101
|
Gardiner SJ, Begg EJ. Pharmacogenetics, drug-metabolizing enzymes, and clinical practice. Pharmacol Rev 2006; 58:521-90. [PMID: 16968950 DOI: 10.1124/pr.58.3.6] [Citation(s) in RCA: 235] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.
Collapse
Affiliation(s)
- Sharon J Gardiner
- Department of Medicine, Christchurch School of Medicine, Private Bag 4345, Christchurch, New Zealand.
| | | |
Collapse
|
102
|
Quinzler R, Gasse C, Schneider A, Kaufmann-Kolle P, Szecsenyi J, Haefeli WE. The frequency of inappropriate tablet splitting in primary care. Eur J Clin Pharmacol 2006; 62:1065-73. [PMID: 17024485 DOI: 10.1007/s00228-006-0202-3] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Accepted: 08/16/2006] [Indexed: 10/24/2022]
Abstract
INTRODUCTION We assessed the frequency and determinants of tablet splitting in primary care in Germany and evaluated the quality of information on divisibility in the Summary of Product Characteristics (SPCs) and in the Package Leaflet (PL) as legal sources of information for health care providers and patients. METHODS We performed a cross-sectional questionnaire survey among patients of 59 general practitioners in the German Federal State Saxony-Anhalt in 2005 in order to collect detailed information on all drugs of patients maintained on more than three drugs. RESULTS The response rate was 82.1% (n=905) and 3,158 drugs (tablets and dragées) were included in the analyses. Of all drugs, 24.1% were split (762 of 3,158): 8.7% of all split tablets were unscored (66 of 762) and 3.8% of all split tablets were not allowed to be split (29 of 762). Tablets of the higher price categories and higher strengths were twice as likely to be split. Only 22.5% of the SPCs (9 of 40) of the split unscored tablet brands contained explicit information on divisibility and only 36.4% of the PLs (8 of 22) of the split brands that were not allowed to be split stated that splitting was not appropriate. CONCLUSION The splitting of tablets in primary care is a frequent habit likely driven by medical and economic considerations. Almost 1% of all tablets are split that must not be fragmented. However, the SPC and PL provide only limited information on divisibility stressing the need to improve this information promptly to avoid medication errors.
Collapse
Affiliation(s)
- R Quinzler
- Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | | | | | | | | | | |
Collapse
|
103
|
Weinshilboum RM, Wang L. Pharmacogenetics and Pharmacogenomics: Development, Science, and Translation. Annu Rev Genomics Hum Genet 2006; 7:223-45. [PMID: 16948615 DOI: 10.1146/annurev.genom.6.080604.162315] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. This discipline evolved from the convergence of rapid advances in molecular pharmacology and genomics. Originally, pharmacogenetic studies focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire "pathways" encoding proteins that influence both pharmacokinetics--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics, the drug target itself, as well as genome-wide approaches. Pharmacogenomics is also increasingly moving across the "translational interface" into the clinic and is being incorporated into the drug development process and the governmental regulation of that process. However, significant challenges remain to be overcome if pharmacogenetics-pharmacogenomics is to achieve its full potential as a major medical application of genomic science.
Collapse
Affiliation(s)
- Richard M Weinshilboum
- Division of Clinical Pharmacology, Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Mayo Medical School-Mayo Foundation, Rochester, Minnesota 55905, USA.
| | | |
Collapse
|
104
|
Thuerauf N, Lunkenheimer J. The impact of the CYP2D6-polymorphism on dose recommendations for current antidepressants. Eur Arch Psychiatry Clin Neurosci 2006; 256:287-93. [PMID: 16783493 DOI: 10.1007/s00406-006-0663-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
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.
Collapse
Affiliation(s)
- Norbert Thuerauf
- Department of Psychiatry and Psychotherapy, Friedrich-Alexander-Univeristy of Erlangen-Nuremberg, Schwabachanlage 6, 91054 Erlangen, Germany.
| | | |
Collapse
|
105
|
Abstract
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.
Collapse
Affiliation(s)
- Greer M Murphy
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94305-5485, USA.
| |
Collapse
|
106
|
Abstract
Functional gastrointestinal disorders, including irritable bowel syndrome and functional dyspepsia, are highly prevalent disorders affecting approximately one in four people in Western societies. This article reviews examples of the role of pharmacogenomics in the safety and efficacy of medications used in the management of such disorders. These include variations in the effects of medications metabolized by cytochrome P450 enzymes (e.g., 2D6 and 2C19), and the effects of genetic polymorphisms in the promoter of the serotonin transporter protein, which influence the response to alosetron in patients with diarrhea-predominant irritable bowel syndrome. These observations suggest that pharmacogenomics will introduce a new era in pharmacotherapeutics in gastroenterology.
Collapse
Affiliation(s)
- Michael Camilleri
- Mayo Clinic College of Medicine, Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Gastroenterology Research Unit, Charlton 8-110200 First Street S.W., Rochester, MN 55905, USA
| |
Collapse
|
107
|
Abstract
So far no pharmacogenetic/genomic study has been conducted specifically for anxiety disorders. Some of the presented results, however, do pertain to such disorders. For example, pharmacokinetic aspects of antidepressant drug therapy likely also apply to patients with anxiety disorders, and several genetic polymorphisms in the cytochrome P450 (CYP) gene family and drug transporter molecules, such as the multidrug resistance (MDR) gene type 1, have been reported to influence the pharmacokinetics of antidepressant drugs. At this stage of pharmacogenomics research, it is difficult to interpret the relevance of pharmacodynamic-genetic association studies conducted in depressed patients for anxiety disorders. A number of studies have reported an influence of polymorphisms of genes mostly in the serotonergic pathway on the response to antidepressant drugs in patients suffering from depression. In order to know whether they can be extrapolated to patients with anxiety disorders, clinical studies are warranted. Despite all the shortcomings of the currently available pharmacogenetic studies, this field holds great promise for the treatment of anxiety disorders. In the future, psychiatrists may be able to base treatment decisions (i.e., the type and dose of prescribed drug) on more objective parameters than only the diagnostic algorithms used now. This will limit unwanted side effects and adverse drug reactions, and could reduce time to response, resulting in a more individualized pharmacotherapy.
Collapse
Affiliation(s)
- E B Binder
- Max-Planck Institute of Psychiatry, Kraepelinstr. 10, 80804 Munich, Germany
| | | |
Collapse
|
108
|
Lee SY, Sohn KM, Ryu JY, Yoon YR, Shin JG, Kim JW. Sequence-based CYP2D6 Genotyping in the Korean Population. Ther Drug Monit 2006; 28:382-7. [PMID: 16778723 DOI: 10.1097/01.ftd.0000211823.80854.db] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
For clinical application of pharmacogenetic tests, quantitative prediction of enzyme activity based on accurate determination of genotype is essential. There has been limited information available on the genetic polymorphism of CYP2D6 in the Korean population. In this study, CYP2D6 genotypes were assessed in 400 Korean subjects. Twenty-eight different CYP2D6 alleles and 35 genotypes were detected. On the basis of the genotype determined, the frequency of poor metabolizers and ultrarapid metabolizers were 0.22% and 1.25%, respectively. The CYP2D6 activity expected in regard to different allele combinations varies widely within the extensive and intermediate metabolizer groups. The frequencies of CYP2D6*10 and CYP2D6*5 were 45.00% and 6.13%, respectively. CYP2D6*10xN was found in 4 out of 9 cases with a CYP2D6 duplication. Fifteen heterozygotes for *41 were noted. In addition, the authors measured plasma concentrations of 16 healthy volunteers after administration of nortriptyline and identified the impact of the CYP2D6 genotype on nortriptyline metabolism. This is the first large-scale study to examine the genetic polymorphism of CYP2D6 using sequence-based genotyping in an Asian population. Our results further the understanding of CYP2D6 pharmacogenetics and could be helpful for future clinical studies in the Asian population.
Collapse
Affiliation(s)
- Soo-Youn Lee
- Department of Laboratory Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | | | | | | | | | | |
Collapse
|
109
|
Abstract
It has become a truism that we humans are genetically about 99% identical to chimpanzees. The origins of this assertion are clear: among early studies of DNA sequences, nucleotide identity between humans and chimpanzees was found to average around 98.9%.(1) However, this figure is correct only with respect to regions of the genome that are shared between humans and chimpanzees. Often ignored are the many parts of their genomes that are not shared. Genomic rearrangements, including insertions, deletions, translocations and duplications, have long been recognized as potentially important sources of novel genomic material(2,3) and are known to account for major genomic differences between humans and chimpanzees.(4) Further, such changes have been implicated in a number of genetic disorders, such as DiGeorge, Angelman/Prader-Willi and Charcot-Marie-Tooth syndromes.(5)
Collapse
Affiliation(s)
- Stephen Wooding
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, 84112, USA
| | | |
Collapse
|
110
|
Abstract
Pharmacogenetics deals with inherited differences in the response to drugs. The best-recognized examples are genetic polymorphisms of drug-metabolizing enzymes, which affect about 30% of all drugs. Loss of function of thiopurine S-methyltransferase (TPMT) results in severe and life-threatening hematopoietic toxicity if patients receive standard doses of mercaptopurine and azathioprine. Gene duplication of cytochrome P4502D6 (CYP2D6), which metabolizes many antidepressants, has been identified as a mechanism of poor response in the treatment of depression. There is also a growing list of genetic polymorphisms in drug targets that have been shown to influence drug response. A major limitation that has heretofore moderated the use of pharmacogenetic testing in the clinical setting is the lack of prospective clinical trials demonstrating that such testing can improve the benefit/risk ratio of drug therapy.
Collapse
Affiliation(s)
- Michel Eichelbaum
- Dr. Margarete Fischer-Bosch-Institute of Clinical Pharmacology, Auerbachstr. 112, D-70376 Stuttgart, Germany.
| | | | | |
Collapse
|
111
|
Camilleri M, Bueno L, de Ponti F, Fioramonti J, Lydiard RB, Tack J. Pharmacological and pharmacokinetic aspects of functional gastrointestinal disorders. Gastroenterology 2006; 130:1421-34. [PMID: 16678556 DOI: 10.1053/j.gastro.2005.08.062] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2005] [Accepted: 08/05/2005] [Indexed: 02/06/2023]
Abstract
Medications are commonly used for the treatment of patients with functional gastrointestinal disorders. The general goal of this report is to review the pharmacokinetics and pharmacology of medications used in functional gastrointestinal disorders. Methods included literature review, consensus evaluation of the evidence for each topic assigned originally to 1 or 2 authors, and broader review at a harmonization session as part of the Rome III process. This report reviews the animal models that have been validated for the study of effects of pharmacologic agents on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of novel therapeutic agents; the biomarkers validated for studies of sensation and motility end points with experimental medications in humans; the pharmacogenomics applied to these medications and disorders; and the pharmacology of agents that are applied or have potential for treatment of functional gastrointestinal disorders, including psychopharmacologic agents. Clinician and basic investigators involved in the treatment or investigation of functional gastrointestinal disorders or disease models need to have a comprehensive understanding of a vast range of medications. It is anticipated that the interaction between investigators of basic science, basic and applied pharmacology, and clinical trials will lead to better treatment of these disorders.
Collapse
|
112
|
Oselin K, Anier K, Tamm R, Kallassalu K, Mäeorg U. Determination of thiopurine S-methyltransferase (TPMT) activity by comparing various normalization factors: Reference values for Estonian population using HPLC-UV assay. J Chromatogr B Analyt Technol Biomed Life Sci 2006; 834:77-83. [PMID: 16517227 DOI: 10.1016/j.jchromb.2006.02.031] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Revised: 02/10/2006] [Accepted: 02/17/2006] [Indexed: 10/24/2022]
Abstract
Thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) is the key enzyme in the metabolism of thiopurine drugs. Determination of TPMT activity has been used for the individualization of thiopurine dose. We developed HPLC-UV assay for the determination of TPMT activity in human erythrocytes using 6-mercaptopurine as a substrate. Various extraction and chromatographic conditions were compared. In-house developed extraction with acetonitrile provided the lowest limit of quantification. TPMT activity was determined in 99 previously genotyped healthy Estonians. TPMT activity was expressed as the formation of 6-methylmercaptopurine ng/ml/h and normalized either to haemoglobin, haematocrit, erythrocyte count or protein content. The receiver-operating characteristic curve analysis revealed similar accuracy values for TPMT activity in predicting heterozygous and wild type individuals for each method of calculation. In healthy Estonians, TPMT activity varied from 21.5 to 129.6 ng/ml/h. For heterozygous individuals (n = 18), TPMT activity was 48.1 +/- 11.7 ng/ml/h. Wild type individuals (n = 81) revealed significantly higher TPMT activity 79.3 +/- 20.7 ng/ml/h (P < 0.001). This sensitive HPLC assay for quantitative determination of TPMT activity could easily be used in clinical settings. Under constant experimental conditions for haemolysate preparation no normalization is required.
Collapse
Affiliation(s)
- Kersti Oselin
- Department of Pharmacology, Tartu University, 51014 Tartu, Estonia.
| | | | | | | | | |
Collapse
|
113
|
Sabbagh A, Darlu P. Data-Mining Methods as Useful Tools for Predicting Individual Drug Response: Application to CYP2D6 Data. Hum Hered 2006; 62:119-34. [PMID: 17057402 DOI: 10.1159/000096416] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Accepted: 08/22/2006] [Indexed: 11/19/2022] Open
Abstract
OBJECTIVES Selecting a maximally informative subset of polymorphisms to predict a clinical outcome, such as drug response, requires appropriate search methods due to the increased dimensionality associated with looking at multiple genotypes. In this study, we investigated the ability of several pattern recognition methods to identify the most informative markers in the CYP2D6 gene for the prediction of CYP2D6 metabolizer status. METHODS Four data-mining tools were explored: decision trees, random forests, artificial neural networks, and the multifactor dimensionality reduction (MDR) method. Marker selection was performed separately in eight population samples of different ethnic origin to evaluate to what extent the most informative markers differ across ethnic groups. RESULTS Our results show that the number of polymorphisms required to predict CYP2D6 metabolic phenotype with a high accuracy can be dramatically reduced owing to the strong haplotype block structure observed at CYP2D6. MDR and neural networks provided nearly identical results and performed the best. CONCLUSION Data-mining methods, such as MDR and neural networks, appear as promising tools to improve the efficiency of genotyping tests in pharmacogenetics with the ultimate goal of pre-screening patients for individual therapy selection with minimum genotyping effort.
Collapse
Affiliation(s)
- Audrey Sabbagh
- Unité de Recherche en Génétique Epidémiologique et Structure des Populations Humaines, INSERM U535, Villejuif, France.
| | | |
Collapse
|
114
|
Jaquenoud Sirot E, van der Velden JW, Rentsch K, Eap CB, Baumann P. Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance. Drug Saf 2006; 29:735-68. [PMID: 16944962 DOI: 10.2165/00002018-200629090-00001] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.
Collapse
|
115
|
Abstract
While antidepressant pharmacotherapy is an effective treatment of depression, it still is hampered by a delayed time of onset of clinical improvement and a series of side effects. Moreover, a substantial group of patients has only limited response or fails to respond at all. One source accounting for these variations are genetic differences as currently analysed by single nucleotide polymorphisms (SNP) mapping. In recent years a number of pharmacogenetic studies on antidepressant drugs have been published. So far they mostly focused on metabolizing enzymes of the cytochrome P450 (CYP) families and genes within the monoaminergic system with compelling evidence for an effect of CYP2D6 polymorphisms on antidepressant drug plasma levels and of a serotonin transporter promoter polymorphism on clinical response to a specific class of antidepressants, the selective serotonin reuptake inhibitors. It is clear, however, that other candidate systems have to be considered in the pharmacogenetics of antidepressant drugs, such as neuropeptidergic systems, the hypothalamus-pituitary adrenal (HPA) axis and neurotrophic systems. There is recent evidence that polymorphisms in genes regulating the HPA axis have an important impact on response to antidepressants. These studies mark the beginning of an emerging standard SNP profiling system that ultimately allows identifying the right drug for the right patient at the right time.
Collapse
|
116
|
Gardiner SJ, Begg EJ. Pharmacogenetic testing for drug metabolizing enzymes: is it happening in practice? Pharmacogenet Genomics 2005; 15:365-9. [PMID: 15864139 DOI: 10.1097/01213011-200505000-00013] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
It is widely claimed that pharmacogenetics may form the basis of 'personalized medicine'. We sought to determine the current utilization of pharmacogenetic testing for drug metabolizing enzymes (DMEs). The hypothesis was that these tests were rarely performed clinically. Questionnaires were sent to 629 individuals representing laboratories, hospitals and universities throughout Australia and New Zealand. The questionnaires asked which facilities performed pharmacogenetic tests for selected DMEs, and details about the tests, if performed. The overall response rate was 81.1% (510/629); three respondents declined to participate. Clinical genotyping and phenotyping tests for DMEs could be performed by 10 (2.0% of 507) and 18 (3.6%) facilities, respectively. The most frequently performed genetic tests were for thiopurine methyltransferase (approximately 400 times in 2003) and pseudocholinesterase (approximately 250 times). The frequency of phenotyping exceeded genotyping by five- and eight-fold, respectively. One centre performed CYP2D6 phenotyping frequently (approximately 4200 times in 2003) for perhexiline. Genotyping and phenotyping tests for other cytochrome P450 enzymes, N-acetyltransferase-2 and dihydropyrimidine dehydrogenase were effectively never undertaken for clinical purposes. Pharmacogenetic tests for DMEs are currently performed rarely in clinical practice, despite repeated claims that they may benefit patient care. The only tests performed with any regularity in Australasia are for thiopurine methyltransferase and pseudocholinesterase, and CYP2D6 phenotyping in one centre for patients on perhexiline. The low clinical utilization reflects a poor evidence base, unestablished clinical relevance and, in the few cases with the strongest rationale, a slow translation to the clinical setting.
Collapse
Affiliation(s)
- Sharon J Gardiner
- Department of Medicine, Christchurch School of Medicine and Health Sciences, Christchurch, New Zealand.
| | | |
Collapse
|
117
|
Abstract
The goal of personalized medicine is to maximize the likelihood of therapeutic efficacy and to minimize the risk of drug toxicity for an individual patient. One of the major contributors to this concept is pharmacogenomics. Marked interindividual genetic variation contributes significantly to both susceptibility to diseases, and response to drugs. Even though pharmacogenomics is not a new science, the translation of pharmacogenomics into clinical practice (i.e., personalized medicine) has not taken place at the same pace as science is delivering new results. It is felt that a large number of recent pharmacogenomic findings allow bold steps to be taken toward personalized medicine. This review collates a variety of examples that have great potential for immediate and effective introduction into clinical practice. In addition, other exploratory examples with a particular focus on drug safety and targeted cancer therapy are summarized.
Collapse
Affiliation(s)
- Hong-Guang Xie
- Vanderbilt University School of Medicine, Division of Clinical Pharmacology, Departments of Medicine and Pharmacology, Nashville, TN 37232-6602, USA. .,US Food & Drug Administration, Center for Drug Evaluation and Research, Office of Clinical Pharmacology and Biopharmaceutics, 1451 Rockville Pike, HFD-860, Room 2040, Rockville, MD 20852, USA
| | - Felix W Frueh
- Vanderbilt University School of Medicine, Division of Clinical Pharmacology, Departments of Medicine and Pharmacology, Nashville, TN 37232-6602, USA. .,US Food & Drug Administration, Center for Drug Evaluation and Research, Office of Clinical Pharmacology and Biopharmaceutics, 1451 Rockville Pike, HFD-860, Room 2040, Rockville, MD 20852, USA
| |
Collapse
|
118
|
Samer CF, Piguet V, Dayer P, Desmeules JA. Polymorphisme génétique et interactions médicamenteuses : leur importance dans le traitement de la douleur. Can J Anaesth 2005; 52:806-21. [PMID: 16189332 DOI: 10.1007/bf03021775] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
OBJECTIVES To evaluate the impact of certain genetic polymorphisms on variable responses to analgesics SOURCES Systematic review, by means of a structured computerized search in the Medline database (1966-2004). Articles in English and French were selected. References in relevant articles were also retrieved. MAIN FINDINGS Most analgesics are metabolized by CYP isoenzymes subject to genetic polymorphism. NSAIDs are metabolized by CYP2C9; opioids described as "weak" (codeine, tramadol), anti-depressants and dextromethorphan are metabolized by CYP2D6 and some "potent" opioids (buprenorphine, methadone or fentanyl) by CYP3A4/5. After the usual doses have been administered, drug toxicity or, on the contrary, therapeutic ineffectiveness may occur, depending on polymorphism and the substance. Drug interactions mimicking genetic defects because of the existence of CYP inhibitors and inducers, also contribute to the variable response to analgesics. Some opioids are substrates of P-gp, a transmembrane transporter also subject to genetic polymorphism. However, P-gp could only play a minor modulating role in man on the central effects of morphine, methadone and fentanyl. CONCLUSION In the near future, pharmacogenetics should enable us to optimize therapeutics by individualizing our approach to analgesic drugs and making numerous analgesics safer and more effective. The clinical usefulness of these individualized approaches will have to be demonstrated by appropriate pharmacoeconomic studies and analyses.
Collapse
Affiliation(s)
- Caroline F Samer
- Service de pharmacologie et toxicologie cliniques et Centre multidisciplinaire d'étude et de traitement de la douleur, Hôpitaux Universitaires de Genève, Genève, Suisse.
| | | | | | | |
Collapse
|
119
|
Shah RR. Pharmacogenetics in drug regulation: promise, potential and pitfalls. Philos Trans R Soc Lond B Biol Sci 2005; 360:1617-38. [PMID: 16096112 PMCID: PMC1569525 DOI: 10.1098/rstb.2005.1693] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Pharmacogenetic factors operate at pharmacokinetic as well as pharmacodynamic levels-the two components of the dose-response curve of a drug. Polymorphisms in drug metabolizing enzymes, transporters and/or pharmacological targets of drugs may profoundly influence the dose-response relationship between individuals. For some drugs, although retrospective data from case studies suggests that these polymorphisms are frequently associated with adverse drug reactions or failure of efficacy, the clinical utility of such data remains unproven. There is, therefore, an urgent need for prospective data to determine whether pre-treatment genotyping can improve therapy. Various regulatory guidelines already recommend exploration of the role of genetic factors when investigating a drug for its pharmacokinetics, pharmacodynamics, dose-response relationship and drug interaction potential. Arising from the global heterogeneity in the frequency of variant alleles, regulatory guidelines also require the sponsors to provide additional information, usually pharmacogenetic bridging data, to determine whether data from one ethnic population can be extrapolated to another. At present, sponsors explore pharmacogenetic influences in early clinical pharmacokinetic studies but rarely do they carry the findings forward when designing dose-response studies or pivotal studies. When appropriate, regulatory authorities include genotype-specific recommendations in the prescribing information. Sometimes, this may include the need to adjust a dose in some genotypes under specific circumstances. Detailed references to pharmacogenetics in prescribing information and pharmacogenetically based prescribing in routine therapeutics will require robust prospective data from well-designed studies. With greater integration of pharmacogenetics in drug development, regulatory authorities expect to receive more detailed genetic data. This is likely to complicate the drug evaluation process as well as result in complex prescribing information. Genotype-specific dosing regimens will have to be more precise and marketing strategies more prudent. However, not all variations in drug responses are related to pharmacogenetic polymorphisms. Drug response can be modulated by a number of non-genetic factors, especially co-medications and presence of concurrent diseases. Inappropriate prescribing frequently compounds the complexity introduced by these two important non-genetic factors. Unless prescribers adhere to the prescribing information, much of the benefits of pharmacogenetics will be squandered. Discovering highly predictive genotype-phenotype associations during drug development and demonstrating their clinical validity and utility in well-designed prospective clinical trials will no doubt better define the role of pharmacogenetics in future clinical practice. In the meantime, prescribing should comply with the information provided while pharmacogenetic research is deservedly supported by all concerned but without unrealistic expectations.
Collapse
|
120
|
van der Weide J, van Baalen-Benedek EH, Kootstra-Ros JE. Metabolic Ratios of Psychotropics as Indication of Cytochrome P450 2D6/2C19 Genotype. Ther Drug Monit 2005; 27:478-83. [PMID: 16044105 DOI: 10.1097/01.ftd.0000162868.84596.c3] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The cytochrome P450 enzymes (CYP) 2C19 and 2D6 are involved in the metabolism of many psychotropic drugs. Variability in enzyme activity results in variable metabolic capacities, affecting the metabolism of substrates. The metabolic ratio (MR) of drugs metabolized via these enzymes may therefore reflect the enzyme's activity and/or genotype. To serve as an example for different groups of medications, the selective serotonin reuptake inhibitor venlafaxine, the tricyclic antidepressant amitriptyline, and the antipsychotic risperidone were studied to examine a possible correlation between the MRs of these drugs and the CYP2C19 and/or CYP2D6 genotype. For this purpose data from routine genotyping and serum level analysis were used. The relationships between the observed metabolic ratios and CYP2D6 and/or CYP2C19 genotype were characterized using nonparametric statistical analysis. A clear correlation was observed between the CYP2D6 genotype and the metabolic ratio of venlafaxine. Genotyping of individuals with a log(MR) < -0.6 or a log(MR) > 0.2 would include all patients with an aberrant genotype but would result in a reduction of 52% of genotyping reactions. Slow metabolism of amitriptyline is correlated with a log(MR) > 0.4. Genotyping only those subjects with a log(MR) > 0.4 would result in 88% fewer genotyping reactions. For risperidone, genotyping individuals with a log(MR) > 0.4 would include all CYP2D6 poor metabolizers while reducing the number of genotyping reactions by 93%. According to these data, correlations exist between the log(MR) of venlafaxine, amitriptyline, and risperidone and the genotype of the CYP enzymes involved in their metabolism. From the ranges of log(MR) defined here, a high percentage of aberrant metabolizers can be detected even when patients are not routinely genotyped. Thus, the metabolic ratio may serve as an indication of when genotyping should be considered.
Collapse
Affiliation(s)
- Jan van der Weide
- Department of Clinical Chemistry, St Jansdal Hospital, Harderwijk, The Netherlands.
| | | | | |
Collapse
|
121
|
Sharp AJ, Locke DP, McGrath SD, Cheng Z, Bailey JA, Vallente RU, Pertz LM, Clark RA, Schwartz S, Segraves R, Oseroff VV, Albertson DG, Pinkel D, Eichler EE. Segmental duplications and copy-number variation in the human genome. Am J Hum Genet 2005; 77:78-88. [PMID: 15918152 PMCID: PMC1226196 DOI: 10.1086/431652] [Citation(s) in RCA: 682] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2005] [Accepted: 05/04/2005] [Indexed: 01/15/2023] Open
Abstract
The human genome contains numerous blocks of highly homologous duplicated sequence. This higher-order architecture provides a substrate for recombination and recurrent chromosomal rearrangement associated with genomic disease. However, an assessment of the role of segmental duplications in normal variation has not yet been made. On the basis of the duplication architecture of the human genome, we defined a set of 130 potential rearrangement hotspots and constructed a targeted bacterial artificial chromosome (BAC) microarray (with 2,194 BACs) to assess copy-number variation in these regions by array comparative genomic hybridization. Using our segmental duplication BAC microarray, we screened a panel of 47 normal individuals, who represented populations from four continents, and we identified 119 regions of copy-number polymorphism (CNP), 73 of which were previously unreported. We observed an equal frequency of duplications and deletions, as well as a 4-fold enrichment of CNPs within hotspot regions, compared with control BACs (P < .000001), which suggests that segmental duplications are a major catalyst of large-scale variation in the human genome. Importantly, segmental duplications themselves were also significantly enriched >4-fold within regions of CNP. Almost without exception, CNPs were not confined to a single population, suggesting that these either are recurrent events, having occurred independently in multiple founders, or were present in early human populations. Our study demonstrates that segmental duplications define hotspots of chromosomal rearrangement, likely acting as mediators of normal variation as well as genomic disease, and it suggests that the consideration of genomic architecture can significantly improve the ascertainment of large-scale rearrangements. Our specialized segmental duplication BAC microarray and associated database of structural polymorphisms will provide an important resource for the future characterization of human genomic disorders.
Collapse
Affiliation(s)
- Andrew J Sharp
- Department of Genome Sciences, University of Washington School of Medicine, Seattle, WA 98195, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
122
|
Asanuma Y, Xie HG, Stein CM. Pharmacogenetics and rheumatology: Molecular mechanisms contributing to variability in drug response. ACTA ACUST UNITED AC 2005; 52:1349-59. [PMID: 15880820 DOI: 10.1002/art.21027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Yu Asanuma
- Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | | | | |
Collapse
|
123
|
Dorne JLCM, Renwick AG. The refinement of uncertainty/safety factors in risk assessment by the incorporation of data on toxicokinetic variability in humans. Toxicol Sci 2005; 86:20-6. [PMID: 15800035 DOI: 10.1093/toxsci/kfi160] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The derivation of safe levels of exposure in humans for compounds that are assumed to cause threshold toxicity has relied on the application of a 100-fold uncertainty factor to a measure for the threshold, such as the no observed adverse effect level (NOAEL) or the benchmark dose (BMD). This 100-fold safety factor consists of the product of two 10-fold factors allowing for human variability and interspecies differences. The International Programme on Chemical Safety has suggested the subdivision of these 10-fold factors to allow for variability in toxicokinetics and toxicodynamics. This subdivision allows the replacement of the default uncertainty factors with a chemical-specific adjustment factor (CSAF) when suitable data are available. This short review describes potential options to refine safety factors used in risk assessment, with particular emphasis on pathway-related uncertainty factors associated with variability in kinetics. These pathway-related factors were derived from a database that quantified interspecies differences and human variability in phase I metabolism, phase II metabolism, and renal excretion. This approach allows metabolism and pharmacokinetic data in healthy adults and subgroups of the population to be incorporated in the risk-assessment process and constitutes an intermediate approach between simple default factors and chemical-specific adjustment factors.
Collapse
Affiliation(s)
- J L C M Dorne
- Division of Developmental Origins of Health and Disease, Institute of Human Nutrition, Clinical Pharmacology Group, School of Medicine, University of Southampton, Bassett Crescent East, Southampton, UK.
| | | |
Collapse
|
124
|
Söderbäck E, Zackrisson AL, Lindblom B, Alderborn A. Determination of CYP2D6 Gene Copy Number by Pyrosequencing. Clin Chem 2005; 51:522-31. [PMID: 15650034 DOI: 10.1373/clinchem.2004.043182] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Abstract
Background: Identification of CYP2D6 alleles *5 (deletion of the whole CYP2D6 gene) and *2xN (gene duplication) is very important because they are associated with decreased or increased metabolism of many drugs. The most commonly used method for analysis of these alleles is, however, considered to be laborious and unreliable.
Methods: We developed a method to determine the copy number of the CYP2D6*5 and CYP2D6*2xN alleles by use of Pyrosequencing™ technology. A single set of PCR and sequencing primers was used to coamplify and sequence a region in the CYP2D6 gene and the equivalent region in the CYP2D8P pseudogene, and relative quantification between these fragments was performed. The CYP2D8P-specific Pyrosequencing peak heights were used as references for the CYP2D6-specific peak heights.
Results: Analysis of 200 pregenotyped samples showed that this approach reliably resolved 0–4 genome copies of the CYP2D6 gene. In 15 of these samples, the peak pattern from one analyzed position was unexpected but could be solved by conclusive results from a second position. The method was verified on 270 other samples, of which 267 gave results that corresponded to the expected genotype. One of the samples could not be interpreted. The reproducibility of the method was high.
Conclusions: CYP2D6 gene copy determination by Pyrosequencing is a reliable and rapid alternative to other methods. The use of an internal CYP2D8P control as well as generation of a sequence context ensures a robust method and hence facilitates method validation.
Collapse
|
125
|
Dorne JLCM, Walton K, Renwick AG. Human variability in xenobiotic metabolism and pathway-related uncertainty factors for chemical risk assessment: a review. Food Chem Toxicol 2005; 43:203-16. [PMID: 15621332 DOI: 10.1016/j.fct.2004.05.011] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2004] [Accepted: 05/21/2004] [Indexed: 11/24/2022]
Abstract
This review provides an account of recent developments arising from a database that defined human variability in phase I metabolism (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, hydrolysis, alcohol dehydrogenase), phase II metabolism (N-acetyltransferases, glucuronidation, glycine conjugation, sulphation) and renal excretion. This database was used to derive pathway-related uncertainty factors for chemical risk assessment that allow for human variability in toxicokinetics. Probe substrates for each pathway of elimination were selected on the basis that oral absorption was >95% and that the metabolic route was the primary route of elimination of the compound (60-100% of a dose). Intravenous data were used for compounds for which absorption was variable. Human variability in kinetics was quantified for each compound from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups of the population using parameters relating to chronic exposure (metabolic and total clearances, area under the plasma concentration-time curve (AUC)) and acute exposure (Cmax) (data not presented here). The pathway-related uncertainty factors were calculated to cover 95%, 97.5% and 99% of the population of healthy adults and of each subgroup. Pathway-related uncertainty factors allow metabolism data to be incorporated into the derivation of health-based guidance values. They constitute an intermediate approach between the general kinetic default factors (3.16) and a chemical-specific adjustment factor. Applications of pathway-related uncertainty factors for chemical risk assessment and future refinements of the approach are discussed. A knowledge-based framework to predict human variability in kinetics for xenobiotics showing a threshold dose below which toxic effects are not observed, is proposed to move away from default assumptions.
Collapse
Affiliation(s)
- J L C M Dorne
- Clinical Pharmacology Group, School of Medicine, University of Southampton, Biomedical Sciences Building, Bassett Crescent East, Southampton SO16 7PX, UK.
| | | | | |
Collapse
|
126
|
Steimer W, Zöpf K, von Amelunxen S, Pfeiffer H, Bachofer J, Popp J, Messner B, Kissling W, Leucht S. Amitriptyline or Not, That Is the Question: Pharmacogenetic Testing of CYP2D6 and CYP2C19 Identifies Patients with Low or High Risk for Side Effects in Amitriptyline Therapy. Clin Chem 2005; 51:376-85. [PMID: 15590749 DOI: 10.1373/clinchem.2004.041327] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractBackground: Amitriptyline has been replaced in many countries by alternative and more expensive drugs based on claims of improved tolerability and toxicity and despite slightly reduced efficacy. Preliminary studies indicate that adverse effects could be linked to polymorphisms of drug-metabolizing enzymes, but information on their clinical impact remains scanty and includes mainly case reports. We conducted a prospective blinded two-center study seeking correlations between CYP2C19 and CYP2D6 genotypes, drug concentrations, adverse events, and therapy response.Methods: Fifty Caucasian inpatients with at least medium-grade depressive disorder received amitriptyline at a fixed dose of 75 mg twice a day. Blood samples for concentration monitoring of amitriptyline and nortriptyline were taken weekly until discharge along with evaluations of depression (Hamilton Depression Scale and Clinical Global Impression Scale) and side effect (Dosage Record and Treatment Emergent Symptoms Scale; DOTES) scores.Results: In a ROC analysis, nortriptyline but not amitriptyline concentrations correlated with side effects (DOTES sum score ≥5; area under the curve, 0.733; P = 0.008). Carriers of two functional CYP2D6 alleles had a significantly lower risk of side effects than carriers of only one functional allele (12.1% vs 76.5%; P = 0.00001). The lowest risk was observed for carriers of two functional CYP2D6 alleles combined with only one functional CYP2C19 allele [0 of 13 (0%) vs 9 of 11 (81.8%) for the high-risk group; P = 0.00004]. We found no correlations between drug concentrations or genotypes and therapeutic response.Conclusions: Combined pharmacogenetic testing for CYP2D6 and CYP2C19 identifies patients with low risk for side effects in amitriptyline therapy and could possibly be used to individualize antidepressive regimens and reduce treatment cost. Identification of genotypes associated with slightly reduced intermediate metabolism may be more important than currently anticipated. It could also be the key to demonstrating cost-effectiveness for CYP2D6 genotyping in critical dose drugs.
Collapse
Affiliation(s)
- Werner Steimer
- Institut für Klinische Chemie und Pathobiochemie, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
| | | | | | | | | | | | | | | | | |
Collapse
|
127
|
Kim K, Johnson JA, Derendorf H. Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms. J Clin Pharmacol 2005; 44:1083-105. [PMID: 15342610 DOI: 10.1177/0091270004268128] [Citation(s) in RCA: 156] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.
Collapse
Affiliation(s)
- Kiman Kim
- Department of Pharmaceutics, University of Florida, Gainesville, FL 32610, USA
| | | | | |
Collapse
|
128
|
Abstract
Drug-drug interactions continue to be underappreciated and misunderstood by most clinicians. Although life-threatening drug interactions are rare, serious clinical consequences, including altered drug response, poor tolerability with reduced medication adherence, and increased costs for care tied to the increased complexity of therapy, are fairly commonplace. Drug interactions may be further complicated by genetic differences in metabolic capacity. Patients who routinely require long-term treatment for depression have an increased likelihood of experiencing a drug-drug interaction since they will take over-the-counter and prescription medications for intercurrent and/or co-morbid illness. Antidepressants can be the object of drug interactions when their metabolic pathways are affected by other substances, or they can precipitate interactions by inhibiting enzyme pathways. Clinicians can improve the short- and long-term outcomes of patients with a depressive disorder by considering the possibility of drug-drug interactions both before prescribing a specific antidepressant and while monitoring for response, adverse effects and patient compliance.
Collapse
Affiliation(s)
- Larry Ereshefsky
- University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
| | | | | |
Collapse
|
129
|
Bhasi K, Zhang L, Zhang A, Ramanathan M. Analysis of pharmacokinetics, pharmacodynamics, and pharmacogenomics data sets using VizStruct, a novel multidimensional visualization technique. Pharm Res 2004; 21:777-80. [PMID: 15180333 PMCID: PMC2607483 DOI: 10.1023/b:pham.0000026427.30177.61] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE Data visualization techniques for the pharmaceutical sciences have not been extensively investigated. The purpose of this study was to evaluate the usefulness of VizStruct, a multidimensional visualization tool, for applications in pharmacokinetics, pharmacodynamics, and pharmacogenomics. METHODS The VizStruct tool uses the first harmonic of the discrete Fourier transform to map multidimensional data to two dimensions for visualization. The mapping was used to visualize several published pharmacokinetic, pharmacodynamic, and pharmacogenomic data sets. The VizStruct approach was evaluated using simulated population pharmacokinetics data sets, the data from Dalen and colleagues (Clin. PharmacoL Ther. 63:444-452, 1998) on the kinetics of nortriptyline and its 10-hydroxynortriptyline metabolite in subjects with differing number of copies of the CYP2D6, and the gene expression profiling data of Bohen and colleagues (Proc. Natl. Acad. Sci. USA 100:1926-1930, 2003) on follicular lymphoma patients responsive and nonresponsive to rituximab. RESULTS The VizStruct mapping preserves the key characteristics of multidimensional data in two dimensions in a manner that facilitates visualization. The mapping is computationally efficient and can be used for cluster detection and class prediction in pharmaceutical data sets. The VizStruct visualization succinctly summarized the salient similarities and differences in the nortriptyline and 10-hydroxynortriptyline pharmacokinetic profiles in subjects with increasing number of CYP2D6 gene copies. In the simulated population pharmacokinetic data sets, it was capable of discriminating the subtle differences between pharmacokinetic profiles derived from 1- and 2-compartment models with the same area under the curve. The two-dimensional VizStruct mapping computed from a subset of 102 informative genes from the Bohen and colleagues data set effectively separated the rituximab responder, rituximab nonresponder, and control subject groups. CONCLUSIONS The VizStruct approach is a computationally efficient and effective approach for visualizing complex, multidimensional data sets. It could have many useful applications in the pharmaceutical sciences.
Collapse
Affiliation(s)
- Kavitha Bhasi
- Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, New York 14260, USA
| | - Li Zhang
- Department of Computer Science, State University of New York at Buffalo, Buffalo, New York 14260, USA
| | - Aidong Zhang
- Department of Computer Science, State University of New York at Buffalo, Buffalo, New York 14260, USA
| | - Murali Ramanathan
- Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, New York 14260, USA
- To whom correspondence should be addressed. (e-mail )
| |
Collapse
|
130
|
Dorne JLCM. Impact of inter-individual differences in drug metabolism and pharmacokinetics on safety evaluation. Fundam Clin Pharmacol 2004; 18:609-20. [PMID: 15548231 DOI: 10.1111/j.1472-8206.2004.00292.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Safety evaluation aims to assess the dose-response relationship to determine a dose/level of exposure for food contaminants below which no deleterious effect is measurable that is 'without appreciable health risk' when consumed daily over a lifetime. These safe levels, such as the acceptable daily intake (ADI) have been derived from animal studies using surrogates for the threshold such as the no-observed-adverse-effect-level (NOAEL). The extrapolation from the NOAEL to the human safe intake uses a 100-fold uncertainty factor, defined as the product of two 10-fold factors allowing for human variability and interspecies differences. The 10-fold factor for human variability has been further subdivided into two factors of 10(0.5) (3.16) to cover toxicokinetics and toxicodynamics and this subdivsion allows for the replacement of an uncertainty factor with a chemical-specific adjustment factor (CSAF) when compound-specific data are available. Recently, an analysis of human variability in pharmacokinetics for phase I metabolism (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, hydrolysis, alcohol dehydrogenase), phase II metabolism (N-acetyltransferase, glucuronidation, glycine conjugation, sulphation) and renal excretion was used to derive pathway-related uncertainty factors in subgroups of the human population (healthy adults, effects of ethnicity and age). Overall, the pathway-related uncertainty factors (99th centile) were above the toxicokinetic uncertainty factor for healthy adults exposed to xenobiotics handled by polymorphic metabolic pathways (and assuming the parent compound was the proximate toxicant) such as CYP2D6 poor metabolizers (26), CYP2C19 poor metabolizers (52) and NAT-2 slow acetylators (5.2). Neonates were the most susceptible subgroup of the population for pathways with available data [CYP1A2 and glucuronidation (12), CYP3A4 (14), glycine conjugation (28)]. Data for polymorphic pathways were not available in neonates but uncertainty factors of up to 45 and 9 would allow for the variability observed in children for CYP2D6 and CYP2C19 metabolism, respectively. This review presents an overview on the history of uncertainty factors, the main conclusions drawn from the analysis of inter-individual differences in metabolism and pharmacokinetics, the development of pathway-related uncertainty factors and their use in chemical risk assessment.
Collapse
Affiliation(s)
- J L C M Dorne
- Clinical Pharmacology Group, University of Southampton, Biomedical Sciences Building, Bassett Crescent East, Southampton, SO16 7PX, UK.
| |
Collapse
|
131
|
Gardiner SJ, Begg EJ. Genotyping for drug-metabolizing enzymes – does the promise meet the reality? Pharmacogenomics 2004; 5:1033-6. [PMID: 15584874 DOI: 10.1517/14622416.5.8.1033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Affiliation(s)
- Sharon J Gardiner
- Department of Medicine, Christchurch School of Medicine, Private Bag 4345, Christchurch, New Zealand.
| | | |
Collapse
|
132
|
Breyer-Pfaff U. The Metabolic Fate of Amitriptyline, Nortriptyline and Amitriptylinoxide in Man. Drug Metab Rev 2004; 36:723-46. [PMID: 15554244 DOI: 10.1081/dmr-200033482] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Amitriptyline (AT), the most widely used tricyclic antidepressant, undergoes oxidative metabolism in the side chain with production of the secondary amine nortriptyline (NT), a primary amine, and the N-oxide amitriptylinoxide (AT-NO); in addition, direct conjugation leads to a quaternary ammonium-linked glucuronide. Hydroxylation of AT or NT at the ethylene bridge of the central seven-membered ring results in four isomeric alcohols and occurs with high stereo- and enantioselectivity, the (-)-(E)-10-hydroxy compounds usually being the major products. The disposition of the alcohols is also partially enantioselective, for instance with regard to glucuronidation and reversible oxidation to ketones. Introduction of a second hydroxy group results in isomeric glycols. Oxidative attack at an aromatic ring is a minor pathway leading to dihydrodiols and phenols. Numerous metabolites originate by combinations of reactions in the ring system and the side chain. AT-NO is by about one-third excreted in unchanged form or as 10-hydroxy derivative; the major part is reduced to AT and metabolized further. The review covers current knowledge on the enzymes participating in the individual pathways. Their quantitative importance is inferred from kinetic studies in volunteers and patients and from experiments in vitro. Clinical consequences of biochemical findings mainly derive from the impact of the polymorphic CYP2D6 mediating (-)-(E)-10-hydroxylation and from its potential inhibition by other psychoactive drugs.
Collapse
Affiliation(s)
- Ursula Breyer-Pfaff
- Department of Pharmacology and Toxicology, University of Tübingen, Tübingen, Germany
| |
Collapse
|
133
|
Lee SY, Ki CS, Hong KS, Kim JW. A case report of a poor metabolizer of CYP2D6 presented with unusual responses to nortriptyline medication. J Korean Med Sci 2004; 19:750-2. [PMID: 15483356 PMCID: PMC2816343 DOI: 10.3346/jkms.2004.19.5.750] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We present a case with decreased metabolic activity of CYP2D6, a cytochrome P450 enzyme catalyzing the metabolism of nortriptyline (NT). Conventional dosage regimen led to toxic plasma concentration of NT and adverse effects such as dry mouth, constipation, and dizziness in this case with genotype CYP2D6*5/*10B. This case suggests the clinical usefulness of pharmacogenetic testing in individualized dosage adjustments of NT.
Collapse
Affiliation(s)
- Soo-Youn Lee
- Department of Laboratory Medicine, Sungkyunkwan University School of Medicine Samsung Medical Center, Seoul, Korea
| | | | | | | |
Collapse
|
134
|
Ng CH, Schweitzer I, Norman T, Easteal S. The emerging role of pharmacogenetics: implications for clinical psychiatry. Aust N Z J Psychiatry 2004; 38:483-9. [PMID: 15255819 DOI: 10.1080/j.1440-1614.2004.01400.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
OBJECTIVE This article aims to review the implications of pharmacogenetics for clinical psychiatry; these are discussed in the context of environmental and sociocultural factors. METHOD A selective literature review was conducted using Medline search and other relevant references available to the authors. RESULTS The individual differences in therapeutic and adverse effects of psychotropic drugs are largely determined by genetic factors. Recent advances in pharmacogenetics have highlighted the potential utility in predicting metabolic phenotypes, risks for side-effects and likelihood of drug response for the individual patient. CONCLUSIONS Genotyping, especially for drug metabolizing enzymes, could enable more rational, cost-effective and optimal prescribing in future psychopharmacotherapy. Although the advances of pharmacogenetics may have many benefits in clinical practice, the importance of non-genetic factors must also be considered as cultural and environmental factors significantly impinge on response to medications. To clarify the extent pharmacogenetics can be adopted in clinical practice to predict drug response in patients from diverse backgrounds, further studies in different ethnic groups and clinical settings are required.
Collapse
Affiliation(s)
- Chee Hong Ng
- The Melbourne Clinic, Department of Psychiatry, University of Melbourne, Victoria, Australia.
| | | | | | | |
Collapse
|
135
|
Shah RR. Pharmacogenetic aspects of drug-induced torsade de pointes: potential tool for improving clinical drug development and prescribing. Drug Saf 2004; 27:145-72. [PMID: 14756578 DOI: 10.2165/00002018-200427030-00001] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Drug-induced torsade de pointes (TdP) has proved to be a significant iatro-genic cause of morbidity and mortality and a major reason for the withdrawal of a number of drugs from the market in recent times. Enzymes that metabolise many of these drugs and the potassium channels that are responsible for cardiac repolarisation display genetic polymorphisms. Anecdotal reports have suggested that in many cases of drug-induced TdP, there may be a concealed genetic defect of either these enzymes or the potassium channels, giving rise to either high plasma drug concentrations or diminished cardiac repolarisation reserve, respectively. The presence of either of these genetic defects may predispose a patient to TdP, a potentially fatal adverse reaction, even at therapeutic dosages of QT-prolonging drugs and in the absence of other risk factors. Advances in pharmacogenetics of drug metabolising enzymes and pharmacological targets, together with the prospects of rapid and inexpensive genotyping procedures, promise to individualise and improve the benefit/risk ratio of therapy with drugs that have the potential to cause TdP. The qualitative and the quantitative contributions of these genetic defects in clinical cases of TdP are unclear because not all of the patients with TdP are routinely genotyped and some relevant genetic mutations still remain to be discovered. There are regulatory guidelines that recommend strategies aimed at uncovering the risk of TdP associated with new chemical entities during their development. There are also a number of guidelines that recommend integrating pharmacogenetics in this process. This paper proposes a strategy for integrating pharmacogenetics into drug development programmes to optimise association studies correlating genetic traits and endpoints of clinical interest, namely failure of efficacy or development of repolarisation abnormalities. Until pharmacogenetics is carefully integrated into all phases of development of QT-prolonging drugs and large-scale studies are undertaken during their post-marketing use to determine the genetic components involved in induction of TdP, routine genotyping of patients remains unrealistic. Even without this pharmacogenetic data, the clinical risk of TdP can already be greatly minimised. Clinically, a substantial proportion of cases of TdP are due to the use of either high or usual dosages of drugs with potential to cause TdP in the presence of factors that inhibit drug metabolism. Therefore, choosing the lowest effective dose and identifying patients with these non-genetic risk factors are important means of minimising the risk of TdP. In view of the common secondary pharmacology shared by these drugs, a standard set of contraindications and warnings have evolved over the last decade. These include factors responsible for pharmacokinetic or pharmacodynamic drug interactions. Among the latter, the more important ones are bradycardia, electrolyte imbalance, cardiac disease and co-administration of two or more QT-prolonging drugs. In principle, if large scale prospective studies can demonstrate a substantial genetic component, pharmacogenetically driven prescribing ought to reduce the risk further. However, any potential benefits of pharmacogenetics will be squandered without any reduction in the clinical risk of TdP if physicians do not follow prescribing and monitoring recommendations.
Collapse
Affiliation(s)
- Rashmi R Shah
- Medicines and Healthcare products Regulatory Agency, London, United Kingdom.
| |
Collapse
|
136
|
Ishiguro A, Kubota T, Ishikawa H, Iga T. Metabolic activity of dextromethorphan O-demethylation in healthy Japanese volunteers carrying duplicated CYP2D6 genes: duplicated allele of CYP2D6*10 does not increase CYP2D6 metabolic activity. Clin Chim Acta 2004; 344:201-4. [PMID: 15149890 DOI: 10.1016/j.cccn.2004.03.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2004] [Revised: 03/02/2004] [Accepted: 03/03/2004] [Indexed: 11/25/2022]
Abstract
BACKGROUND This study was designed to assess the metabolic activities of dextromethorphan O-demethylation in healthy Japanese subjects carrying duplicated CYP2D6 alleles, CYP2D6*1 x 2, CYP2D6*2 x 2 or CYP2D6*10 x 2. METHODS Forty-one unrelated healthy Japanese subjects containing carriers who had previously been genotyped as CYP2D6*1 x 2/*2, CYP2D6*1/*2 x 2, and CYP2D6*10/*10 x 2 were phenotyped with dextromethorphan. RESULTS The metabolic ratios of dextromethorphan/dextrorphan in subjects with CYP2D6*1 x 2/*2 or CYP2D6*1/*2 x 2 were lower than those in subjects with CYP2D6*1/*2, while the metabolic ratios in subjects with CYP2D6*10/*10 x 2, as well as homozygotes for CYP2D6*10, were significantly (P<0.01) higher than those in homozygotes for CYP2D6*1. CONCLUSIONS The results suggested that carriers with three functional CYP2D6 genes, CYP2D6*1 x 2/*2 or CYP2D6*1/*2 x 2, are ultrarapid metabolizer phenotypes in Japanese. The results also suggested that there is no gene-dose effect with the dextromethorphan O-demethylation activities between carriers with two and three CYP2D6*10 mutated genes per genome. Therefore, CYP2D6*10 x 2 may play an important role for the treatment of Japanese patients as well as CYP2D6*10 which is mainly responsible for the intermediate metabolizers in Japanese.
Collapse
Affiliation(s)
- Akihiro Ishiguro
- Department of Pharmacy, Faculty of Medicine, University of Tokyo Hospital, 7-3-1 Hongoh, Bunkyo, Tokyo 113-8655, Japan
| | | | | | | |
Collapse
|
137
|
Ingelman-Sundberg M. Pharmacogenetics of cytochrome P450 and its applications in drug therapy: the past, present and future. Trends Pharmacol Sci 2004; 25:193-200. [PMID: 15063083 DOI: 10.1016/j.tips.2004.02.007] [Citation(s) in RCA: 406] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The field of cytochrome P450 pharmacogenetics has progressed rapidly during the past 25 years. All the major human drug-metabolizing P450 enzymes have been identified and cloned, and the major gene variants that cause inter-individual variability in drug response and are related to adverse drug reactions have been identified. This information now provides the basis for the use of predictive pharmacogenetics to yield drug therapies that are more efficient and safer. Today, we understand which drugs warrant dosing based on pharmacogenetics to improve drug treatment. It is anticipated that, in the future, genotyping could be used to personalize drug treatment for vast numbers of subjects, decreasing the cost of drug treatment and increasing the efficacy of drugs and health in general. I estimate that such personalized P450 gene-based treatment would be relevant for 10-20% of all drug therapy.
Collapse
|
138
|
Kirchheiner J, Nickchen K, Bauer M, Wong ML, Licinio J, Roots I, Brockmöller J. Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response. Mol Psychiatry 2004; 9:442-73. [PMID: 15037866 DOI: 10.1038/sj.mp.4001494] [Citation(s) in RCA: 470] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.
Collapse
Affiliation(s)
- J Kirchheiner
- Institute of Clinical Pharmacology, Campus Charité Mitte, University Medicine Berlin, Berlin, Germany.
| | | | | | | | | | | | | |
Collapse
|
139
|
Eap CB, Jaquenoud Sirot E, Baumann P. Therapeutic Monitoring of Antidepressants in the Era of Pharmacogenetics Studies. Ther Drug Monit 2004; 26:152-5. [PMID: 15228156 DOI: 10.1097/00007691-200404000-00011] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
As for other drugs, there is a large interindividual variability of the plasma concentrations of antidepressants for a given dose. Within the last 2 decades, a very large number of pharmacogenetic studies have made it possible to understand the importance of genetic factors on the disposition of drugs in the organism, many of them at the levels of drug metabolism. Polymorphism of CYP2D6 and of other drug-metabolizing enzymes may thus lead to very large differences in drug exposure between patients and possibly also to toxicity or ineffective drug concentrations in some subjects. In consequence, dose recommendations of antidepressants based on genotypes, justified by the principle of administering bioequivalent individualized drug doses, are now proposed. However, blood (and thus possibly brain) concentrations also depend on other factors than the genetic makeup of the patients. Therapeutic drug monitoring of antidepressants allows us to take into account the influence of factors such as comedications, diet, smoking habit, impaired organ function, and compliance. Therapeutic drug monitoring and genotyping are thus complementary, and their combined use contributes to improve pharmacotherapy with antidepressants and other drugs.
Collapse
Affiliation(s)
- C B Eap
- Unité de Biochimie et Psychopharmacologie Clinique, Centre de Neurosciences Psychiatriques, Département Universitaire de Psychiatrie Adulte, Hôpital de Cery, CH-1008 Prilly-Lausanne, Switzerland.
| | | | | |
Collapse
|
140
|
Abstract
PURPOSE/OBJECTIVES The purpose of this article is to describe how the new genomic era will affect advanced practice registered nurses (APRNs) patient care, education, and research. BACKGROUND/RATIONALE Given the exponential growth of genetic information and that 9 of the top 10 leading causes of mortality have genetic components (www.cdc.gov), it is imperative to educate advanced practice nurses about this salient topic. DESCRIPTION OF THE PROCESS Because few APRNs in practice or academia have had formal education on genetics, the first step of nursings' own gene discovery is recognizing that there is an ongoing need to understand state of the science genetic information to gain clinical and educational utility. OUTCOMES By recognizing APRNs need to know genetics, APRNs will clamor within their workplace for continuing education about this dynamic information. It is critical knowledge for APRNs to classify risk based on family history, target individualized patient prevention and education, modify pharmacologic interventions, and refer when genetic testing is necessary. INTERPRETATION/CONCLUSION This article stresses the timely relevance of applying genetics and genomics to practice, teaching, and research. IMPLICATIONS FOR NURSING PRACTICE APRNs need to maintain a place at the genetic table with all healthcare providers by developing strategies to expand this nursing knowledge to their practice, teaching, and research. Nurses need to be cognizant of the keen genetic value of family histories, how risk classification will individualize prevention recommendations, and the exciting role of pharmacogenetics, given many APRNs' prescriptive authority. Our core professional belief that each human is highly unique has probably never been more accurate than with the future in genetic and genomic nursing.
Collapse
Affiliation(s)
- Theresa A Beery
- Adult Health Nursing, College of Nursing, University of Cincinnati, Cincinnati, Ohio, USA
| | | |
Collapse
|
141
|
Lavedan C, Birznieks G, Dressman M, McCullough K, Paczkowski R, Torres R, Wolfgang C, Polymeropoulos M. Translating the Genome into individualized therapeutics. Drug Dev Res 2004. [DOI: 10.1002/ddr.10390] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
|
142
|
Kirchheiner J, Sasse J, Meineke I, Roots I, Brockmöller J. Trimipramine pharmacokinetics after intravenous and oral administration in carriers of CYP2D6 genotypes predicting poor, extensive and ultrahigh activity. ACTA ACUST UNITED AC 2003; 13:721-8. [PMID: 14646691 DOI: 10.1097/00008571-200312000-00003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE The tricyclic antidepressant trimipramine is one of the drugs with the most pronounced differences in pharmacokinetics caused by the CYP2D6 genetic polymorphism. However, the effect of CYP2D6 genotype on steady state kinetics and on bioavailability has not been studied so far. In addition, we were interested in trimipramine pharmacokinetics in genetically defined ultra rapid metabolizers. METHODS We studied intravenous and multiple dose oral application of 50 mg trimipramine in five, seven, and three healthy volunteers with CYP2D6 genotypes predicting deficient, highly active and ultrarapid metabolism. The latter group included carriers of one wild-type and one duplication allele. Trimipramine and desmethyltrimipramine concentrations were measured by HPLC over a time interval of 72 h after intravenous and after one oral application. RESULTS Both bioavailability and systemic clearance significantly depended on CYP2D6 genotype with a linear gene dose relationship. Mean bioavailability was 44, 16 and 12% in carriers of zero, two and three active genes of CYP2D6, respectively, and the corresponding data for systemic clearance were 12.0, 24.2, and 30.3 l/h. Consequently, the mean total oral clearances were 27.3, 151, and 253 l/h in poor, extensive and ultrarapid metabolizers. CONCLUSIONS High bioavailability combined with low systemic clearance of trimipramine in poor metabolizers of CYP2D6 substrates results in a very high exposure to trimipramine with the risk of adverse drug reactions. On the other hand, the extremely high systemic and presystemic elimination may result in sub-therapeutic drug concentrations in carriers of CYP2D6 gene duplications with a high risk of poor therapeutic response.
Collapse
Affiliation(s)
- Julia Kirchheiner
- Institute of Clinical Pharmacology, University Medical Center Charité, Humboldt University of Berlin, Berlin.
| | | | | | | | | |
Collapse
|
143
|
Schaeffeler E, Schwab M, Eichelbaum M, Zanger UM. CYP2D6 genotyping strategy based on gene copy number determination by TaqMan real-rime PCR. Hum Mutat 2003; 22:476-85. [PMID: 14635107 DOI: 10.1002/humu.10280] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The genetic polymorphism of the cytochrome P450 monooxygenase, CYP2D6, comprises at least 43 alleles giving rise to distinct drug metabolism phenotypes termed ultrarapid, extensive, intermediate, and poor metabolizers. As a consequence, drug side effects or lack of drug effect may occur if standard doses are applied. Genetic prediction of drug oxidation phenotype as a basis for dose selection requires analysis of single nucleotide polymorphisms and of alleles with duplicated or deleted genes. Here we developed a novel method to determine the CYP2D6 gene dose per genome. A TaqMan real-time PCR assay to specifically amplify genomic CYP2D6 was established by using a specific set of amplification primers and probe, located in exon 9, which effectively prevent amplification of CYP2D7 and CYP2D8 pseudogenes. Quantitative CYP2D6 amplification data were normalized to albumin as an internal reference gene which was coamplified simultaneously in a single-tube biplex assay. The assay was validated with a selection of previously genotyped DNA samples containing none, one, two, or three CYP2D6 gene copies. The results were highly reproducible and closely matched the number of genes with no overlap between the groups. Analysis of DNA samples comprising all major alleles and genotypes revealed high sensitivity and specificity of the assay, as demonstrated by agreement of the determined gene dose with the presence of CYP2D6(*)2 x 2 (gene duplication) and CYP2D6(*) 5 (gene deletion) alleles. The predictability of the new strategy was systematically evaluated. The semiautomatic TaqMan assay allows high sample throughput and will be useful for pharmacogenetic studies and in the clinical setting.
Collapse
Affiliation(s)
- Elke Schaeffeler
- Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany
| | | | | | | |
Collapse
|
144
|
Zanger UM, Raimundo S, Eichelbaum M. Cytochrome P450 2D6: overview and update on pharmacology, genetics, biochemistry. Naunyn Schmiedebergs Arch Pharmacol 2003; 369:23-37. [PMID: 14618296 DOI: 10.1007/s00210-003-0832-2] [Citation(s) in RCA: 553] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2003] [Accepted: 09/18/2003] [Indexed: 01/21/2023]
Abstract
Of about one dozen human P450 s that catalyze biotransformations of xenobiotics, CYP2D6 is one of the more important ones based on the number of its drug substrates. It shows a very high degree of interindividual variability, which is primarily due to the extensive genetic polymorphism that influences expression and function. This so-called debrisoquine/sparteine oxidation polymorphism has been extensively studied in many different populations and over 80 alleles and allele variants have been described. CYP2D6 protein and enzymatic activity is completely absent in less than 1% of Asian people and in up to 10% of Caucasians with two null alleles, which do not encode a functional P450 protein product. The resulting "poor metabolizer" (PM) phenotype is characterized by the inability to use CYP2D6-dependent metabolic pathways for drug elimination, which affect up to 20% of all clinically used drugs. The consequences are increased risk of adverse drug reactions or lack of therapeutic response. Today, genetic testing predicts the PM phenotype with over 99% certainty. At the other extreme, the "Ultrarapid Metabolizer" (UM) phenotype can be caused by alleles carrying multiple gene copies. "Intermediate Metabolizers" (IM) are severely deficient in their metabolism capacity compared to normal "Extensive Metabolizers" (EM), but in contrast to PMs they express a low amount of residual activity due to the presence of at least one partially deficient allele. Whereas the intricate genetics of the CYP2D6 polymorphism is becoming apparent at ever greater detail, applications in clinical practice are still rare. More clinical studies are needed to show where patients benefit from drug dose adjustment based on their genotype. Computational approaches are used to predict and rationalize substrate specificity and enzymatic properties of CYP2D6. Pharmacophore modeling of ligands and protein homology modeling are two complementary approaches that have been applied with some success. CYP2D6 is not only expressed in liver but also in the gut and in brain neurons, where endogenous substrates with high-turnover have been found. Whether and how brain functions may be influenced by polymorphic expression are interesting questions for the future.
Collapse
Affiliation(s)
- Ulrich M Zanger
- Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstrasse 112, 70376, Stuttgart, Germany.
| | | | | |
Collapse
|
145
|
Flockhart DA, Rae JM. Cytochrome P450 3A pharmacogenetics: the road that needs traveled. THE PHARMACOGENOMICS JOURNAL 2003; 3:3-5. [PMID: 12629575 DOI: 10.1038/sj.tpj.6500144] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- D A Flockhart
- Division of Clinical Pharmacology, Indiana University School of Medicine, Indianapolis 46202, USA.
| | | |
Collapse
|
146
|
Ohnuma T, Shibata N, Matsubara Y, Arai H. Haloperidol plasma concentration in Japanese psychiatric subjects with gene duplication of CYP2D6. Br J Clin Pharmacol 2003; 56:315-20. [PMID: 12919180 PMCID: PMC1884346 DOI: 10.1046/j.0306-5251.2003.01872.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AIMS The cytochrome P-450 2D6 (CYP2D6) gene duplication/multiduplication producing an increase in enzyme activity, and the common Japanese mutation, CYP2D6*10A producing a decrease of enzyme activity were screened in a large number of Japanese psychiatric subjects (n = 111) in order to investigate whether these mutated alleles affected the plasma concentration of haloperidol. METHODS Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed to identify the CYP2D6*10A and CYP2D6*2 genotypes in subjects who had been taking haloperidol. For the screening of duplicated active CYP2D6 gene, allele-specific long PCR was performed. Plasma concentration of haloperidol was measured by the enzyme immunoassay, and expressed as "plasma concentration dose ratio" to normalize individual differences. RESULTS The plasma concentration-dose ratio showed large interindividual differences of approximately 18-fold. PCR-RFLP methods revealed that 29 (26.1%), 10 (9.0%), 39 (35.1%), 0 (0%), seven (6.3%) and 26 (23.4%) cases possessed the CYP2D6 genotypes *1/*1, *1/*2, *1/*10A, *2/*2, *2/*10A and *10 A/*10A, respectively. Six cases (5.4%) had duplicated CYP2D6 genes. There were no significant differences of plasma concentration-dose ratio between the groups classified by CYP2D6*10A and *2 genotypes (Kruskal-Wallis test; P = 0.37), even in those cases whose daily doses were lower than 20 mg (n = 90, P = 0.91). Subjects having duplicated genes (n = 6) did not show significant differences of plasma concentration-dose ratio by comparison with subjects who had no duplicated genes (Mann-Whitney U-test; P = 0.80). CONCLUSIONS Gene duplication, and the common Japanese mutation CYP2D6*10A on CYP2D6 gene are not likely to be the main modulatory factors of plasma concentration of haloperidol in Japanese psychiatric subjects.
Collapse
Affiliation(s)
- Tohru Ohnuma
- Department of Psychiatry, Juntendo Koshigaya Hospital, 560 Fukuroyama, Koshigaya-shi Saitama, 343-0032 Japan.
| | | | | | | |
Collapse
|
147
|
Someya T, Shimoda K, Suzuki Y, Sato S, Kawashima Y, Hirokane G, Morita S, Yokono A, Takahashi S. Effect of CYP2D6 genotypes on the metabolism of haloperidol in a Japanese psychiatric population. Neuropsychopharmacology 2003; 28:1501-5. [PMID: 12784098 DOI: 10.1038/sj.npp.1300213] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We investigated the effect of CYP2D6 genotypes on plasma levels of haloperidol (HAL) and reduced haloperidol (RHAL) in 88 Japanese schizophrenic inpatients being treated with HAL. Some subjects carrying CYP2D6*5 allele (CYP2D6*1/CYP2D6*5, CYP2D6*5/CYP2D6*10) showed extremely high concentrations of both HAL and RHAL, and the groups with CYP2D6*5 allele seemed to have higher plasma concentrations of HAL (1.14+/-0.69 ng/ml/mg) and RHAL (1.10+/-1.05 ng/ml/mg) than the other groups. Among those without CYP2D6*5 allele, there were no significant differences in plasma concentrations of HAL and RHAL between those without CYP2D6*10 allele (HAL=0.68+/-0.31 ng/ml/mg, RHAL=0.28+/-0.37 ng/ml/mg), those with one CYP2D6*10 (HAL=0.70+/-0.23 ng/ml/mg, RHAL=0.31+/-0.16 ng/ml/mg) and those with two CYP2D6*10 alleles (HAL=0.69+/-0.14 ng/ml/mg, RHAL=0.40+/-0.09 ng/ml/mg), although there was a tendency of higher plasma concentration of RHAL in those with two CYP2D6*10 alleles. At a lower daily dosage of HAL (<10 mg/day), the subjects with two or one CYP2D6*10 allele(s) showed significantly higher plasma concentrations of RHAL (0.43+/-0.23 ng/ml/mg, 0.34+/-0.16 ng/ml/mg) than those without CYP2D6*10 allele (0.18+/-0.16 ng/ml/mg). The results of this study indicate that CYP2D6*10 allele plays significant but modest role in HAL metabolism in Japanese; nevertheless, we should not lump CYP2D6*10 allele with CYP2D6*5 allele because these two mutated alleles seem to have different impacts in the metabolism of HAL.
Collapse
Affiliation(s)
- Toshiyuki Someya
- Department of Psychiatry, Niigata University Graduate School of Medical and Dental Sciences, 757 Asahimachidori-ichibancho, Niigata 951-8510, Japan.
| | | | | | | | | | | | | | | | | |
Collapse
|
148
|
Abstract
Many drugs exhibit variable efficacy and toxicity. Pharmacogenetics explores the genetic underpinnings of variable drug response. Pharmacogenetic testing is beginning to enter the clinic and will have a significant impact on the practice of clinical gastroenterology. Thiopurine S-methyltransferase screening, which will likely become routine for thiopurine recipients, illustrates the promise and limitations of pharmacogenetics. Testing for variation in other drug metabolism pathways may also become important. Pharmacogenetics will complement but not replace traditional methods for choosing drugs and for selecting dosing regimens for narrow-therapeutic-index drugs.
Collapse
Affiliation(s)
- Raymond C Givens
- General Clinical Research Center, University of North Carolina at Chapel Hill, 27514, USA
| | | |
Collapse
|
149
|
Dalén P, Dahl ML, Roh HK, Tybring G, Eichelbaum M, Wilkinson GR, Bertilsson L. Disposition of debrisoquine and nortriptyline in Korean subjects in relation to CYP2D6 genotypes, and comparison with Caucasians. Br J Clin Pharmacol 2003; 55:630-4. [PMID: 12814461 PMCID: PMC1884261 DOI: 10.1046/j.1365-2125.2003.01804.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AIMS To study the influence of the CYP2D6*10 allele on the disposition of debrisoquine and nortriptyline. METHODS The pharmacokinetics of debrisoquine and nortriptyline and their main metabolites were determined in ten Koreans with the CYP2D6*1/*1 (n = 5) and CYP2D6*1/*10 (n = 5) genotypes after single oral doses of 20 mg debrisoquine and 25 mg nortriptyline, respectively. The data were compared with previously published findings from 21 Caucasians with 0, one, two, three, four or 13 functional CYP2D6 genes. RESULTS The AUC0-8 of 4-hydroxydebrisoquine was significantly lower in Koreans with CYP2D6*1/*10 genotype compared with CYP2D6*1/*1[95% confidence interval (CI) for the ratio between means 1.17, 1.85]. No other genotype-related differences were found in the plasma kinetics of nortriptyline and debrisoquine, or their hydroxy metabolites. The AUCnortriptyline/AUC10-hydroxynortriptyline ratio did not differ between the *1/*1 and *1/*10 genotype groups (95% CI for the ratio of means 0.60, 1.26). Similarly, there was no difference between these genotypes with respect to the AUCdebrisoquine/AUC4-hydroxydebrisoquine ratio (95% CI for the ratio of mean values 0.38, 1.46). Both Korean genotype groups had similar AUCs and parent compound/metabolite AUC ratios of debrisoquine and nortriptyline to Caucasians with two functional CYP2D6 genes. CONCLUSIONS Heterozygosity for CYP2D6*10 decreases the CYP2D6-dependent elimination of nortriptyline and debrisoquine to only a limited degree. Further studies in subjects homozygous for CYP2D6*10 are required to elucidate fully the pharmacokinetic consequences of this CYP2D6 genotype in Orientals.
Collapse
Affiliation(s)
- P Dalén
- Department of Medical Laboratory Sciences & Technology, Division of Clinical Pharmacology, Karolinska Institutet, Huddinge University Hospital, Sweden
| | | | | | | | | | | | | |
Collapse
|
150
|
Affiliation(s)
- Richard Weinshilboum
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Medical School, Mayo Clinic, and Mayo Foundation, Rochester, Minn 55905, USA.
| |
Collapse
|