Science, medicine, and the future: Pharmacogenetics

DNA microarray technology in the clinical environment: the AmpliChip CYP450 test for CYP2D6 and CYP2C19 genotyping

INTRODUCTION

An important technological advance in genetic testing is the DNA microarray, which allows for the simultaneous testing of thousands of DNA sequences. The AmpliChip CYP450 Test employs this microarray technology for cytochrome P450 (CYP) 2D6 and CYP2C19 genotyping. Isoenzymes encoded by these genes are responsible for the metabolism of many widely prescribed drugs. The objectives of this study were to identify CYP2D6 and CYP2C19 alleles and phenotypes in a psychiatric patient population in Kentucky, and to describe practical issues associated with DNA microarray technology.

METHODS

A total of 4,532 psychiatric patients were recruited from three state hospitals in Kentucky. Whole blood, buccal swabs, or saliva samples were genotyped with the AmpliChip CYP450 Test to derive a predicted phenotype.

RESULTS

In this cohort, the overall prevalence of CYP2D6 poor metabolizers was 7.6% (95% CI 7%, 8.3%), 8.2% in the Caucasians (95% CI 7.4%, 9.%) and 1.8% in the African Americans (95% CI 0.9%, 3.5%). The overall prevalence of CYP2D6 ultrarapid metabolizers was 1.5% (95% CI 1.2%, 1.9%), 1.5% in the Caucasians (95% CI 1.1%, 1.9%) and 2.0% in the African Americans (95% CI 1.1%, 3.7%). The overall prevalence of CYP2C19 poor metabolizers was 2.0% (95% CI 1.8%, 2.7%), 2.2% in Caucasians (95% CI 1.6%, 2.5%) and 4.0% in African Americans (95% CI 2.6%, 6.1%).

CONCLUSION

We also propose a numeric system for expression of CYP2D6 and CYP2C19 enzyme activity to aid clinicians in determining treatment strategy for patients receiving therapeutics that are metabolized by the CYP2D6 or CYP2C19 gene products.

Pharmacogenomics: the promise of personalized medicine for CNS disorders

This review focuses first on the concept of pharmacogenomics and its related concepts (biomarkers and personalized prescription). Next, the first generation of five DNA pharmacogenomic tests used in the clinical practice of psychiatry is briefly reviewed. Then the possible involvement of these pharmacogenomic tests in the exploration of early clinical proof of mechanism is described by using two of the tests and one example from the pharmaceutical industry (iloperidone clinical trials). The initial attempts to use other microarray tests (measuring RNA expression) as peripheral biomarkers for CNS disorders are briefly described. Then the challenge of taking pharmacogenomic tests (compared to drugs) into clinical practice is explained by focusing on regulatory oversight, the methodological/scientific issues concerning diagnostic tests, and cost-effectiveness issues. Current information on medicine-based evidence and cost-effectiveness usually focuses on average patients and not the outliers who are most likely to benefit from personalized prescription. Finally, future research directions are suggested. The future of 'personalized prescription' in psychiatry requires consideration of pharmacogenomic testing and environmental and personal variables that influence pharmacokinetic and pharmacodynamic drug response for each individual drug used by each patient.

Use of plasmid-derived external quality control samples in pharmacogenetic testing

Objectives: Genetic variation in genes encoding for drug-metabolizing enzymes, drug targets and signaling pathways have proven to contribute significantly to differences in drug response. Pharmacogenetics is now expanding from clinical pharmacological research to its application in clinical practice. Genotyping of patients in a routine clinical setting requires robust and reliable genotyping methods. Materials & methods: A survey of pharmacogenetic association studies for quality control samples published from 2005 to 2007 in the two most prominent pharmacogenetic journals, and development of plasmid-derived external controls. Results: Surveying journals revealed that only a minority of papers report the use of quality controls, and no standard procedures are applied. We established 12 plasmid-derived external controls and applied these in pharmacogenetic testing. Conclusion: There still is a need for quality control materials, especially for application in pharmacogenetic testing. We hope that our initiative to create plasmid-derived controls will help to facilitate quality in the pharmacogenetic genotyping tests applied in research, as well as in routine patient care.

Avoiding adverse drug reactions by pharmacogenetic testing: A systematic review of the economic evidence in the case of TPMT and AZA-induced side effects

Objectives:The study aims at evaluating the economic evidence related to testing for genetic variants of the drug-metabolizing enzyme, TPMT. Detecting TPMT genetic variants before the administration of azathioprine (AZA) has the potential to prevent serious and costly adverse drug reactions (ADRs), such as neutropenia. In particular, our analysis concentrated on assessing the reliability of data on costs of neutropenia and performing the tests, the two main cost categories that could inform an economic evaluation of TPMT pharmacogenetic testing.

Methods:A systematic literature review was performed to gather evidence on the costs of testing and neutropenia. Articles were critically appraised for their comprehensiveness and quality. To better estimate costs of TPMT tests, a small-scale survey of European diagnostic laboratories was conducted.

Results:Only seven articles were retrieved specifying the costs associated with the management and treatment of AZA-induced neutropenia. Most of these studies are based on theoretical modeling reconstructed with key-informants or on very few cases of ADRs, and either the methodology for cost calculation is not specified or costs are based on national cost databases and tariffs. After critical appraisal of these studies, we considered €2,116 as the most reliable estimate for the cost of a case of neutropenia. Literature review accompanied by the survey of several diagnostic laboratories also provided an estimate (€68) for TPMT testing. Based on these values, the net cost per prevented case of neutropenia equals to €5,300.

Conclusions:Solid economic considerations related to TPMT pharmacogenetic testing are still limited by underreporting of ADRs and high level of approximation related to cost data. Ad hoc observational studies and the ADR recording process embedded in pharmacovigilance systems, established across Europe, should represent more reliable sources of cost data in the future.

Pharmacogenomics and treatment for dementia induced by Alzheimer’s disease

Pharmacogenomics is the study of interindividual genetic variability, which plays a significant role in defining drug response and toxicity. As research has graduated from studying single candidate genes to whole-genome scans, pharmacogenomics is beginning to make its impact on the therapeutics of complex CNS disorders, such as schizophrenia, Parkinson’s disease and Alzheimer’s disease. Alzheimer’s disease is a progressive complex disorder, where genetic predisposition interacts with environmental factors. With conventional therapeutics only providing symptomatic treatment, the current focus of the pharmaceutical industry is on novel strategies with an etiopathogenic orientation. In this review, we have summarized the current knowledge of pathogenetic mechanisms of Alzheimer’s disease, with a focus on the known relevant molecules and the potential of pharmacogenomics in translating this knowledge of human genome variability into efficacious and safer therapeutics.

Biological treatments for amfetamine dependence : recent progress

Amfetamine abuse has grown into a worldwide epidemic. Methamfetamine, a derivative of amfetamine made from readily accessible chemicals, has plagued the US since the 1960s, with an alarming recent surge in the numbers of those meeting the criteria for amfetamine abuse and dependence. We review this problem using a computerised literature search (PubMed 1964-2007) to summarise knowledge from animal and human studies about treatments for amfetamine dependence, while exploring the potential of pharmacogenetics to help uncover new treatment targets. Several promising therapeutic targets have come from animal models of reward, drug-taking behaviour and withdrawal. Although preclinical and selected clinical results have been promising, clinical studies have yielded inconsistent results. To improve these outcomes, pharmacogenetic studies may be used to identify candidate alleles that predict therapeutic response. Exciting preclinical findings and a steady progression of clinical results offer hope for the development of a treatment for amfetamine dependence.

Genotypic Approaches to Therapy in Children: A National Active Surveillance Network (GATC) to Study the Pharmacogenomics of Severe Adverse Drug Reactions in Children

A striking failure of modern medicine is the debilitating and lethal consequences of adverse drug reactions (ADRs), which rank as one of the top 10 leading causes of death and illness in the developed world with direct medical costs of 137-177 billion annually US dollars in the USA. Although many factors influence the effect of medications (e.g., age, organ function, drug interactions), genetic factors account for 20% to 95% of drug response variability and play a significant role in the incidence and severity of ADRs. The field of pharmacogenomics seeks to identify genetic factors responsible for individual differences in drug efficacy and ADRs. Pharmacogenomics has led to several genetic tests that provide clinical dosing recommendations. The Genetic Approaches to Therapy in Children (GATC) project is a national project established in Canada to identify novel predictive genomic markers for severe ADRs in children. An ADR surveillance network has been established in eight of Canada's major children's hospitals, serving up to 75% of all Canadian children. The goal of the project is to identify patients experiencing specific ADRs and matched controls, collect DNA samples, and apply genomics-based technologies to identify ADR-associated genetic markers with the goal of preventing serious ADRs in susceptible children.

Apnea in a child after oral codeine: a genetic variant - an ultra-rapid metabolizer

We present a case of a 29 months old previously healthy child who experienced apnea resulting in brain injury following a dose of acetaminophen and codeine 2 days after an uneventful anesthetic for tonsillectomy. A genetic polymorphism leading to ultra-rapid metabolism of codeine into morphine resulted in narcosis and apnea. This paper discusses the use of codeine for pain relief, obstructive sleep apnea, the alteration of the CYP2D6 gene and the resulting effect on drug metabolism.

Challenges for Australia's Bio/Nanopharma Policies: trade deals, public goods and reference pricing in sustainable industrial renewal

Industrial renewal in the bio/nanopharma sector is important for the long term strength of the Australian economy and for the health of its citizens. A variety of factors, however, may have caused inadequate attention to focus on systematically promoting domestic generic and small biotechnology manufacturers in Australian health policy. Despite recent clarifications of 'springboarding' capacity in intellectual property legislation, federal government requirements for specific generic price reductions on market entry and the potential erosion of reference pricing through new F1 and F2 categories for the purposes of Pharmaceutical Benefits Scheme (PBS) assessments, do not appear to be coherently designed to sustainably position this industry sector in 'biologics,' nanotherapeutics and pharmacogenetics. There also appears to have been little attention paid in this context to policies fostering industry sustainability and public affordability (as encouraged by the National Medicines Policy). One notable example includes that failure to consider facilitating mutual exchanges on regulatory assessment of health technology safety and cost-effectiveness (including reference pricing) in the context of ongoing free trade negotiations between Australia and China (the latter soon to possess the world's largest generic pharmaceutical manufacturing capacity). The importance of a thriving Australian domestic generic pharmaceutical and bio/nano tech industry in terms of biosecurity, similarly appears to have been given insufficient policy attention.Reasons for such policy oversights may relate to increasing interrelationships between generic and 'brand-name' manufacturers and the scale of investment required for the Australian generics and bio/nano technology sector to be a significant driver of local production. It might also result from singularly effective lobbying pressure exerted by Medicines Australia, the 'brand-name' pharmaceutical industry association, utilising controversial interpretations of reward of pharmaceutical 'innovation' provisions in the Australia-US Free Trade Agreement (AUSFTA) through the policy-development mechanisms of the AUSFTA Medicines Working Group and most recently an Innovative Medicines Working Group with the Department of Health and Ageing. This paper critically analyses such arguments in the context of emerging challenges for sustainable industrial renewal in Australia's bio/nanopharma sector.

[Pharmacogenetics I. Concept, history, objectives and areas of study]

There is great interindividual variability in the response to drugs, both in effectiveness and toxicity. Different patients respond differently to the same medication as a consequence of genetic and non-genetic factors. Pharmacogenetics represents the study of the individual pharmacological response based on the genotype. Its objective is to optimize treatment in an individual basis, thereby creating an individualized therapy, more safe and efficient, that will allow the clinician to select the correct drug, at the adequate dose, for the right patient. In the first part of this review we discuss several aspects of the relationship between genetics and therapeutic response, as well as the concept, history, objectives and different areas of study of pharmacogenetics.

The Evolving Role of Drug Metabolism in Drug Discovery and Development

Drug metabolism in pharmaceutical research has traditionally focused on the well-defined aspects of absorption, distribution, metabolism and excretion, commonly-referred to ADME properties of a compound, particularly in the areas of metabolite identification, identification of drug metabolizing enzymes (DMEs) and associated metabolic pathways, and reaction mechanisms. This traditional emphasis was in part due to the limited scope of understanding and the unavailability of in vitro and in vivo tools with which to evaluate more complex properties and processes. However, advances over the past decade in separate but related fields such as pharmacogenetics, pharmacogenomics and drug transporters, have dramatically shifted the drug metabolism paradigm. For example, knowledge of the genetics and genomics of DMEs allows us to better understand and predict enzyme regulation and its effects on exogenous (pharmacokinetics) and endogenous pathways as well as biochemical processes (pharmacology). Advances in the transporter area have provided unprecedented insights into the role of transporter proteins in absorption, distribution, metabolism and excretion of drugs and their consequences with respect to clinical drug-drug and drug-endogenous substance interactions, toxicity and interindividual variability in pharmacokinetics. It is therefore essential that individuals involved in modern pharmaceutical research embrace a fully integrated approach and understanding of drug metabolism as is currently practiced. The intent of this review is to reexamine drug metabolism with respect to the traditional as well as current practices, with particular emphasis on the critical aspects of integrating chemistry and biology in the interpretation and application of metabolism data in pharmaceutical research.

Pharmacogenomics and its implications for autoimmune disease

A striking failure of modern medicine is the debilitating and lethal consequences of adverse drug reactions (ADRs) which rank as one of the top ten leading causes of death and illness in the developed world with direct medical costs of 137-177 billion US dollars annually in the USA. Although many factors influence the effect of medications (i.e. age, organ function, drug interactions), genetic factors account for 20-95% of drug response variability and play a significant role in the incidence and severity of ADRs. The field of pharmacogenomics seeks to identify genetic factors responsible for individual differences in drug efficacy and adverse drug reactions. Pharmacogenomics has led to several genetic tests that provide clinical dosing recommendations. For autoimmune disease, pharmacogenomics has led to several DNA-based tests to improve drug selection, optimize dosing, and minimize the risk of toxicity. The 'GATC' project is a nation-wide project established in Canada to identify novel predictive genomic markers of severe ADRs in children. An ADR surveillance network has been established in all of Canada's major children's hospitals, serving up to 75% of all Canadian children. The goal of the project is to identify patients experiencing specific ADRs, collect DNA samples, and apply genomics-based technologies to identify ADR-associated genetic markers.

Regulation of cutaneous drug-metabolizing enzymes and cytoprotective gene expression by topical drugs in human skin in vivo

BACKGROUND

Individuality in the expression and regulation of hepatic drug-metabolizing enzymes (DMEs) and cytoprotective (CP) genes is an important determinant of treatment response. There is increasing evidence that many DMEs and CP genes are also expressed in human skin. Responses to topical drugs used to treat common skin diseases, such as psoriasis, are unpredictable and may potentially be rationalized, at least in part, by interindividual differences in cutaneous DME and CP gene expression.

OBJECTIVES

We investigated whether three topical drugs [coal tar, all-trans retinoic acid (atRA) and clobetasol 17-propionate] used in routine clinical practice modulated the expression of a variety of DME and CP genes [cytochrome P450s, glutathione S-transferases (GSTs) and drug transporters] in healthy human skin in vivo.

METHODS

Healthy adult volunteers (n = 30) were invited to participate in the study. Each subject was randomly allocated to receive two of the three study chemicals and one control site application. Crude coal tar (n = 13), atRA (n = 14) or clobetasol 17-propionate (n = 10) was applied under occlusion to photoprotected buttock skin for 96 h. A vehicle control (white soft paraffin) was also applied under the same conditions at an adjacent site in all subjects. Full-thickness punch biopsies (4-mm diameter) were then taken from treated and control sites. Total RNA was extracted and reverse transcribed into cDNA, which was used as a template in subsequent real-time polymerase chain reaction analysis, where fluorescent output was directly proportional to input cDNA concentration. Triplicate measurements of skin mRNA expression were made from each sample, and the arithmetic mean values taken. After logarithmic transformation, the paired t-test was used to compare values between treated and control skin.

RESULTS

Cytochrome P450s CYP1A1, CYP1A2, CYP1B1, CYP2C18, quinone reductase (NQO-1), GSTP1, gamma-glutamyl cysteine synthetase (gamma-GCS), glutathione peroxidase-1 (GPx-1), cyclooxygenase-2 (COX-2) and haem oxygenase-1 (HO-1) were induced by coal tar; CYP26, NADPH P450 reductase (CPR), GSTP1 and HO-1 by atRA; and CYP3A5 by clobetasol 17-propionate. In contrast, CYP1A1 and CYP1A2 expression was suppressed by atRA, and gamma-GCS and MRP1 by clobetasol 17-propionate. Marked interindividual variation in gene regulation by topical drugs was seen for the majority of genes examined.

CONCLUSIONS

These data demonstrate that topical drugs can modulate DME gene expression in human skin in vivo and indicate that variation in the expression and regulation of these genes may be a determinant of individuality in response to topical therapies for common skin diseases.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

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.

Preoperative Cotreatment With Dextromethorphan and Ketorolac Provides an Enhancement of Pain Relief After Laparoscopic-assisted Vaginal Hysterectomy

OBJECTIVES

Both N-methyl-D-aspartate receptor antagonists and nonsteroidal anti-inflammatory drugs have been demonstrated to produce better postoperative pain relief. The concept of multimodal analgesia has also been used for clinical pain management. The aim of the present study was to examine the analgesic effect of preoperative cotreatment with dextromethorphan (DM) and ketorolac on postoperative pain management after laparoscopic-assisted vaginal hysterectomy (LAVH).

METHODS

Eighty ASA physical status I or II patients scheduled for LAVH were included and randomly assigned to 1 of 4 groups. Patients received intramuscular (IM) chorpheniramine 20 mg+ intravenous (IV) 2 mL of normal saline, IM DM 40 mg+IV 2 mL of normal saline, IM chorpheniramine 20 mg+IV 60 mg (2 mL) of ketorolac, and IM DM 40 mg+IV ketorolac 60 mg as the groups C, DM, Keto, and DM+Keto, respectively. All patients were given a patient-controlled analgesia (PCA) with morphine for pain relief postoperatively. Analgesic effects were evaluated using Visual Analog Scale pain scores at rest and during coughing, time to first PCA request for pain relief, total morphine consumption, bed rest time, and the time to first passage of flatus for 48 hours after surgery.

RESULTS

Patients in DM and Keto groups had significantly better pain relief than patients in group C. Patients in DM+Keto group exhibited the best postoperative pain relief among groups in the following several categories: time to first trigger of PCA, total morphine consumption, the worst Visual Analog Scale, bed rest time, and the time to first passage of flatus, demonstrating an enhanced effect between DM and ketorolac. Neither synergistic nor antagonistic interaction was observed between DM and ketorolac.

DISCUSSION

Preoperative treatment with both DM and ketorolac diminish postoperative pain. Our results suggest that the N-methyl-D-aspartate antagonist-DM and the nonsteroidal anti-inflammatory drugs-ketorolac cotreatment provide an enhancement of analgesia for postoperative pain management in patients after LAVH surgery.

The AmpliChip CYP450 genotyping test: Integrating a new clinical tool

The AmpliChip CYP450 Test, which analyzes patient genotypes for cytochrome P450 (CYP) genes CYP2D6 and CYP2C19, is a major step toward introducing personalized prescribing into the clinical environment. Interest in adverse drug reactions (ADRs), the genetic revolution, and pharmacogenetics have converged with the introduction of this tool, which is anticipated to be the first of a new wave of such tools to follow over the next 5-10 years. The AmpliChip CYP450 Test is based on microarray technology, which combines hybridization in precise locations on a glass microarray and a fluorescent labeling system. It classifies individuals into two CYP2C19 phenotypes (extensive metabolizers [EMs] and poor metabolizers [PMs]) by testing three alleles, and into four CYP2D6 phenotypes (ultrarapid metabolizers [UMs], EMs, intermediate metabolizers [IMs], and PMs) by testing 27 alleles, including seven duplications. CYP2D6 is a metabolic enzyme with four activity levels (or phenotypes): UMs with unusually high activity; normal subjects, known as EMs; IMs with low activity; and PMs with no CYP2D6 activity (7% of Caucasians and 1-3% in other ethnic groups). Levels of evidence for the association between CYP2D6 PMs and ADRs are relatively reasonable and include systematic reviews of case-control studies of some typical antipsychotics and tricyclic antidepressants (TCAs). Evidence for other phenotypes is considerably more limited. The CYP2D6 PM phenotype may be associated with risperidone ADRs and discontinuation due to ADRs. Venlafaxine, aripiprazole, duloxetine, and atomoxetine are newer drugs metabolized by CYP2D6 but studies of the clinical relevance of CYP2D6 genotypes are needed. Non-psychiatric drugs metabolized by CYP2D6 include metoprolol, tamoxifen, and codeine-like drugs. CYP2C19 PMs (3-4% of Caucasians and African Americans, and 14-21% of Asians) may require dose adjustment for some TCAs, moclobemide, and citalopram. Other drugs metabolized by CYP2C19 are diazepam and omeprazole. The future of pharmacogenetics depends on the ability to overcome serious obstacles, including the difficulties of conducting and publishing studies in light of resistance from grant agencies, pharmaceutical companies, and some scientific reviewers. Assuming more studies are published, pharmacogenetic clinical applications may be compromised by economic factors and the lack of physician education. The combination of a US FDA-approved test, such as the AmpliChip CYP450 Test, and an FDA definition of CYP2D6 as a 'valid biomarker' makes CYP2D6 genotyping a prime candidate to be the first successful pharmacogenetic test in the clinical environment. One can use microarray technology to test for hundreds of single nucleotide polymorphisms (SNPs) but, taking into account the difficulties for single gene approaches such as CYP2D6, it is unlikely that very complex pharmacogenetic approaches will reach the clinical market in the next 5-10 years.

Context, ethics and pharmacogenetics

Most of the literature on pharmacogenetics assumes that the main problems in implementing the technology will be institutional ones (due to funding or regulation) and that although it involves genetic testing, the ethical issues involved in pharmacogenetics are different from, even less than, 'traditional' genetic testing. Very little attention has been paid to how clinicians will accept this technology, their attitudes towards it and how it will affect clinical practice. This paper presents results from interviews with clinicians who are beginning to use pharmacogenetics and explores how they view the ethics of pharmacogenetic testing, its use to exclude some patients from treatment, and how this kind of testing fits into broader debates around genetics. In particular this paper examines the attitudes of breast cancer and Alzheimer's disease specialists. The results of these interviews will be compared with the picture of pharmacogenetics painted in the published literature, as a way of rooting this somewhat speculative writing in clinical practice.

IN SILICO PREDICTION OF DRUG BINDING TO CYP2D6: IDENTIFICATION OF A NEW METABOLITE OF METOCLOPRAMIDE

Patients with cancer often take many different classes of drugs to treat the effects of their malignancy and the side effects of treatment, as well as their comorbidities. The potential for drug-drug interactions that may affect the efficacy of anticancer treatment is high, and a major source of such interactions is competition for the drug-metabolizing enzymes, cytochromes P450 (P450s). We have examined a series of 20 drugs commonly prescribed to cancer patients to look for potential interactions via CYP2D6. We used a homology model of CYP2D6, together with molecular docking techniques, to perform an in silico screen for binding to CYP2D6. Experimental IC50 values were determined for these compounds and compared with the model predictions to reveal a correlation with a regression coefficient of r2= 0.61. Importantly, the docked conformation of the commonly prescribed antiemetic metoclopramide predicted a new site of metabolism that was further investigated through in vitro analysis with recombinant CYP2D6. An aromatic N-hydroxy metabolite of metoclopramide, consistent with predictions from our modeling studies, was identified by high-performance liquid chromatography/mass spectrometry. This metabolite was found to represent a major product of metabolism in human liver microsomes, and CYP2D6 was identified as the main P450 isoform responsible for catalyzing its formation. In view of the prevalence of interindividual variation in the CYP2D6 genotype and phenotype, we suggest that those experiencing adverse reactions with metoclopramide, e.g., extrapyramidal syndrome, are likely to have a particular CYP2D6 genotype/phenotype. This warrants further investigation.

PHARMACOGENETICS APPROACH TO THERAPEUTICS

1. Pharmacogenetics refers to the study of genetically controlled variations in drug response. Functional variants caused by single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolising enzymes, transporters, ion channels and drug receptors have been known to be associated with interindividual and interethnic variation in drug response. Genetic variations in these genes play a role in influencing the efficacy and toxicity of medications. 2. Rapid, precise and cost-effective high-throughput technological platforms are essential for performing large-scale mutational analysis of genetic markers involved in the aetiology of variable responses to drug therapy. 3. The application of a pharmacogenetics approach to therapeutics in general clinical practice is still far from being achieved today owing to various constraints, such as limited accessibility of technology, inadequate knowledge, ambiguity of the role of variants and ethical concerns. 4. Drug actions are determined by the interplay of several genes encoding different proteins involved in various biochemical pathways. With rapidly emerging SNP discovery technological platforms and widespread knowledge on the role of SNPs in disease susceptibility and variability in drug response, the pharmacogenetics approach to therapeutics is anticipated to take off in the not-too-distant future. This will present profound clinical, economic and social implications for health care.

Patients' and physicians' perspectives on pharmacogenetic testing

INTRODUCTION

The integration of pharmacogenetic testing into routine care will, in part, depend upon the patients' and physicians' acceptance of these tests. Empirical data regarding patients' and physicians' views on pharmacogenetic testing are lacking.

OBJECTIVES

To explore patients' and physicians' perspectives on the potential implications of pharmacogenetic testing, particularly focusing on asthma, and to analyze the possible determinants of their expectations, hopes and fears.

METHODS

We conducted telephone interviews with patients with asthma or chronic obstructive pulmonary disease taking part in a larger pharmacogenetic study, in addition to general practitioners (GPs) from a different region in Germany. A total of 328 patients and 378 GPs were invited to participate. Determinants of their attitudes toward pharmacogenetic testing were assessed using logistic regression analysis.

RESULTS

Informed consent to participate in this study was given by 196 patients (60%) and 106 GPs (28%). Most patients (96%) and physicians (52%) appreciated the availability of pharmacogenetic tests for a disease such as asthma. Approximately a third of the patients worried about potential unfavorable test results (35%) and violation of privacy (36%). Female patients were more likely to have a fearful attitude (odds ratio [OR]=2.85; 95% confidence interval [CI]=1.58-5.12). Younger patients were generally more likely to be hopeful about the usefulness of pharmacogenetic testing (OR=2.12; CI=1.01-4.46). The GPs' concerns were mainly related to the possibility that patients might either be put under pressure to be tested (72%) or be disadvantaged at private health insurance agencies (61%). The nature of the responsible institution, the clarity of the research aim and explicit informed consent from patients influenced a physicians' decision regarding whether to support a pharmacogenetic study.

CONCLUSION

The concerns of patients and GPs differ somewhat with respect to negative psychosocial consequences, discrimination or violation of privacy. Development of information for physicians and patients would be helpful in preventing unrealistic fears or hopes.

Update on pharmacogenetics in epilepsy: a brief review

Recent developments in the pharmacogenetics of antiepileptic drugs provide new prospects for predicting the efficacy of treatment and potential side-effects. Epilepsy is a common, serious, and treatable neurological disorder, yet current treatment is limited by high rates of adverse drug reactions and lack of complete seizure control in a significant proportion of patients. The disorder is especially suitable for pharmacogenetic investigation because treatment response can be quantified and side-effects can be assessed with validated measures. Additionally, there is substantial knowledge of the pharmacodynamics and kinetics of antiepileptic drugs, and some candidate genes implicated in the disorder have been identified. However, recent studies of the association of particular genes and their genetic variants with seizure control and adverse drug reactions have not provided unifying conclusions. This article reviews the published work and summarises the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualising treatment for epilepsy are discussed.

The impact of Cytochrome P450-2D6 genotype on the use and interpretation of therapeutic drug monitoring in long-stay patients treated with antidepressant and antipsychotic drugs in daily psychiatric practice

PURPOSE

This retrospective follow-up study investigates whether cytochrome P450-2D6 (CYP2D6) genotype explains variability in plasma concentrations of psychotropic drugs in daily psychiatric practice.

METHODS

The study population consisted of 62 hospitalised psychiatric patients genotyped for CYP2D6. Primary endpoint was the normalised plasma concentration ratio which was defined as the [measured concentration]/[mean therapeutic concentration] allowing comparison of plasma concentrations of different substrates. Secondary endpoint was a plasma concentration above the therapeutic range. The determinant was CYP2D6 genotype classified as ultrarapid metaboliser (UM), extensive metaboliser (EM), intermediate metaboliser (IM), or poor metaboliser (PM). The relation between CYP2D6 genotype and the normalised plasma concentration ratio was assessed with a linear mixed-effects model after adjustment for the Prescribed Daily Dose (PDD). The risk of having a plasma concentration above the therapeutic range was assessed with a logistic mixed-effects model.

RESULTS

For antidepressants, CYP2D6 genotype PM (1.68 (95%CI: 1.01-2.28)) and IM (1.09 (95%CI: 0.77-1.29)) were associated with higher normalised plasma concentration ratios of antidepressants compared to EMs (0.56 (95%CI: 0.26-0.74)). In addition, the risk of a plasma concentration above the therapeutic range was increased for PMs (OR 33.1 (95%CI: 2.0-544.6)) and IMs (OR 8.2 (95%CI: 1.1-60.3)) relative to EMs using antidepressants. CYP2D6 genotype could not clearly explain variability in plasma concentrations of antipsychotics possibly due to a low frequency of therapeutic drug monitoring (TDM) in antipsychotics primarily metabolised by CYP2D6 in daily psychiatric practice.

CONCLUSIONS

CYP2D6 genotype contributes to clinically relevant variability in plasma concentrations of antidepressants but probably not antipsychotics in daily clinical practice.

Pharmacogenetic testing for drug metabolizing enzymes: is it happening in practice?

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.

Communication of pharmacogenetic research results to HIV-infected treated patients: standpoints of professionals and patients

The aim of pharmacogenetic studies is to adapt therapeutic strategies to individual genetic profiles, thus maximising their efficacy and minimising the likelihood of adverse side effects. Since the advent of personalised medicine, the issue of communicating research results to participants has become increasingly important. We addressed this question in the context of HIV infection, as patients and associations are particularly concerned by research and therapeutic advances. We explored the standpoints of both research professionals and participants involved in a pharmacogenetic study conducted in a cohort of HIV-infected patients. The setting of the research protocol was followed over a 2-year period. Participants' standpoints were collected through a questionnaire and interviews were conducted with research professionals. Of 125 participants, 76% wished to receive individual results and 71% wished to receive collective results; 39% did not know when results might be expected. Communication of global research results is a principle that is generally accepted by professionals. Concerning individual feedback, the professionals felt that it was necessary if it could be of direct benefit to the participant, but they expressed doubts for situations with no recognised benefit. Our results highlight the necessity to consider this issue in greater detail. We suggest the need to anticipate the debates concerning individual feedback, to differentiate between situations and the importance of further investigations on the opportunities and modalities of communication. Finally, our work emphasised the opposite pressures between the pursuit of scientific knowledge and the therapeutic orientation of clinical trials.

The new look of behavioral genetics in developmental psychopathology: gene-environment interplay in antisocial behaviors

This article reviews behavioral-genetic research to show how it can help address questions of causation in developmental psychopathology. The article focuses on studies of antisocial behavior, because these have been leading the way in investigating environmental as well as genetic influences on psychopathology. First, the article illustrates how behavioral-genetic methods are being newly applied to detect the best candidates for genuine environmental causes among the many risk factors for antisocial behavior. Second, the article examines findings of interaction between genes and environments (G x E) associated with antisocial behavior, outlining steps for testing hypotheses of measured G x E. Third, the article envisages future work on gene-environment interplay, arguing that it is an interesting and profitable way forward for psychopathology research.

Pharmacogenetic testing in the clinical management of schizophrenia: a decision-analytic model

Clinical application of pharmacogenetic testing has been proposed as a means of improving treatment outcomes in psychiatry. The identification of a putative genetic test for better clozapine response in schizophrenia offers an opportunity to evaluate the cost-effectiveness of such testing. The authors performed a cost-effectiveness analysis of a genetic test that may identify individuals with greater likelihood of responding to clozapine treatment. We modeled a target population of schizophrenia patients in an acute psychotic episode, using a lifetime time horizon and societal perspective. Outcome measures included life expectancy, quality-adjusted life expectancy, costs, and incremental cost-effectiveness. Effects of variations in testing parameters were also examined. For a 30-year-old with schizophrenia, applying the pharmacogenetic test and treating those predicted to respond to clozapine with clozapine-first cost US $47,705 per additional quality-adjusted life-year, compared with treating all patients with conventional agents and reserving clozapine for treatment-resistant patients. In 1-way sensitivity analyses, test sensitivity and cost had the greatest impact on the incremental cost-effectiveness. We conclude that pharmacogenetic tests may achieve utility in clinical psychiatry, although their cost-effectiveness depends on several clinical parameters. More consistent reporting of test parameters such as sensitivity and specificity would greatly facilitate assessment of future pharmacogenetic studies.

The impact of genetic testing on complex diseases

OBJECTIVE

Wide applications for genetic testing in the clinical care of complex diseases have been discussed. However, it has never been quantified to what extent genetic testing could eventually be useful in the clinical care of common disorders. We aimed to quantify the theoretically possible utilization in common ischemic stroke, an example of a complex disease.

METHODS

We computed the possible impact of genetic testing on risk assessment, secondary prevention and prognosis of ischemic stroke. This was done for hypothetical genotypes with different frequencies and effects.

RESULTS

To apply pharmacogenetic secondary prevention based on a genotype with a frequency of 10% and 33% risk reduction, 204 subjects would have to be screened and 110 given genotype specific treatment for 1 year, in order to prevent one recurrent stroke, compared with standard therapy. The application of genetic testing seems to be less promising in risk assessment and the assessment of prognosis of common ischemic stroke.

CONCLUSIONS

The highest impact of genetic testing on clinical practice of stroke will be in the areas of secondary prevention. Given the weak effects of reported susceptibility genotypes, it is theoretically unlikely that genetic screening will be used for the assessment of risk or prognosis of a complex disorder, except for Mendelian types of disease.

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

Background: 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.

[Pharmacogenetics: Important aspects for dermatology]

Pharmacogenetics, pharmacogenomics or metabonomics are terms reflecting a new trend in pharmacology taking into consideration individual factors which influence the effects of drugs. Examples in dermatology include glucose-6-phosphate dehydrogenase-polymorphism (DADPS), dihydropyrimidine dehydrogenase-deficiency (5-Fluoruracil), thiopurine-S-methyltransferase-deficiency (azathioprine), cytochrome P450 isoenzymes and transferases (drug allergy and allergic contact dermatitis), and intolerant reactions to NSAIDs.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

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.

Genetic and Environmental Influences on Antisocial Behaviors: Evidence from Behavioral–Genetic Research

This article reviews behavioral-genetic research into human antisocial behavior. The focus is on studies of antisocial behavior that have been leading the way in investigating environmental and genetic influences on human behavior. The first generation of studies, which provided quantitative estimates attesting that genes and environments each influence about half of the population's variation in antisocial behaviors is interpreted. Then how behavioral-genetic methods are being applied to test developmental theory and to detect environmental causes of antisocial behavior is illustrated. Evidence for interactions between genes and the environment in the etiology of antisocial behavior is also examined. The article ends by envisioning future work on gene-environment interplay in the etiology of antisocial behavior.

Cytochrome P450 Polymorphisms in Geriatric Patients

BACKGROUND AND OBJECTIVE

Up to 23% of the population, depending on their ethnic background, has genetically determined differences in the metabolism of drugs by the cytochrome P450 (CYP) enzymes CYP2C9, CYP2C19 and CYP2D6. The aim of this survey was to determine the relationship between genetical polymorphisms in these CYP enzymes and adverse drug reactions (ADRs) in geriatric patients.

STUDY DESIGN

In a prospective 6-month cohort study of 243 patients in a geriatric rehabilitation ward, mean age 80.2 +/- 7.7 years, ADRs were identified by intensive monitoring by a pharmacoepidemiological team, consisting of pharmacists and physicians. 125 out of these 243 patients were genotyped cross-sectionally for polymorphisms of CYP2C9, CYP2C19 and CYP2D6 by the TaqMan-polymerase chain reaction. The main outcome measures were the prevalence of genetical polymorphisms and the patients' risk for developing an ADR as related to the genotype.

RESULTS

Patients received an average of 14.2 drugs during hospitalisation which led to 251 ADRs in the whole cohort and 149 ADRs in the cross-sectional genotyping study. Genotype frequencies of CYP2C9 enzyme were 25.9% (n = 29) intermediate metabolisers (IMs) and 2.7% (n = 3) poor metabolisers (PMs). For the enzyme CYP2C19, 26.8% (n = 33) IMs and 0.8% (n = 1) PMs were detected. For the enzyme CYP2D6, 24.1% (n = 26) IMs and 3.7% (n = 4) PMs were found in the analysed patient population. In total, 61.6% (n = 77) of genotyped patients experienced mutations in at least one of the three cytochrome enzymes. The ADR rate did not differ significantly between patients with genetic mutations and wild-type genotype patients. Moreover, only eight out of 40 ADRs which were associated with drugs metabolised by CYP2C9, CYP2C19 or CYP2D6 were detected in patients with IM genotype and none in patients with PM genotype.

CONCLUSION

In this investigation geriatric patients showed a high rate of ADRs. However, no association between the ADR rate and the patients' genotype could be detected, which most likely was a result of the small number of patient samples analysed. Although prophylactic genotyping would have not prevented ADRs in this pilot study, physicians nevertheless have to be aware of potential genetic mutations in patients with polypharmacy.

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.

Cost-effectiveness analysis of HLA B*5701 genotyping in preventing abacavir hypersensitivity

OBJECTIVE

Abacavir, a human immunodeficiency virus-1 (HIV-1) nucleoside-analogue reverse transcriptase inhibitor, causes severe hypersensitivity in 4-8% of patients. HLA B*5701 is a known genetic risk factor for abacavir hypersensitivity in Caucasians. Our aim was to confirm the presence of this genetic factor in our patients, and to determine whether genotyping for HLA B*5701 would be a cost-effective use of healthcare resources.

METHODS

Patients with and without abacavir hypersensitivity were identified from a UK HIV clinic. Patients were genotyped for HLA B*5701, and pooled data used for calculation of test characteristics. The cost-effectiveness analysis incorporated the cost of testing, cost of treating abacavir hypersensitivity, and the cost and selection of alternative antiretroviral regimens. A probabilistic decision analytic model (comparing testing versus no testing) was formulated and Monte Carlo simulations performed.

RESULTS

Of the abacavir hypersensitive patients, six (46%) were HLA B*5701 positive, compared to five (10%) of the non-hypersensitive patients (odds ratio 7.9 [95% confidence intervals 1.5-41.4], P = 0.006). Pooling of our data on HLA B*5701 with published data resulted in a pooled odds ratio of 29 (95% CI 6.4-132.3; P < 0.0001). The cost-effectiveness model demonstrated that depending on the choice of comparator, routine testing for HLA B*5701 ranged from being a dominant strategy (less expensive and more beneficial than not testing) to an incremental cost-effectiveness ratio (versus no testing) of Euro 22,811 per hypersensitivity reaction avoided.

CONCLUSIONS

Abacavir hypersensitivity is associated with HLA B*5701, and pre-prescription pharmacogenetic testing for this appears to be a cost-effective use of healthcare resources.

Genetic variation and exposure related risk estimation: will toxicology enter a new era? DNA repair and cancer as a paradigm

With the vast technological and informational resources increasingly available from investments in "genomics," toxicology and much of biological science, is faced with previously undreamed of opportunities and equally daunting challenges. The ability to generate the large quantities of data becoming routinely available could not be imagined a decade ago. The complexities of data analysis are increasingly the rate-limiting element in scientific advances. The expectations that these large scientific investments will reduce the incidence of human disease and improve health are very high. An emphasis on genetic variation and Toxicogenetics is expected to yield risk estimates for specific rather than average individuals and individuals with varied lifestyles and complex patterns of exposure. Examples from studies of polymorphic variation in DNA repair genes in the healthy population and cancer risk highlight the complexity and challenges of incorporating genetic variation into quantitative estimates of risk associated with environmentally relevant exposures. Similar issues exist in selecting the animal models most appropriate for predicting human risk from environmental exposures to toxic agents.

Ethical implications in genetic counseling and family studies of the epilepsies

Most of the inherited epilepsies do not follow a Mendelian inheritance pattern but rather are complex disorders. This leads us to reconsider the traditional ethical framework applying to genetics, which is still based largely on the understanding of Mendelian inheritance, to ethically use the genetic tests likely to be forthcoming for the prevention and surveillance of epilepsies. This article is a review of the ethical issues raised by family studies of the epilepsies, in both a clinical and a research context. These issues include the use of genetic tests, the scope of genetic counseling, the upholding of the risk-benefit ratio in pharmacogenetics, as well as those related to the availability of treatments, health professionals' changing responsibilities, and the communication within families. A reasonable approach calls for a case-by-case determination of whether the benefit and harm of genetic testing outweigh benefit and harm of protecting autonomy and nonmaleficence.

Pharmacogenetics

This article provides an introduction to the discipline of pharmacogenetics and discusses the implications of pharmacogenetics research for primary care practice. Examples are given of how genetic information can predict and inform; drug interactions influencing drug efficacy, metabolism, dosing, and toxicity. Caveats on the need for vigilance in the interpretation of pharmacogenetics studies are discussed briefly, together with the need for a convergence of biomolecular research, translational research, education,and policy to promote evidence-based genetic medicine.

Allele-specific change of concentration and functional gene dose for the prediction of steady-state serum concentrations of amitriptyline and nortriptyline in CYP2C19 and CYP2D6 extensive and intermediate metabolizers

BACKGROUND

Recently, new polymorphisms were described in connection with intermediate and ultrarapid CYP2D6 metabolism. These may allow a much desired prediction of metabolic activity within the extensive metabolizer group. The functional consequences are still being discussed with few data available for clinical patients.

METHODS

We conducted a prospective, blinded two-center study seeking correlations between CYP2C19 (*2,*3, and *4; conventional PCR) and CYP2D6 genotypes (*1 to *10, *35, and *41; real-time and multiplex PCR) and drug concentrations (Emit and HPLC) in 50 Caucasians receiving amitriptyline (AT; 75 mg twice a day).

RESULTS

Eighteen CYP2C19 heterozygotes (*1/*2) had higher AT (P = 0.033) and lower nortriptyline (NT; P = 0.059) concentrations than 30 homozygotes (*1/*1). For CYP2D6, we calculated two new indices, i.e., the allele-specific change of concentration on identical background (ASCOC) and a quantitative functional gene dose. The ASCOC describes the change in NT concentration attributable to a mutant allele compared with the wild type. We found significantly higher concentrations for alleles *4 (95.6%; P <0.0001), *10 (63.3%; P <0.001), and *41 (39.8%; P <0.0001) but not for *2 and *35. Assigning of semiquantitative gene doses of 0, 0.5, or 1 to each allele instead of applying the current classification system (predicted phenotypes: 3 intermediate metabolizers, 46 extensive metabolizers, and 1 ultrarapid metabolizer) produced significant NT concentration differences: gene doses of 0.5 (n =3), 1 (n = 14), 1.5 (n = 11), 2 (n = 21) and 3 (n = 1; P <0.00001).

CONCLUSIONS

AT and NT concentrations can be predicted within the group of CYP2D6 extensive metabolizers. The ASCOC provides substantial advantages compared with current methods of analysis. CYP2D6 but not CYP2C19 correlates with the sum of both concentrations used to guide AT therapy.

Pharmacogenetics and individual variation in the range of amino acid adequacy: the biological aspects

There have been major developments in our understanding of the ways in which genetic variation among individuals in a population can affect responses to drugs, and use of such information can improve the safety and efficacy of medicines. The brief review summarizes the emergence of modern pharmacogenetics, illustrating the importance of the field using the CYP 2D6 polymorphism as a paradigm. These pharmacogenetic polymorphisms are compared and contrasted with the long-established inborn errors of amino acid biochemistry, exemplified by phenylketonuria, suggesting ways in which the approaches of pharmacogenetics might inform the safe and effective use of amino acids as food additives and supplements.

Genetic Testing for Enzymes of Drug Metabolism: Does It Have Clinical Utility for Pain Medicine at the Present Time? A Structured Review

STUDY DESIGN

This is a structured review of genomic (genetic) testing for enzymes of drug metabolism.

OBJECTIVES

Recently, industry began offering genomic testing for enzymes of drug metabolism. As such, the objective of this review was to determine if genomic testing for enzymes of drug metabolism has any imminent clinical relevance for the practice of pain medicine.

METHODS

Relevant references relating to pharmacogenetics, pharmacogenomics, and the metabolizing of drugs used in pain medicine by cytochrome P-450 enzymes were located and reviewed in detail. The P-450 enzymes that metabolize each drug and whether that drug had been identified as being subject to a clinical consequence of a genetic polymorphism of the P-450 enzyme involved in its metabolism were placed into tabular form.

RESULTS OF DATA SYNTHESIS

1) For a large number of drugs, we do not yet know which cytochrome P-450 enzymes are involved in their metabolism; 2) For a large number of drugs, the consequences of a P-450 genetic polymorphism have yet to be determined; 3) Genetic polymorphism can lead to important potential clinical consequences for some opioids, anticonvulsants (phenytoin), benzodiazepines (diazepam), muscle relaxants (succinylcholine), antidepressants (imipramine, nortriptyline, venlafaxine), typical neuroleptics, alcohol, antihypertensives (propranolol, timolol), local anesthetics (procainamide), L-dopa, nicotine, and warfarin. Based on these results, factors for and against using genomic testing were reviewed.

CONCLUSIONS/RECOMMENDATIONS

It was concluded that genomic testing for enzymes of drug metabolism has significant potential for improving the efficacy of drug treatment and reducing adverse drug reactions. Recommendations for when such testing would be useful are outlined.

Using pharmacogenetics and pharmacogenomics in the treatment of psychiatric disorders: some ethical and economic considerations

Current pharmacotherapies for psychiatric disorders are generally incompletely effective. Many patients do not respond well or suffer adverse reactions to these drugs, which can result in poor patient compliance and poor treatment outcome. Adverse drug reactions and non-response are likely to be influenced by genetic polymorphisms. Pharmacogenetics holds some promise for improving the treatment of mood disorders by utilising information about genetic polymorphisms to match patients to the drug therapy that is the most effective with the fewest side effects. Pharmacogenomics promises to facilitate the development of new drugs for treatment. However, these technologies raise many ethical, economic and regulatory issues that need to be addressed before they can be integrated into psychiatry, and medicine more generally. We discuss ethical and policy issues arising from pharmacogenetic testing and pharmacogenomics research, such as informed consent, privacy and confidentiality, research on vulnerable persons and discrimination; and economic viability of pharmacogenetics and pharmacogenomics. We conclude with recommendations for the regulation and distribution of pharmacogenetic testing services and pharmacogenomic drugs.

Pharmacogenomic profiling in postmarketing surveillance: prospects and challenges

Adverse drug reactions (ADRs) represent a major public health and economic global problem. Growing evidence suggests that pharmacogenomics may potentially play a role in reducing drug-induced adverse events. Research efforts are increasingly directed towards this goal. However, knowledge about whether or not pharmacogenomics may be useful as a novel approach in postmarketing surveillance programs is at present rather limited. A critical analysis of some of the methodological design and ethical issues generated by the potential incorporation of pharmacogenomic profiling into pharmacosurveillance programs is presented.