CYP2D6的多态性与文拉法辛的临床效应

背景:文拉法辛(V)是一种5-羟色胺和去甲肾上腺素重摄取抑制剂,用于抑郁症的一线治疗。它主要是由具有高度多态性的细胞色素P450酶CYP2D6代谢,产生有药理学活性的代谢物O-去甲基文拉法辛(ODV)。还有一小部分是由CYP3A4代谢,生成N-去甲基文拉法辛(NDV)。目的:本研究的目的是评价文拉法辛的ODV表型是否对药物动力学和临床结果有影响。方法:100例行文拉法辛治疗的患者,测定血清中V、ODV和NDV的浓度,并计算ODV/V浓度的比值,以测定O-去甲基化作用。对于ODV/V比率异常高或异常低的个体进行基因分型。用临床综合印象量表(ClinicalGl…     

CYP2D6＊10等位基因多态性对文拉法辛血药浓度的影响

目的旨在研究细胞色素P450酶2D6＊10（CYP2D6＊10）基因多态性对文拉法辛血药浓度的影响。方法随机选择65例抑郁症患者为研究对象,提取其外周血中的DNA并利用特异性的引物对其进行扩增,对得到的扩增产物进行酶切,通过电泳表征酶切结果并分析65例抑郁患者CYP2D6＊10基因的基因类型。根据所选择患者基因类型的不同,将其分为3组,即A组：纯合突变（CYP2D6＊10/＊14）,B组：杂合体[CYP2D6＊1（＊2）/＊14]及C组：野生型纯合体[CYP2D6＊1（＊2）/＊5];各组患者口服文拉法辛225 mg后,使用高效液相色谱仪测定患者文拉法辛（VL）和O-去甲文拉法辛（ODVL）的血药浓度以研究文拉法辛在不同基因携带者体内的代谢情况。通过汉密尔顿抑郁量表（HAMD）和药物不良反应量表（TESS）来明确文拉法辛对不同CYP2D6＊10基因携带者的治疗效果和产生不良反应情况。结果电泳结果显示,在65名患者中,纯合突变（CYP2D6＊10/＊14）为29例（44.6%）,杂合体（[CYP2D6＊1（＊2）/＊14]为17例（26.1%）,野生型纯合体[CYP2D6＊1（＊2）/＊5]为19例（29.3%）;3组间CVL、CODVL及CODVL/CVL比较均具有显著地差异（P〈0.05）;根据CODVL/CVL值可知,A组、B组及C组对文拉法辛的代谢类型分别为快型（EM）、中型（IM）及慢型（PM）。各组间TESS评分和HAMD评分差异具有统计学意义（P〈0.05）。结论不同CYP2D6＊10基因是通过决定抑郁症患者对文拉法辛的代谢类型而影响其血药浓度。     

临床治疗剂量氯氮平人体内代谢机制研究

目的本课题主要探讨临床治疗剂量氯氮平的代谢机制，为临床合理用药提供指导。方法15例精神分裂症男性住院病人，单用氯氮平治疗，达到稳态浓度后，采用自身前后对照设计试验，研究氟西汀抑制前后氯氮平及其代谢产物药代动力学参数的变化及其与酶活性的相关性。CYP1A2、CYP3A4和CYP2136的活性分别用咖啡因、咪达唑仑和右美沙芬探测。体内氯氮平及其代谢产物、咪哒唑仑及其代谢产物、尿中右美沙芬及其代谢产物用HPLC-MS测定。血中咖啡因及其代谢产物用HPlC-UV测定。数据用SPSS软件进行统计分析。结果氯氮平合用氟西汀后，氯氮平的Cmax、AUC0-24显著增加，t1/2增加趋势，但没有显著性差异。代谢产物去甲氯氮平的AUC0-24显著降低，Cmax和t1／2无显著性差异。N-氧化氯氮平的Cmax和AUC0-24显著性降低，t1／2没有显著性差异。合用氟西汀前后CYP1A2活性无差异，CYP3A4和CYP2D6活性显著降低。合用氟西汀前后CYP1A2活性分别与合用氟西汀前后氯氮平的AUC0-24以及去甲氯氮平的AUC0-24相关，与N-氧化氯氮平的AUC0-24无显著相关。CYP3A4和CYP2D6活性与氯氮平、去甲氯氮平、N-氧化氯氮平的AUC0-24均无显著相关，但是合用氟西汀后CYP3A4活性变化与N-氧化氯氮平的AUC0-24变化显著相关，CYP2D6活性变化与去甲氯氮平的AUC0-24变化显著相关。结论临床剂量氯氮平的代谢途径为去甲基化和N-氧化，其中去甲基代谢为主要代谢途径主要由CYP1A2催化。CYP3A4和CYP2D6不是催化CLZ代谢的主要酶，但是CYP3A4参与了CLZN-氧化代谢，CYP2D6参与去甲基代谢。     

葛根素对细胞色素P450酶活性的影响

目的研究葛根素体外对细胞色素P450酶 1A2（CYP1A2）、CYP2C9、CYP2C19、CYP2D6和CYP3A4活性的影响。方法 分别以咖啡因、甲苯磺丁脲、美芬妥因、美托洛尔和咪达唑仑为探针药, 利用高效液相色谱法测定探针药与相应代谢产物的浓度,采用重组酶研究葛根素对CYP1A2、CYP2C9、CYP2C19、CYP2D6和CYP3A4酶活性的影响。结果 在体外重组酶反应体系中,葛根素对CYP2C9、CYP2C19及CYP3A4酶活性无明显影响。但低浓度葛根素（0.1 mmol•L-1）使CYP1A2的活性降低（48±9）%（P＜0.05）,CYP2D6的活性降低 （61±8）%（P＜0.01）;高浓度（0.4 mmol•L-1） 使CYP1A2的活性降低（82±8）%（P＜0.01）,CYP2D6的活性降低（88±6）%（P＜0.01）。结论 葛根素（0.1 mmol•L-1）对CYP1A2和CYP2D6酶活性有较明显的体外抑制作用;且随着葛根素浓度的增高,对这两种酶活性的抑制作用也增强。为研究葛根素与其他药物的相互作用及作用机制等奠定了基础。     

葛根素对5种细胞色素P450酶体外活性影响研究

目的 研究葛根素体外对细胞色素P450酶亚型 CYP1A2、CYP2C9、CYP2C19、CYP2D6和CYP3A4等活性的影响。方法分别以咖啡因、甲苯磺丁脲、美芬妥因、美托洛尔和咪哒唑仑为探针药，采用高效液相色谱法测定探针药与相应代谢产物的浓度，采用重组酶研究葛根素对CYP1A2、CYP2C9、CYP2C19、CYP2D6和CYP3A4酶体外活性的影响。结果在体外重组酶反应体系中，葛根素对CYP2C9、CYP2C19及CYP3A4酶活性无明显影响。但低浓度(0.1 mmol·L 1)下可使CYP1A2活性降低 (48±9)%(P＜0.05)，使CYP2D6活性降低(61±8)%(P＜0.01)；高浓度(0.4 mmol·L 1)下使CYP1A2活性降低（82 ±8）%(P＜0.01)，使CYP2D6活性降低（88 ± 6）%(P＜ 0.01)。结论葛根素对CYP1A2和CYP2D6酶体外活性有较明显的抑制作用；随着葛根素浓度的增高，抑制作用也相应增强。     

非典型抗精神病药物的代谢途径

非典型抗精神病药的代谢主要由细胞色素P450催化，氮平主要由CYP1A2和CYP3A4催化代谢成去甲氯氮平和N－氧化氯氮平；利培酮由CYP2D6和CYP3A4催化代谢生成9－羟利培酮；奥氮平由CYP1A2、CYP2D6催化代谢成2－羟基甲基奥氮平、4′－N－氧化物等；硅硫平主要通过CYP3A4催化代谢生成7－羟基代谢产物；齐哌西酮由CYP3A4催化代谢生成硫氧化物等代谢产物；思庭多由CYP2D6催化代谢成脱氢思庭多和由CYP3A4代谢为去甲基－思庭多。正常人使用非典型抗精神病药可以导致强烈的镇静作用，因此研究药物的代谢时，其剂量远低于临床治疗剂量。临床治疗剂量的药物代谢值得进一步研究。     

吴茱萸次碱在人肝微粒体中对细胞色素P450酶的抑制作用

目的研究吴茱萸次碱(WZY)在人肝微粒体中对细胞色素P450酶的抑制作用。方法对照组和抑制组酶活性均用探针药测定,探针药物及其代谢产物用HPLC进行检测。用代谢产物与母药比值来表达酶的活性。结果加入50μmol·L-1吴茱萸次碱组CYP1A2,CYP2C19,CYP2E1和CYP2D6的活性显著降低,CYP3A4和CYP2C9活性无显著变化。结论吴茱萸次碱对CYP1A2,CYP2C19,CYP2E1和CYP2D6的活性有显著抑制作用,而对CYP2C9和CYP3A4的活性无显著影响。     

浙贝乙素与浙贝乙素胆酸酯对人细胞色素P450酶活性的影响

目的探讨浙贝乙素和浙贝乙素胆酸酯对人细胞色素P450（CYP）酶5种主要亚型（同工酶）活性的影响。方法人CYP酶探针底物非那西丁（CYP1A2）、甲苯磺丁脲（CYP2C9）、奥美拉唑（CYP2C19）、右美沙芬（CYP2D6）、睾酮（CYP3A4）和咪达唑仑（CYP3A4）分别与不同浓度的浙贝乙素或浙贝乙素胆酸酯在体外与人肝微粒体共孵育20 min,以液质联用（LC/MS/MS）法同时测定各探针底物相应代谢产物的生成量并计算半数抑制浓度（IC50）值,评价浙贝乙素及浙贝乙素胆酸酯对5种CYP酶同工酶的抑制作用。结果浙贝乙素在所考察的0～200 μmol•L－1浓度范围内对5种主要的人肝微粒体CYP酶亚型基本没有抑制作用（CYP1A2,CYP2C9,CYP2C19,CYP3A4）或者仅有很弱的抑制效应（CYP2D6,IC50≥200 μmol•L－1）;浙贝乙素胆酸酯在0～200 μmol•L－1浓度范围内对5种主要的人肝微粒体CYP亚型均有很强的抑制效应,其中对CYP2D6,CYP2C9,CYP2C19,CYP3A4四种亚型的抑制强度最大,IC50≤10 μmol•L－1,对CYP1A2亚型也有较强的抑制作用,IC50约为128 μmol•L－1。结论浙贝乙素对人肝微粒体5种主要的CYP同工酶活性无抑制作用,而浙贝乙素胆酸酯对人肝微粒体5种主要的CYP同工酶活性均有很强的抑制作用。     

丹红注射液对大鼠肝微粒体5种CYP亚型酶活性的影响

摘要目的研究丹红注射液对5种细胞色素P450亚型酶活性的影响,为临床合理用药提供参考。方法采用大鼠体外肝微粒体孵育法,分别以非那西丁、甲苯磺丁脲、右美沙芬、氯唑沙宗、睾酮为CYP1A2、CYP2C9、CYP2D6、CYP2E1、CYP3A4的探针药物,在大鼠肝微粒体孵育体系中孵育,用高效液相色谱（HPLC）法测定相应的代谢产物,比较空白对照组和丹红注射液低、中、高剂量组之间探针药物代谢率的差异,评价丹红注射液对各亚型酶活性的影响。结果在体外肝微粒体孵育体系中,丹红注射液低剂量组中CYP1A2 和CYP2C9活性与空白对照组相比,差异无统计学意义（P＞0.05）;中和高剂量组中CYP1A2和CYP2C9活性与空白对照组相比降低,差异有统计学意义（P＜0.05或P＜0.01）;丹红注射液低、中、高剂量组中CYP2D6、CYP2E1、CYP3A4的活性与空白对照组相比,差异无统计学意义（P＞0.05）。丹红注射液对大鼠肝微粒体CYP1A2酶活性的半数抑制浓度（IC50）和抑制常数（Ki）分别为0.54%和0.226%。结论丹红注射液对大鼠肝微粒体CYP1A2酶活性有抑制作用,且为混合型抑制;对CYP2C9有弱抑制作用;对CYP2D6、CYP2E1、CYP3A4酶活性无明显影响。     

文拉法辛缓释胶囊与舍曲林治疗抑郁症的临床疗效和安全性对照研究

<正>文拉法辛及其活性代谢产物O-去甲基文拉法辛(ODV)是一种二环类苯乙胺族化合物,是5-羟色胺和去甲肾上腺素再摄取抑制剂(serotonin and noradrenaline reuptake inhibitor,SNRI)类抗抑郁药物,能选择性阻断5-羟色胺(5-HT)转运体和去甲肾上腺素(NE)转运体的再摄取作用,具有双重活性,能快速起效,起到抗抑郁作用。本研究比较文拉法辛与舍曲林对抑郁症的治疗效果及安全性,     

Effect of the CYP2D6*10 genotype on venlafaxine pharmacokinetics in healthy adult volunteers

AIMS: Interindividual differences in the pharmacokinetics of venlafaxine, a new antidepressant, were shown during early clinical trials in Japan. Venlafaxine is metabolized mainly by CYP2D6 to an active metabolite, O-desmethylvenlafaxine (ODV). Therefore, the influence of the CYP2D6 genotypes on venlafaxine pharmacokinetics was examined in a Japanese population. METHODS: Twelve adult Japanese men in good health participated in this study. Genomic DNA was isolated from peripheral lymphocytes, and the CYP2D6 genotypes were determined by codon 188C/T, 1934G/A, 2938G/A and 4268G/C mutations using endonuclease tests based on PCR and by Xba I-RFLP analysis. Subjects were categorized into the following 3 groups (n=4 in each group); Group1: CYP2D6*10/*10, *5/*10, Group2: CYP2D6*1/*10, *2/*10 and Group3: CYP2D6*1/*1, CYP2D6*1/*2. Venlafaxine (25 mg, n=6; 37.5 mg, n=6) was administered orally at 09.00 h following an overnight fast. Plasma concentrations of venlafaxine and ODV were monitored by h.p.l.c. for 48 h. RESULTS: The Cmax and AUC of venlafaxine were 184% and 484% higher in the group 1 subjects than in the group 3 subjects, and 101% and 203% higher in the group 1 than in the group 2, respectively. CONCLUSIONS: These results suggest that CYP2D6*10 influences the pharmacokinetics of venlafaxine in a Japanese population.     

Effect of cytochrome P450 enzyme polymorphisms on pharmacokinetics of venlafaxine

This study examines the relationship between blood concentrations of venlafaxine and its active metabolite, O-desmethyl venlafaxine (ODV), and genetic variants of the cytochrome P450 enzymes CYP2D6 and CYP2C19 in human subjects. Trough blood concentrations were measured at steady state in patients treated with venlafaxine extended release in a clinical practice setting. CYP2D6 and CYP2C19 genotypes were converted to activity scores based on known activity levels of the two alleles comprising a genotype. After adjusting for drug dose and gender effects, higher CYP2D6 and CYP2C19 activity scores were significantly associated with lower venlafaxine concentrations (P < 0.001 for each). Only CYP2D6 was associated with the concentration of ODV (P < 0.001), in which genotypes with more active alleles were associated with higher ODV concentrations. The sum of venlafaxine plus ODV concentration showed the same pattern as venlafaxine concentrations with CYP2D6 and CYP2C19 genotypes with higher activity scores being associated with a lower venlafaxine plus ODV concentration (2D6 P = 0.01; 2C19 P < 0.001). Because allelic variants in both CYP2D6 and CYP2C19 influence the total concentration of the active compounds venlafaxine and ODV, both CYP2D6 and CYP2C19 genotypes should be considered when using pharmacogenomic information for venlafaxine dose alterations.     

Metabolic ratios of psychotropics as indication of cytochrome P450 2D6/2C19 genotype

The cytochrome P450 enzymes (CYP) 2C19 and 2D6 are involved in the metabolism of many psychotropic drugs. Variability in enzyme activity results in variable metabolic capacities, affecting the metabolism of substrates. The metabolic ratio (MR) of drugs metabolized via these enzymes may therefore reflect the enzyme's activity and/or genotype. To serve as an example for different groups of medications, the selective serotonin reuptake inhibitor venlafaxine, the tricyclic antidepressant amitriptyline, and the antipsychotic risperidone were studied to examine a possible correlation between the MRs of these drugs and the CYP2C19 and/or CYP2D6 genotype. For this purpose data from routine genotyping and serum level analysis were used. The relationships between the observed metabolic ratios and CYP2D6 and/or CYP2C19 genotype were characterized using nonparametric statistical analysis. A clear correlation was observed between the CYP2D6 genotype and the metabolic ratio of venlafaxine. Genotyping of individuals with a log(MR) < -0.6 or a log(MR) > 0.2 would include all patients with an aberrant genotype but would result in a reduction of 52% of genotyping reactions. Slow metabolism of amitriptyline is correlated with a log(MR) > 0.4. Genotyping only those subjects with a log(MR) > 0.4 would result in 88% fewer genotyping reactions. For risperidone, genotyping individuals with a log(MR) > 0.4 would include all CYP2D6 poor metabolizers while reducing the number of genotyping reactions by 93%. According to these data, correlations exist between the log(MR) of venlafaxine, amitriptyline, and risperidone and the genotype of the CYP enzymes involved in their metabolism. From the ranges of log(MR) defined here, a high percentage of aberrant metabolizers can be detected even when patients are not routinely genotyped. Thus, the metabolic ratio may serve as an indication of when genotyping should be considered.     

Effect of venlafaxine on CYP1A2-dependent pharmacokinetics and metabolism of caffeine

Venlafaxine is a clinically effective antidepressant. Caffeine is a metabolic probe for the quantitative measurement of CYP1A2 activity in vivo. This open-label study evaluated the effect of steady-state venlafaxine on CYP1A2-dependent metabolism, as measured by the pharmacokinetic disposition of caffeine, and urinary caffeine metabolite ratios (CMRs). Sixteen healthy subjects received 200 mg of caffeine orally before (Day 1) and after (Day 8) venlafaxine was titrated to steady-state (37.5 mg every 12 hours on Days 2-4, then 75 mg every 12 hours on Days 5-8). Samples were collected before and for 24 hours after caffeine dosing for the determination of caffeine in plasma and 1,7-dimethylxanthine, 3,7-dimethylxanthine, 1,7-dimethyluric acid (17U), 1-methylxanthine (1X) and 1-methyluric acid (1U), and 5-acetylamino-6-amino-3-methyluracil (AAMU) in urine. Blood samples were obtained before venlafaxine doses on Days 7 and 8 (morning dose only) for the determination of trough venlafaxine and O-desmethylvenlafaxine levels. Venlafaxine did not significantly alter the pharmacokinetics of caffeine and its metabolites. Plasma caffeine AUC was unchanged and remained within the bioequivalence criteria (90% confidence interval: 87.9%-102%) in the presence of venlafaxine. Urine metabolite data showed variable increases and decreases in the CMR [(AAMU + 1U + 1X)/17U] for individual subjects. However, the mean CMR was altered by < 10% in the presence of venlafaxine. This in vivo study demonstrated that venlafaxine did not alter the pharmacokinetic profile of caffeine and confirms in vitro data that venlafaxine does not inhibit CYP1A2 metabolism. Therefore, venlafaxine appears to have a relatively low potential for drug interactions based on CYP1A2 inhibition.     

Differential outcomes from metabolic ratios in the identification of CYP2D6 phenotypes–focus on venlafaxine and O-desmethylvenlafaxine

Background  

Venlafaxine (VEN), a well accepted anti-depressant, is metabolized through the cytochrome P 450 (CYP) 2D6 isozyme to form O-desmethyvenlafaxine (ODV). Due to the involvement of CYP2D6, the formation of ODV is influenced by genetic polymorphism. We used standard tools of assessment to explore the phenotypic distribution in a retrospective manner using the pharmacokinetic (PK) data of VEN and ODV obtained from several bioavailability/bioequivalence (BA/BE) studies in healthy subjects using the reference formulation.     

O- and N-demethylation of venlafaxine in vitro by human liver microsomes and by microsomes from cDNA-transfected cells: effect of metabolic inhibitors and SSRI antidepressants.

The biotransformation of venlafaxine (VF) into its two major metabolites, O-desmethylvenlafaxine (ODV) and N-desmethylvenlafaxine (NDV) was studied in vitro with human liver microsomes and with microsomes containing individual human cytochromes from cDNA-transfected human lymphoblastoid cells. VF was coincubated with selective cytochrome P450 (CYP) inhibitors and several selective serotonin reuptake inhibitors (SSRIs) to assess their inhibitory effect on VF metabolism. Formation rates for ODV incubated with human microsomes were consistent with Michaelis-Menten kinetics for a single-enzyme mediated reaction with substrate inhibition. Mean parameters determined by non-linear regression were: Vmax = 0.36 nmol/min/mg protein, K(m) = 41 microM, and Ks 22901 microM (Ks represents a constant which reflects the degree of substrate inhibition). Quinidine (QUI) was a potent inhibitor of ODV formation with a Ki of 0.04 microM, and paroxetine (PX) was the most potent SSRI at inhibiting ODV formation with a mean Ki value of 0.17 microM. Studies using expressed cytochromes showed that ODV was formed by CYP2C9, -2C19, and -2D6. CYP2D6 was dominant with the lowest K(m), 23.2 microM, and highest intrinsic clearance (Vmax/K(m) ratio). No unique model was applicable to the formation of NDV for all four livers tested. Parameters determined by applying a single-enzyme model were Vmax = 2.14 nmol/min/mg protein, and K(m) = 2504 microM. Ketoconazole was a potent inhibitor of NDV production, although its inhibitory activity was not as great as observed with pure 3A substrates. NDV formation was also reduced by 42% by a polyclonal rabbit antibody against rat liver CYP3A1. Studies using expressed cytochromes showed that NDV was formed by CYP2C9, -2C19, and -3A4. The highest intrinsic clearance was attributable to CYP2C19 and the lowest to CYP3A4. However the high in vivo abundance of 3A isoforms will magnify the importance of this cytochrome. Fluvoxamine (FX), at a concentration of 20 microM, decreased NDV production by 46% consistent with the capacity of FX to inhibit CYP3A, 2C9, and 2C19. These results are consistent with previous studies that show CYP2D6 and -3A4 play important roles in the formation of ODV and NDV, respectively. In addition we have shown that several other CYPs have important roles in the biotransformation of VF.     

Venlafaxine: in vitro inhibition of CYP2D6 dependent imipramine and desipramine metabolism; comparative studies with selected SSRIs, and effects on human hepatic CYP3A4, CYP2C9 and CYP1A2

Aims In order to anticipate drug-interactions of potential clinical significance the ability of the novel antidepressant, venlafaxine, to inhibit CYP2D6 dependent imipramine and desipramine 2-hydroxylation was investigated in human liver microsomes. The data obtained were compared with the selective serotonin re-uptake inhibitors, fluoxetine, sertraline, fluvoxamine and paroxetine. Venlafaxine’s potential to inhibit several other major P450s was also studied (CYP3A4, CYP2D6, CYP1A2). Methods K_i values for venlafaxine, paroxetine, fluoxetine, fluvoxamine and sertraline as inhibitors of imipramine and desipramine 2-hydroxylation were determined from Dixon plots of control and inhibited rate data in human hepatic microsomal incubations. The inhibitory effect of imipramine and desipramine on liver microsomal CYP2D6 dependent venlafaxine O-demethylation was determined similarly. Venlafaxine’s IC₅₀ values for CYP3A4, CYP1A2 CYP2C9 were determined based on inhibition of probe substrate activities (testosterone 6β-hydroxylation, ethoxyresorufin O-dealkylase and tolbutamide 4-hydroxylation, respectively). Results Fluoxetine, paroxetine, and fluvoxamine were potent inhibitors of imipramine 2-hydroxylase activity (K_i values of 1.6±0.8, 3.2±0.8 and 8.0±4.3 μm, respectively; mean±s.d., n=3), while sertraline was less inhibitory (K_i of 24.7±8.9 μm ). Fluoxetine also markedly inhibited desipramine 2-hydroxylation with a K_i of 1.3±0.5 μm. Venlafaxine was less potent an inhibitor of imipramine 2-hydroxylation (K_i of 41.0±9.5 μm ) than the SSRIs that were studied. Imipramine and desipramine gave marked inhibition of CYP2D6 dependent venlafaxine O-demethylase activity (K_i values of 3.9±1.7 and 1.7±0.9 μm, respectively). Venlafaxine did not inhibit ethoxyresorufin O-dealkylase (CYP1A2), tolbutamide 4-hydroxylase (CYP2C9) or testosterone 6β-hydroxylase (CYP3A4) activities at concentrations of up to 1 mm. Conclusions It is concluded that venlafaxine has a low potential to inhibit the metabolism of substrates for CYP2D6 such as imipramine and desipramine compared with several of the most widely used SSRIs, as well as the metabolism of substrates for several of the other major human hepatic P450s.     

Venlafaxine and generalised anxiety disorder: new preparation. Minimise recourse to drugs

(1) Generalised anxiety disorder is defined as excessive anxiety for at least 6 months. (2) Management is based primarily on psychological measures, with the aim of limiting recourse to drugs. The reference drugs are benzodiazepines. The treatment period should be as short as possible, to avoid adverse effects such as sedation and dependence. (3) Venlafaxine is a non tricyclic, non MAOI antidepressant. A sustained-release formulation has just been granted marketing authorisation in France for generalised anxiety disorder. (4) The clinical assessment file on venlafaxine in this indication includes results from two 8-week trials and a placebo-controlled trial with 6 months follow-up. The trials showed a significant improvement with venlafaxine on standard anxiety scales, but the clinical impact (at best moderate) has been poorly assessed. We found no comparison between venlafaxine and benzodiazepines. (5) In one trial venlafaxine was no more effective than buspirone. (6) The most frequent adverse effects of venlafaxine are gastrointestinal disorders, insomnia and dizziness. Venlafaxine carries a risk of drug interactions and withdrawal symptoms. (7) In practice, venlafaxine provides nothing new in the treatment of generalised anxiety disorder. The reference drug treatment remains a benzodiazepine.     

Influence of CYP2D6 activity on the disposition and cardiovascular toxicity of the antidepressant agent venlafaxine in humans

According to in-vitro studies with microsomes from human livers and from yeast expression systems with high CYP2D6 activity, the major oxidation pathway of venlafaxine is catalysed by CYP2D6. In this study, we investigated the role of the CYP2D6 polymorphism and the effects of low-dose quinidine, a selective inhibitor of, CYP2D6, on the disposition of venlafaxine. Fourteen healthy men, eight with the extensive metabolizer and six with the poor metabolizer phenotype were administered venlafaxine hydrochloride 18.75 mg orally every 12 h for 48 h on two occasions (1 week apart); once alone and once during the concomitant administration of quinidine sulfate 100 mg every 12 h. Blood and urine samples were collected under steady-state conditions over one dosing interval (12 h). When venlafaxine was administered alone, the oral clearance of venlafaxine was more than fourfold less in poor metabolizers compared to extensive metabolizers (P < 0.05). This was mainly due to a decreased capability of poor metabolizers to form O-desmethylated metabolites at the position 4 of the aromatic moiety. In extensive metabolizers, quinidine decreased venlafaxine oral clearance from 100 +/- 62 l/h to 17 +/- 5 l/h (mean +/- SD; P < 0.05) without any effects on renal clearance (4 +/- 1 l/h during venlafaxine alone and 4 +/- 1 l/h during venlafaxine plus quinidine). In these individuals, the sequential metabolism of venlafaxine to O-desmethylvenlafaxine and to N,O-didesmethylvenlafaxine was inhibited by quinidine coadministration so that metabolic clearances to O-desmethylated metabolites decreased from 43 +/- 32 l/h to 2 +/- 1 l/h (P < 0.05). In poor metabolizers, coadministration of quinidine did not cause significant changes in oral clearance and partial metabolic clearances of venlafaxine to its various metabolites. Decreased CYP2D6 activity could also be associated with cardiovascular toxicity as observed in four patients during treatment with the drug. Thus, genetically determined or pharmacologically altered CYP2D6 activity represents a major determinant of venlafaxine disposition in humans.