The impact of the CYP2D6-polymorphism on dose recommendations for current antidepressants

Cytochrome P450 CYP2D6 represents an extensively characterized polymorphic drug-metabolizing enzyme. The CYP2D6-gene is highly polymorphic and more than 70 different alleles are known currently. The activity of the enzyme markedly varies among individuals from poor to intermediate and extensive up to ultrarapid metabolism on the basis of the polymorphism of the CYP2D6 gene. Association studies provide growing evidence for the clinical importance of the CYP2D6 polymorphism investigating whether the CYP2D6 genotype distribution differs from that of the normal population either in patients with marked adverse effects or in nonresponders during treatment with CYP2D6 substrates. However, these scientifically important studies present less information for dose adjustments necessary to individualize pharmacotherapy in a given clinical case. With respect to psychopharmacological drug metabolism several antidepressants were characterized as being CYP2D6 substrates. Thus, this review summarizes dose recommendations of current antidepressants.     

Utility and adoption of CYP2D6 and CYP2C19 genotyping and its translation into psychiatric clinical practice

Jürgens G, Jacobsen CB, Rasmussen HB, Werge T, Nordentoft M, Andersen SE. Utility and adoption of CYP2D6 and CYP2C19 genotyping and its translation into psychiatric clinical practice. Objective: To describe clinical utility and adoption of routinely offered CYP2D6 and CYP2C19 genotyping (CYP test) in daily clinical practice of a psychiatric centre. Method: We described psychiatrists translations of CYP test results in patients with genotypes indicating poor or ultrarapid metabolizer status and treated with at least one CYP‐dependent drug based on a retrospective review of medical records. Complementary, we used ethnographic participant observation and qualitative interviews to identify the barriers and incentives for the use of CYP test results. Results: The cohort study included 101 of 1932 cases genotyped between 2003 and 2009. In 53 of 101 cases, test results were addressed in medical records. The most frequent response was to monitor drug concentrations (23 cases), observe for adverse events (18 cases) and adjust dosage (13 cases). In 33 of 101 cases, results were mentioned in the discharge letter. The ethnographic study indicated a poor adoption of the CYP test in clinical praxis. Test results were lost in workflows and knowledge transfer between laboratory and clinician and were absent from clinical routines, treatment conferences and educational fora. Conclusion: The CYP test has not gained foothold in clinical practice, and its potential clinical benefits are not utilized.     

利培酮治疗与细胞色素P4502D6/C188T酶基因多态性的关联分析

目的　研究利培酮临床效应的个体差异与其代谢酶细胞色素P4 5 0 2D6 (cytochromeP4 5 02D6 ,CYP2D6 )酶基因多态性的相关性。方法　对 88例符合CCMD 3精神分裂症诊断标准的患者和 96例健康对照者作病例 -对照分析。精神分裂症患者给予利培酮治疗 8周 ,用阳性和阴性症状量表 (posi tiveandnegativesymptomscale ,PANSS)评分评价利培酮疗效。采用聚合酶链反应扩增及限制性片段长度多态性 (PCR RFLP)技术对CYP2D6exonⅠ的C188T位点突变进行检测 ,分析利培酮临床效应与其主要代谢酶CYP2D6 /C188T酶基因多态性的相关性。结果　中国上海地区人群的CYP2D6 /C188T突变率(弱代谢型 )为 36 .3% ,病例组和正常对照组间基因型频率总体分布比较无显著差异 (χ2 =1.15 ,df=2 ,P >0 .0 5 ) ,两组间的等位基因频率之间比较也无显著性差异 (χ2 =0 .78,df=1,P >0 .0 5 )。进行性别及有否家族史分组后分析 ,亦无差异存在 ,且CYP2D6 /C188T突变与利培酮临床效应之间并无相关性 (χ2 =1.12 ,df=2 ;χ2 =0 .0 3,df=1,P >0 .0 5 )。结论　未发现中国人CYP2D6 /C188T多态性与利培酮临床效应的个体差异有相关性。     

细胞色素P450CYP2D6＊10B缺陷等位基因与利培酮治疗效应的关系

目的探讨CYP2D6＋10B缺陷等位基因与利培酮治疗效应的关系。方法采用等位基因的特异性扩增法,根据是否含有突变型CYP2D6＋10B缺陷等位基因将70例精神分裂症患者分为野生型等位基因的纯合型（w／w）组（16例）,突变型等位基因的纯合型（m／m）组（16例）以及野生型和突变型等位基因的杂合型（m／w）组（38例）,观察3组患者利培酮4—6mg／d治疗6周后疗效与不良反应。采用阳性和阴性症状量表（PANSS）评价疗效,副反应量表（TESS）和锥体外系不良反应量表（RSESE）评定药物不良反应。PANSS减分率≥30％为有效。结果治疗6周后,有效者58例。有效组W等位基因频率（0．43）明显低于无效组（0．83）,有效组的in等位频率（0．57）明显高于无效组（0．17）。自第4周起,m／w,m／m型PANSS减分值明显多于w／w型。3种基因型患者组间不良反应差异无统计学意义。结论利培酮治疗携带CYP2D6＊10B缺陷等位基因患者的疗效优于治疗野生型等位基因患者的疗效。CYP2D6t10B缺陷等位基因与利培酮不良反应无关联。     

The effect of cytochrome P450 2D6 genotypes on haloperidol metabolism: a preliminary study in a psychiatric population

We investigated the effect of cytochrome P450 (CYP2D6) genotypes on plasma levels of haloperidol (HAL) and reduced haloperidol (RHAL) in 47 Japanese male schizophrenic inpatients being treated with HAL. Mutation-specific polymerase chain reaction (PCR) analysis was used to detect CYP2D6*10 as the C188C1T mutation in exon 1. A long-PCR analysis method was used to detect CYP2D6*5. Allele frequencies of CYP2D6*5 and CYP2D6*10 were 4.3% and 34.0%, respectively. Plasma concentrations of HAL and RHAL were measured using high-performance liquid chromatography. The ranges of the plasma concentration of HAL and RHAL corrected to the dose were 0.28-1.60 (mean +/- SD, 0.66+/-0.25, n = 47) ng/mL/mg and 0.03-3.00 (mean+/-SD, 0.36+/-0.46, n = 47) ng/mL, respectively. Plasma RHAL/HAL ratios (R/H ratios) ranged from 0.06 to 1.88 (mean +/- SD, 0.48+/-0.32, n = 47). The analysis was performed among the four genotype groups: CYP2D6*1/CYP2D6*1 (n = 11), CYP2D6*1/CYP2D6*10 (n = 11), CYP2D6*10/CYP2D6*10 (n = 6) and those who have CYP2D6*5 allele (CYP2D6*1/ CYP2D6*5 or CYP2D6*5/CYP2D6*10 (n = 4). We observed significant tendency in effects of CYP2D6 genotypes on plasma concentration of HAL and significant effects on plasma concentration of RHAL, and R/H ratio. These results we obtained suggested that the plasma concentration of HAL and RHAL were determined partly by CYP2D6 polymorphic activity.     

Analysis of CYP2D6 genotype and response to tetrabenazine

Tetrabenazine is effective in the treatment of the chorea associated with Huntington disease and other hyperkinetic movement disorders. Following oral administration, tetrabenazine is hepatically transformed into 2 active metabolites that are CYP2D6 substrates. There are 4 CYP2D6 genotypes: poor metabolizers, intermediate metabolizers, extensive metabolizers, and ultrarapid metabolizers. CYP2D6 genotyping was performed on sequential subjects treated with tetrabenazine, but results were not known at the time of titration. Duration of titration to a stable dose, total daily dose, response rating scores, and adverse events were retrospectively collected and subsequently analyzed. Of 127 patients, the majority (n = 100) were categorized as extensive metabolizers, 14 as intermediate metabolizers, 11 as poor metabolizers, and 2 as ultrarapid metabolizers. Ultrarapid metabolizer patients needed a longer titration (8 vs 3.3, 4.4, and 3 weeks, respectively; P < .01) to achieve optimal benefit and required a higher average daily dose than the other patients, but this difference did not reach statistical significance. The treatment response was less robust in the intermediate metabolizer group when compared with the extensive metabolizer patients (P = .013), but there were no statistically significant differences between the various groups with regard to adverse effects. Our findings demonstrate that, aside from the need for a longer titration in the ultrarapid metabolizers, there are no distinguishing features of patients with various CYP2D6 genotypes, and therefore the current recommendation to systematically genotype all patients prescribed more than 50 mg/day of tetrabenazine should be reconsidered. © 2012 Movement Disorder Society     

High-dose venlafaxine treatment in a depressed patient with a genetic CYP2D6 deficiency

A female patient (47 years) who suffered from a severe episode of a recurrent depression with psychotic symptoms (F33.3) firstly underwent several unsuccessful treatments. She was then submitted to a combined treatment with 2×300 mg/day extended-release venlafaxine (VEN) and lithium (0.7 mmol/l). She responded within 7 weeks and, after 9 weeks, she showed full remission. Moreover, she tolerated this medication well. Steady-state plasma concentrations of VEN and its metabolites and their enantiomers were measured. The concentrations of VEN and its metabolite O-demethyl-VEN (ODV) were 1024 and 234 ng/ml, respectively. The unusually high concentration of the parent compound in comparison to the metabolite is mainly explained by an impaired metabolism of R-VEN in this patient, who by genotyping was shown to have a genetic deficiency of CYP2D6. In conclusion, in patients suffering from non-response to an antidepressant treatment, an individualised treatment strategy should be developed, and stereoselective therapeutic drug monitoring and genotyping may be recommended.     

CYP2D6 P34S Polymorphism and Outcomes of Escitalopram Treatment in Koreans with Major Depression

Objective

Cytochrome P450 (CYP) enzymatic activity, which is influenced by CYP genetic polymorphism, is known to affect the inter-individual variation in the efficacy and tolerability of antidepressants in major depressive disorder (MDD). Escitalopram is metabolized by CYP2D6, and recent studies have reported a correlation between clinical outcomes and CYP2D6 genetic polymorphism. The purpose of this study was to determine the relationship between the CYP2D6 P34S polymorphism (C188T, rs1065852) and the efficacy of escitalopram treatment in Korean patients with MDD.

Methods

A total of 94 patients diagnosed with MDD were recruited for the study and their symptoms were evaluated using the 21-item Hamilton Depression Rating scale (HAMD-21). The association between the CYP2D6 P34S polymorphism and the clinical outcomes (remission and response) was investigated after 1, 2, 4, 8, and 12 weeks of escitalopram treatment using multiple logistic regression analysis and χ² test.

Results

The proportion of P allele carriers (PP, PS) in remission status was greater than that of S allele homozygotes (SS) after 8 and 12 weeks of escitalopram treatment. Similarly, P allele carriers exhibited a greater treatment response after 8 and 12 weeks of escitalopram treatment than S allele homozygotes.

Conclusion

Our results suggest that the P allele of the CYP2D6 P34S polymorphism is a favorable factor in escitalopram treatment for MDD, and that the CYP2D6 P34S polymorphism may be a good genetic marker for predicting escitalopram treatment outcomes.     

CYP2D6 gene deletion allele in patients with neuroleptic malignant syndrome: preliminary report

Neuroleptic malignant syndrome (NMS) is a potentially fatal adverse reaction to psychopharmacologic treatment. Reported herein are two NMS patients with schizophrenia who were found to possess a CYP2D6 gene deletion allele (CYP2D6*5). The deletion results in decreased CYP2D6 activity, possibly leading to drug accumulation. Both patients with NMS had been treated with neuroleptics, including CYP2D6 substrates. Polymerase chain reaction (PCR) followed by restriction fragment length polymorphism analyses and long PCR were performed to detect CYP2D6 genotype. One patient was found to possess *5/*10; the other had a *1/*5 genotype. The present preliminary report suggests that pharmacokinetic factors cannot be excluded and the CYP2D6 polymorphism is possibly associated with the etiology of NMS.     

Interaction between GSTM1-null and CYP2D6-deficient alleles in the pathogenesis of Parkinson''s disease

The present study was conducted to examine the interaction between cytochrome p450 2D6: CYP2D6 (phase I) poor metabolizer (PM) and glutathione S-transferase M1: GSTM1 (phase II) null genotypes, among 103 unrelated French Parkinson's disease (PD) patients. Both genes are involved in the biotransformation process, and the main objective of that work is to assess synergic effect between CYP2D6 PM and GSTM1 null genotypes in PD patients. Patients with both GSTM1 null genotype and poor metabolizer CYP2D6 have shown a strong dependency of multiplicative interaction (9.50; P = 0.016); this have also been observed when combining GSTM1 null with CYP2D6*4 deficient alleles, but were at the limit of significance (2.18; P = 0.076). Such a combination of polymorphic peculiarities in studied metabolic genes might represent additional risk factor for development of sporadic PD.     

A case study: neuroleptic malignant syndrome with risperidone and CYP2D6 gene variation

We present a schizophrenic patient who experienced neuroleptic malignant syndrome with risperidone treatment due to variants of the CYP2D6 gene with reduced function. Clinicians need to be aware of this potential complication.     

精神分裂症患者细胞色素P450 2D6酶基因多态性与利培酮治疗效应的关系

目的研究精神分裂症患者细胞色素P450 2D6酶(CYP2D6)多态性是否与利培酮治疗效应有关.方法采用阳性和阴性症状量表(PANSS)、大体评定量表(GAS)、治疗时需处理的副反应量表(TESS)以及锥体外系副反应量表(RSESE)对52例精神分裂症[PANSS基线分(105.59±17.30)分;GAS基线分(31.75±3.32)分]患者,分别在利培酮治疗前及治疗[(5±3)mg/d]第1～8周末各进行一次药物反应评定,采用聚合酶链反应技术对CYP2D6 exon Ⅰ C/T188和CYP2D6 G/A1934两个多态性位点进行检测.根据CYP2D6 exonI C/T188基因型将患者分为三组(C/C组 13例,C/T组20例,T/T组19例);采用治疗前后PANSS 30%减分率为标准 ,将52例患者分为治疗有效组和治疗无效组,比较组间药物治疗效应的差异.结果从利培酮治疗后第5周末开始,三组之间PANSS评分的差异有显著性(P<0.01);两两比较发现,C/C组PANSS分低于T/T组(P<0.01);三组之间GAS评分的差异从第6周开始出现显著性(P<0.01),其中C/C组GAS分明显高于T/T组(P<0.01).多因素方差分析显示,三组的PANSS总分 (F=2.64, P<0.01)及GAS评分(F=1.85,P<0.05)差异有非常显著性;CYP2D6 exon Ⅰ C/T188多态性基因型频率(χ2＝6.56,P<0.05)和等位基因频率(χ2＝5.03,P<0.05,相对风险＝2.54,95%可信区间＝1.40～8.32).利培酮治疗有效组与无效组之间的差异有显著性.样本中未发现CYP2D6 G/A1934多态性.结论中国人群精神分裂症CYP2D6 exon Ⅰ C/T188多态性可能是影响利培酮临床疗效的遗传易感因素.     

No evidence of an association between CYP2D6 polymorphisms among Japanese and dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most frequent degenerative dementia among the elderly, following Alzheimer-type dementia (ATD). An association of DLB with CYP2D6*4, one of the cytochrome P450IID6 (debrisoquine 4-hydroxylase; CYP2D6) gene polymorphisms, was reported previously, but this is controversial. Moreover, these reports have been restricted to Caucasian populations. Therefore, we compared frequencies of CYP2D6*3, *4, and *10 mutant alleles in 17 Japanese DLB patients to those among Alzheimer-type dementia (ATD) patients and healthy controls. Polymerase chain reaction amplification and restriction fragment length polymorphism analyses were used for genotyping. No significant difference of genotype or mutant allele frequencies was detected between DLB, ATD, and healthy controls. The present results do not support the suggestion that the CYP2D6 gene is related to DLB susceptibility, at least in the Japanese population.     

CYP2D6*4 polymorphism is not associated with Parkinson's disease and has no protective role against Alzheimer's disease in the Korean population

CYP2D6*4 polymorphism is reported to be associated with Parkinson's disease (PD) and to have protective role against Alzheimer's disease (AD). Such findings are not extensively studied in the Oriental population, especially Koreans. The effects of CYP2D6*4 polymorphism on AD and PD were investigated by polymerase chain reaction-restriction fragment length polymorphism in Korean subjects. Heterozygous mutant allele was found in four of 93 patients with PD, 0 of 32 patients with AD and one of 121 control subjects (59 stroke, 59 normal controls and four other psychiatric disorders), but no homozygous mutant allele was found. There were no statistically significant differences between the AD group and controls, and between the PD group and controls. In conclusion, we suggest that CYP2D6*4 polymorphism does not confer susceptibility to PD in the Korean population. Also, due to such a rare occurrence of the CYP2D6*4 polymorphism, we can not confirm the protective role of the polymorphism against AD in the Korean population.     

Association of CYP2D6 100 C > T and 2850 C > T polymorphisms with generalized tonic clonic seizures among Indians

Summary. Multiple avenues of research have provided evidence for the role of genetic and environmental factors in epilepsy. Previous studies indicated an association of debrisoquine hydroxylase (CYP2D6) with susceptibility to epilepsy. In this study, association of CYP2D6 100C > T and 2850C > T polymorphisms with generalized tonic clonic seizures (GTCS) among Indians has been analysed using case-control approach. A significant association of 2850C > T (P = 0.015) has been observed. Comparison between phenytoin toxic and others among patients showed no association of these polymorphisms with phenytoin toxicity. The first two authors contributed equally in this work     

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.     

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。     

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.