Cytochrome P450 3A4 genetic polymorphisms and post-operative fentanyl requirements

What is known and Objective: Interindividual variability in drug responses may be attributable to genetically determined alteration in enzyme activity. In this study, we investigated the association between cytochrome P450 3A4 (CYP3A4) genetic polymorphisms and post‐operative fentanyl requirements. Methods: Patients (n = 94) scheduled for gynaecological laparotomy received i.v. fentanyl infusion (3 μg/kg/h) after induction of general anaesthesia. Post‐operative fentanyl requirements were quantified by using a patient‐controlled analgesia and the number of i.v. fentanyl rescue analgesia required were recorded. Pain control was assessed using visual analogue scores (VAS) and fentanyl’s adverse effects were documented. CYP3A4*4, CYP3A4*5 and CYP3A4*18 alleles of cytochrome P450 3A4 were identified by polymerase chain reaction–restriction fragment length polymorphism. Differences in fentanyl requirements, VAS scores and adverse effects among the various genotypes were compared. Results and Discussion: No CYP3A4*4 and CYP3A4*5 alleles were detected. Eighty‐nine patients (94·7%) were wild‐type, five (5·3%) were heterozygous and none was homozygous. No significant difference was demonstrated between the genotype groups in terms of fentanyl consumption, pain control and adverse effects. What is new and Conclusion: CYP3A4*4 and CYP3A4*5 are rare in the Malaysian Malay population. Genetic polymorphism of CYP3A4*18 may not play an important role in influencing postoperative fentanyl requirements.     

CYP3A4*1G基因多态性对老年患者全髋置换术后舒芬太尼药效学的影响

目的探讨CYP3A4*1G基因多态性对老年患者全髋置换术后舒芬太尼药效学的影响。 方法选择2016年1月至2017年8月台州市中心医院择期行全髋置换手术的老年患者116例,术后患者静脉自控镇痛（PCIA）。采用焦磷酸测序法检测CYP3A4*1G基因多态性,根据基因型将患者分成野生型纯合子（AA）组69例、突变型杂合子（GA）组39例和突变型纯合子（GG）组8例。记录并比较所有患者术后6、12、24、48 h静息状态下的视觉模拟疼痛评分（VAS）,术后48 h的舒芬太尼总用量、PCIA次数。 结果三组患者术后6、12、24、48 h的VAS的比较差异均无统计学意义（F=0.907、0.192、0.757、0.256,P均>0.05）。而达到相同镇痛效果的GG组患者术后48 h舒芬太尼消耗量[（89.8 ± 0.8）、（95.8 ± 0.5）、（96.0 ± 0.4）μg,F=25.113,P<0.001]及PCIA次数[（10.9 ± 2.0）、（17.4 ± 4.5）、（18.3 ± 3.7）次,F=35.227,P<0.001]均显著少于AA组和GA组患者。而GA组和AA组术后48 h舒芬太尼消耗量及PCIA次数比较差异均无统计学意义（P均>0.05）。 结论结合患者基因型调整舒芬太尼药量可减少老年患者药物使用量。     

OATP1B1 388A>G polymorphism and pharmacokinetics of pitavastatin in Chinese healthy volunteers

Purpose: To investigate the contribution of the most frequent single nucleotide polymorphism (SNPs) of the organic anion transporting polypeptide 1B1 (OATP1B1) 388A>G to the pharmacokinetics of pitavastatin in Chinese healthy volunteers. Methods: Eighteen healthy volunteers participated in this study. Group 1 consisted of nine subjects who were of 388AA wild‐type OATP1B1 genotype. Group 2 consisted of seven subjects with the 388GA genotype and two 388GG homozygotes. Two milligram of pitavastatin was administered orally to the volunteers. The plasma concentration of pitavastatin was measured for up to 48 h by liquid chromatography–mass spectrometry (LC–MS). Results: The pharmacokinetic parameters of pitavastatin were significantly different between the two genotyped groups. The concentration (C_max) value was higher in the 388GA + 388GG group than that in the 388AA group (39·22 ± 8·45 vs. 22·90 ± 4·03 ng/mL, P = 0·006). The area under the curve to the last measurable concentration (AUC_0–48) and area under the curve extrapolated to infinity (AUC_0–∞) of pitavastatin were lower in the 388AA group than in the 388GA + 388GG group (100·42 ± 21·19 vs. 182·19 ± 86·46 ng h/mL, P = 0·024; 108·12 ± 24·94 vs. 199·64 ± 98·70ng h/mL, P = 0·026) respectively. The oral clearance (Cl/F) was lower in the 388GA + 388GG group than that in the 388AA group (12·46 ± 4·79 vs. 19·21 ± 3·74/h, P = 0·012). The elimination of half‐life (t_1/2) and peak concentration times (T_max) values showed no difference between these groups. Conclusions: The OATP 388A>G polymorphism causes significant alterations in the pharmacokinetics of pitavastatin in healthy Chinese volunteers and this may well be clinically significant.     

Impact of CYP3A4*1G polymorphism on metabolism of fentanyl in Chinese patients undergoing lower abdominal surgery

PurposeThis study aimed to investigate the impact of CYP3A4*1G genetic polymorphism on metabolism of fentanyl in Chinese patients undergoing lower abdominal surgery.Methods176 patients receiving elective lower abdominal surgery under general anesthesia were recruited into this study. Genotyping of CYP3A4*1G was carried out by direct sequencing. The plasma fentanyl concentration was detected 30 min after anesthesia induction by high performance liquid chromatography–ultraviolet ray (HPLC–UV). The visual analog scale (VAS) was used for pain evaluation at rest during patient-controlled analgesia (PCA) treatment 0 h, 12 h and 24 h after operation. PCA fentanyl consumption and adverse effects were recorded during the first 24 h after surgery.ResultsThe frequency of CYP3A4*1G variant allele was 0.227 (80/352, 95% CI 0.165, 0.289) in these patients. After grouping according to the genotype of CYP3A4*1G, plasma fentanyl concentration in the *1/*1 variant (wild-type) group (12.8 ± 6.5 ng/ml) was significantly lower than that in the *1/*1G group (16.8 ± 9.0 ng/ml, P < 0.01) and the *1G/*1G group (28.1 ± 9.5 ng/ml, P < 0.01). Patients in the *1G/*1G group (247.1 ± 73.2 μg) consumed significantly less fentanyl than that in either the wild-type group (395.0 ± 138.5 μg) or the *1/*1G group (359.8 ± 120.2 μg) (P < 0.01). There was a significant correlation between plasma fentanyl concentration and PCA fentanyl consumption (r = ?0.552, P < 0.001).ConclusionsCYP3A4*1G polymorphism is related to the pharmacokinetics of fentanyl, and patients with CYP3A4*1G variant A allele have a lower metabolic rate of fentanyl. The specific CYP3A4*1G polymorphism may predict the individual requirement of fentanyl.     

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

What is known and Objective: Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re‐evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3. Methods: 295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics. Results: The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC_0–∞ value (490% of the reference value) and a lower oral clearance rate (18% of the reference). What is new and Conclusion: This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild‐type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.     

Interactions between CYP7A1 A-204C and ABCG8 C1199A polymorphisms on lipid lowering with atorvastatin

What is known and Objective: Cholesterol excretion by ATP binding cassette transporters G5 and G8 (ABCG5/G8) and bile acid biosynthesis by 7a‐hydroxylase (CYP7A1) are major pathways for the removal of cholesterol into bile. This suggests that variations in the CYP7A1 and ABCG8 genes may influence the statin response. We aimed to investigate the effect of CYP7A1 A‐204C and ABCG8 C1199A polymorphisms and their interactions on the lipid‐lowering response to atorvastatin in a Chinese population. Methods: Genotypes were determined by using polymerase chain reaction‐restrict fragment length polymorphism (PCR‐RFLP) in 185 hyperlipidaemic patients treated with atorvastatin, 20 mg once daily for 4 weeks. Serum levels of triglycerides (TGs), total cholesterol (TC), low‐density lipoprotein cholesterol (LDL‐C), and high‐density lipoprotein cholesterol (HDL‐C) were determined before and after treatment. Results and Discussion: For 181 patients (89 males), variant allele frequencies of CYP7A1 ‐204C and ABCG8 1199A were 0·347 and 0·128, respectively. Among all patients, homozygotes for the ‐204A allele showed a slightly significant mean percentage reduction from baseline in TG level after treatment than heterozygotes and homozygotes for the ‐204C allele (?25·49 ± 8·12%vs. ?22·80 ± 8·72%, P = 0·054, and ?25·49 ± 8·12%vs.?22·51 ± 8·82%, P = 0·048, respectively). For patients with the ABCG8 C1199A variant allele, the difference in percentage reduction from baseline in TG level was increased between the CYP7A1 A‐204C wild‐type allele homozygotes and variant allele homozygotes after atorvastatin treatment (?28·35%vs.?19·28%, P = 0·001), and increased differences were found between the CYP7A1 A‐204C wild‐allele homozygotes and variant allele homozygotes (?18·95%vs.?15·61%, P = 0·009) and between the CYP7A1 A‐204C variant allele heterozygotes and homozygotes (?18·69%vs.?15·61%, P = 0·012, respectively). What is new and Conclusion: The CYP7A1 ‐204A and ABCG8 1199A alleles appear to interact to affect lipid‐lowering response to atorvastatin. However, given the relatively small number of subjects with the influential variant allele combinations, and the heterogeneity in response, even in the selected sub‐populations, testing would be of little clinical utility in the Chinese population sampled.     

Relationship of CYP2D6 genetic polymorphisms and the pharmacokinetics of tramadol in Chinese volunteers

Objective: To investigate the relationship between CYP2D6 genetic polymorphisms and the pharmacokinetics of tramadol in Chinese volunteers. Method: A gene chip was established for determining CYP2D6 genotype. Forty adult healthy Chinese subjects were categorized as: group 1, CYP2D6*1/*1; group 2, CYP2D6*2/*2; group 3, CYP2D6*2/*10; group 4, CYP2D6*10/*10. After oral administration of 100 mg tramadol, plasma and urine samples were collected over a 32‐h period. Results: The main pharmacokinetic parameters of tramadol and its metabolite O‐demethyltramadol (M₁) in groups 1 and 2 were not significantly different. However, they were significantly different between groups 3 and 1, groups 4 and 1 and groups 4 and 3. Conclusion: CYP2D6*2 does not alter the pharmacokinetics of tramadol, whereas CYP2D6*10 did with homozygotes showing a more pronounced reduction than heterozygotes. The 32‐h metabolic ratio of tramadol to M₁ were (mean ± SD) 2·05 ± 1·01, 2·13 ± 0·83, 4·24 ± 2·75 and 6·85 ± 2·78, respectively, in CYP2D6*1/*1, CYP2D6*2/*2, CYP2D6*2/*10 and CYP2D6*10/*10 subjects, respectively.     

胃肠手术患者瑞芬太尼相关基因位点检测在术中麻醉药物剂量评估中的应用

目的　通过检测麻醉药物瑞芬太尼（remifentanil，REM）体内代谢和转运相关基因位点，探讨其与术中瑞芬太 尼使用剂量的关系，为患者提供精准的麻醉药物个体化用药指导。方法　收集5 249 例胃肠手术患者血液样本，应用荧 光探针原位杂交技术检测瑞芬太尼相关基因位点OPRM1(118A ＞ G)，CYP3A4*1G(25343C ＞ T)，ABCB1(3435T>C)， CYP3A4*18B(A>G) 并进行分析，评估不同基因型患者麻醉药物的使用剂量。结果　OPRM1(118A ＞ G) 位点AA/AG 基因型4 636 例（88.32%），GG基因型613 例（11.68%），CYP3A4*1G( 25343C ＞ T) 位点CC/CT 基因型4 922 例（93.77%）， TT 基因型327 例（6.23%），ABCB1(3435T>C) 位点TT 基因型1 842 例（35.09%），TC/CC 基因型3 407 例（64.91%）， CYP3A4*18B(A>G) 位点AA 基因型5 149 例（98.09%），AG/GG 基因型100 例（1.91%）。54 例OPRM1 AA/AG， CYP3A4*1G TT，ABCB1 TT 基因型患者麻醉诱导及术中维持中应减低瑞芬太尼剂量，严格控制静脉泵注速度；118 例 OPRM1 GG，CYP3A4*1G CC 和ABCB1 CC 基因型患者，术中麻醉维持应根据其麻醉程度适当提高瑞芬太尼剂量和泵 注速度；100 例CYP3A4*18B AG/GG 基因型患者适当减少瑞芬太尼剂量，降低静脉泵注速度。结论　不同患者应根据 其瑞芬太尼基因型别合理用药，为麻醉药物使用的患者提供精准的用药指导。     

Differences in genotype and allele frequency distributions of polymorphic drug metabolizing enzymes CYP2C19 and CYP2D6 in mainland Chinese Mongolian, Hui and Han populations

What is known and Objective: Cytochrome P450 2C19 (CYP2C19) and CYP2D6 are important xenobiotic metabolic enzymes and both show considerable genetic variability between Orientals and Caucasians. There are known marked heterogeneity in susceptibility to various cancers and hypertension among Chinese Mongolian, Hui and Han ethnic groups, but the molecular mechanisms are unknown. Our objective was to investigate the patterns of distribution of CYP2C19 and CYP2D6 polymorphisms among healthy Chinese subjects to determine whether any observed inter‐ethnic variability might be worth further investigation as possible contributors to the known differences in disease prevalence. Methods: Blood samples were collected from 454 unrelated Chinese healthy subjects (214 Han, 111 Hui, 129 Mongolian) for genotyping analysis. The single nucleotide polymorphisms (SNPs) CYP2C19*2 (681G>A in exon 5), CYP2C19*3 (636G>A in exon 4) and CYP2D6*10 (188C>T in exon 1) were determined by the polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) method. Results and Discussion: Significantly higher frequencies of the CYP2C19 poor metabolic genotypes were observed in Chinese Han (18·7%), Chinese Hui (25·0%) and Chinese Mongolian (10·9%) subjects than has been reported for Caucasians (1·7–3·0%, P < 0·01). The prevalent defective allele CYP2C19*2 occurred more frequently in both Chinese Hui (32·4%) and Han (29·7%) than in Chinese Mongolian (18·2%, P < 0·01) subjects. The CYP2C19*2 and CYP2C19*3 defective alleles were significantly more frequent in Chinese Han and Chinese Hui ethnic groups than have been reported for Caucasians (11·1–16·3% and 0–0·2%, P < 0·01). CYP2D6*1/*10 heterozygotes and CYP2D6*10/*10 homozygotes were observed more frequently in Chinese Han (43·1% and 27·2%), Hui (40·6% and 30·7%) and Mongolian subjects (31·3% and 9·6%, both P < 0·01) than have been reported for Caucasians (5·5% and 0·3%, P < 0·01). In Chinese Mongolians, the CYP2D6*10 allele occurred at a frequency (25·2%, P < 0·01) intermediate between those reported for Caucasians and the other two Chinese ethnic populations. What is new and Conclusions: This is first report of interethnic differences in frequencies of functional CYP2C19 and CYP2D6 genes among Chinese Mongolian, Hui and Han populations. These differences may be important in explaining reported inter‐ethnic differences in disease prevalence and response to drugs.     

白血病患者伏立康唑血药浓度监测的回顾性研究

目的探讨白血病患者伏立康唑血药浓度、基因代谢型及G、GM实验结果的关联性。 方法建立测定伏立康唑血药浓度的高效液相色谱串联质谱法（HPLC-MS/MS）,并利用MATLAB软件对所测血药浓度进行分析,开展G、GM实验,采用t检验比较2种实验结果为阳性和阴性的患者伏立康唑的血药浓度值;使用DNA序列测定法检测CYP2C19*2和CYP2C9*3基因代谢型并探讨其与伏立康唑血药浓度的关联性。 结果所有患者伏立康唑血药浓度的平均值为（1.47±1.35）μg/ml,伏立康唑在白血病患者中的有效血药浓度为0.44~2.49 μg/ml;G、GM实验阳性的患者伏立康唑血药浓度均小于G、GM实验阴性的患者［（1.32±1.21）μg/ml vs（2.25±1.20）μg/ml;（1.27±0.92）μg/ml vs（2.15±0.81）μg/ml］,且差异具有统计学意义（t=-2.941,P=0.032;t=-12.674,P=0.001）;CYP2C19*2基因代谢型杂合弱代谢基因型GA的血药浓度值高于野生型正常代谢型GG［（1.42±1.13）μg/ml vs（1.30±1.40）μg/ml］,但差异无统计学意义（t=-1.689,P=0.129）;CYP2C9*3基因代谢型杂合弱代谢基因型AC的血药浓度值高于野生型正常代谢型AA［（2.30±2.05）μg/ml vs（1.43±1.15）μg/ml］,差异具有统计学意义（t=12.386,P=0.006）。 结论白血病患者伏立康唑血药浓度、基因代谢型及G、GM实验阳性存在一定的关联性即患者伏立康唑弱代谢基因型,伏立康唑血药浓度高;患者G、GM实验阳性,伏立康唑血药浓度低。     

DNA微阵列芯片法与直接测序法检测CYP2C19基因型的比较研究

目的 用DNA微阵列芯片法和直接测序法两种方法检测氯吡格雷相关基因CYP2C19的突变情况,并进行比较分析。同时将基因型检测结果与临床资料进行分析,初步探讨CYP2C19基因型检测在氯吡格雷用药治疗中的临床意义。方法收集180例诊断为急性冠脉综合症并首次接受经皮冠状动脉介入治疗术(PCI)的全血标本。其中90例患者术后服用氯吡格雷之前,采用DNA微阵列芯片法和DNA直接测序法检测CYP2C19突变位点,确定其基因型。另外90例对照组患者使用氯吡格雷药物但不检测CYP2C19基因型。分析两组患者随访过程中发生冠脉血栓事件的差异。结果 ①两种检测方法准确度比较:在试验组90例患者中,DNA微阵列芯片法和DNA测序法均检出4种基因型组合:*1/*1(636GG,681GG),*1/*2(636GG,681GA),*2/*2(636GG,681AA)和*1/*3(636GA,681GG),分布频率分别为44例(48.9%),36例(40%),5例(5.6%)和5例(5.6%),而*3/*3(636AA,681GG)和*2/*3(636GA,681GA)未检测到。两种方法的准确度完全一致。②将检测结果与临床资料进行相关性分析:经CYP2C19基因型指导氯吡格雷用药的患者发生支架冠脉血栓事件的比例(0%)明显低于对照组(3.33%,P<0.05)。结论①DNA微阵列芯片法灵敏度和准确度与DNA直接测序法(金标准方法)检测相符率为100%。②DNA微阵列芯片法是一种快速、准确发现CYP2C19突变位点,鉴别CYP2C19基因型的检测方法。③检测结果与临床相关性分析结果显示基因型指导氯吡格雷用药有助于患者用药剂量的调整,或选用其它抗凝血药物,从而可降低冠脉血栓事件的发生率。     

CYP7A1 polymorphism influences the LDL cholesterol‐lowering response to atorvastatin

What is known and Objective: Response to the lipid‐lowering effect of the statins is known to show significant inter‐individual variability. Our aim was to investigate whether genetic variants of the CYP3A5 gene, CYP7A1 gene and ABCG8 gene influence the lipid‐lowering response to atorvastatin. Methods: One hundred and seven unrelated Chinese Han hypercholesterolemia patients were recruited from among the inpatients and outpatients of Tangshan Gongren Hospital of Hebei, China. Three polymorphisms of the CYP3A5 gene, seven polymorphisms of the CYP7A1 gene and seven polymorphisms of the ABCG8 gene were selected using a tagging single‐nucleotide polymorphism (tSNP) strategy and genotyped using Snapshot platform. Results: SNP rs8192870, located in the first intron of the CYP7A1 gene, was associated with the LDL level lowering response to atorvastatin. The LDL levels were reduced by 27·89% for the GG/GA genotype carriers and 35·26% for the AA genotype carriers, respectively, after atorvastatin treatment (P = 0·021). The significance remained after adjusting for covariates. In addition, we observed that rs4148222 in the 11th intron of the ABCG8 gene significantly associated with the baseline levels of HDL (P = 0·046). What is new and Conclusion: CYP7A1 gene polymorphism influences the LDL‐lowering effects of atorvastatin in Chinese Hans. If replicated by others, identification of the tagged functional variant would be needed.     

Influence of CYP2C9 and CYP2C19 genetic polymorphisms on pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers

Background and objective: CYP2C9 is the major contributor to gliclazide metabolic clearance in vitro, while the pharmacokinetics of gliclazide modified release are affected mainly by CYP2C19 genetic polymorphisms in vivo. This study aims to investigate the influence of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers. Methods: Eighteen healthy Han subjects with various combinations of CYP2C9 and CYP2C19 genotypes received 80 mg gliclazide. Plasma gliclazide concentrations were measured by a liquid chromatography–tandem mass spectrometry method for 84 h and plasma glucose and insulin levels were measured up to 15 h post‐dose. Results and discussion: There was no difference in either pharmacokinetic and or pharmacodynamic parameters of gliclazide when group A (CYP2C9*1/*1, CYP2C19 extensive metabolizers) was compared with group B (CYP2C9*1/*3, CYP2C19 *1/*1). When group C (CYP2C9*1/*1 and CYP2C19 poor metabolizers) was compared with group A, the AUC_0–∞ and C_max in group C were significantly higher [83·94 ± 40·41 vs. 16·39 ± 5·10 μg·h/mL (P = 0·000) and 1·50 ± 0·85 vs. 0·45 ± 0·18 μg/mL (P = 0·000)], and the oral clearance was significantly lower [1·17 ± 0·63 vs. 5·38 ± 1·86 L/h (P = 0·000)]. The half‐life of gliclazide was also significantly prolonged in group C subjects when compared with that of group A (33·47 ± 12·39 vs. 19·34 ± 10·45 h), but the difference was not significant (P = 0·052). The increase in serum glucose level at 11 h after dosing (ΔC_glu11) in group C was significantly higher than that of group A (?1·08 ± 0·42 vs. 0·22 ± 1·01 mmol/L, P = 0·022). The corresponding insulin levels showed no difference between the two groups. Conclusion: CYP2C9*3 was not associated with any change in the disposition of gliclazide. CYP2C19 polymorphisms appear to exert the dominant influence on the pharmacokinetics of gliclazide in healthy Chinese Han subjects, and may also affect the observed pharmacodynamics of the drug as a result.     

Influence of CYP2D6*10 on the pharmacokinetics of metoprolol in healthy Korean volunteers

Background and objective: Genetic polymorphism of CYP2D6 leads to differences in pharmacokinetics of CYP2D6 substrates. The CYP2D6*10 allele is clinically important in Koreans because of its high frequency in Asians. We investigated whether the pharmacokinetics of metoprolol was altered by the presence of the CYP2D6*10 allele in Korean subjects. Methods: One hundred and seven volunteers were recruited and grouped as CYP2D6*1/*1, CYP2D6*1/*10 and CYP2D6*10/*10 according to their genotypes. Metoprolol tartrate 100 mg (Betaloc^®) was administered orally once to each subject in these three groups (n = 6, 7 and 5, respectively). The pharmacokinetic parameters of metoprolol and its metabolite, α‐hydroxymetoprolol, and the metabolic ratio for the three groups were estimated and compared. Results and discussion: The area under the plasma concentration–time curve (AUC_0→∞), the maximum plasma concentration (C_max) and the elimination half‐life (T_1/2) of metoprolol and α‐hydroxymetoprolol for the CYP2D6*10/*10 group were all significantly different from those of the CYP2D6*1/*1 group (P < 0·05). The AUC_0→∞s of metoprolol were 443·7 ± 168·1, 995·6 ± 321·4 and 2545·3 ± 632·0 ng·h/mL, and the AUC_0→∞s of α‐hydroxymetoprolol were 1232·0 ± 311·2, 1344·0 ± 288·1 and 877·4 ± 103·4 ng·h/mL for groups CYP2D6*1/*1, *1/*10 and *10/*10, respectively. The corresponding T_1/2 values of metoprolol were 2·7 ± 0·5, 3·2 ± 1·3 and 5·0 ± 1·1 h, while those of α‐hydroxymetoprolol were 5·4±1·5, 6·0 ± 1·4 and 10·5 ± 4·2 h, respectively. The metabolic ratios of the three groups were significantly different (P < 0·05). Conclusion: The CYP2D6*10 allele altered the pharmacokinetics of metoprolol in Korean subjects and is likely to affect other drugs metabolized by the CYP2D6 enzyme, similarly.     

Pharmacogenetic determinants for interindividual difference of tacrolimus pharmacokinetics 1 year after renal transplantation

What is known and objective: Tacrolimus, a widely used immunosuppressive agent in organ transplantation, has a narrow therapeutic window. It has been suggested that its interaction with lansoprazole could be dependent on polymorphisms of CYP3A5 and CYP2C19. The objective of this study was to investigate how, 1 year after renal transplantation, CYP3A5 and CYP2C19 polymorphisms, biochemical parameters and coadministration with lansoprazole, influenced tacrolimus pharmacokinetics. Methods: The pharmacokinetics of tacrolimus was studied 1 year after renal transplantation, in 75 recipients who were all receiving continuation treatment with 12‐hourly oral tacrolimus, and 30 mg lansoprazole daily (Group 1; n = 20) or, 10 mg rabeprazole daily or no proton pump inhibitor (Group 2; n = 55). Results: There were no significant differences in the dose‐adjusted area under the plasma concentration–time curve (AUC_0–12) and maximum plasma concentration (C_max) of tacrolimus between CYP2C19 genotype groups, but there were significant differences between CYP3A5 genotypes groups (*1/*1 + *1/*3 vs. *3/*3 = 45·2 ± 20·0 vs. 71·0 ± 34·1 ng·h/mL/mg, P < 0·0001 and 6·3 ± 2·6 vs. 9·3 ± 7·0 ng/mL/mg, P = 0·0017, respectively) and between co‐administration with and without lansoprazole (74·5 ± 34·0 vs. 52·4 ± 27·4 ng·h/mL/mg, P = 0·0054 and 10·9 ± 8·8 vs. 6·7 ± 3·0 ng/mL/mg, P = 0·0024, respectively). In a multiple regression analysis, the dose‐adjusted AUC_0–12 and C_max of tacrolimus were associated with CYP3A5*3/*3 and co‐administration with lansoprazole. What is new and conclusion: CYP2C19 does not seem to contribute to the interaction between tacrolimus and lansoprazole. The long‐term combination of tacrolimus and lansoprazole requires careful monitoring of patients with the CYP3A5*3/*3 genotype.     

Analysis of cytochrome P450 gene polymorphism in a lupus nephritis patient in whom tacrolimus blood concentration was markedly elevated after administration of azole antifungal agents

What is known and Objective: Both itraconazole (ITCZ) and voriconazole (VCZ) are potent inhibitors of cytochrome P450 (CYP) 3A, and their effects have been reported to be equal. However, ITCZ is metabolized by CYP3A, whereas VCZ is mainly metabolized by CYP2C9 and CYP2C19 and only partially by CYP3A. We experienced the case of a patient who showed a 5‐fold increase in trough levels of tacrolimus (FK) level after switching from ITCZ to VCZ. Our objective is to discuss the mechanism of the increase drug–drug interaction in terms of serum concentration of the azole drugs and patient pharmacogenomics. Case summary: A 53‐year‐old woman was treated with FK (1 mg/day) for lupus nephritis. Because fungal infection was suspected, she received ITCZ (100 mg/day). When ITCZ was replaced with VCZ (400 mg/day), the blood concentration of FK increased markedly from 6·1 to 34·2 ng/mL. During coadministration with FK, the levels of ITCZ and VCZ were 135·5 ng/mL and 5·5 μg/mL, respectively, with the VCZ level around 3‐fold higher than the previously reported level (1·4–1·8 μg/mL). Her CYP genotypes were CYP2C19*1/*2, CYP3A4*1/*1 and CYP3A5*3/*3. What is new and Conclusion: The patient was a CYP2C19 intermediate metabolizer (IM) and deficient in CYP3A5. The increase in plasma VCZ level appears to have been at least in part, associated with the CYP2C19 IM phenotype. One possible explanation for the marked increase in blood FK concentration was increased inhibition of CYP3A because of the impaired metabolism and subsequent increased plasma concentration of VCZ. This case shows that the severity of drug interactions may be influenced by metabolic gene polymorphism.     

Association of ABCB1, CYP3A4*18B and CYP3A5*3 genotypes with the pharmacokinetics of tacrolimus in healthy Chinese subjects: a population pharmacokinetic analysis

What is known and Objective: Tacrolimus (TAC) is metabolized mainly by the CYP3A subfamily and extruded into the intestine by P‐glycoprotein, which is encoded by the ABCB1 gene. Several studies have suggested that the CYP3A5*3 genotype influenced the pharmacokinetics (PK) of TAC. The CYP3A4*18B and CYP3A5*3 alleles are clinically important in Chinese subjects because of their relatively high frequency. The present study aimed at evaluating the effects of ABCB1 (C1236T‐G2677T/A‐C3435T), CYP3A4*18B and CYP3A5*3 genetic polymorphisms on TAC PK in healthy Chinese subjects. Methods: Data were obtained from a comparative bioavailability study of oral TAC formulations (n = 22). TAC whole blood concentrations were measured by LC‐MS/MS. Genetic polymorphisms were determined using a direct sequencing method. Nonlinear mixed‐effects modelling (NONMEM) was performed to assess the effect of genotypes and demographics on TAC PKs. Results and Discussion: Both CYP3A4*18B and CYP3A5*3 polymorphisms affected the TAC PK, whereas ABCB1 genetic polymorphisms and other demographic characteristics did not. The combined genotypes of CYP3A4*18B and CYP3A5*3 had a greater impact than either genotype alone, and they were estimated to account for 28·4% of the inter‐subject variability of apparent clearance (CL/F) by NONMEM. The CL/F in subjects with CYP3A4*1/*1‐CYP3A5*3/*3 was 10·3 L/h and was 48·5% in those not carrying CYP3A4*1/*1‐CYP3A5*3/*3. What is new and Conclusion: This is the first study to extensively explore the influence of CYP3A4*18B, CYP3A5*3 and ABCB1 genetic polymorphisms on TAC PK in healthy Chinese subjects. The results demonstrated that subjects with a combined genotype of CYP3A4*1/*1‐CYP3A5*3/*3 may require lower TAC doses to achieve target concentration levels and further investigation is needed in larger populations to confirm the clinical benefits.     

Frequencies of CYP3A5 genotypes and haplotypes in a Korean population

Background and objective: CYP3A, the drug‐metabolizing enzyme is an important factor in the pharmacokinetics of many drugs. Polymorphism of the CYP3A5 gene is known to influence the functionality of the CYP3A5 enzymes. The full extent of CYP3A5 genetic polymorphism was analysed in a Korean population. Methods: Specific polymerase chain reaction‐restriction fragment length polymorphism tests for CYP 3AP1 through CYP3A5*7 or direct sequencing were used to identify reported CYP3A5 variant alleles, using 194 unrelated samples. Results and discussion: The most frequent single nucleotide polymorphism (SNP) was 6986A>G (CYP3A5*3). The next most frequent SNP was 31611C>T. Haplotype analysis using detected SNPs revealed that the most frequent haplotype was *3A (frequency: 0·724), followed by *1E (frequency: 0·211), *3C (frequency: 0·034) and *1A (frequency: 0·023). We did not find CYP3AP1*3, CYP3A5*6, or *7 in this Korean sample. Conclusion: A large proportion of Koreans may have relatively low levels of metabolically active CYP3A5 protein and therefore may be at risk of high levels of drugs metabolized by this enzyme, after administration of conventional doses.     

Distribution of CYP2C19*17 allele and genotypes in an Indian population

What is known and Objective: CYP2C19*17 allele increases the metabolic activity of CYP2C19 resulting in decreased therapeutic levels of CYP2C19 substrates. There exist inter‐ethnic differences in the distribution of this allele. The present study was aimed at establishing the allele and genotype frequencies of CYP2C19*17 in a South Indian Tamilian population. Furthermore, we describe the haplotype structure of the three common variant alleles of CYP2C19 in the Tamilian population. Methods: Two hundred and six subjects of South Indian Tamilian origin were genotyped for CYP2C19*17 allele by nested polymerase chain reaction and restriction fragment length polymorphism. A subset of 87 subjects were also genotyped for CYP2C19*2 and CYP2C19*3 alleles. After ascertaining linkage disequilibrium (LD), haplotypes were constructed. Allele and genotype frequencies, LD pattern and haplotype frequency were compared with those of the HapMap populations. Results and Discussion: The CYP2C19*17 allele frequency in the Tamilian population (n = 206) was found to be 19·2% (95% CI: 15·4 – 20·3). The CYP2C19*2 allele frequency (n = 87) was found to be 40·2% (95% CI: 32·9 – 47·5), whereas the CYP2C19*3 allele was not detected in the study subjects (n = 97). The high frequency of the CYP2C19*17 allele in the study population has resulted in a revision of frequencies for CYP2C19*1/*2 (31·0%) and CYP2C19*1/*1 (16·1%) genotypes in the Tamilian population. We also observed significant differences in haplotype structure and frequencies of these variant alleles in the HapMap population compared to Tamilian population. What is new and conclusion: CYP2C19*17 allele is present at high frequency in the Tamilian population. This study also demonstrates the need for reassessment of wild‐type allele frequencies in view of CYP2C19*17 allele. The estimated high frequency of CYP2C19*17 allele will aid in genotype–phenotype association studies in the Tamilian population. Further genotype–phenotype association studies are required to evaluate the clinical utility of this allele in South Indians.     

Clinical relevance of VKORC1 (G-1639A and C1173T) and CYP2C9*3 among patients on warfarin

What is known and Objectives: Testing for cytochrome P450‐2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) variant alleles is recommended by the FDA for dosing of warfarin. However, dose prediction models derived from data obtained in one population may not be applicable to another. We therefore studied the impact of genetic polymorphisms of CYP2C9 and VKORC1 on warfarin dose requirement in Malaysia. Methods: Patients who were attending clinics at our hospital and prescribed warfarin with stabilized INR levels of 2–4 were selected. DNA was extracted from blood samples and subsequently genotyped for CYP2C9*1, *2, *3, VKORC1 (G‐1639A) and VKORC1 C1173T. Linear regression modelling using age, CYP2C9 and VKORC1 genotypes, sex, weight and height was undertaken to define a warfarin dosing algorithm. An initial model was developed using data from one cohort of patients and validated using data from a second cohort. Results and Discussion: A model which included age and variants of CYP2C9 and VKORC1 account for about 37% of the variability in warfarin dose required to achieve INR of 2–4. Among the parameters evaluated, only VKORC1 (G‐1639A) and (C1173T) alleles, and age correlated with warfarin dose at 6 month. The mean dose predicted using the algorithm derived from cohort 1 was lower than the actual dose for cohort 2 (3·30 mg, SD 0·84 vs. 3·45 mg, SD 1·42). There was no relationship between INR values and the dose taken by the patients. Race, sex, weight and height did not correlate with dose. What is new and Conclusion: This study identifies factors which affect warfarin dosing in the Malaysia population. However, our best model does not account sufficiently for the variability in dose requirements for it to be used in dose prediction for the individual patient. Other important influential factors affecting warfarin dose requirement remain to be identified.