluvoxamine to fluvoxamino alcohol using human liver microsomes and cDNA-expressed human CYP enzymes. The mean Km and Vmax values for the formation of fluvoxamino alcohol from fluvoxamine in human liver microsomes were 76.3 microM and 37.5 pmol min(-1) mg(-1) protein, respectively. The formation of fluvoxamino alcohol from fluvoxamine in pooled human liver microsomes was significantly inhibited by quinidine, a relatively specific CYP2D6 inhibitor, with a Ki value of 2.2 microM, whereas other several relatively specific CYP inhibitors did not inhibit the formation of fluvoxamino alcohol. In addition, only CYP2D6 of several cDNA-expressed human CYP enzymes examined showed substantial activity for the formation of fluvoxamino alcohol. Furthermore, the formation of fluvoxamino acid from fluvoxamino alcohol is potently inhibited by 4-methylpyrazole in human liver cytosol. These data suggest that CYP2D6 is the only enzyme predominantly responsible for the first-step oxidation of fluvoxamine to fluvoxamino alcohol, and alcohol dehydrogenase is involved in the second-step oxidation of fluvoxamino alcohol to the corresponding carbolic acid.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Effects of Caffeine on the Kinetics of Fluvoxamine and its Major Metabolite in Plasma After a Single Oral Dose of the Drug

The effects of caffeine on the kinetics of fluvoxamine (FLV) and its major metabolite fluvoxamino acid (FLA) in plasma, after a single oral dose of the drug, were studied in 12 healthy male volunteers. The subjects received caffeine 300 mg/d or placebo for 11 days in a double-blind randomized crossover manner, and on the eighth day they received a single oral 50-mg dose of FLV. Blood sampling and pharmacodynamic evaluation were conducted up to 72 hours after FLV dosing. Plasma concentrations of FLV and FLA were measured by high-performance liquid chromatography. Caffeine significantly decreased the plasma concentrations at 6 time points (P<0.05) and total area under the plasma concentration-time curve (156.5+/-51.7 vs. 118.9+/-38.2 ng/h/mL, P<0.01) of FLV. Plasma concentration and pharmacokinetic parameters of FLA were not affected by caffeine. Caffeine induced no significant change in the pharmacodynamic effects of FLV. The present study suggests that caffeine slightly induces the metabolism of FLV, probably mediated by CYP1A2.

Drug disposition of chiral and achiral drug substrates metabolized by cytochrome P450 2D6 isozyme: case studies, analytical perspectives and developmental implications

The concepts of drug development have evolved over the last few decades. Although number of novel chemical entitities belonging to varied classes have made it to the market, the process of drug development is challenging, intertwined as it is with complexities and uncertainities. The intention of this article is to provide a comprehensive review of novel chemical entities (NCEs) that are substrates to cytochrome P450 (CYP) 2D6 isozyme. Topics covered in this review aim: (1) to provide a framework of the importance of CYP2D6 isozyme in the biotransformation of NCEs as stand-alones and/or in conjunction with other CYP isozymes; (2) to provide several case studies of drug disposition of important drug substrates, (3) to cover key analytical perspectives and key assay considerations to assess the role and involvement of CYP2D6, and (4) to elaborate some important considerations from the development point of view. Additionally, wherever applicable, special emphasis is provided on chiral drug substrates in the various subsections of the review.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Interaction study between enoxacin and fluvoxamine

Authors examined a possible interaction between enoxacin, an inhibitor of cytochrome P4501A2, and fluvoxamine (FLV), a substrate for this enzyme. Ten healthy male volunteers received enoxacin 200 mg/d or placebo for 11 days in a double-blind randomized crossover manner, and on the eighth day they received a single oral 50-mg dose of FLV. Blood samplings and pharmacodynamic evaluation were conducted up to 72 hours after FLV dosing. Plasma concentrations of FLV and its active metabolite fluvoxamino acid (FLA) were measured by high-performance liquid chromatography. Enoxacin significantly increased the plasma concentrations at 2 hours (placebo versus enoxacin, mean+/-SD: 4.4+/-2.4 vs 7.0+/-4.1 ng/mL, P<0.05) and 3 hours (7.4+/-2.7 vs 11.2+/-3.8 ng/mL, P<0.01) and the Cmax (10.2+/-2.9 vs 11.6+/-4.0 ng/mL, P<0.05) of FLV. Plasma concentration and pharmacokinetic parameters of FLA were not affected by enoxacin. Enoxacin significantly (P<0.05) increased the scores of the Stanford Sleepiness Scale from 0.5 to 4 hours, suggesting that enoxacin increased the sleepiness produced by FLV. The present study suggests that enoxacin slightly inhibits the metabolism of FLV, and enoxacin should be combined with FLV with caution.

Effects of the CYP 2D6 genotype and cigarette smoking on the steady-state plasma concentrations of fluvoxamine and its major metabolite fluvoxamino acid in Japanese depressed patients

The effects of the cytochrome P450 (CYP) 2D6 genotype and cigarette smoking on the steady-state plasma concentrations (C(ss)) of fluvoxamine (FLV) and its demethylated metabolite fluvoxamino acid (FLA) were studied in 49 Japanese depressed patients receiving FLV 200 mg/d. The C(ss) of FLV and FLA were measured by HPLC, and the wild-type allele (*1) and two mutated alleles causing absent (*5) or decreased (*10) CYP 2D6 activity were identified by PCR methods. The patients were divided into three genotype groups by the number of mutated alleles: 12 cases with no (*1/*1), 27 cases with one (*1/*5 and *1/*10), and 10 cases with two (*5/*10 and *10/*10) mutated alleles. The means +/- SD of the C(ss) of FLV and FLA and the FLA/FLV ratio of all patients were 169.1 +/- 147.5 ng/mL, 83.9 +/- 52.7 ng/mL, and 0.71 +/- 0.50, respectively. The C(ss) of FLV and FLA were not significantly different among the three genotype groups. However, the FLA/FLV ratio was significantly lower in the patients with one (P < 0.05) and two (P < 0.01) mutated alleles than in those with no mutated allele. There was no significant difference between nonsmokers (n = 34) and smokers (n = 15) in these values. In the stepwise multiple regression, the C(ss) of FLA (P < 0.05) and FLA/FLV ratio (P < 0.001) showed significant negative correlations with the number of mutated alleles, and the FLA/FLV ratio was significantly (P < 0.05) lower in women than in men. The present study suggests that the CYP 2D6 genotype and cigarette smoking have no major impact on the C(ss) of FLV and FLA, though CYP 2D6 is involved in the demethylation of FLV.

Comparison of in vitro and in vivo inhibition potencies of fluvoxamine toward CYP2C19

A previous study suggested that fluvoxamine inhibition potency toward CYP1A2 is 10 times greater in vivo than in vitro. The present study was designed to determine whether the same gap exists for CYP2C19, another isozyme inhibited by fluvoxamine. In vitro studies examined the effect of nonspecific binding on the determination of inhibition constant (K(i)) values of fluvoxamine toward CYP2C19 in human liver microsomes and in a cDNA-expressed microsomal (Supersomes) system using (S)-mephenytoin as a CYP2C19 probe. K(i) values based on total added fluvoxamine concentration (K(i,total)) and unbound fluvoxamine concentration (K(i,ub)) were calculated, and interindividual variability in K(i) values was examined in six nonfatty livers. K(i,total) values varied with microsomal protein concentration, whereas the corresponding K(i,ub) values were within a narrow range (70-80 nM). In vivo inhibition constants (K(i)iv) were obtained from a study of the disposition of a single oral dose (100 mg) of the CYP2C19 probe (S)-mephenytoin in 12 healthy volunteers receiving fluvoxamine at 0, 37.5, 62.6, and 87.5 mg/day to steady state. In this population, the ratio of (S)-4-hydroxy-mephenytoin formation clearances (uninhibited/inhibited) was positively correlated with fluvoxamine average steady-state concentration with an intercept of 0.85 (r(2) = 0.88, p < 0.001). The mean (+/-S.D.) values of K(i)iv based on total and unbound plasma concentrations were 13.5 +/- 5.6 and 1.9 +/- 1.1 nM, respectively. Comparison of in vitro and in vivo K(i) values, based on unbound fluvoxamine concentrations, suggests that fluvoxamine inhibition potency is roughly 40 times greater in vivo than in vitro.

Antidepressant drugs in the elderly--role of the cytochrome P450 2D6

Depression, the most common mental health problem of the elderly, is often under-diagnosed and under-treated. As patients age, antidepressant pharmacologic treatment becomes more complicated due to an increased risk of adverse drug events. These risks are associated with age-related physiological changes and individual variability in drug metabolism related to several factors, the most frequent of which is polymedication as a result of coexisting chronic illnesses. Comedications induce drug interactions that depend on the patient's metabolic capacity linked to the genetically determined cytochrome P450 enzyme (CYP450) function. The effect of some isoenzyme polymorphism on the pharmacokinetics of many antidepressants and other psychotropic drugs is well characterized. The author approaches successively the notions of the cytochrome P450 (2D6), its role in the drug biotransformation, and the importance of knowing its substrates, inhibitors and inducers in order to predict drug interactions. The clinical significance of this notion, and the help that could be given by genotyping and phenotyping, are also explained. The author's experience on the relation between drug side effects and patient metabolic status, and on the antidepressant interactions with fluoxetine, fluvoxamine and citalopram, is given in order to rationalize and individualize antidepressant choice in elderly.