丙戊酸药物浓度与CYP286基因多态性的相关性研究

目的:探讨丙戊酸(VPA)药物浓度与细胞色素P4502B6(CYP2B6)基因多态性的关系。方法:选择符合入选条件的癫患者72例,提取外周血DNA,应用聚合酶链反应和限制性核酸内切酶方法分析患者的CYP2B6基因型及等位基因;应用荧光偏振免疫法测定患者VPA的血药浓度。结果:72例癫患者中CYP2B6基因型为*1/*1为39例(54.2%),*1/*6为29例(40.3%),*6/*6为4例(5.5%),根据基因型将患者分为两组,A组(CYP2B6*1/*1)和B组(CYP2B6*1/*6或CYP2B6*6/*6)。B组患者VPA的标准血药浓度平均值较A组高,且差异有统计学意义(P<0.05)。结论:CYP2B6是VPA的代谢酶,CYP2B6基因多态性可影响VPA的血药浓度,对含有CYP2B6*6等位基因的患者应用VPA时,其血药浓度高,提示对VPA药物代谢有影响。     

回、汉族癫痫患者CYP2C9和CYP2C19基因多态性与苯巴比妥血药浓度的相关性研究

目的研究CYP2C9*3和CYP2C19*2的单核苷酸多态性在回、汉族癫痫人群中的分布特点;探讨两种基因型与苯巴比妥血药浓度的关系。方法对宁夏地区回、汉族癫痫患者185例采用聚合酶链反应-限制性片段长度多态性技术(PCR-RFLP)分析CYP2C9*3和CYP2C19*2基因型,并进行回、汉族间基因型及等位基因频率的比较;应用反相高效液相色谱法(RP-HPLC)测定其中113例单用苯巴比妥患者的血药浓度,再将其标准化后,分析两种基因型与苯巴比妥血药浓度的关系。结果 (1)回、汉族癫痫患者中CYP2C9*3和CYP2C19*2基因型及等位基因频率均无统计学差异(P>0.05)。(2)根据所携带的CYP2C9和CYP2C19突变等位基因的数量,将113例单用苯巴比妥的患者分为强代谢(EM)组、中间代谢(IM)组和弱代谢(PM)组,IM组和PM组苯巴比妥血药浓度明显高于EM组,且突变基因携带数量与血药浓度呈正相关。结论苯巴比妥血药浓度在CYP2C9和CYP2C19变异基因携带者中增高,根据患者CYP2C9和CYP2C19基因型可以预测患者药物浓度,指导临床选择合适的苯巴比妥初始剂量。     

CBZ和CBZE血药浓度个体差异与CYP3A5*3基因多态性的相关性分析

目的 探讨卡马西平(CBZ)药物代谢个体差异性的遗传学机制,从而指导临床抗癫痫治疗中的个体化用药.方法 选取确诊为癫痫并适用CBZ的患者58例.首先利用PCR技术扩增患者外周血中包含等位基因CYP3A5*3(rs776746)的基冈片段;其次采用基因测序法确定该等位基因各基因型的分布,将包含原始碱基(A)的基因序列归为A组,而将只含有突变碱基(C)的基因序列归为B组;最后,应用高效液相色谱法测定两组患者外周血中CBZ及其代谢产物10,11-环氧化卡马西平(CBZE)的血药浓度.采用t检验,比较A、B两组患者CBZ和CBZE血药浓度的差异.结果 A组患者CBZ的浓度明显低于B组(P＜0.01);A组患者CBZE的浓度明显高于B组(P＜0.05).CYP3A5 * 3的基因多态性与CBZ及其代谢产物CBZE的血药浓度相关,CYP3A5*3突变纯合型CBZ代谢减慢,血药浓度相应增高,应给予相对小剂量的CBZ,以提高临床用药的安全性.结论 CYP3A5*3的基因多态性可能作为临床治疗中CBZ剂量个体化的一项重要参考依据.     

缺血性脑血管病患者 CYP2 C19 基因多态性的相关性研究

目的探讨缺血性脑血管病(ischemic cerebrovascular disease,ICVD)患者CYP2C19基因单核苷酸多态性(single nucleotide polymorphism,SNP)与临床特征、治疗效果之间的关系。为脑血管疾病患者服用抗血小板药物的个体化治疗提供参考依据。方法昆明医科大学第一附属医院神经外科2015年1月—2017年4月间完善CYP2C19(*2、*3、*17)基因检测的153例患者作为研究对象。将所有患者分别按每个基因位点基因检测的结果分为突变组及非突变组,分析CYP2C19基因各位点突变与患者临床特征、缺血性脑血管病发病及服药后发生缺血事件的关系。结果本组153例患者中,男70例(45. 8%),女83例(54. 2%),平均年龄(53. 2±11. 6)岁; CYP2C19(*2、*3、*17)各位点基因型突变的频率分别为53. 6%、9. 2%及2. 0%。CYP2C19*2位点突变与非突变组患者的吸烟、饮酒比率及血胆固醇(TC)、低密度脂蛋白胆固醇含量比较,差异均有统计学意义(P 0. 05-0. 01); CYP2C19*3位点突变与非突变组患者的血高密度脂蛋白胆固醇含量的差异有统计学意义(P 0. 005)。CYP2C19 3个位点突变与与非突变组患者发生ICVD的差异均无统计学意义(均P 0. 05)。CYP2C19*2位点突变患者服药后的缺血事件发生率比非突变患者明显增加(P 0. 05)。结论患者是否患有ICVD与CYP2C19(*2、*3、*17)基因位点多态性无明显关系;抗血小板治疗后是否发生缺血性事件与CYP2C19*2基因位点突变有关。因CYP2C19*2基因的突变率较高(本组患者达53. 6%),建议患者服抗血小板药前先行基因检测,以避免可能预后不佳。     

CYP基因多态性与抗癫痫药物代谢相关性的研究进展

癫痫( epilepsy,EP)是一种常见的神经系统疾患,已成为重要的公共卫生问题[1].目前癫痫治疗仍以抗癫痫药物(antiepileptic drugs,AEDs)控制发作为主,通过规范的诊疗,大多数患者可以控制发作.但在癫痫的临床治疗过程中,作者发现AEDs的代谢存在较大的个体差异,即使患者发作类型相同,应用相同剂量的同种AEDs治疗,其血药浓度与疗效也相差甚远,有的患者用到最大耐受剂量时,仍不能控制发作,而有的患者应用常规剂量,就会出现严重的药物副作用.单核苷酸多态性(single nucleotide polymorphism,SNPs)是指同一物种不同个体基因组DNA等位基因序列存在差别的现象.诸多研究表明[2-5]:细胞色素P450( cytochrome P450,CYP)基因SNPs是影响多种AEDs代谢的重要因素,特别是CYP2C9与CYP2C19基因突变后会引起多种AEDs血药浓度升高,如苯妥英( phenytoin,PHT)、苯巴比妥(phenobarbital,PB)、丙戊酸(valproic acid,VPA)等,说明CYP基因SNPs影响多种AEDs的代谢,是导致AEDs个体代谢差异的重要原因.基于不同个体的特定基因型选择合适的药物剂量,以求达到临床个体化治疗的目的.本文将从与AEDs代谢相关的CYP基因SNPs及其对AEDs代谢的影响等几个方面做一综述.     

CYP2C19基因多态性与奥氮平所致药物性肝损伤的关联性研究

目的:研究细胞色素酶CYP2C19基因多态性与奥氮平所致药物性肝损伤(DILI)间的关联性。方法:对127例单一服用奥氮平的精神分裂症患者的CYP2C19位点rs4244285、rs4986893、rs12248560进行基因分型检测,分析比较服药后出现药物性肝损伤(DILI)患者(DILI组)与未出现DILI患者(非DILI组)3个SNPs等位基因及基因型频率差异。结果:两组间3个等位基因和基因型频率、各代谢类型频率比较差异无统计学意义(P0.05),在3位点基因类型比较中,DILI组*1/*3基因频率低于非DILI组,差异有统计学意义(P=0.034)。结论:CYP2C19基因多态性与奥氮平所致DILI易感性可能有关,CYP2C19中*1/*3基因型可能是奥氮平所致DILI的保护性因素。     

丙戊酸代谢相关CYP2C19基因多态性在癫痫患儿体内的分布及治疗个体化研究

目的：对癫痫患儿体内CYP2C19的基因多态性进行研究,并进行基因型与患儿体内丙戊酸血药浓度关系的研究,以对患儿进行治疗个体化。方法采用聚合酶链反应－限制性片段长度多态性检测技术对2012‐12—2014‐03来我院及其他医院神经内科654例确诊为癫痫患儿的CYP2C19基因型进行检测,同时对仅服用丙戊酸进行抗癫痫治疗的228例患儿体内的丙戊酸稳态血药浓度进行检测,进而探求CYP2C19的基因型与血药浓度的相关性。结果 CYP2C19具有基因多态性,各基因型分布频率不同,其中*1／*1型为41.9％、*1／*2型为41.1％、*1／*3型为6.4％、*2／*2型为7.4％、*2／*3型为2.9％和*3／*3型为0.3％;同时入选组的228例患儿中快、中、慢代谢型所占的频率分别为40.8％、44.7％和13.5％;同时测得*1／*1型、*1／*2型、*1／*3型、*2／*2型、*2／*3型所对应的稳态血药浓度（m g／L ）分别为45±20、64±16、68±21、73±28、72±18;经统计分析发现,*2／*2型与*1／*1型血药浓度体质量剂量比值存在差异具有统计学意义（ P＜0.05）。结论癫痫患儿体内CYP2C19具有多态性,其分布规律与其他正常人群的分布规律基本一致,患儿服用丙戊酸时,其CYP2C19基因型与体内丙戊酸的血药浓度具有相关性。因此提醒我们,对癫痫患儿应用丙戊酸进行抗癫痫治疗时,可参考CYP2C19基因分型结果,预测血药浓度变化,对患儿进行个体化的治疗。     

细胞色素P450等位基因多态性与丙戊酸钠血药浓度的相关性

目的探讨细胞色素P450(CYP)2A6及CYP2B6等位基因多态性与丙戊酸钠血药浓度的关系。方法选择165例服用丙戊酸钠单药治疗且无肝肾功能异常的癫疒间患者,应用多聚酶链反应(PCR)方法分别进行CYP2A6(95例)和CYP2B6(70例)等位基因多态性频率分析;应用荧光偏振免疫法(FPIA)测定含不同等位基因患者丙戊酸钠的血药浓度。结果95例患者中,CYP 2A6*4等位基因频率为13.2%,CYP2A6*4等位基因携带者丙戊酸钠的血药浓度[(4.23±0.27)mg/ml]明显高于非CYP2A6*4等位基因携带者[(3.35±0.38)mg/ml](P<0.05);70例患者中,CYP2B6*6等位基因频率为24.3%,CYP2B6*6等位基因携带者丙戊酸钠的血药浓度[(4.12±0.34)mg/ml]明显高于非CYP2B6*6等位基因携带者[(3.07±0.28)mg/ml](P<0.05)。结论CYP2A6或(和)CYP2B6等位基因多态性均影响丙戊酸钠的血药浓度,CYP2A6*4或(和)CYP2B6*6等位基因携带者丙戊酸钠用量应低于常规剂量,以减少不良反应的发生和避免药物资源的浪费。     

CYP2A6基因多态性对丙戊酸钠血药浓度的影响

目的探讨细胞色素P4502A6(CYP2A6)基因多态性对丙戊酸钠血药浓度的影响。方法选择单药服用丙戊酸钠的癫患者98例,应用巢式PCR(nested-primerpolymerasechainreaction)方法分析其CYP2A6基因型,分析等位基因CYP2A6*1及CYP2A6*4;同时应用荧光偏振免疫法(FPIA)测定患者丙戊酸钠的血药浓度。结果98例患者中CYP2A6基因型为*1/*1者73例(74·5%),*1/*4者24例(24·5%),*4/*4者1例(1·0%),根据基因型分为A组(CYP2A6*1/*1)和B组(CYP2A6*1/*4或CYP2A6*4/*4)。B组患者丙戊酸钠的标准血药浓度平均值(4·1393±0·2793)较A组(3·3486±0·3919)高,差异有统计学意义(P<0·05)。结论CYP2A6基因多态性影响丙戊酸钠的血药浓度,含有CYP2A6*4等位基因的患者应用丙戊酸钠应较常规降低用量。     

急性脑梗死患者基因多态性对氯吡格雷疗效及终点事件的影响

目的探讨急性脑梗死患者基因多态性对氯吡格雷疗效及终点事件的影响。方法选取2016-06—2017-06新乡市第一人民医院神经内科收治的急性脑梗死患者418例。口服氯吡格雷5 d后抽取外周肘静脉血,血栓弹力图仪测定血小板抑制率。采用改良多重高温连接酶检测反应技术(iMLDR)对患者CYP2C19与ABCBl基因多态性进行分型。出院后进行24个月的随访,记录主要终点事件发生类别及时间。结果根据CYP2C19*2/*3快速代谢型、中间代谢型、慢代谢型的血小板抑制率之间,以及ABCBl C3435T不同基因型之间差异均有统计学意义(P0.01);而ABCBlT(-620)C不同基因型的血小板抑制率之间差异无统计学意义(P0.05)。校正可能的混杂因素后,进行多元线性回归分析显示,CYP2C19*2/*3、ABCBl C3435T是血小板抑制率的独立影响因素;同时还发现体重指数(BMI)26 kg/m~2也是血小板抑制率的独立影响因素。共382例患者完成随访研究,终点事件发生率为13.61%(52/382),其中缺血性脑卒中复发36例(9.42%),心肌梗死4例(1.05%),血管性死亡12例(3.14%)。根据是否携带CYP2C19*2/*3基因分为2组,生存分析Log-Rank检验显示差异有统计意义(P0.05);而ABCBlT(-620)C、ABCBl C3435T基因的显性与阴性患者生存曲线间差异无统计学意义(P0.05)。多因素Cox回归分析显示,CYP2C19*2/*3基因携带是临床终点时间的独立危险因素;同时年龄也是临床终点时间的独立危险因素。结论携带CYP2C19*2/*3、ABCBl C3435T等位基因的急性脑梗死患者氯吡格雷疗效降低,其中携带CYP2C19*2/*3等位基因的患者终点事件风险增高。     

The Effects of Genetic Polymorphisms of CYP2C9 and CYP2C 19 on Phenytoin Metabolism in Japanese Adult Patients with Epilepsy: Studies in Stereoselective Hydroxylation and Population Pharmacokinetics

Summary: Purpose : The aim of this study was to clarify the effects of genetic polymorphisms of cytochrome P450 (CYP) 2C9 and 2C19 on the metabolism of phenytoin (PHT). In addition, a population pharmacokinetic analysis was performed.
Methods: The genotype of CYP2C9 (Arg¹⁴⁴/Cys, Ile³⁵⁹/Leu) and CYP2C19 (*1, *2 or *3) in 134 Japanese adult patients with epilepsy treated with PHT were determined, and their serum concentrations of 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) enantiomers, being major metabolites of PHT, were measured. A population pharmacokinetic analysis (NONMEM analysis) was performed to evaluate whether genetic polymorphism of CYP2C9/19 affects the clinical use of PHT by using the 336 dose-serum concentration data.
Results: The mean maximal elimination rate (Vmax) was 42% lower in the heterozygote for Leu359 allele in CYP2C9, and the mean Michaelis-Menten constants (K,) in the heterozygous extensive metabolizers and the poor metabolizers of CYP2C19 were 22 and 54%, respectively, higher than those without the mutations in CYP2C9/19 genes. (R)- and (5')- p -HPPHPHT ratios were lower in patients with mutations in CYP2C9 or CYP2C19 gene than those in patients without mutations.
Conclusions: Although the hydroxylation capacity of PHT was impaired with mutations of CYP2C9/19, the impairment was greater for CYP2C9. In view of the clinical use of PHT, two important conclusions were derived from this population study. First, the serum PHT concentration in patients with the Leu359 allele in CYP2C9 would increase dramatically even at lower daily doses. Second, the patients with CYP2C19 mutations should be treated carefully at higher daily doses of PHT.     

The influence of cytochrome oxidase CYP2A6, CYP2B6, and CYP2C9 polymorphisms on the plasma concentrations of valproic acid in epileptic patients

Objectives

To investigate influences of the functional polymorphisms of Cytochrome P450 isozymes 2A6 (CYP2A6), 2B6 (CYP2B6), and 2C9 (CYP2C9) on pharmacokinetics of VPA in vivo.

Patients and methods

In the study, we analyzed the genotypes of CYP2A6, CYP2B6, and CYP2C9 and their contribution to the steady-state standardized plasma VPA concentrations in 179 subjects with epilepsy of a Northern Han Chinese population. The genotypes were detected by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Results

The subjects with one or two variant CYP2A6*4 alleles showed higher mean plasma VPA concentrations compared with non-*4 alleles [(3.4 ± 0.4) μg kg ml⁻¹ mg⁻¹ vs. (3.6 ± 0.4) μg kg ml⁻¹ mg⁻¹, p = 0.0055]. A significant difference [one-way ANOVA (p = 0.0203)] was also found between mean plasma VPA concentrations and the CYP2B6 genotypes. In addition, subjects with the heterozygous genotype CYP2C9*3 had higher mean plasma VPA concentrations than did those subjects with the wild-type genotype [(3.9 ± 0.4) μg kg ml⁻¹ mg⁻¹ vs. (3.4 ± 0.4) μg kg ml⁻¹ mg⁻¹, p = 0.0001].

Conclusion

The presently evaluated variant alleles in the CYP2A6, CYP2B6, and CYP2C9 genes may explain part of the substantial variability in VPA pharmacokinetics between different subjects.     

Paradoxical urinary phenytoin metabolite (S)/(R) ratios in CYP2C19*1/*2 patients

Phenytoin (PHT) is primarily metabolized to 5-(4'-hydroxyphenyl)-5-phenylhydantoin (p-HPPH), accounting for 67-88% of an administered dose in humans. p-HPPH is formed by the cytochrome (CYP) 450 enzymes CYP2C9 and CYP2C19, then glucuronidated and excreted into the urine. CYP2C9 catalyses the prochiral formation of (R) and (S)-p-HPPH, and is approximately 40 times more stereoselective towards the formation of the (S) isomer whereas CYP2C19 is not stereoselective. Because of differential stereoselectivity, polymorphisms in the genes can alter the (S)/(R)-p-HPPH ratios. Genotyping for CYP2C9 and CYP2C19 was accomplished by a Taqman based assay. Twelve and twenty-four hour urine samples were collected from 45 epilepsy patients taking PHT under steady-state conditions and (S)/(R) ratios of p-HPPH were determined by chiral HPLC separation. The mean urinary (S)/(R) ratio in the 12-24h urine collection in subjects homozygous for CYP2C9*1/*1, CYP2C19*1/*1 was 24.2+/-3.1(n=21), whereas ratios in CYP2C9*1/*2 and CYP2C9*1/*3 subjects, were 11.1+/-3.3(n=7) and 2.7+/-0.6(n=2), respectively. One CYP2C9*2/*3 patient had a ratio of 2.1. Unexpectedly, CYP2C9*1/*1, CYP2C19*1/*2 subjects had a mean (S)/(R) ratio as low as 12.9+/-1.7(n=12). Our results are generally consistent with single dose PHT studies. However, the (S)/(R)-p-HPPH ratios for the CYP2C9*1/*1, CYP2C19*1/*2 subjects, expected to be in the range of 30-40, were only 12.9, suggesting some undetected linkage disequilibrium between CYP2C9 and CYP2C19 genes that could affect PHT elimination. Furthermore, our study suggests that measurement of urine ratios cannot be used as a marker for genotype determination.     

CYP2C19 polymorphism and risk for essential tremor

Many patients with essential tremor (ET) develop acute adverse effects to primidone. We investigated the association between CYP2C19 polymorphism (possibly related to primidone metabolism) and the risk for developing essential ET and acute adverse effects to primidone. Leukocytary DNA from 200 ET patients and 300 healthy controls was studied for the genotype CYP2C19 and the occurrence of CYP2C19 allelic variants by using allele-specific PCR amplification and Sma I and BamH I RFLP analyses. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and of the allelic variant CYP2C19*2 were significantly higher in ET patients than in controls. The mean age at onset of ET did not differ significantly between patients with genotypes CYP2C19*1/CYP2C19*2andCYP2C19*1/CYP2C19*1. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and the allelic variant CYP2C19*2 were similar in ET patients who developed acute adverse effects to primidone, in those who tolerated primidone and in controls; the frequencies were also similar in patients with head, voice, tongue and chin tremor compared with controls. These results suggest that heterozygosis CYP2C19*1/CYP2C19*2 is associated with the risk for ET, but not with the age at onset of ET, the presentation of acute side effects of primidone, or the existence of head, voice, tongue or chin tremor.     

Clinical Side Effects of Phenobarbital, Primidone, Phenytoin, Carbamazepine, and Valproate During Monotherapy in Children

The rate of onset of side effects was examined in 392 pediatric outpatients who received long-term monotherapy with phenobarbital (PB), primidone (PRM), phenytoin (PHT), carbamazepine (CBZ), or valproate (VPA) for epilepsy or febrile convulsions. The severity of side effects (based on need to alter treatment), the nature of each drug's most common side effects, and the doses and plasma levels of occurrence were recorded. Our results show that usually accepted therapeutic ranges are well tolerated. Indeed, although some form of side effect occurred in 50% of patients, treatment had to be changed in only 18% and the drug had to be stopped in only 7%. In decreasing order, the rates for side effects were PHT (71%) greater than PB (64%) greater than CBZ (43%) greater than VPA (43%) greater than PRM (29%). Serious side effects requiring withdrawal of treatment occurred at the following rates: PHT (10%) greater than VPA (8%) greater than PRM (8%) greater than PB (4%) greater than CBZ (3%). Among our patients, the best tolerated antiepileptic drug (AED) was CBZ, and the least tolerated was PHT. Behavioral disorders were most common with PB, neurologic disorders with PHT, digestive tract disorders with VPA, and gingival hyperplasia and hirsutism with PHT. Behavioral disorders involving excitement seen with PB and PRM occurred most commonly at low plasma levels. Behavioral disorders involving depression seen with PB and VPA, those involving excitement seen with PHT and VPA, and digestive disorders seen with VPA occurred particularly when plasma levels were high.     

Association of graded allele-specific changes in CYP2D6 function with imipramine dose requirement in a large group of depressed patients

The inactivation and clearance of the tricyclic antidepressant imipramine is dependent on CYP2D6 activity. First, CYP2C19 converts imipramine into the active metabolite desipramine, which is then inactivated by CYP2D6. This retrospective single center study aimed to prove whether CYP2C19 and ample CYP2D6 genotyping (taking into consideration four null alleles and three decreased-activity alleles) could be used to predict imipramine and desipramine plasma concentrations in depressed patients, and whether genotype-based drug dose recommendations might assist in the early management of imipramine pharmacotherapy. In 181 subjects with major depressive disorder, drug doses were recorded, imipramine and desipramine plasma concentrations were monitored and CYP2C19 (*2) and CYP2D6 genotype (*3, *4, *5, *6, *9, *10, *41 and gene duplication) were obtained, yielding graded allele-specific CYP2D6 patient groups. Desipramine and imipramine+desipramine plasma concentration per drug dose unit, imipramine dose at steady state, and imipramine dose requirement significantly depended on CYP2D6 genotype (Kruskal-Wallis test, P<0.0001). Mean (+/-s.d.) drug dose requirements were 131 (+/-109), 155 (+/-70), 217 (+/-95), 245 (+/-125), 326 (+/-213), and 509 (+/-292) mg imipramine/day in carriers of 0, 0.5, 1, 1.5, 2, and >2 active CYP2D6 genes, respectively. Our protocol for CYP2D6 genotyping will thus importantly aid in the prediction of imipramine metabolism, allowing for the use of an adjusted starting dose and faster achievement of predefined imipramine+desipramine plasma levels in all genetic patient subgroups. Therefore, therapeutic efficacy and efficiency may be improved, the number of adverse drug reactions decreased, and hospital stay reduced.     

Topiramate and phenytoin pharmacokinetics during repetitive monotherapy and combination therapy to epileptic patients

PURPOSE: To evaluate the potential pharmacokinetic interactions between topiramate (TPM) and phenytoin (PHT) in patients with epilepsy by studying their pharmacokinetics (PK) after monotherapy and concomitant TPM/PHT treatment. METHODS: Twelve patients with epilepsy stabilized on PHT monotherapy were enrolled in this study, with 10 and seven patients completing the phases with 400 and 800 mg TPM daily doses, respectively. TPM was added at escalating doses, and after stabilization at the highest tolerated TPM dose, PHT doses were tapered. Serial blood and urine samples were collected for PK analysis during the monotherapy phase or the lowest PHT dose after taper and the concomitant TPM/PHT phase. Potential metabolic interaction between PHT and TPM also was studied in vitro in human liver microsomal preparations. RESULTS: In nine of the 12 patients, PHT plasma concentrations remained stable, with a mean (+/-SD) area under the curve (AUC) ratio (combination therapy/monotherapy) of 1.13 +/- 0.17 (range, 0.89-1.23). Three patients had AUC ratios of 1.25, 1.39, and 1.55, respectively, and with the addition of TPM (800, 400, and 400 mg daily, respectively), their peak PHT plasma concentrations increased from 15 to 21 mg/L, 28 to 36 mg/L, and 27 to 41 mg/L, respectively. Human liver microsomal studies with S-mephenytoin showed that TPM partially inhibited CYP2C19 at very high concentrations of 300 microM (11% inhibition) and 900 microM (29% inhibition). Such high plasma concentrations would correspond to doses in humans that are 5 to 15 times higher than the recommended dose (200-400 mg). TPM clearance was approximately twofold higher during concomitant TPM/PHT therapy CONCLUSIONS: This study provides evidence that the addition of TPM to PHT generally does not cause clinically significant PK interaction. PHT induces the metabolism of TPM, causing increased TPM clearance, which may require TPM dose adjustments when PHT therapy is added or is discontinued. TPM may affect PHT concentrations in a few patients because of inhibition by TPM of the CYP2C19-mediated minor metabolic pathway of PHT.