Detection of the poor metabolizer-associated CYP2D6(D) gene deletion allele by long-PCR technology

Elucidation of CYP2D6 genetic diversity in a unique African population: implications for the future application of pharmacogenetics in the Xhosa population

Genetic variation of the CYP2D6 gene has been associated with altered drug metabolism; however, limited studies have investigated CYP2D6 sequence diversity in African populations. We devised a CYP2D6 genotyping strategy to analyse the South African Xhosa population and genotype a Xhosa schizophrenia cohort, as CYP2D6 metabolises many antipsychotics and antidepressants. The entire CYP2D6 gene locus was sequenced in 15 Xhosa control individuals and the data generated were used to design a comprehensive genotyping strategy. Over 25 CYP2D6 alleles were genotyped in Xhosa controls and Xhosa schizophrenia patients using long-range PCR, DNA sequencing and single nucleotide primer extension analysis. Bioinformatic algorithms were used to predict the functional consequences of relevant mutations and samples were assigned CYP2D6 activity scores. A unique allele distribution was revealed and two rare novel alleles, CYP2D6*73 and CYP2D6*74, were identified. No significant differences in allele frequencies were detected between Xhosa controls and schizophrenia patients. This study provides i) comprehensive data on a poorly characterised population, ii) a valuable CYP2D6 genotyping strategy and iii) due to their unique genetic profile, provides the basis for pharmacogenetic intervention for Xhosa individuals.

Genetic polymorphisms of cytochrome P450 enzymes influence metabolism of the antidepressant escitalopram and treatment response

AIMS

The antidepressant escitalopram (S-CIT) is metabolized by the cytochrome-P450 (CYP) enzymes CYP 2D6, 2C19 and 3A4. This study evaluated the impact of CYP2D6, 2C19 and 3A4 genetic polymorphisms on plasma concentrations of S-CIT and patient treatment response.

MATERIALS & METHODS

A total of 100 patients diagnosed with major depressive disorder were recruited to the study and their depression symptoms were assessed using the Hamilton Depression Rating Scale. The genetic polymorphisms *4, *5 and *10 on CYP2D6, *2, *3 and *17 on CYP2C19, and *18 on CYP3A4 were selected based on their function and respective allele frequencies in Asian populations. Polymorphisms were analyzed using the SNPstream genotyping system, PCR and direct sequencing methods. The steady-state serum concentrations of S-CIT and its metabolites S-desmethylcitalopram and S-didesmethylcitalopram were analyzed by HPLC. According to semiquantitative gene dose (SGD) and gene dose (GD) models for allele combinations of these polymorphisms, CYP2D6 was clustered into intermediate (0.5, 1 and 1.5 SGD) and extensive (2 SGD) metabolizers, while CYP2C19 was clustered into poor (0 GD) and extensive (1 and 2 GDs) metabolizers.

RESULTS

The group of patients with intermediate CYP2D6 metabolism (0.5 SGD) had a significantly higher frequency of remitters from major depressive disorder during the 8-week treatment (p = 0.0001). Furthermore, CYP2C19 poor metabolizers had significantly higher S-CIT serum levels than did extensive metabolizers at weeks 2, 4 and 8 (p < 0.05). The allele frequencies in CYP3A4*18 and CYP2C19*17 were too low to permit further subgroup analyses.

CONCLUSION

Our results suggest that the genetic polymorphisms in CYP2C19 may be influencing S-CIT serum concentrations, and that specific CYP2D6 polymorphisms may be predicting patient treatment outcomes based on gene dosage analyses.

Pharmacokinetic and pharmacodynamic interactions between carbamazepine and aripiprazole in patients with schizophrenia

Pharmacokinetic and pharmacodynamic interactions between carbamazepine and aripiprazole were studied in 18 inpatients with schizophrenia being treated with aripiprazole. The daily dose of aripiprazole was 24 mg in 15 cases and 12 mg in 3 cases. Carbamazepine 400 mg/d was coadministered for 1 week, and blood samples were taken twice before the start of carbamazepine coadministration and then 1 week after completion. In addition, on these days, the severity of illness and side effects were evaluated using the Positive and Negative Syndrome Scale and the Udvalg for Kliniske Undersøgelser side effects rating scale, respectively. Plasma concentrations of aripiprazole and dehydroaripiprazole were measured using liquid chromatography with mass spectrometric detection. Carbamazepine significantly decreased both plasma concentrations of aripiprazole and dehydroaripiprazole by 64% and 68%, respectively (P < 0.001). Despite these decreases in plasma concentrations, the total and negative scores in Positive and Negative Syndrome Scale, together with the neurological score in Udvalg for Kliniske Undersøgelser, decreased slightly but significantly (P < 0.05) after carbamazepine coadministration. The present study implies that carbamazepine augmentation may be effective for patients with schizophrenia treated with aripiprazole, although carbamazepine dramatically decreases plasma concentrations of aripiprazole and dehydroaripiprazole, by inducing the metabolism of these compounds.

CYP2D6: novel genomic structures and alleles

OBJECTIVE

CYP2D6 is a polymorphic gene. It has been observed to be deleted, to be duplicated and to undergo recombination events involving the CYP2D7 pseudogene and surrounding sequences. The objective of this study was to discover the genomic structure of CYP2D6 recombinants that interfere with clinical genotyping platforms that are available today.

METHODS

Clinical samples containing rare homozygous CYP2D6 alleles, ambiguous readouts, and those with duplication signals and two different alleles were analyzed by long-range PCR amplification of individual genes, PCR fragment analysis, allele-specific primer extension assay, and DNA sequencing to characterize alleles and genomic structure.

RESULTS

Novel alleles, genomic structures, and the DNA sequence of these structures are described. Interestingly, in 49 of 50 DNA samples that had CYP2D6 gene duplications or multiplications where two alleles were detected, the chromosome containing the duplication or multiplication had identical tandem alleles.

CONCLUSION

Several new CYP2D6 alleles and genomic structures are described which will be useful for CYP2D6 genotyping. The findings suggest that the recombination events responsible for CYP2D6 duplications and multiplications are because of mechanisms other than interchromosomal crossover during meiosis.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

CYP2D6 gene test in psychiatric patients and healthy volunteers

BACKGROUND

Antipsychotic drug therapy meets difficulties in predicting response in psychiatric patients. The medical treatment of these patients may be improved significantly by systematic phamacogenetic diagnosis identifying the drug metabolic capacities of each patient. Genetic polymorphisms in the coding sequence for the drug metabolizing cytochrome P450 enzyme CYP2D6 represent a pharmacogenetic target.

METHODS

A cohort (n = 225) representing psychiatric patients seen during an 18-month trial period was included in the project after the subjects accepted a blood sample being taken to analyse their CYP2D6 allelic composition. To investigate any putative difference in allele frequencies among the psychiatric patients compared to earlier publications on allele frequencies in Caucasian populations, another cohort (n = 122) of local healthy volunteers was likewise included.

RESULTS

Allelic frequencies in the psychiatric patients and healthy volunteers were indistinguishable. Alleles *1 and *2 encoding for normal enzyme activity and alleles *3, *4, *5, *6, *13/*16 representing non-active forms were found as well as alleles *9, *10, *41 encoding for enzymes with decreased activity. Furthermore, examples of the previously described duplications of *1 and *2, which result in enhanced enzyme activity, were also identified.

CONCLUSION

A systematic CYP2D6 gene test of hospitalized psychiatric patients revealed the identification of pharmacogenetically relevant alleles affecting capacity to metabolize antipsychotics. The frequencies of phenotypes in affected patients were 8.4 % intermediate metabolizers (IMs), 8.4 % poor metabolizers (PMs) and 3.1 % ultrafast metabolizers (UMs), whereas 52.4 % were extensive metabolizers (EMs) and 27.6 % heterozygous EMs.

Genotyping of the cytochrome P450 2D6 4469 C>T polymorphism using SimpleProbes™

BACKGROUND

Genotyping of human cytochrome P450s is a pharmacogenetic approach to diagnosing inherited deficiencies in drug metabolizing enzymes that influence therapeutic responses. The P450 CYP2D6 (debrisoquine hydroxylase) metabolizes numerous antidepressants and neuroleptic agents and there is evidence of a relationship between gene polymorphism and variant therapeutic response. Polymorphism in CYP2D6 causes poor, intermediate, efficient or ultrarapid metabolization of substrate drugs affecting pharmacokinetic parameters and requiring dose adjustments. Predictive genotyping for broader clinical application is reliant on fast, technically simple analyses. A new genotyping method was explored. It identifies the single nucleotide polymorphism (SNP) 4469 C>T (NCBI access no. M33388) with one fluorescent hybridization probe (SimpleProbes; SP) using the LightCycler (LC). This SNP is found in 21 alleles, comprising 30% in Caucasian populations and encoding enzymes with poor, intermediate or efficient activity. The remaining 65 known alleles either harbour a C in position 4469 or are deletion mutants.

METHODS

Comparative detection of C>T polymorphism was done using a well-established polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique and PCR followed by melting-point (T(m)) analysis with an SP covering the SNP position in 144 samples encompassing alleles *2 and *41 with a T, alleles *1,*3, *4, *6, *9, *10, *15 with a C and the deletion mutant allele *5.

RESULTS

C>T polymorphism was detected with complete concordance. T(m) of SP/target heteroduplex complexes for C was: T(m) 67, 89 degrees C to 68, 62 degrees C and for T: T(m) 60, 70 degrees C to 61, 51 degrees C.

CONCLUSION

By one-step SP methodology it proved possible within 2 h to identify an SNP in genotypes comprising >90% in Caucasian populations.

Pharmacogenetic Screening of the Gene Deletion and Duplications of CYP2D6

Cytochrome P450 (CYP) 2D6 is one of the most important enzymes involved in the metabolism of drugs. Multiple, clinically relevant, genetic variants of this gene have been identified and, among them, a gene deletion as well as multiplications of the gene. These large structural mutations in CYP2D6 occur at a relatively high frequency in several populations. Genotyping of CYP2D6 could therefore be applied to individualize drug therapy to improve therapeutic efficacy and decrease adverse effects in patients. However, a prerequisite for the pharmacogenetic screening of CYP2D6 in a clinical setting is the development of fast, reliable and cost-effective techniques for the routine genotyping of patients. In the case of CYP2D6, besides the general problems that arise in the detection of large gene deletions and multiplications, the presence of two highly homologous pseudogenes, CYP2D7 and CYP2D8, forms an extra challenge. This review provides an overview of the techniques that have been described to detect the CYP2D6 gene deletion and multiplication: Southern-blotting RFLP, long-template PCR, and real-time PCR. Of these techniques, real-time PCR is the only technique giving quantitative information about the exact copy number of the gene. Considering all of the other advantages of this method over other methods, such as cost-effectiveness and suitability for high throughput screening, real-time PCR is the most promising method for the genotyping of large structural alterations in the CYP2D6 gene in a routine clinical setting.

Gene polymorphism influencing treatment response in psychotic patients in a naturalistic setting

RATIONALE

Many patients with psychotic symptoms respond poorly to treatment. Factors possibly affecting treatment response include the presence of polymorphisms in genes coding for various receptor populations, drug-metabolizing enzymes or transport proteins.

OBJECTIVES

To investigate whether genetic polymorphisms could be indicators of treatment response to antipsychotic drugs. The genes of interest were the dopamine D2 receptor gene (DRD2), the serotonin 2A and 2C receptor genes (HTR2A and HTR2C), the P-glycoprotein gene (ABCB1 or MDR1) and the drug-metabolizing cytochrome P450 2D6 gene (CYP2D6).

MATERIAL AND METHODS

Data for this naturalistic, cross-sectional study of patients requiring antipsychotic drugs and attending the Psychosis Outpatient Care clinic in Jönköping, Sweden were obtained from patient interviews, blood samples and information from patient files. Blood samples were genotyped for DRD2 Taq1 A, Ins/Del and Ser311Cys, HTR2A T102C, HTR2C Cys23Ser, ABCB1 1236C>T, 2677G>T/A, 3435C>T and genetic variants of CYP2D6. The patients (n=116) were grouped according to the CANSEPT method regarding significant social and clinical needs and significant side effects.

RESULTS

Patients on olanzapine homozygous for ABCB1 3435T, had more significant social and clinical needs than others. Patients with one or two DRD2 Taq1 A1 alleles had a greater risk of significant side effects, particularly if they were male, Caucasian, had a schizophrenic or delusional disorder or were taking strong dopamine D2-receptor antagonistic drugs.

CONCLUSION

If these results are confirmed, patients carrying the DRD2 Taq1 A1 allele would benefit from using drugs without strong dopamine D2 receptor antagonistic properties.

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.

The CYP2D6 activity score: translating genotype information into a qualitative measure of phenotype

Inferring CYP2D6 phenotype from genotype is increasingly challenging, considering the growing number of alleles and their range of activity. This complexity poses a challenge in translational research where genotyping is being considered as a tool to personalize drug therapy. To simplify genotype interpretation and improve phenotype prediction, we evaluated the utility of an "activity score" (AS) system. Over 25 CYP2D6 allelic variants were genotyped in 672 subjects of primarily Caucasian and African-American heritage. The ability of genotype and AS to accurately predict phenotype using the CYP2D6 probe substrate dextromethorphan was evaluated using linear regression and clustering methods. Phenotype prediction, given as a probability for each AS group, was most accurate if ethnicity was considered; among subjects with genotypes containing a CYP2D6*2 allele, CYP2D6 activity was significantly slower in African Americans compared to Caucasians. The AS tool warrants further prospective evaluation for CYP2D6 substrates and in additional ethnic populations.

Serotonin transporter polymorphism (5-HTTLPR) and citalopram effectiveness and side effects in children with depression and/or anxiety disorders

OBJECTIVE

The aim of this study was to examine the association between polymorphism in the serotonin transporter gene and citalopram effectiveness and side effects in children and adolescents with major depressive disorder (MDD) and/or anxiety disorders.

METHODS

Outpatients, aged 7- 18 years with a Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision (DSM-IV-TR) MDD and/or anxiety disorder were treated in an 8-week open trial with 20-40 mg/day of citalopram. Subjects were genotyped with respect to short (s) versus long (l) forms of the 5-HTTLPR polymorphism of the serotonin transporter, and the relationship between genotype and outcome and side effects was assessed.

RESULTS

Subjects with 5-HTTLPR ss genotype showed a less vigorous response with regard to depressive symptoms measured by the Children's Depression Rating Scale-Revised (CDRS-R) scores over time compared to subjects with sl/ll genotypes (beta = 0.67, z = 2.02, p = 0.04). In addition, the 5-HTTLPR ss group exhibited lower rates of agitation compared to those with sl/ll genotype (6.3% vs. 32.8%, p = 0.05). Also, subjects with 5-HTTLPR ss genotype had consistently higher scores of suicidality at each week compared to the sl/ll group (beta = 0.76, z = 2.04, p = 0.04) as measured by item number 13 of the CDRS-R.

CONCLUSIONS

The 5-HTTLPR ss genotype was associated with a poorer clinical response with regard to depressive symptoms as well with fewer reports of agitation. The 5-HTTLPR polymorphism may be a genetic marker of response to citalopram in children and adolescents with depression and/or anxiety.

Effects of CYP2D6 and SULT1A1 genotypes including SULT1A1 gene copy number on tamoxifen metabolism

BACKGROUND

Tamoxifen is hydroxylated by cytochrome P450 (CYP) 2D6 to the potent metabolites 4-hydroxytamoxifen (4OHtam) and 4-hydroxy-N-demethyltamoxifen (4OHNDtam), which are both conjugated by sulphotransferase (SULT)1A1. Clinical studies indicate that CYP2D6 and SULT1A1 genotypes are predictors for treatment response to tamoxifen. Therefore, we examined the relationship between CYP2D6 genotype, SULT1A1 genotype, SULT1A1 copy number and the pharmacokinetics of tamoxifen.

PATIENTS AND METHODS

The serum levels of tamoxifen and metabolites of 151 breast cancer patients were measured by high-pressure liquid chromatography-tandem mass spectrometry. The CYP2D6 and SULT1A1 polymorphisms and SULT1A1 copy number were determined by long PCR, PCR-based restriction fragment length polymorphism, DNA sequencing and fluorescence-based PCR.

RESULTS

The levels of 4OHtam, 4OHNDtam and N-demethyltamoxifen were associated with CYP2D6 predicted enzymatic activity (P < 0.05). The SULT1A1 genotype or copy number did not influence the levels of tamoxifen and its metabolites. However, the ratios of N-demethyltamoxifen/tamoxifen and N-dedimethyltamoxifen/N-demethyltamoxifen were related to SULT1A1 genotype.

CONCLUSION

CYP2D6 and SULT1A1 genotypes may partly explain the wide inter-individual variations in the serum levels of tamoxifen and its metabolites. We propose that therapeutic drug monitoring should be included in studies linking CYP2D6 and SULT1A1 genotypes to clinical outcome.

Impact of CYP2D6 genetic polymorphism on tramadol pharmacokinetics and pharmacodynamics

BACKGROUND AND OBJECTIVE

Tramadol is metabolized by the highly polymorphic enzyme cytochrome P450 (CYP)2D6. Patients with different CYP2D6 genotypes may respond differently to tramadol in terms of pain relief and adverse events. In this study, we compare the pharmacokinetics and effects of tramadol in Malaysian patients with different genotypes to establish the pharmacokinetic-pharmacodynamic relationship of tramadol.

STUDY DESIGN AND SETTING

All patients received an intravenous dose of tramadol 100mg as their first postoperative analgesic. Blood was sampled at 0 minutes and subsequently at 15 and 30 minutes, 1, 2, 4, 8, 16, 20, and 24 hours for serum tramadol and analyzed by high-performance liquid chromatography (HPLC). Patients were genotyped for CYP2D6*1, *3, *4, *5, *9, *10, and *17 alleles and duplication of the gene by means of an allele-specific PCR. Pain was measured using the Visual Analog Scales, and adverse effects were recorded.

RESULTS

About half of the patients had the wild-type allele (CYP2D6*1), with the 'Asian'CYP2D6*10 allele accounting for most of the rest (40%). None of the genotypes predicted poor metabolism. Twenty-seven percent of the patients were intermediate metabolizers (IM) and 2.9% were ultra-rapid (UM) metabolizers; the remaining 70% were extensive metabolizers (EM). The mean total clearance (CL) predicted by the model was lower (19 L/h) and the half-life longer (5.9 hours) than those reported in Western populations. This may due to the high frequency of the CYP2D6*10 allele amongst Malaysian patients. The UM and EM groups had 2.6- and 1.3-times faster CL, respectively, than the IM. CL was 16, 18, 23, and 42 L/h while mean half-lives were 7.1, 6.8, 5.6, and 3.8 hours among the IM, EM1, EM2, and UM groups, respectively. However, the analgesic effects of tramadol were not measured adequately among the postoperative patients to establish its full therapeutic effects. There were significant differences in the adverse-effect profiles amongst the various genotype groups, with the IM group experiencing more adverse effects than the EM, and the EM having more adverse effects than the UM.

CONCLUSION

CYP2D6 activity may play an important role in determining the pharmacokinetics of tramadol and in predicting its adverse effects. If these results can be confirmed in a larger population, genotyping may be an important tool in determining the dose of tramadol.

Evaluation of effects of polymorphism for metabolic enzymes on pharmacokinetics of carvedilol by population pharmacokinetic analysis

In our previous study it was observed that the frequencies of UGT1A1*6, UGT2B7*3 and CYP2D6*10 in patients who have a low level ability of glucuronidation were significantly higher than those in patients with a high level of ability of glucuronidation. The same tendency was found in the frequency of CYP2D6*5, though there was no significant difference. The purpose of this study was to evaluate the effects of the polymorphism on pharmacokinetics of carvedilol by population pharmacokinetic analysis. Population pharmacokinetic analysis was performed using 373 plasma concentrations from 41 patients with chronic heart failure or angina pectoris. A one compartment pharmacokinetic model with first-order absorption (for oral dosing) was used to describe the concentration-versus-time data for carvedilol. We examined the effects of various clinical and genetic covariables in the regression models for clearance and volume of distribution. The results suggested that the factors of interindividual variation for carvedilol clearance were creatinine clearance and polymorphisms of UGT2B7 and CYP2D6 in the Japanese population with heart disease. It was estimated that UGT2B7*3 decreased the clearance of carvedilol by 37%, but UGT2B7*2 did not show any effect. Clearance in the patients who have intermediate activity of CYP2D6 was decreased by 39%.

Validation of a CYP2D6 Genotyping Panel on the NanoChip Molecular Biology Workstation

Background: CYP2D6 is a highly polymorphic phase I enzyme that metabolizes 20%–25% of clinically used drugs. The objective of this study was to validate a CYP2D6 genotyping assay with the NanoChip® Molecular Biology Workstation.

Methods: We genotyped 200 anonymized human DNA samples with the Pyrosequencing® platform at the Medical College of Wisconsin and with the NanoChip platform at Dartmouth Medical School. We compared CYP2D6 genotypes and resolved samples with genotypic discrepancies with the Jurilab CYP2D6 duplication/deletion assay or with traditional DNA sequencing. The Jurilab assay is a long-range PCR assay used to evaluate sequence structures 3′ of the CYP2D7 and CYP2D6 coding regions. For the NanoChip platform, we performed multipad addressing and duplicate runs to test the intra- and intercartridge precision, within- and between-run precision, and reproducibility of the defined genotypes.

Results: We used both platforms to genotype all 200 DNA samples for CYP2D6*3, *4, *5, *6, *7, *8, and gene duplication. The 2 methods showed 99.4% concordance in the genotyping results; we found only 8 discrepant genotypes among 1400 DNA analyses. Confirmatory molecular analysis of the discrepant genotypes revealed that the NanoChip assay showed better agreement. The imprecision of the NanoChip method (CV) was 8.9%–17.7%.

Conclusions: This validation study of the NanoChip electronic microarray–based CYP2D6 genotyping assay revealed a CV &lt;20% and good concordance with the Pyrosequencing method and a confirmatory sequencing method.

Concentrations of tramadol and O-desmethyltramadol enantiomers in different CYP2D6 genotypes

The influence of CYP2D6 genotype and CYP2D6 inhibitors on enantiomeric plasma levels of tramadol and O-desmethyltramadol as well as response to tramadol was investigated. One hundred and seventy-four patients received one hundred intravenous tramadol 3 mg/kg for postoperative analgesia. Blood samples drawn 30, 90, and 180 min after administration were analyzed for plasma concentrations of the enantiomers (+)-, (-)tramadol and (+)-, (-)O-desmethyltramadol by liquid chromatography-tandem mass spectrometry. Different CYP2D6 genotypes displaying zero (poor metabolizer (PM)), one (heterozygous individual (HZ)/intermediate metabolizer (IM)), two extensive metabolizer (EM), and three (ultra rapid metabolizer (UM)) active genes were compared. Concentrations of O-desmethyltramadol differed in the four genotype groups. Median (1/3 quartile) area under the concentration-time curves for (+)O-desmethyltramadol were 0 (0/11.4), 38.6 (15.9/75.3), 66.5 (17.1/118.4), and 149.7 (35.4/235.4) ng x h/ml for PMs, HZ/IMs, EMs, and UMs (P<0.001). Comedication with CYP2D6 inhibitors decreased (+) O-desmethyltramadol concentrations (P<0.01). In PMs, non-response rates to tramadol treatment increased fourfold compared with the other genotypes (P<0.001). In conclusion, CYP2D6 genotype determined concentrations of O-desmethyltramadol enantiomers and influenced efficacy of tramadol treatment.

The effect of Shoseiryuto, a traditional Japanese medicine, on cytochrome P450s, N-acetyltransferase 2 and xanthine oxidase, in extensive or intermediate metabolizers of CYP2D6

OBJECTIVE

Shoseiryuto (TJ-19) contains eight herbal components, including Ephedra sinica, and has been used for treating asthma and allergic rhinitis in Asian countries for several centuries. In this study, we investigated the potential herb-drug interaction of TJ-19 in healthy volunteers and attempted to ascertain whether or not the interaction might be affected by the cytochrome P450 (CYP) 2D6 genotype.

METHODS

We assessed the effect of TJ-19 on the activities of CYP1A2, CYP2D6, CYP3A, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2) in 37 healthy subjects. The subject pool consisted of 19 extensive metabolizers (EMs) with CYP2D6*Wild/*Wild, and 18 intermediate metabolizers (IMs) with CYP2D6*10/*10. The baseline activities of five enzymes were ascertained by their respective urinary metabolic ratios from an 8-h urine sample, after an oral 150-mg and 30-mg dose of caffeine and dextromethorphan were administrated, respectively. Thereafter, the subjects received 4.5 g of TJ-19 twice daily for 7 days, and underwent the same phenotyping test on postdose day 7.

RESULTS

The activities of all enzymes examined did not differ before or after the 7-day administration of TJ-19. Consequently, the influence of the CYP2D6 genotype on the herb-drug interaction remained unsolved.

CONCLUSION

Our results indicate that TJ-19 at the generally recommended dosage is unlikely to cause pharmacokinetic interaction with co-administered medications primarily dependent on the CYP1A2, CYP2D6, CYP3A, XO, and NAT2 pathways for elimination.

Allelic distributions of CYP2D6 gene copy number variation in the Eastern Han Chinese population

AIM

The human cytochrome P450 2D6 (CYP2D6) gene copy number variation, involving CYP2D6 gene deletion (CYP2D6*5) and duplication or multiduplication (CYP2D6*xN), can result in reduced or increased metabolism of many clinically used drugs. The identification of CYP2D6*5 and CYP2D6*xN and the investigation of their allelic distributions in ethnic populations can be important in determining the right drug and dosage for each patient.

METHODS

The CYP2D6*5 and CYP2D6 genes, and CYP2D6 gene duplication were identified by 2 modified long PCR, respectively. To determine duplicated alleles, a novel long PCR was developed to amplify the entire duplicated CYP2D6 gene which was used as template for subsequent PCR amplification. A total of 363 unrelated Eastern Han Chinese individuals were analyzed for CYP2D6 gene copy number variation.

RESULTS

The frequency of CYP2D6*5 and CYP2D6*xN were 4.82% (n=35) and 0.69% (n=5) in the Eastern Han Chinese population, respectively. Of the 5 duplicated alleles, 3 were CYP2D6*1xN and 2 were CYP2D6*10xN. One individual was a carrier of both CYP2D6*5 and CYP2D6*1xN. Taken together, the CYP2D6 gene rearrangements were present in 10.74% of subjects.

CONCLUSION

Allelic distributions of the CYP2D6 gene copy number variation differ among Chinese from different regions, indicating ethnic variety in Chinese. Long PCR are convenient, cost effective, specific and semiquantitative for the detection of the CYP2D6 gene copy number variation, and amplification of the entire duplicated CYP2D6 gene is necessary for the accurate identification of duplicated alleles.

Prolactin release in children treated with risperidone: impact and role of CYP2D6 metabolism

OBJECTIVE

Little is known about the role of CYP2D6 polymorphism in risperidone-induced prolactin release in children.

METHOD

Twenty-five children (aged 5-15 years) with pervasive developmental disorders were genotyped for CYP2D6 polymorphisms. Serum prolactin, risperidone, and 9-hydroxyrisperidone were assessed at baseline and after 8 weeks of risperidone treatment (mean dosage, 0.06 +/- 0.03 mg/kg/d). After 24 weeks of treatment, prolactin was measured in a subsample of 15 children. Adverse effects were evaluated using a clinician-rated survey.

RESULTS

Mean +/- SD prolactin levels increased from 7.8 +/- 8.0 ng/mL at baseline to 33.2 +/- 12.8 ng/mL at week 8 (P < 0.001), with a slight decrease to 28.8 +/- 13.6 ng/mL at week 24. At week 8, serum prolactin level was positively correlated with dose per kilogram (r = 0.648, P < 0.001), number of functional CYP2D6 genes (J = 2.117, P = 0.034), and serum 9-hydroxyrisperidone concentration (r = 0.664, P = 0.001) and was negatively correlated with the risperidone/9-hydroxyrisperidone ratio (r = -0.571, P = 0.004) but not with risperidone concentration (r = -0.243, P = 0.264) nor age (r = 0.072, P = 0.733). Prolactin elevation was not associated with adverse effects.

CONCLUSIONS

Low-to-intermediate doses of risperidone induced a 4-fold prolactin increase in children without a clear development of tolerance up to 6 months. CYP2D6 ultrarapid metabolism may be a risk factor for more pronounced prolactin elevation.

Frequency of single nucleotide polymorphisms of CYP2D6 in the Czech population

CYP2D6 is a member of cytochrome P450 enzymes that metabolise over 25% of commonly used drugs. Genetic polymorphisms can cause insufficient drug efficacy at usually administered doses or can be the cause of adverse drug reaction. CYP2D6 genotyping can be used to predict CYP2D6 phenotype and thereby explain some abnormalities in drug response and thus optimize pharmacotherapy. The aim of this study was to investigate the frequency of functionally important variant alleles of the CYP2D6 gene throughout the Czech population to predict the prevalence of ultra-rapid and poor metabolizer phenotypes. The DNA of 223 unrelated, healthy volunteers was analysed to detect the presence of CYP2D6*6, *5, *4, *3 and gene duplication. The variant allele frequencies in our population were 0.22%, 3.14%, 22.87%, 1.12% and 3.14% for CYP2D6*6, CYP2D6*5, CYP2D6*4, CYP2D6*3 and CYP2D6*MxN, respectively. Fifteen subjects carried two variant alleles leading to predicted poor type of metabolism, 84 subjects were heterozygous extensive metabolizers (het-EM). The full-text contains detailed comparison with European white populations. The distribution of variant alleles complies with the Hardy-Weinberg equilibrium. The frequencies of functional variant alleles of CYP2D6 in Czech population are in concordance with other Caucasian populations.

Effects of DRD2 and CYP2D6 genotypes on delta EEG power response to aripiprazole in healthy male volunteers: a preliminary study

The aim of the present study was to evaluate the effects of polymorphisms in dopamine D2 receptor (DRD2) and cytochrome P450 (CYP) 2D6 genes on delta EEG power response to aripiprazole in healthy male volunteers. Seventeen volunteers were recruited according to the DRD2 Taq1A genotype, and separated into the following groups: homozygous wild-type (A2/A2, n = 7), heterozygous (A2/A1, n = 5) and homozygous variant-type (A1/A1, n = 5) groups. After enrollment in this study, they were genotyped for CYP2D6. The volunteers received single 10 mg oral doses of aripiprazole, in accordance with an open-label parallel group study design. Plasma levels of aripiprazole and its metabolite were determined and EEGs were obtained simultaneously. The pharmacodynamic parameter was absolute delta power in the Cz channel. The changes of delta power were not different according to DRD2 Taq1A genotypes. As to the CYP2D6 allele, the subjects had the following CYP2D6 genotypes: *10/*10 (n = 4), *1/*10 (n = 5), *1/*5 (n = 2), *1/*1 (n = 3), *2/*41 (n = 1), *2/*2 (n = 1), *2N/*10 (n = 1). Subjects exhibiting the *1/*5 and *1/*10 genotypes showed a trend toward high area under the plasma aripiprazole concentration-time curve (AUC), which was linearly related to area under the EEG response-time curve (AUEC). Our results demonstrate a need for further evaluation of the CYP2D6 genotypic effect on the pharmacodynamics of aripiprazole.

The influence of CYP2D6 phenotype on the clinical response of nebivolol in patients with essential hypertension

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* The variability in drug metabolism has been recognized as an important factor in the occurrence of adverse effects or lack of therapeutic efficacy. * The metabolism of the third-generation beta(1)-receptor antagonist nebivolol has been shown to be highly dependent on cytochrome P450 2D6 enzymatic activity in preclinical studies.

WHAT THIS STUDY ADDS

* This paper assesses the role of a cytochrome P450 2D6 gene defect on the antihypertensive response to nebivolol in a clinical setting. * Despite significant differences in drug disposition, the chronic administration of nebivolol produced similar efficacy and tolerability in hypertensive patients either characterized as poor or extensive metabolizers of the drug. * The study offers insight into the relative contribution of nebivolol enantiomers in systemic blood pressure control.

AIMS

Nebivolol is a beta(1)-adrenergic receptor antagonist with vasodilating properties used in the treatment of hypertension. It is administered as a racemic mixture (D- and L-nebivolol) and is highly metabolized by the cytochrome P-450 2D6 (CYP2D6). The purpose of this study was to determine the role of CYP2D6 phenotypes on the efficacy and tolerability of nebivolol during chronic administration to patients with essential hypertension.

METHODS

Two hundred and eighteen patients were genotyped and phenotyped for CYP2D6 activity, allowing to find and match 14 poor metabolizers (PMs) with 23 extensive metabolizers (EMs). Patients took rac-nebivolol 5 mg daily for 12 weeks. Blood pressure (BP), heart rate, adverse events, plasma levels of the two enantiomers D- and L-nebivolol and their corresponding hydroxymetabolites were assessed.

RESULTS

The metabolic disposition of nebivolol was enantioselective and highly influenced by CYP2D6 phenotypes. Mean steady-state plasma concentrations of D- and L-nebivolol were 10- and 15-fold greater in PMs than in EMs, respectively (P < 0.0001). Despite these differences in the pharmacokinetics of nebivolol, EMs and PMs displayed similar BP responses. Mean reductions in sitting systolic and diastolic BPs were -11/-10 +/- 9/4 mmHg in EMs and -11/-9 +/- 10/5 mmHg in PMs. Side-effects were mild to moderate and not different between groups.

CONCLUSION

Polymorphisms in the gene encoding CYP2D6 significantly influenced the metabolism of nebivolol, but not its antihypertensive efficacy and tolerability. The similar clinical response between EMs and PMs could be explained by the contribution of active hydroxylated metabolites of nebivolol to its antihypertensive actions in EMs.

Impact of CYP2D6*10 on H1-antihistamine-induced hypersomnia

OBJECTIVE

This study investigated the relevance of the cytochrome P450 (CYP) 2D6 genotype to the adverse drug reactions (ADRs) of H1-antihistamines and the level of sedation.

METHODS

Japanese participants in a health screening program were asked to describe any past history of ADRs. Any subjects reporting ADRs induced by H1-antihistamines were then individually interviewed and defined as cases. Excessive daytime sleepiness, which had occurred in the cases as an H1-antihistamine-induced ADR, was assessed by the Epworth sleepiness scale (ESS), and an ESS score >or=12 was considered hypersomnia. CYP2D6*4, *5, *14, and *10 were genotyped by a panel of polymerase chain reaction techniques.

RESULTS

Out of 2,074 participants, 100 cases (M:F = 37:63, mean age 51.9 +/- 9.2 years) were eligible for analysis. The most common etiological drug was chlorpheniramine, which is the most frequently used H1-antihistamine in Japan. CYP2D6*10 allele and genotypes were more frequently found in the cases than in the healthy Japanese population in a large study (P < 0.005 and P = 0.039, respectively), but no difference was observed in the null alleles and genotypes. The ESS scores in 75 cases (M:F=25:50) who had experienced excessive daytime sleepiness were 9.5 +/- 5.5 in men and 12.9 +/- 6.1 in women (P < 0.001, cases vs. 34 subjects without symptoms; P = 0.001 men vs. women). The occurrence of hypersomnia increased as the number of CYP2D6 mutant alleles increased (P = 0.045).

CONCLUSION

The results suggest that the presence of the CYP2D6*10 allele is a risk factor for development of H1-antihistamine-induced ADRs in Japanese.

CYP2D6 genetic polymorphism in South Indian populations

This study aimed to determine the prevalence of genetic polymorphism in the CYP2D6 gene, which codes for the polymorphically expressed CYP2D6 drug-metabolizing enzyme. The common variants CYP2D6 *2, *3, *4, *5, *10, *14, and *17 were studied in the populations (n=447) of the four South Indian states namely Tamilnadu (TN), Kerala (Ker), Karnataka (Kar) and Andhra Pradesh (AP). Genetic polymorphisms were identified using polymerase chain reaction (PCR) and PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) based methods. Differences in frequencies of CYP2D6 polymorphism between each South Indian state were statistically compared, and also the frequency of South Indian population as a whole in relation to other major populations. The CYP2D6*2 allele was the most frequent variant (34.8%), followed by the *10 allele (10.2%). The *4 and *5 alleles occurred at 7.3% and 1.9% respectively. The *3, *14 and *17 alleles were not detected in the study. The *1/*2, *1/*1 and *2/*2 genotypes were the most common CYP2D6 genotypes, representing 32.7%, 19.4% and 11.8% of the South Indian population. Genotypes that predict poor metabolizer phenotype i.e. *4/*4 and *4/*5 were found at 0.6% in South Indian population. The genetic composition at the CYP2D6 locus in South Indians is distinct from Caucasian, African and even other Asian (Chinese and Japanese) populations.

AmpliChip CYP450 GeneChip®: A New Gene Chip That Allows Rapid and Accurate CYP2D6 Genotyping

Methods for Cytochrome P450-2D6 (CYP2D6) genotyping are often time-consuming and laborious, which can restrict their use in pretherapeutic screening programs. Gene chip technology could overcome this problem. The aim of this study was to evaluate CYP2D6 genotyping by a new improved gene chip compared to a PCR-RFLP method. AmpliChip CYP450 GeneChip(R) (AmpliChip) is a microarray hybridization method for genotyping CYP2D6 and CYP2C19. One hundred fifty-nine DNA samples were genotyped both by AmpliChip as well as by PCR-RFLP and, where applicable, by a SNaPshot technique which detects single nucleotide polymorphisms based on the single base extension principle. In 152 of the 159 samples, CYP2D6 genotypes determined with the AmpliChip were in accordance with the results of PCR-RFLP. All seven discrepant samples had gene duplications and were subjected to SNaPshot analysis. SNaPshot results concurred with those of the AmpliChip for six out of seven samples. In the one divergent result, DNA sequencing confirmed that the AmpliChip had assigned the correct genotype. In conclusion, AmpliChip is a highly reliable method for CYP2D6 genotyping that allows the correct determination of all relevant CYP2D6 alleles in one single run. It therefore represents a very efficient and fast method, offering new perspectives for the application of pharmacogenetics in clinical medicine.

Paroxetine: population pharmacokinetic analysis in late-life depression using sparse concentration sampling

AIM

To develop a population pharmacokinetic (PK) model using sparse sampling of long-term treatment with paroxetine in elderly depressed subjects, incorporating CYP2D6 genotype as well as other covariates.

METHODS

Elderly subjects (age>or=70 years) with nonpsychotic, nonbipolar major depressive disorder from the inpatient and outpatient clinic were treated with paroxetine in a 5-year clinical trial investigating 'Maintenance Therapies in Late-Life Depression' (MTLD-2). Plasma concentrations were collected during regular visits. CYP2D6 genotype was determined using polymerase chain reaction (PCR) for each individual. A nonlinear mixed-effects model was developed with NONMEM for these subjects who received 10-40 mg day-1 of paroxetine during treatment. One- and two-compartment models with linear and nonlinear elimination (Michaelis-Menten) were evaluated. PK parameters as well as interindividual and residual variability were estimated. The effects of age, weight, sex, race and CYP2D6 genotypes on the pharmacokinetics of paroxetine were evaluated.

RESULTS

One hundred and seventy-one subjects with a mean age of 77 years (range 69-95) and a mean weight of 72.0 kg (range 32.9-137.0) were enrolled in the MTLD-2 clinical trial. A total of 1970 paroxetine concentrations were available for population PK analyses. Approximately 10 samples were taken per subject. A two-compartment nonlinear PK model with additive and proportional error provided the best base model for description of the data. Weight and CYP2D6 polymorphisms were found to have a significant effect on maximal velocity (Vm), whereas sex had an effect on volume of distribution of the central compartment. The Vm estimates in each of the CYP2D6 phenotypic groups were: 125 microg h-1 in poor metabolizer (n=1), 182 microg h-1 in intermediate metabolizers (n=28), 454 microg h-1 in extensive metabolizers (n=36) and 3670 microg h-1 in ultra-rapid metabolizers (n=5).

CONCLUSIONS

The population PK model adequately described paroxetine data in this elderly depressed population. The data indicate that female and male subjects with different CYP2D6 polymorphisms have different elimination rates and therefore may need to be dosed differently based on metabolizer genotype.

Application of microarray technology in psychotropic drug trials

Microarrays can be manufactured to detect hundreds of thousands of polymorphisms in DNA from patients in psychotropic drug trials. Some of these polymorphisms may be useful as pharmacogenetic predictors of treatment outcomes. We tested a microarray designed to detect common polymorphisms in the CYP2D6 gene that encodes debrisoquine hydroxylase (DH). DH is involved in the hepatic metabolism of many psychotropics. CYP2D6 genotypes predicted plasma steady state concentrations of nortriptyline, a classic DH substrate, in a sample of geriatric patients with major depression. However, in a sample of 246 geriatric patients treated with paroxetine or mirtazapine, both of which are metabolized in part by DH, CYP2D6 genotypes determined with microarrays did not predict discontinuations due to adverse events or severity of adverse events. For modern antidepressants such as paroxetine and mirtazapine, pharmacokinetic factors that are regulated by CYP2D6 such as plasma drug concentrations may be less important than pharmacodynamic factors in determining outcomes. Studies of single candidate genes such as CYP2D6 have only begun to utilize the potential of microarrays for pharmacogenetic prediction. Yet, there is controversy as to whether genome-wide studies designed to detect millions of genotypes with microarrays will lead to new pharmacogenetic discoveries, or whether a more focused, hypothesis-driven approach is better.

Effects of Caffeine on the Kinetics of Fluvoxamine and its Major Metabolite in Plasma After a Single Oral Dose of the Drug

The effects of caffeine on the kinetics of fluvoxamine (FLV) and its major metabolite fluvoxamino acid (FLA) in plasma, after a single oral dose of the drug, were studied in 12 healthy male volunteers. The subjects received caffeine 300 mg/d or placebo for 11 days in a double-blind randomized crossover manner, and on the eighth day they received a single oral 50-mg dose of FLV. Blood sampling and pharmacodynamic evaluation were conducted up to 72 hours after FLV dosing. Plasma concentrations of FLV and FLA were measured by high-performance liquid chromatography. Caffeine significantly decreased the plasma concentrations at 6 time points (P<0.05) and total area under the plasma concentration-time curve (156.5+/-51.7 vs. 118.9+/-38.2 ng/h/mL, P<0.01) of FLV. Plasma concentration and pharmacokinetic parameters of FLA were not affected by caffeine. Caffeine induced no significant change in the pharmacodynamic effects of FLV. The present study suggests that caffeine slightly induces the metabolism of FLV, probably mediated by CYP1A2.

The impact of CYP2D6 genotypes on the plasma concentration of paroxetine in Japanese psychiatric patients

The authors investigated the impact of the CYP2D6 genotypes on the plasma concentration of paroxetine (PAX) in 55 Japanese psychiatric patients. They were administered 10 to 40 mg/day (24+/-10.0 mg/day) of PAX and maintained at the same daily dose for at least two weeks to obtain the steady-state concentrations. The plasma levels of PAX were 15.8+/-15.0, 47.4+/-32.0, 101.2+/-59.9 and 177.5+/-123.6 ng/ml at the daily dose of 10, 20, 30 and 40 mg, respectively, which suggested dose dependent kinetics of PAX. The allele frequencies of the CYP2D65, CYP2D610 and CYP2D641 were 1.8%, 41.8% and 1.8%, respectively. Significantly higher PAX concentrations were observed in the patients having one functional allele compared with those with two functional alleles (150.9+/-20.6 vs. 243.6+/-25.2 ng/ml mg(-1) kg(-1), p<0.05, Newman-Keuls multiple comparison test) or no functional (243.6+/-25.2 vs. 76.7+/-6.1 ng/ml mg(-1) kg(-1), p<0.05, Newman-Keuls multiple comparison test) in the subjects with 30 mg/day of paroxetine. The same trend of findings as in the subjects treated with 30 mg/day were observed in the subjects with 40 mg/day of PAX. The present results suggest that having one non-functional allele is the marker for high plasma concentration of PAX when relatively high daily dose of PAX is administered.

Rapid detection of common cytochrome P450 2D6 alleles in Caucasians

CYP2D6 is a highly polymorphic enzyme that mediates the metabolism of around 20% of all currently prescribed drugs. Genetic variability within CYP2D6 results in poor (PM), intermediate (IM), extensive (EM) and ultra-rapid metabolisers (UM) of CYP2D6 substrates. Here we describe an assay which is able to detect the major PM (CYP2D6*3, *4, *5, *6), IM (CYP2D6*9, *10, *41) and UM (CYP2D6*nxn) alleles found in Caucasians. This assay is performed in two stages. The first stage is a multiplex long-range PCR which is used to simultaneously screen for whole gene deletions and duplications while isolating CYP2D6 from the CYP2D gene cluster to avoid pseudogene contamination. In the second stage, individuals with one or more copies of CYP2D6 are genotyped for PM and IM alleles using a two-tube multiplex Amplification Refractory Mutation System (ARMS). The specificity and reliability of the multiplex long-range PCR and subsequent ARMS were confirmed using a panel of positive controls that had been previously validated by PCR-RFLPs and DNA sequencing. This two-stage assay offers a robust and cheap alternative to many currently available CYP2D6 genotyping approaches. Our entire assay, once patient DNA has been extracted, can be run within 7 h using 10 microl PCRs.

Polymorphisms in the 5-hydroxytryptamine 2A receptor and CytochromeP4502D6 genes synergistically predict fluvoxamine-induced side effects in japanese depressed patients

5-Hydroxytryptamine (5-HT) receptors are thought to be associated with the gastrointestinal side effects induced by selective serotonin reuptake inhibitors. CytochromeP450 (CYP) 2D6 may also be associated with the side effects induced by fluvoxamine, since the plasma fluvoxamine concentration depends on a CYP2D6 gene polymorphism. This study investigated whether 5-HT receptor and CYP2D6 gene polymorphisms could predict the occurrence of the side effects. The effects of 5-HT receptor and CYP2D6 gene polymorphisms on the incidence of gastrointestinal side effects induced by fluvoxamine were investigated in 100 depressed outpatients who gave written consent to participate in the study. The patients visited every 2 weeks until the week 12 end point and the fluvoxamine dose was changed in response to their clinical symptoms. All side effects, including the gastrointestinal side effects, were assessed at each visit. Polymerase chain reaction was used to determine A-1438G of the 5-HT2A receptor, C195T and Pro16Ser of the 5-HT3A receptor, Tyr129Ser of the 5-HT3B receptor, and the *5 and *10 alleles of CYP2D6. Both the A-1438G polymorphism of the 5-HT2A receptor gene and the CYP2D6 gene polymorphism had significant effects on the incidence of gastrointestinal side effects. Cox regression was used to analyze the combination effect of the two polymorphisms on the gastrointestinal side effects. Cox regression analysis showed that lower metabolizers (LMs) of CYP2D6 with the G/G genotype of the 5-HT2A A-1438G polymorphism had a 4.242-fold (P = 0.009) and LMs with the A/G genotype had a 4.147-fold (P = 0.004) higher risk of developing gastrointestinal side effects than normal metabolizers with the A/A genotype. The 5-HT3A and 3B gene polymorphisms had no significant effects on the incidence of gastrointestinal side effects. 5-HT2A receptor and CYP2D6 gene polymorphisms had a synergistic effect for the prediction of fluvoxamine-induced gastrointestinal side effects.

Effect of CYP2D6 genetic polymorphism on the population pharmacokinetics of tipifarnib

OBJECTIVE

Evaluate the effect of CYP2D6 genotype on the pharmacokinetics of tipifarnib.

METHODS

A total of 268 subjects included in six clinical trials were treated orally with tablet formulation of tipifarnib, as a single dose or as multiple b.i.d. doses (range 50-600 mg), and/or intravenously following 1, 2, and 24 h infusions. A total of 2,575 tipifarnib concentrations were fitted to an open three-compartment linear disposition model with sequential zero-order input into the depot compartment, followed by a first-order absorption process, and lag time, using NONMEM V. The effect of CYP2D6 genotype was explored as a covariate for tipifarnib systemic clearance and absolute bioavailability. Likelihood ratio test was used to compare these parameters in homozygous extensive metabolizers (EM) (N=152), heterozygous EM (N=97), or poor metabolizers (PM) (N=19). Computer simulations were undertaken to explore the CYP2D6 genotype effect on the tipifarnib pharmacokinetics.

RESULTS

The ratio of tipifarnib systemic clearance for the heterozygous EM and the PM subjects, relative to the homozygous EM group, were 0.95 (95%CI 0.87-1.03) and 0.96 (95%CI 0.82-1.11), respectively (chi2=2.376, df=2, P=0.305). The ratio of tipifarnib absolute bioavailability for the heterozygous EM and the PM, relative to the homozygous EM, were 1.06 (95%CI 0.83-1.30) and 0.95 (95%CI 0.55-1.34), respectively (chi2=1.398, df=2, P=0.497).

CONCLUSIONS

These results indicate that CYP2D6 genetic polymorphism does not appreciably influence the pharmacokinetics of tipifarnib. Hence, concomitant administration of potent CYP2D6 inhibitors is anticipated to have little or no significant impact on the systemic exposure to tipifarnib.

The effect of 5-hydroxytryptamine 3A and 3B receptor genes on nausea induced by paroxetine

We investigated the effect of 5-hydroxytryptamine 3A and 3B receptor (HTR3A and HTR3B) gene polymorphisms on nausea induced by paroxetine in Japanese psychiatric patients. Blood samples were collected from 78 individuals after at least 2 weeks treatment with the same daily dose of paroxetine. The patients visited every 2 weeks and the paroxetine dose was changed in response to their clinical symptoms. Nausea was assessed at each visit. The Tyr129Ser polymorphism of the HTR3B gene had a significant effect on the incidence of nausea (P=0.038). Logistic regression analysis also showed that patients with the Tyr/Tyr genotype had a 3.95-fold (P=0.048) higher risk of developing nausea than patients with the Ser allele. HTR3A gene polymorphisms and the CYP2D6 gene polymorphisms had no significant effect on the incidence of nausea. The mean score of nausea severity was corrected by the Bonferroni test. HTR3B gene polymorphisms are significant predictors of paroxetine-induced nausea.

Novel structure of the CYP2D6 gene that confuses genotyping for the CYP2D6*5 allele

We encountered DNA samples which showed a positive product using a long PCR-based method for the detection of CYP2D6*5, indicating deletion of the entire CYP2D6 gene, but the samples did not show a band related to CYP2D6*5 in either XbaI- or EcoRI-RFLP analysis. To achieve genotyping with accuracy, we performed a further genetic analysis to clarify the discrepancy. An unknown 1.6-kb insert was identified in a region downstream from the CYP2D6 stop codon where a specific primer was designed for long-PCR analysis for CYP2D6*5 genotyping. This finding suggested that the CYP2D6 gene might not be deleted in the samples even if a positive product was detected by the long-PCR method. Furthermore, the allelic frequency of this type was found to be approximately 0.3% (4 heterozygous/771 samples) in a Japanese population. In conclusion, we found a novel structure of the CYP2D6 gene, which might lead to incorrect genotyping for CYP2D6*5. Although the long PCR-based strategy for the detection of CYP2D6*5 has been widely used due to its usefulness and convenience, we recommend caution when adopting this method and propose re-evaluating the method for detecting CYP2D6*5.

Pharmacokinetic variability of routinely administered bisoprolol in middle-aged and elderly Japanese patients

The nonlinear mixed effects model (NONMEM) was used to analyze the pharmacokinetics of routinely administered bisoprolol in middle-aged and elderly Japanese patients. The subjects consisted of 29 males and 11 females with a mean age of 63.5+/-10.1. Data on the plasma concentration of bisoprolol from 94 blood samples obtained at steady-state following repetitive oral administration were analyzed using the NONMEM program, where a one-compartment model with repetitive bolus dosing was parameterized in terms of oral clearance (CL/F) and apparent volume of distribution (V/F). Individual CL/F values were correlated with body weight (WT) and creatinine clearance (CLcr). The relation between CLcr and the CL/F of bisoprolol was not altered by the CYP2D6 and CYP2C19 genotypes, gender, or age. The mean CL/F value estimated with NONMEM was 0.0612.WT+1.15.CLcr (l/h), and the mean V/F value was 2.61.WT (l). The residual interindividual variability of CL/F and V/F were 22.0% and 12.6%, respectively. The pharmacokinetic variability of bisoprolol is small even in routinely treated Japanese patients, provided that both body weight and renal function are taken into account for the prediction of oral clearance of the drug.

Dose-dependent interaction of paroxetine with risperidone in schizophrenic patients

Augmentation with paroxetine (10-40 mg/d) for antipsychotic treatment may improve the negative symptoms in schizophrenic patients but involves a risk of drug-drug interaction. We studied the effects of paroxetine on plasma concentrations of risperidone and 9-hydroxyrisperidone and their clinical symptoms in risperidone-treated patients. Twelve schizophrenic inpatients with prevailingly negative symptoms receiving risperidone 4 mg/d were, in addition, treated with incremental doses of paroxetine for 12 weeks (10, 20, and 40 mg/d for 4 weeks each). Plasma concentrations of risperidone and 9-hydroxyrisperidone were quantified with liquid chromatography-mass spectrometry mass-mass spectrometry together with clinical assessments before and after each phase of the 3 paroxetine doses. Risperidone concentrations during coadministration of paroxetine 10, 20, and 40 mg/d were 3.8-fold (95% confidence interval, 3.2-5.8, P < 0.01), 7.1-fold (95% confidence interval, 5.3-16.5, P < 0.01), and 9.7-fold (95% confidence interval, 7.8-22.5, P < 0.01) higher than that before paroxetine coadministration, respectively. Active moiety (risperidone plus 9-hydroxyrisperidone) concentration was not increased during the paroxetine 10 mg/d (1.3-fold, not significant) or 20 mg/d (1.6-fold, not significant), but were significantly increased by 1.8-fold (95% confidence interval, 1.4-2.7, P < 0.05) during the paroxetine 40 mg/d. Significant improvement in negative symptoms was observed from 10 to 40 mg/d of paroxetine, whereas scores in extrapyramidal side effects during 20 and 40 mg/d of paroxetine were significantly higher than baseline score. This study indicates that paroxetine increases plasma risperidone concentration and active moiety concentration in a dose-dependent manner. Low-dose coadministration of paroxetine with risperidone may be safe and effective in the treatment of schizophrenic patients with negative symptoms.

High-throughput detection of multiple genetic polymorphisms influencing drug metabolism with mismatch primers in allele-specific polymerase chain reaction

Because of genetic polymorphisms of drug-metabolizing enzyme genes, the activities of the enzymes in humans vary widely and alter the metabolism of commonly used clinical agents. Severe adverse effects or resistance to therapy may result. We have developed a rapid and high-throughput genotyping method for detecting polymorphisms of the drug-metabolizing enzyme genes CYP2C9*3, CYP2C19*2, *3, CYP2D6*2, *4, *10, *14, *21, NAT2*5, *6, *7, and TPMT*3 using allele-specific polymerase chain reaction (PCR) with mismatch primers (ASPCR-MP) and CYP2D6*5, *36, and CYP2D6xN using stepdown PCR with detection by SYBR Green I. We analyzed genomic DNA from 139 Japanese volunteers. Identical genotyping results were obtained by using ASPCR-MP, stepdown PCR, and conventional PCR. We found that the methods clearly differentiate three specific profiles with no overlap in the signals. Moreover, both ASPCR-MP and stepdown PCR for genotyping took less than 3-4h. To our knowledge, this is the first report of successful simultaneous detection of multiple genetic polymorphisms with point mutations using ASPCR-MP or multiple genetic polymorphisms with large structural alterations using stepdown PCR. In conclusion, ASPCR-MP and stepdown PCR appear to be suitable for large clinical and epidemiological studies as methods that enable highly sensitive genotyping and yield a high-throughput.