中国汉族人S-美芬妥英4′-羟化代谢的遗传多态性(英文)

目的:研究我国汉族人S-美芬妥英(S-Mep)4′-羟化代谢的遗传多态性。方法:148名互无血缘关系的汉族健康志愿者和5个家族21名成员,口服美芬妥英100mg后,用HPLC法测定0-12h尿中S-Mep 4′-羟化代谢的代谢比值(lg MR)和羟化指数(lg HI)。结果:lg MR和lg HI均呈两态性分布,分型点(antimode)分别为-1.00和1.50,羟化代谢缺陷的频发率为13.5％(20/148)。系谱分析表明S-Mep 4′-羟化代谢缺陷为常染色体隐性遗传。结论:S-Mep 4′-羟化代谢缺陷频发率东方人高于高加索人,遗传方式均为常染色体隐性遗传。     

中国汉族人群S-美芬妥英4''-羟化酶的表型与基因分析

目的:研究中国汉族人群S-美芬妥英4'-羟化代谢遗传多态性.方法:以美芬妥英为探针药物采用手性毛细管气相色谱法测定尿中S-/R-MP浓度比值, 对90名志愿者进行了表型分型测定,应用PCR技术对其中的26名志愿者进行了S-美芬妥英4'-羟化酶(CYP2C19)基因分析.结果:表型分析结果,11人属慢代谢者(PM),S/R比值0.95;基因分析结果,6人为野生型纯合子(wt/wt);10人为杂合子(wt/m1和wt/m2),9人为CYP2C19m1突变型纯合子(m1/m1),1人为两突变型杂合子(m1/m2).结论:表型分析与基因分析结果显示了很好的相关性,本实验测得慢代谢者的频发率为12.2%,与文献报道相符.     

中国壮族志愿者S—美芬妥英和异喹胍羟化代谢多态性研究

118名中国壮族（广西壮族自治区）志愿者一次口服消旋美芬妥黄100mg和异喹胍10mg后，应用气相色谱法分别测定尿中S－和R－美芬妥英含量比值和异喹胍及其代谢物4羟异喹胍含量比值，作为体内药物羟化代谢能力的指标，实验结果表明，118名志愿者中有12名的S／R美芬妥英比值大于1.0，是为S－美芬妥英弱羟化代谢者。说明我国壮族人群中S－美芬妥英羟化代谢缺陷频发率高达10.2%。但在118名壮族志愿者中未发现异喹胍弱羟化代谢者，且S－美芬妥英的羟化代谢多态发生态性和异喹胍羟化代谢多态性不存在着相关性，另外，选择其中16名志愿者（4名弱代谢者，12名强代谢者）研究了尿中美芬妥英和异喹胍及其代谢物的消除动力学规律，并估算了它们主要的药代动力学参数。     

体外中国成人肝微粒体中氯胍活化为氯胍三嗪由CYP2C19和CYP3A4介导(英文)

目的:鉴定中国成人肝微粒体中介导氯胍(PG)活化为氯胍三嗪(CG)的细胞色素P450(CYP450).方法:分析中国成人(n=6)肝微粒体中PG活化为CG的酶促动力学,各种CYP450抑制剂对该代谢的作用及其与S-美芬妥英4′-羟化的关系.结果:6个标本中,除一个外(两酶米氏模型),PG活化为CG的酶促动力学符合米氏一酶模型;CYP3A4和CYP2E1的选择性抑制剂醋竹桃霉素(81.1％)和二乙二硫基苯甲酸(47.23％)可抑制CG生成,其它抑制剂没有明显作用;在低PG浓度时,PG的环化与S-美芬妥英4′-羟化显著相关(r=0.805,P<0.05),高浓度时相关性明显减小.结论:在中国成人肝微粒体中CYP2C19和CYP3A4参与了PG活化为CG.     

中国汉族人群S-美芬妥英4'-羟化酶的表型与基因分析

目的：研究中国汉族人群S-美芬妥英4'-羟化代谢遗传多态性。方法：以美芬妥英为探针药物采用手性毛细管气相色谱法测定尿中S-/R-MP浓度比值, 对90名志愿者进行了表型分型测定,应用PCR技术对其中的26名志愿者进行了S-美芬妥英4'-羟化酶（CYP2C19）基因分析。结果：表型分析结果,11人属慢代谢者（PM）,S/R比值0.95;基因分析结果,6人为野生型纯合子（wt/wt）;10人为杂合子（wt/m₁和wt/m₂）,9人为CYP2C19m₁突变型纯合子（m₁/m₁）,1人为两突变型杂合子（m₁/m₂）。结论：表型分析与基因分析结果显示了很好的相关性,本实验测得慢代谢者的频发率为12.2%,与文献报道相符。     

氯米帕明在体外人肝微粒体中的氮位去甲基代谢

采用人肝微粒体应用酶促动力学分析,观察特异性细胞色素P450(CYP450)抑制剂对氯米帕明(CIM) N-去甲基代谢的作用以及CIM去甲基代谢与S-美芬妥英4′-羟化代谢的相关性,以阐明参与CIM N-去甲基代谢的CYP450的种类, 性质及其在代谢中的作用. 酶促动力学分析结果表明有高亲和力酶及具有底物别构激活特性的低亲和力酶参与了CIM的N-去甲基代谢. 抑制实验结果表明CYP 1A2特异性抑制剂呋拉茶碱（Fur）主要抑制低浓度CIM的去甲基代谢,CYP 3A4特异性 抑制剂醋竹桃霉素（TAO）主要抑制高浓度CIM去甲基代谢. 相关实验发现3 μmol·L^-1 CIM代谢生成N-去甲基CIM的速率与200 μmol·L^-1 S-美芬妥英生成4′-羟基美芬妥英的速率无显著相关性, 提示CYP 2C19对于催化人肝微粒体中CIM的去甲基代谢仅起较为次要或很小的作用. 结果表明,CYP 1A2主要参与低浓度CIM在体外人肝微粒体N-去甲基代谢,CYP 3A4因其底物激活特性主要在高浓度CIM的去甲基代谢中起作用,CYP 2C19则作用很小.     

中国壮族志愿者S─美芬妥英和异喹胍羟化代谢多态性研究

１１８名中国壮族（广西壮族自治区）志愿者一次口服消旋美芬妥英１００ｍｇ和异喹胍１０ｍｇ后，应用气相色谱法分别测定尿中Ｓ─和Ｒ─美芬妥英含量比值和异喹胍及其代谢物４羟异喹胍含量比值，作为体内药物羟化代谢能力的指标。实验结果表明，１１８名志愿者中有１２名的Ｓ／Ｒ美芬妥英比值大于１．０，是为Ｓ─美芬妥英弱羟化代谢者。说明我国壮族人群中Ｓ─美芬妥英羟化代谢缺陷频发率高达１０．２％。但在１１８名壮族志愿者中未发现异喹胍弱羟化代谢者，且Ｓ─美芬妥英的羟化代谢多态性和异喹胍羟化代谢多态性不存在着相关性。另外，选择其中１６名志愿者（４名弱代谢者，１２名强代谢者）研究了尿中美芬妥英和异喹胍及其代谢物的消除动力学规律。并估算了它们主要的药代动力学参数。     

中国汉族人S—美芬妥英4‘—羟化代谢的遗传多态性

研究我国汉族人Ｓ－美芬妥英４＇－羟化代谢的遗传多态性。１４８名互无血缘关系的汉族健康志愿者和５个家庭２１名成员，口服美芬妥英１００ｍｇ后，用ＨＰＬＣ法测定０－１２ｈ尿中Ｓ－Ｍｅｐ４＇－羟化代谢的代谢比值和羟化指数。     

CYP2C19基因多态性与肿瘤易感性关系的研究进展

细胞色素氧化酶P4502C19（CYP2C19）又称S-美芬妥英羟化酶，其表型和基因型的遗传多态性决定了不同个体对不同致癌物代谢的差异性和肿瘤的化学致癌易感性。本文对CYP2C19基因多态性分子机制、基因多态性与肿瘤发病易感性的关系等研究进行了综述     

豆腐果苷对人肝微粒体CYP450酶体外抑制作用研究

目的:通过评价豆腐果苷在体外对人肝微粒体CYP450酶的7种亚型酶活性的影响,预测服用豆腐果苷可能出现的食物-药物及药物-药物代谢的影响。方法:将豆腐果苷与CYP450酶7种亚型的特异性探针底物咖啡因(CYP1A2)、右美沙芬(CYP2D6)、甲苯磺丁脲(CYP2C9)、S-美芬妥因(CYP2C19)、氯唑沙宗(CYP2E1)、香豆素(CYP2A6)及咪达唑仑(CYP3A4)与人肝微粒体进行孵育反应,采用HPLC和LC-MS/MS法测定对应的7种代谢产物(1,7-二甲基黄嘌呤、去甲右美沙芬、4-羟基甲苯磺丁脲、4-羟基美芬妥因、6-羟基氯唑沙宗、7-羟基香豆素和1-羟基咪达唑仑)的浓度,与对照组比较,确定豆腐果苷对以上7种亚酶活性的影响。结果:豆腐果苷在1～100μmol.L-1时对7种酶的抑制作用均无明显统计学意义(P>0.05)。结论:豆腐果苷可能不会引起有临床意义的CYP450酶抑制现象的发生。     

No correlation between side-chain of propranolol oxidation and S-mephenytoin 4'-hydroxylase activity.

AIM: To determine if any correlation between the side-chain oxidative capacity for propranolol and S-mephenytoin 4'-hydroxylase (cytochrome P-450 2C19, CYP2C19) activity in healthy Chinese of Han nationality. METHODS: S-mephenytoin oxidative metabolite 4'-hydroxymephenytoin (4'OH-M), S- and R-mephenytoin, and naphthoxyl-actic acid (NLA) excreted in urine, and propranolol in plasma were measured after 14 healthy extensive metabolizers of S-mephenytoin oxidation were given a single oral dose of racemic mephenytoin 100 mg and racemic propranolol 80 mg, respectively. S/R-mephenytoin in urine was determined by chiral capillary gas chromatography with nitrogen-phosphorus detection, 4'-OH-M in urine by reversed-phase liquid chromatography (RPLC) with ultraviolet detection, and plasma propranolol or urinary NLA by the RPLC with fluorescence detection. RESULTS: No significant correlations were found between the partial metabolic clearance (Clm) of propranolol to NLA and 8 h urinary S/R ratio of mephenytoin (rs = -0.0484; P = 0.8695), nor between the Clm and log10 of 8 h urinary excretion of 4'-OH-M (rs = -0.1077; P = 0.7140). CONCLUSIONS: CYP2C19 is not a principal P-450 isozyme responsible for the in vivo side-chain oxidation of propranolol in the Chinese.     

液相色谱手性分离与紫外检测人尿中美芬妥英S／R比值及其与气相？…

AIM: To improve HPLC method for rapid determination of urinary S/R-ratio of mephenytoin, a widely used metabolic index for cytochrome P-450 2C19 (CYP2C19) activity. METHODS: Aliquots of 0-8-h urine sample after dosing racemic mephenytoin 100 mg underwent one-step extraction with dichloromethane. Analysis was performed on a chiral column (250 mm x 4 mm, 5 microns) at lambda = 207 nm. The eluent was a mixture of acetronitrile and water containing both 0.1% glacial acetic acid and 0.2% triethylamine (14:86, vol/vol) at a flow-rate of 0.9 mL.min-1. RESULTS: The enatiomers of mephenytoin in urine were well separated within 9 min. A linear correlation was observed between 50-5000 micrograms.L-1 with the detection limit of 12.5 micrograms.L-1 for both enantiomers of mephenytoin. This HPLC analysis was comparable to gas chromatography in accuracy and sensitivity, but with much shorter retention time and better resolution. CONCLUSION: The present HPLC method is good for rapid determination of the ability of subjects to hydroxylate S-mephenytoin after oral administration of the racemic drug.     

Identification of human CYP isoforms involved in the metabolism of propranolol enantiomers--N-desisopropylation is mediated mainly by CYP1A2.

1. Studies using human liver microsomes and six recombinant human CYP isoforms (i.e. CYP1A2, 2A6, 2B6, 2D6, 2E1 and 3A4) were performed to identify the cytochrome P450 (CYP) isoform(s) involved in the ring 4-hydroxylation and side-chain N-desisopropylation of propranolol enantiomers in humans. 2. alpha-Naphthoflavone and 7-ethoxyresorufin (selective inhibitors of CYP1A1/2) inhibited the N-desisopropylation of R- and S-propranolol by human liver microsomes by 20 and 40%, respectively, while quinidine (a selective inhibitor of CYP2D6) abolished the 4-hydroxylation of both propranolol enantiomers almost completely. In contrast, sulphaphenazole (CYP2C8/9 inhibitor), S-mephenytoin (CYP2C19 inhibitor), troleandomycin (CYP3A3/4 inhibitor) and diethyldithiocarbamate (CYP2E1 inhibitor) elicited only weak inhibitory effects on propranolol metabolism via the two measured metabolic pathways. 3. Significant (P < 0.01) correlations were observed between the microsomal N-desisopropylation of both propranolol enantiomers and that for the O-deethylation of phenacetin among the 11 different human liver microsome samples (r = 0.98 and 0.77 for R- and S-propranolol, respectively). A marginally significant (r = 0.60, P congruent to 0.05) correlation was also observed between N-desisopropylation of S-, but not of R-propranolol and the 4'-hydroxylation of S-mephenytoin. No significant correlations were observed between the N-desisopropylation of propranolol enantiomers and the 2-hydroxylation of desipramine, the hydroxylation of tolbutamide or the 6 beta-hydroxylation of testosterone. 4. Significant (P < 0.01) correlations were observed between the microsomal 4-hydroxylation of R- and S-propranolol and the 2-hydroxylation of desipramine (r = 0.85 and 0.98, respectively). A weak (r = 0.66), albeit significant (P < 0.05) correlation was observed between the 4-hydroxylation of R-, but not of S-propranolol and the hydroxylation of tolbutamide. No significant correlations were observed between the 4-hydroxylation of propranolol enantiomers and the oxidation of other substrates for CYP1A2, 2C19, and 3A3/4. 5. Recombinant human CYP1A2 and CYP2D6 exhibited comparable catalytic activity with respect to the N-desisopropylation of both propranolol enantiomers; only expressed CYP2D6 exhibited a marked catalytic activity with respect to the 4-hydroxylation of both propranolol enantiomers.(ABSTRACT TRUNCATED AT 400 WORDS)     

CYP2C19基因型和CYP2C9对人肝微粒体中氟西汀N-去甲基代谢的影响(英文)

目的:本实验旨在研究CYP2C19基因型人肝微粒体中氟西汀N-去甲基代谢的酶促动力学特点并鉴定参与此代谢途径的细胞色素P-450酶。方法:测定基因型CYP2C19肝微粒体中去甲氟西汀形成的酶促动力学。鉴定氟西汀N-去甲基酶活性与细胞色素P-450 2C9,2C19,1A2和2D6酶活性的相关性,同时应用各种细胞色素P-450酶的选择性抑制剂和化学探针进行抑制实验,从而确定参与氟西汀N-去甲基代谢的细胞色素P-450酶。结果:去甲氟西汀生成的酶促动力学数据符合单酶模型,并具有Michaelis-Menten动力学特征。当底物浓度为氟西汀25μmol/L和100μmol/L时,去甲氟西汀(N-FLU)的生成率分别与甲磺丁脲3-羟化酶活性显著相关(r_1=0.821,P_1=0.001;r_2=0.668,P_2=0.013),当底物浓度为氟西汀100μmol/L时,N-FLU的生成率与S-美芬妥因4’-羟化酶活性显著相关(r=0.717,P=0.006)。PM肝微粒中磺胺苯吡唑和醋竹桃霉素对氟西汀N-去甲基代谢的抑制作用显著大于EM(73％vs 45％,P<0.01)。结论:在生理底物浓度下,CYP2C9是催化人肝微粒体中氟西汀N-去甲基代谢的主要CYP-450酶;而高底物浓度时,以CYP2C19的作用为主。     

Impact of CYP2D6 Poor Metabolizer Phenotype on Propranolol Pharmacokinetics and Response

We conducted an open-label study to determine the impact of cytochrome P-4502D6 (CYP2D6) on propranolol pharmacokinetics and response in 12 healthy men with CYP2D6 extensive metabolizer (EM) phenotype and 3 healthy men with CYP2D6 poor metabolizer (PM) phenotype. Subjects received R,S-propranolol hydrochloride 80 mg every 8 hours for 16 doses. After the sixteenth dose, blood and urine samples were collected for 24 hours, and serum propranolol and urine metabolite concentrations were determined by chiral high-performance liquid chromatography. Heart rate response to treadmill exercise was measured serially over 24 hours. Apparent oral clearance of propranolol and partial metabolic clearance values of propranolol to 4-hydroxypropranolol (HOP), propranolol glucuronide, and naphloxylactic acid (NLA) were estimated. Apparent oral clearance and elimination half-life of propranolol were not different between EMs and PMs. Partial metabolic clearance of propranolol to HOP was significantly higher and to NLA was significantly lower in EMs than in PMs. No differences in percentage reductions in exercise heart rate were observed between EMs and PMs. The CYP2D6 PM phenotype has no effect on propranolol blood concentrations and does not alter response to propranolol. Our data also suggest that CYP2D6 mediates approximately 65% and 70% of S- and R-propranolol's 4-hydroxylation, respectively.     

Stereoselective inhibition of cytochrome P450 forms by lansoprazole and omeprazole in vitro

The stereoselectivity of the inhibitory interaction potential of lansoprazole and omeprazole isomers on six human cytochrome P450 forms was evaluated using human liver microsomes. Lansoprazole enantiomers showed stereoselective inhibition of CYP2C9-catalysed tolbutamide 4-methylhydroxylation, CYP2C19-catalysed S-mephenytoin 4'-hydroxylation, CYP2D6-catalysed dextromethorphan O-demethylation, CYP2E1-catalysed chlorzoxazone 6-hydroxylation and CYP3A4-catalysed midazolam 1-hydroxylation, whereas omeprazole only inhibited CYP2C19 stereoselectively. Of the P450 forms tested, CYP2C19-catalysed S-mephenytoin 4'-hydroxylation was extensively inhibited by both the lansoprazole and omeprazole enantiomers in a competitive and stereoselective manner; the S-enantiomers of both drugs inhibited the hydroxylation more than the R-enantiomers. The estimated K(i) values determined for CYP2C19-catalysed S-mephenytoin 4'-hydroxylation were 0.6, 6.1, 3.4 and 5.7 microM for S-lansoprazole, R-lansoprazole, S-omeprazole and R-omeprazole, respectively. The results indicate that although both lansoprazole and omeprazole are strong inhibitors of CYP2C19, the inhibition of CYP2C19 by lansoprazole is highly stereoselective, whereas the inhibition by omeprazole is less stereoselective. In addition, S-lansoprazole, the most potent CYP2C19 inhibitor, is not a good CYP2C19-selective inhibitor owing to its inhibition of other P450 forms.     

Effect of antifungal drugs on cytochrome P450 (CYP) 2C9, CYP2C19, and CYP3A4 activities in human liver microsomes

The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, and CYP3A4-mediated nifedipine oxidation activities in human liver microsomes were compared. In addition, the effects of preincubation were estimated to investigate the mechanism-based inhibition. The IC50 value against tolbutamide hydroxylation was the lowest for miconazole (2.0 microM), followed by voriconazole (8.4 microM) and fluconazole (30.3 microM). Similarly, the IC50 value against S-mephenytoin 4'-hydroxylation was the lowest for miconazole (0.33 microM), followed by voriconazole (8.7 microM) and fluconazole (12.3 microM). On the other hand, micafungin at a concentration of 10 or 25 microM neither inhibited nor stimulated tolbutamide hydroxylation and S-mephenytoin 4'-hydroxylation, and the IC50 values for itraconazole against these were greater than 10 microM. These results suggest that miconazole is the strongest inhibitor of CYP2C9 and CYP2C19, followed by voriconazole and fluconazole, whereas micafungin would not cause clinically significant interactions with other drugs that are metabolized by CYP2C9 or CYP2C19 via the inhibition of metabolism. The IC50 value of voriconazole against nifedipine oxidation was comparable with that of fluconazole and micafungin and higher than that of itraconazole and miconazole. The stimulation of the inhibition of CYP2C9-, CYP2C19-, or CYP3A4-mediated reactions by 15-min preincubation was not observed for any of the antifungal drugs, suggesting that these drugs are not mechanism-based inhibitors.     

CYP2C19 polymorphism is not important for the in vivo metabolism of selegiline

OBJECTIVES: To address the relevance of cytochrome P-450 (CYP) 2C19 polymorphism for the pharmacokinetics and dynamics of selegiline and its two known primary metabolites, desmethylselegiline and l-methamphetamine. METHODS: Six extensive (mephenytoin S/R ratio < 0.3; EM) and six poor (mephenytoin S/R ratio > 0.8; PM) hydroxylators of S-mephenytoin ingested a single 10-mg oral dose of selegiline hydrochloride. Serum concentrations of selegiline, desmethylselegiline and l-methamphetamine were measured by gas chromatography--mass spectrometry for up to 48 h. In addition, the platelet monoamine oxidase type B (MAO-B) activity was measured for 14 days to describe possible differences in the pharmacodynamics of selegiline and its metabolites between EM and PM. RESULTS: The CYP2C19 phenotype had no significant effects on the pharmacokinetic variables of selegiline. PM of S-mephenytoin had 68% higher mean AUC of desmethylselegiline (P = 0.0017) than EM, but no significant differences were observed in other pharmacokinetic parameters of desmethylselegiline. Contrary to desmethylselegiline, the serum l-methamphetamine concentrations were slightly lower in PM, but no statistically significant differences were observed in l-methamphetamine pharmacokinetics between the two CYP2C19 phenotypes. Accordingly, the magnitude of MAO-B inhibition showed no significant differences between the study groups. CONCLUSIONS: CYP2C19 polymorphism does not seem to be crucial for the metabolism or clinical effects of selegiline.     

Diazinon is activated by CYP2C19 in human liver.

Phosphorothioate compounds are used throughout the world as agricultural and domestic pesticides. Here, the activation of the phosphorothioate diazinon to diazoxon in human liver is described. In an initial study using three human liver microsomal samples, K(m) for diazoxon formation varied markedly (31, 208, and 660 microM; V(max) 1125, 685, and 1028 pmol/min/mg protein, respectively), suggesting the involvement of more than one P450 enzyme. A wide variation in activity was found using 50 microM diazinon as substrate, (11-648 pmol/min/mg protein, n = 15), whereas, with 500 microM, variation was less (164-978 pmol/min/mg protein). Among eight P450-catalyzed reactions, the putative high-affinity component (50 microM diazinon) correlated with S-mephenytoin 4'-hydroxylase activity (r = 0.686, p < 0.01), suggesting the involvement of CYP2C19. The putative low-affinity component (500 microM diazinon) correlated with both S-mephenytoin 4'-hydroxylase (r = 0.714; p < 0.005) and high-affinity phenacetin O-deethylase activity (r = 0.625; p < 0.05). This activity was partially inhibited by furafylline, troleandomycin, and ketoconazole. These data suggest contributions from CYP2C19, CYP1A2, and CYP3A4. None of the inhibitors affected the high-affinity component. Of seven heterologously expressed human P450 enzymes, CYP2C19 activated diazinon (500 microM) at the fastest rate, followed by CYP3A4, CYP1A2, and CYP2C9. Both hepatic microsomal S-mephenytoin 4'-hydroxylase and high-affinity phenacetin O-deethylase activities were strongly inhibited by diazinon (IC50 < 2.5 microM), while no effect was seen on midazolam 1'-hydroxylase activity. These data indicate that CYP2C19 is the major enzyme involved in diazinon activation in human liver, while other enzymes including CYP1A2 may play a more minor role.     

CYP2B6, CYP3A4, and CYP2C19 are responsible for the in vitro N-demethylation of meperidine in human liver microsomes.

Meperidine is an opioid analgesic metabolized in the liver by N-demethylation to normeperidine, a potent stimulant of the central nervous system. The purpose of this study was to identify the human cytochrome P450 (P450) enzymes involved in normeperidine formation. Our in vitro studies included 1) screening 16 expressed P450s for normeperidine formation, 2) kinetic experiments on human liver microsomes and candidate P450s, and 3) correlation and inhibition experiments using human hepatic microsomes. After normalization by its relative abundance in human liver microsomes, CYP2B6, CYP3A4, and CYP2C19 accounted for 57, 28, and 15% of the total intrinsic clearance of meperidine. CYP3A5 and CYP2D6 contributed to < 1%. Formation of normeperidine significantly correlated with CYP2B6-selective S-mephenytoin N-demethylation (r = 0.88, p < 0.0001 at 75 > microM meperidine, and r = 0.89, p < 0.0001 at 350 microM meperidine, n = 21) and CYP3A4-selective midazolam 1'-hydroxylation (r = 0.59, p < 0.01 at 75 microM meperidine, and r = 0.55, p < 0.01 at 350 microM meperidine, n = 23). No significant correlation was observed with CYP2C19-selective S-mephenytoin 4'-hydroxylation (r = 0.36, p = 0.2 at 75 microM meperidine, and r = 0.02, p = 0.9 at 350 microM meperidine, n = 13). An anti-CYP2B6 antibody inhibited normeperidine formation by 46%. In contrast, antibodies inhibitory to CYP3A4 and CYP2C8/9/18/19 had little effect (<14% inhibition). Experiments with thiotepa and ketoconazole suggested inhibition of microsomal CYP2B6 and CYP3A4 activity, whereas studies with fluvoxamine (a substrate of CYP2C19) were inconclusive due to lack of specificity. We conclude that normeperidine formation in human liver microsomes is mainly catalyzed by CYP2B6 and CYP3A4, with a minor contribution from CYP2C19.