Metabolic Ratios of Psychotropics as Indication of Cytochrome P450 2D6/2C19 Genotype

Therapeutic Drug Monitoring of Psychotropics as a Diagnostic Tool for CYP2D6 Poor Metabolizer Phenotype

BACKGROUND

Interpatient variability in cytochrome P450 2D6 (CYP2D6) enzyme activity alters the serum concentrations of most psychotropics, which often have narrow therapeutic indices. Therefore, preemptive knowledge of CYP2D6 activity is desired. However, accessible indicators for deficient CYP2D6 activity are necessary because genotyping all patients prescribed CYP2D6 metabolized drugs is often not feasible or cost-effective.

METHODS

In this study, the predictive value of the ratio between a CYP2D6 substrate and its metabolite, known as the metabolic ratio (MR), the dose-corrected serum concentration of substrate (CDR), and the dose-corrected sum concentration of substrate and metabolite (Sum CDR) of venlafaxine, risperidone, aripiprazole, and nortriptyline were determined to predict the CYP2D6 poor metabolizer (PM) phenotype. The area-under-the-receiver operator characteristic curve, as well as the sensitivity, specificity, and positive and negative predictive values of the optimal thresholds, were calculated.

RESULTS

Although the MR, CDR, and Sum CDR all predicted the CYP2D6 PM phenotype, the predictive value of the MR was most robust for venlafaxine and aripiprazole, and the Sum CDR was inferior for all 3 psychotropics. MRs of venlafaxine, risperidone, and aripiprazole, and CDR of nortriptyline showed an area-under-the-receiver operator characteristics (95% confidence interval) of 97.2% (94.7%-99.6%), 93.0% (88.8%-97.2%), 97.8% (95.4%-100.0%), and 85.6% (78.0%-93.1%), respectively. Thresholds of the log(MR) of ≥0.1 for venlafaxine, ≥0.0 for risperidone, and ≥1.5 for aripiprazole, and log(CDR) ≥0.5 for nortriptyline produced >92% sensitivity and >64% specificity.

CONCLUSIONS

If therapeutic drug monitoring is available, the thresholds presented here could serve as a diagnostic tool for the CYP2D6 PM phenotype of psychiatric patients prescribed the aforementioned psychotropic medications.

The Future of Analytical and Interpretative Toxicology: Where are We Going and How Do We Get There?

(Forensic) toxicology has faced many challenges, both analytically and interpretatively, especially in relation to an increase in potential drugs of interest. Analytical toxicology and its application to medicine and forensic science have progressed rapidly within the past centuries. Technological innovations have enabled detection of more substances with increasing sensitivity in a variety of matrices. Our understanding of the effects (both intended and unintended) have also increased along with determination and degree of toxicity. However, it is clear there is even more to understand and consider. The analytical focus has been on typical matrices such as blood and urine but other matrices could further increase our understanding, especially in postmortem (PM) situations. Within this context, the role of PM changes and potential redistribution of drugs requires further research and identification of markers of its occurrence and extent. Whilst instrumentation has improved, in the future, nanotechnology may play a role in selective and sensitive analysis as well as bioassays. Toxicologists often only have an advisory impact on pre-analytical and pre-interpretative considerations. The collection of appropriate samples at the right time in an appropriate way as well as obtaining sufficient circumstance background is paramount in ensuring an effective analytical strategy to provide useful results that can be interpreted within context. Nevertheless, key interpretative considerations such as pharmacogenomics and drug-drug interactions as well as determination of tolerance remain and in the future, analytical confirmation of an individual's metabolic profile may support a personalized medicine and judicial approach. This should be supported by the compilation and appropriate application of drug data pursuant to the situation. Specifically, in PM circumstances, data pertaining to where a drug was not/may have been/was contributory will be beneficial with associated pathological considerations. This article describes the challenges faced within toxicology and discusses progress to a future where they are being addressed.

Quantitation of escitalopram and its metabolites by liquid chromatography-tandem mass spectrometry in psychiatric patients: New metabolic ratio establishment

Therapeutic drug monitoring (TDM) is used to determine the concentration of drug in plasma/serum to adjust the dose of the therapeutic drug. Selective and sensitive analytical methods are used to determine drug and metabolite levels for the successful application of TDM. The aim of the study was to develop and validate using LC-MS/MS to analyse quantitative assay of escitalopram (S-CT) and metabolites in human plasma samples. In order to provide a convenient and safe treatment dose, it was aimed to determine the levels of S-CT and its metabolites in the patients' plasma. A new method with short sample preparation and analysis time was developed and validated using LC-MS/MS to analyse quantitative assay of S-CT and its metabolites in plasma. Also, plasma samples of 30 patients using 20 mg S-CT between the ages of 18 and 65 years were analysed by the validated method. The mean values of S-CT, demethyl escitalopram and didemethyl escitalopram in plasma of patients were 27.59, 85.52 and 44.30 ng/mL, respectively. At the end of the analysis, the metabolic ratio of S-CT and metabolites was calculated. It is considered that the method for the quantitative analysis of S-CT and its metabolites in human plasma samples may contribute to the literature on account of its sensitive and easy application. Additionally, the use of our data by physicians will contribute to the effective drug treatment for their patients who take S-CT.

Seizure Induced by a Therapeutic Dose of Venlafaxine ER: A Case Report

Venlafaxine is a selective serotonin and norepinephrine reuptake inhibitor commonly used for the treatment of depression. Although listed as an adverse reaction, seizure activity associated with a therapeutic dose of venlafaxine has rarely been documented. A review of the literature reveals only 2 cases of venlafaxine-induced seizures, both of which were generalized tonic-clonic seizures in patients on doses at the higher end of the therapeutic range. We report the case of a 44-year-old woman undergoing antituberculosis therapy who suffered complex partial seizures after ingestion of a low therapeutic dose of venlafaxine extended release (ER). Her first seizure was observed soon after venlafaxine ER was titrated from 37.5 to 75 mg daily, with a total of 9 witnessed complex partial seizures. After titrating the dose of the venlafaxine ER back down to 37.5 mg daily and beginning lamotrigine anticonvulsant therapy, the patient exhibited no further seizures. The development of seizure activity under therapeutic dosing of venlafaxine should be brought to the attention of the health care prescriber. The potential for drug-drug interactions involving venlafazine, particularly in combination with multiple drugs, such as isoniazid and levofloxacin, needs to be recognized.

Intuitive pharmacogenetic dosing of risperidone according to CYP2D6 phenotype extrapolated from genotype in a cohort of first episode psychosis patients

Risperidone (R) is the most prescribed antipsychotic drug for patients with a first episode of psychosis (FEP). In a naturalistic cohort of chronic psychiatric inpatients, we demonstrated that clinicians adjust R dosage by CYP2D6 activity, despite being blinded to the genotype, which we described as an "intuitive pharmacogenetic" process. The aim of the present study is to replicate our previous findings of intuitive pharmacogenetic in a cohort of FEP patients using CYP2D6 phenotype extrapolated from genotypes. 70 FEP patients, under baseline treatment with R monotherapy were genotyped using the iPLEX® ADME PGx multiplex panel and TaqMan® Genotyping and Copy Number Assays. Plasma concentrations of R and its metabolite, 9-hydroxyrisperidone (9-OH), were determined. The predictive properties of those variables associated with R dosage were tested using a multiple linear regression model as well as regression trees. Significant differences in the mean daily dosage of R among CYP2D6 phenotypes were observed (Kruskal-Wallis test p=0.02): PM (4.00±2.3mg/mL), IM (4.56±2.44), EM (6.22±4.0mg/day) and UM (10.20±4.91mg/day). However, non-significant differences were observed in the R/9-OH ratio or in the Concentration/Dose ratio. Regression tree provided better estimations of R dosage than the multiple linear regression model (MAE=0.958 and R²=0.871). We confirm the "intuitive pharmacogenetic" dosing of R according to the CYP2D6 phenotype in a FEP cohort. The results presented provides a rationale for the clinical use of CYP2D6 genotyping in personalized medicine.

CYP2D6 and CYP2C19 genotyping in psychiatric patients on psychotropic medication in the former Dutch Antilles

AIM

This study was aimed to asses the prevalence of CYP2D6 and CYP2C19 polymorphisms in psychiatric patients and in volunteers from Dutch caribbean origin.

METHODS

In total, 435 individuals were genotyped for CYP2D6 and CYP2C19. Of these, 269 were psychiatric patients on psychotropic medication, living in Curaçao and 166 were volunteers from the Dutch Caribbean population.

RESULTS

No differences in prevalence of alleles were found.

CONCLUSION

Although prevalence of alleles appeared to be very different from African and Caucasian populations, the distribution into predicted phenotypes shows an equal distribution as in Caucasians.

Should a routine genotyping of CYP2D6 and CYP2C19 genetic polymorphisms be recommended to predict venlafaxine efficacy in depressed patients treated in psychiatric settings?

AIM

The antidepressant venlafaxine (VEN) is metabolized by CYP2D6 and CYP2C19. The aim of this study was to assess the relevance of generalizing to daily practice the genotyping of CYP2D6 and CYP2C19 to predict VEN efficacy in depressed patients treated in psychiatric settings.

PATIENTS & METHODS

This study was nested in a naturalistic cohort, with 206 patients requiring a new antidepressant treatment and genotyped for CYP2D6 *3, *4, *5 del, *6, *2xN, *10, *41 and CYP2C19 *2, *3, *4, *5, *17 alleles.

RESULTS

CYP2D6 and CYP2C19 phenotypes were associated neither with the Hamilton depression rating scale score improvement, nor with response and remission.

CONCLUSION

Routine CYP2D6 and CYP2C19 genotyping cannot be recommended to predict VEN efficacy in depressed patients treated in psychiatry settings.

Clinically relevant genetic variants of drug-metabolizing enzyme and transporter genes detected in Thai children and adolescents with autism spectrum disorder

Single-nucleotide polymorphisms (SNPs) among drug-metabolizing enzymes and transporters (DMETs) influence the pharmacokinetic profile of drugs and exhibit intra- and interethnic variations in drug response in terms of efficacy and safety profile. The main objective of this study was to assess the frequency of allelic variants of drug absorption, distribution, metabolism, and elimination-related genes in Thai children and adolescents with autism spectrum disorder. Blood samples were drawn from 119 patients, and DNA was extracted. Genotyping was performed using the DMET Plus microarray platform. The allele frequencies of the DMET markers were generated using the DMET Console software. Thereafter, the genetic variations of significant DMET genes were assessed. The frequencies of SNPs across the genes coding for DMETs were determined. After filtering the SNPs, 489 of the 1,931 SNPs passed quality control. Many clinically relevant SNPs, including CYP2C19*2, CYP2D6*10, CYP3A5*3, and SLCO1B1*5, were found to have frequencies similar to those in the Chinese population. These data are important for further research to investigate the interpatient variability in pharmacokinetics and pharmacodynamics of drugs in clinical practice.

[Pharmacogenetic-based risk assessment of antipsychotic-induced extrapyramidal symptoms]

"Typical" antipsychotics remain the wide-prescribed drugs in modern psychiatry. But these drugs are associated with development of extrapyramidal symptoms (EPS). Preventive methods of EPS are actively developed and they concentrate on personalized approach. The method of taking into account genetic characteristics of patient for prescribing of treatment was proven as effective in cardiology, oncology, HIV-medicine. In this review the modern state of pharmacogenetic research of antipsychotic-induced EPS are considered. There are pharmacokinetic and pharmacodynamic factors which impact on adverse effects. Pharmacokinetic factors are the most well-studied to date, these include genetic polymorphisms of genes of cytochrome P450. However, evidence base while does not allow to do the significant prognosis of development of EPS based on genetic testing of CYP2D6 and CYP7A2 polymorphisms. Genes of pharmacodynamics factors, which realize the EPS during antipsychotic treatment, are the wide field for research. In separate part of review research of such systems as dopaminergic, serotonergic, adrenergic, glutamatergic, GABAergic, BDNF were analyzed. The role of oxidative stress factors in the pathogenesis of antipsychotic-induced EPS was enough detailed considered. The system of those factors may be used for personalized risk assessment of antipsychotics' safety in the future. Although there were numerous studies, the pharmacogenetic-based prevention of EPS before prescribing of antipsychotics was not introduced. However, it is possible to distinguish the most perspectives markers for further research. Furthermore, brief review of new candidate genes provides here, but only preliminary results were published. The main problem of the field is the lack of high- quality studies. Moreover, the several results were not replicated in repeat studies. The pharmacogenetic-based research must be standardized by ethnicity of patients. But there is the ethnical misbalance in world literature. These facts explain why the introduction of pharmacogenetic testing for risk assessment of antipsychotic-induced EPS is so difficult to achieve.

Pharmacogenetics of major depressive disorder: top genes and pathways toward clinical applications

The pharmacogenetics of antidepressants has been not only a challenging but also frustrating research field since its birth in the 1990s. Indeed, great expectations followed the first evidence of familiar aggregation of antidepressant response. Despite the progress from candidate gene studies to genome-wide association studies (GWAS), results fell out the expectations and they were often inconsistent. Anyway, the cumulative evidence supports the involvement of some genes and molecular pathways in antidepressant efficacy. The best single genes are SLC6A4, HTR2A, BDNF, GNB3, FKBP5, ABCB1, and cytochrome P450 genes (CYP2D6 and CYP2C19). Molecular pathways involved in inflammation and neuroplasticity show the greatest support. The first studies evaluating benefits of genotype-guided antidepressant treatments provided encouraging results and confirmed the relevance of SLC6A4, HTR2A, ABCB1, and cytochrome P450 genes. Further progress in genotyping and data analysis would allow to move forward and complete the understanding of antidepressant pharmacogenetics and its translation into clinical applications.

Pharmacogenetics informed decision making in adolescent psychiatric treatment: a clinical case report

Advances made in genetic testing and tools applied to pharmacogenetics are increasingly being used to inform clinicians in fields such as oncology, hematology, diabetes (endocrinology), cardiology and expanding into psychiatry by examining the influences of genetics on drug efficacy and metabolism. We present a clinical case example of an adolescent male with anxiety, attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder who did not tolerate numerous medications and dosages over several years in attempts to manage his symptoms. Pharmacogenetics testing was performed and DNA results on this individual elucidated the potential pitfalls in medication use because of specific pharmacodynamic and pharmacokinetic differences specifically involving polymorphisms of genes in the cytochrome p450 enzyme system. Future studies and reports are needed to further illustrate and determine the type of individualized medicine approach required to treat individuals based on their specific gene patterns. Growing evidence supports this biological approach for standard of care in psychiatry.

Hydroxylation index of omeprazole in relation to CYP2C19 polymorphism and sex in a healthy Iranian population

BACKGROUND

Polymorphism of CYP2C19 gene is one of the important factors in pharmacokinetics of CYP2C19 substrates. Omeprazole is a proton pump inhibitor which is mainly metabolized by cytochrome P450 2C19 (CYP2C19). The aim of present study was to assess omeprazole hydroxylation index as a measure of CYP2C19 activity considering new variant allele (CYP2C19*17) in Iranian population and also to see if this activity is sex dependent.

METHODS

One hundred and eighty healthy unrelated Iranian individuals attended in this study. Blood samples for genotyping and phenotyping were collected 3 hours after administration of 20 mg omeprazole orally. Genotyping of 2C19 variant alleles *2, *3 and *17 was performed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and semi-nested PCR methods. Plasma concentrations of omeprazole and hydroxyomeprazole were determined by high performance liquid chromatography (HPLC) technique and hydxroxylation index (HI) (omeprazole/ hydroxyomeprazole) was calculated.

RESULTS

The CYP2C19*17 was the most common variant allele in the studied population (21.6%). Genotype frequencies of CYP2C19*17*17, *1*17, and *2*17 were 5.5%, 28.8% and 3.3% respectively. The lowest and the highest median omeprazole HI was observed in *17*17 and *2*2 genotypes respectively (0.36 vs. 13.09). The median HI of omeprazole in subjects homozygous for CYP2C19*1 was 2.16-fold higher than individuals homozygous for CYP2C19*17 (P < 0.001) and the median HI of CYP2C19*1*17 genotype was 1.98-fold higher than CYP2C19 *17*17 subjects (P < 0.001). However, subjects with CYP2C19*2*17 (median HI: 1.74) and CYP2C19*1*2 (median HI: 1.98) genotypes and also CYP2C19*1*17 (median HI: 0.71) and CYP2C19*1*1 (mean HI: 0.78) did not show any significantly different enzyme activity. In addition, no statistically significant difference was found between women and men in distribution of CYP2C19 genotypes. Furthermore, the hydroxylation index of Omeprazole was not different between women and men in the studied population.

CONCLUSION

Our data point out the importance of CYP2C19*2 and CYP2C19*17 variant alleles in metabolism of omeprazole and therefore CYP2C19 activity. Regarding the high frequency of CYP2C19*17 in Iranian population, the importance of this new variant allele in metabolism of CYP2C19 substrates shall be considered.

First MEPS/HPLC assay for the simultaneous determination of venlafaxine and O-desmethylvenlafaxine in human plasma

Background: A new high-performance liquid chromatography–fluorescence detection assay based on microextraction by packed sorbent as sample preparation approach is described to quantify venlafaxine (VEN) and its main metabolite [O-desmethylvenlafaxine (ODV)]in human plasma. Methods & results: Chromatographic separation of the target analytes (VEN and ODV) and internal standard (licarbazepine) was achieved in less than 6 min on a reverse-phase C18 column using isocratic elution. Calibration curves were linear in the ranges of 10–1000 ng ml-1 for VEN and 20–1000 ng ml-1 for ODV. The method was successfully applied to real plasma samples. Conclusion: This microextraction by packed sorbent/high-performance liquid chromatography–fluorescence detection assay offers a cost-effective tool that can be applied for therapeutic drug monitoring and also support other pharmacokinetic-based studies in humans.

Clinical validity of cytochrome P450 metabolism and serotonin gene variants in psychiatric pharmacotherapy

Adverse events, response failures and medication non-compliance are common in patients receiving medications for the treatment of mental illnesses. A systematic literature review assessed whether pharmacokinetic (PK) or pharmacodynamic (PD) responses to 26 commonly prescribed antipsychotic and antidepressant medications, including efficacy or side effects, are associated with nucleotide polymorphisms in eight commonly studied genes in psychiatric pharmacotherapy: CYP2D6, CYP2C19, CYP2C9, CYP1A2, CYP3A4, HTR2C, HTR2A, and SLC6A4. Of the 294 publications included in this review, 168 (57%) showed significant associations between gene variants and PK or PD outcomes. Other studies that showed no association often had insufficient control for confounding variables, such as co-medication use, or analysis of medications not substrates of the target gene. The strongest gene-outcome associations were for the PK profiles of CYP2C19 and CYP2D6 (93% and 90%, respectively), for the PD associations between HTR2C and weight gain (57%), and for SLC6A4 and clinical response (54%), with stronger SLC6A4 response associations for specific drug classes (60-83%). The preponderance of evidence supports the validity of analyzing nucleotide polymorphisms in CYP and pharmacodynamic genes to predict the metabolism, safety, or therapeutic efficacy of psychotropic medications commonly used for the treatment of depression, schizophrenia, and bipolar illness.

CYP450 pharmacogenetic treatment strategies for antipsychotics: a review of the evidence

Although a number of first- and second-generation antipsychotics are available, achieving optimal therapeutic response for patients with schizophrenia can be challenging. The presence of polymorphic alleles for cytochrome P (CYP) 450 may result in lack of expression, altered levels of expression, or altered function of CYP450 enzymes. CYP2D6, CYP1A2, and CYP3A4/5 are major enzymes in the metabolism of antipsychotics and polymorphisms of alleles for these proteins are associated with altered plasma levels. Consequently, standard dosing may result in drug plasma concentrations that are subtherapeutic or toxic in some patients. Patient CYP450 genotype testing can predict altered pharmacokinetics, and is currently available and relatively inexpensive. Evidence-based guidelines provide dose recommendations for some antipsychotics. To date few studies have demonstrated a significant association with genotype-guided antipsychotic use and clinical efficacy. However, many studies have been small, retrospective or cohort designs, and many have not been adequately powered. Numerous studies have shown a significant association between genotype and adverse effects, such as CYP2D6 polymorphisms and tardive dyskinesia. This review summarizes evidence for the role of CYP450 genetic variants in the response to antipsychotic medications and the clinical implications of pharmacogenetics in the management of patients with schizophrenia.

Pharmacogenetics of antidepressant drugs: an update after almost 20 years of research

Major depressive disorder (MDD) is an emergent cause of personal and socio-economic burden, both for the high prevalence of the disorder and the unsatisfying response rate of the available antidepressant treatments. No reliable predictor of treatment efficacy and tolerance in the single patient is available, thus drug choice is based on a trial and error principle with poor clinical efficiency. Among modulators of treatment outcome, genetic polymorphisms are thought to explain a significant share of the inter-individual variability. The present review collected the main pharmacogenetic findings primarily about antidepressant response and secondly about antidepressant induced side effects, and discussed the main strengths and limits of both candidate and genome-wide association studies and the most promising methodological opportunities and challenges of the field. Despite clinical applications of antidepressant pharmacogenetics are not available yet, previous findings suggest that genotyping may be applied in the clinical practice. In order to reach this objective, further rigorous pharmacogenetic studies (adequate sample size, study of better defined clinical subtypes of MDD, adequate covering of the genetic variability), their combination with the results obtained through complementary methodologies (e.g., pathway analysis, epigenetics, transcriptomics, and proteomics), and finally cost-effectiveness trials are required.

Therapeutic Drug Monitoring of Antidepressants and Cytochrome P450 Genotyping in General Practice

In the psychiatric setting, therapeutic drug monitoring and genotyping for cytochrome P450 (CYP) polymorphisms help to ensure and maintain therapeutic drug levels. In this study, the authors extended the therapeutic drug monitoring and genotyping protocol routinely used in their psychiatric clinic to primary care patients treated with antidepressants. They examined the variation in serum concentrations and assessed the role of CYP polymorphisms, wrong dosing, and noncompliance in deviating serum concentrations. Of 227 serum concentrations obtained, 127 (56%) were more than 20% outside therapeutic ranges. Of these 127 cases, 64 (50%) were congruous with aberrant CYP2D6 or CYP2C19 genotypes, incorrect dosing, or a pharmacy record suggesting noncompliance. Prevalence of aberrant CYP2D6 and CYP2C19 genotypes did not differ significantly between the investigated primary care patients and 751 secondary care users of antidepressants. The therapeutic drug monitoring and the genotyping findings resulted in recommendations to physicians to alter the medication strategy of 146 (64%) patients. These results strongly suggest that the rationale for therapeutic drug monitoring and CYP genotyping when prescribing antidepressants in secondary care also applies to the primary care setting.

Effect of cytochrome P450 enzyme polymorphisms on pharmacokinetics of venlafaxine

This study examines the relationship between blood concentrations of venlafaxine and its active metabolite, O-desmethyl venlafaxine (ODV), and genetic variants of the cytochrome P450 enzymes CYP2D6 and CYP2C19 in human subjects. Trough blood concentrations were measured at steady state in patients treated with venlafaxine extended release in a clinical practice setting. CYP2D6 and CYP2C19 genotypes were converted to activity scores based on known activity levels of the two alleles comprising a genotype. After adjusting for drug dose and gender effects, higher CYP2D6 and CYP2C19 activity scores were significantly associated with lower venlafaxine concentrations (P < 0.001 for each). Only CYP2D6 was associated with the concentration of ODV (P < 0.001), in which genotypes with more active alleles were associated with higher ODV concentrations. The sum of venlafaxine plus ODV concentration showed the same pattern as venlafaxine concentrations with CYP2D6 and CYP2C19 genotypes with higher activity scores being associated with a lower venlafaxine plus ODV concentration (2D6 P = 0.01; 2C19 P < 0.001). Because allelic variants in both CYP2D6 and CYP2C19 influence the total concentration of the active compounds venlafaxine and ODV, both CYP2D6 and CYP2C19 genotypes should be considered when using pharmacogenomic information for venlafaxine dose alterations.

Genetic polymorphisms of cytochrome P450 enzymes and antidepressant metabolism

INTRODUCTION

The cytochrome P450 (CYP) enzymes are the major enzymes responsible for Phase I reactions in the metabolism of several substances, including antidepressant medications. Thus, it has been hypothesized that variants in the CYP network may influence antidepressant efficacy and safety. Nonetheless, data on this field are still contradictory. The authors aim to give an overview of the published studies analyzing the influence of CYP highly polymorphic loci on antidepressant treatment in order to translate the acquired knowledge to a clinical level.

AREAS COVERED

The authors collected and compared experimental works and reviews published from the 1980s to the present and included in the Medline database. The included studies pertain to the effects of CYP gene polymorphisms on antidepressant pharmacokinetic parameters and clinical outcomes (response and drug-related adverse effects), with a focus on applications in clinical practice. The authors focused mainly on in vivo studies in humans (patients or healthy volunteers).

EXPERT OPINION

Great variability in antidepressant metabolism among individuals has been demonstrated. Thus, with the current interest in individualized medicine, several genetic tests to detect CYP variants have been produced. They provide a potentially useful way to anticipate some clinical outcomes of antidepressant treatment, although they will only be extensively used in clinical practice if precise and specific treatment options and guidelines based on genetic tests can be provided.

Fatal venlafaxine poisonings are associated with a high prevalence of drug interactions

Venlafaxine (VEN) is an antidepressant found to possess a higher fatal toxicity index (FTI, i.e., deaths in proportion to consumption) than other newer antidepressants and selective serotonin reuptake inhibitors (SSRIs). The aim of this study was to elucidate using post-mortem cases whether the apparent high toxicity of VEN is associated with adverse drug interactions, pharmacogenetic factors and/or the manner of death. Within a 2-year period, a comprehensive post-mortem database and death certificates were searched for cases with laboratory findings of VEN, findings of other drugs, associated background information and the cause and manner of death. In 123 cases, the concentrations of VEN and its two metabolites, O-desmethylvenlafaxine (O-VEN) and N-desmethylvenlafaxine (N-VEN), and the CYP2D6 genotype were determined in post-mortem blood. The median concentrations of VEN, O-VEN and N-VEN were 560, 420 and 49 µg/l, respectively. A prominent feature of the VEN-positive cases was the high abundance of interacting drugs (46%), being more common with higher VEN concentrations. Compared to other common antidepressants, VEN-positive cases showed the highest suicide frequency, but also the proportion of suicidal VEN poisonings of all suicides was substantially higher than that of mirtazapine or SSRIs. Relative CYP2D6 activity did not predispose to high VEN concentrations, and the frequency of the extreme phenotypes followed the general population. In conclusion, the high suicide potential of VEN in combination with the high prevalence of drugs causing adverse interactions could be the reason for the observed high FTI.

Future perspective for diagnosis in autoimmune diseases

Human beings have taken successive approaches for the understanding and management of diseases. Initially brewed in supernatural concepts and mystical procedures, a vigorous scientific approach has emerged on the grounds of fundamental disciplines such as anatomy, microbiology, biochemistry, physiology, immunology, pathology, and pharmacology. The resulting integrated knowledge contributed to the current classification of diseases and the way Medicine is carried out today. Despite considerable progress, this approach is rather insufficient when it comes to systemic inflammatory conditions, such as systemic lupus erythematosus, that covers clinical conditions ranging from mild pauci-symptomatic diseases to rapidly fatal conditions. The treatment for such conditions is often insufficient and novel approaches are needed for further progress in these areas of Medicine. A recent breakthrough has been achieved with respect to chronic auto-inflammatory syndromes, in which molecular dissection of underlying gene defects has provided directions for target-oriented therapy. Such approach may be amenable to application in systemic auto-immune diseases with the comprehension that such conditions may be the consequence of interaction of specific environmental stimuli and an array of several and interconnected gene polymorphisms. On the bulk of this transformation, the application of principles of pharmacogenetics may lead the way towards a progressively stronger personalized Medicine.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

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

Relation between CYP2C19 phenotype and genotype in a group of Brazilian volunteers

The CYP2C19 gene presents polymorphism affecting the pharmacokinetics of several drugs of clinical importance. The purpose of this study was to investigate the correlation between CYP2C19 genotype and metabolic phenotype in a group of 38 Brazilian volunteers, evaluating the phenotype prediction capacity of the genotyping procedure. For CYP2C19 phenotyping, omeprazole was used as the probe drug, using the hydroxylation metabolic ratio as the phenotypic indicator. Venous blood samples were drawn before and three hours after an oral administration of 20 mg omeprazole. The plasma concentrations of omeprazole and hydroxy-omeprazole were determined by high performance liquid chromatography. The genotyping assay was carried out using a Real-Time-PCR-based assay, identifying the alleles *1 (completely functional), *2, *3 and *4 (null). The phenotyping procedure estimated the presence of 4 poor, 34 extensive and 1 ultra-extensive metabolizer. The genotyping identified 4 poor, 23 extensive and 11 intensive metabolizers. The groups of volunteers classified according to the number of active alleles of CYP2C19 had significant differences in the metabolic ratios of omeprazole hydroxylation. However, volunteers exhibiting the same number of active alleles presented different phenotypes. Therefore, the phenotyping of CYP2C19 is a more promising alternative to dose individualization of CYP2C19 substrate drugs.

Haloperidol and risperidone have specific effects on altered pain sensitivity in the ketamine model of schizophrenia

RATIONALE

The ketamine (ket) model reflects features of schizophrenia as well as secondary symptoms such as altered pain sensitivity.

OBJECTIVES

In the present study, we investigated the effect of subchronic oral treatment with haloperidol (hal, 0.075 mg/kg) and risperidone (ris, 0.2 mg/kg) on altered pain perception and locomotor activity in this model.

RESULTS

In reaction to 5 mg/kg morphine, ket pretreated animals showed a diminished analgesic response. Hal had no analgesic effect per se, but the compound normalised the analgesic reaction to morphine in the ket pretreated animals. The effect of ris was complex. First, there was no analgesic effect per se, and control animals showed a dose-dependent increase in the analgesic index after morphine injection. In the ket group treated with ris, the analgesic response to 5 mg/kg morphine was attenuated and in response to 10 mg/kg analgesia was comparable with that measured in controls. The reduced analgesic effect was not due to pharmacokinetic differences in morphine metabolism. After administration via drinking water in saline-injected control animals, the hal blood serum concentration was 2.6 +/- 0.45 ng/ml. In ket-injected animals, the mean serum concentration of hal amounted to 1.2 +/- 0.44 ng/ml. In the experiment using ris, animals in the control group had higher ris serum concentrations compared with ket-injected animals. In control animals, morphine dose dependently decreased locomotor activity. This effect was significantly stronger in the ket pretreated groups.

CONCLUSIONS

Hal and ris had different effects on altered pain sensitivity. It was hypothesised that these results are connected with alterations in dopamine D2 and mu opioid receptor binding.

Influence of cytochrome P450 polymorphisms on drug therapies: pharmacogenetic, pharmacoepigenetic and clinical aspects

The polymorphic nature of the cytochrome P450 (CYP) genes affects individual drug response and adverse reactions to a great extent. This variation includes copy number variants (CNV), missense mutations, insertions and deletions, and mutations affecting gene expression and activity of mainly CYP2A6, CYP2B6, CYP2C9, CYP2C19 and CYP2D6, which have been extensively studied and well characterized. CYP1A2 and CYP3A4 expression varies significantly, and the cause has been suggested to be mainly of genetic origin but the exact molecular basis remains unknown. We present a review of the major polymorphic CYP alleles and conclude that this variability is of greatest importance for treatment with several antidepressants, antipsychotics, antiulcer drugs, anti-HIV drugs, anticoagulants, antidiabetics and the anticancer drug tamoxifen. We also present tables illustrating the relative importance of specific common CYP alleles for the extent of enzyme functionality. The field of pharmacoepigenetics has just opened, and we present recent examples wherein gene methylation influences the expression of CYP. In addition microRNA (miRNA) regulation of P450 has been described. Furthermore, this review updates the field with respect to regulatory initiatives and experience of predictive pharmacogenetic investigations in the clinics. It is concluded that the pharmacogenetic knowledge regarding CYP polymorphism now developed to a stage where it can be implemented in drug development and in clinical routine for specific drug treatments, thereby improving the drug response and reducing costs for drug treatment.

Quantification of Drugs in Plasma Without Primary Reference Standards by Liquid Chromatography-Chemiluminescence Nitrogen Detection: Application to Tramadol Metabolite Ratios

Lack of availability of reference standards for drug metabolites, newly released drugs, and illicit drugs hinders the analysis of these substances in biologic samples. To counter this problem, an approach is presented here for quantitative drug analysis in plasma without primary reference standards by liquid chromatography-chemiluminescence nitrogen detection (LC-CLND). To demonstrate the feasibility of the method, metabolic ratios of the opioid drug tramadol were determined in the setting of a pharmacogenetic study. Four volunteers were given a single 100-mg oral dose of tramadol, and a blood sample was collected from each subject 1 hour later. Tramadol, O-desmethyltramadol, and nortramadol were determined in plasma by LC-CLND without reference standards and by a gas chromatography-mass spectrometry reference method. In contrast to previous CLND studies lacking an extraction step, a liquid-liquid extraction system was created for 5-mL plasma samples using n-butyl chloride-isopropyl alcohol (98 + 2) at pH 10. Extraction recovery estimation was based on model compounds chosen according to their similar physicochemical characteristics (retention time, pKa, logD). Instrument calibration was performed with a single secondary standard (caffeine) using the equimolar response of the detector to nitrogen. The mean differences between the results of the LC-CLND and gas chromatography-mass spectrometry methods for tramadol, O-desmethyltramadol, and nortramadol were 8%, 32%, and 19%, respectively. The sensitivity of LC-CLND was sufficient for therapeutic concentrations of tramadol and metabolites. A good correlation was obtained between genotype, expressed by the number of functional genes, and the plasma metabolite ratios. This experiment suggests that a recovery-corrected LC-CLND analysis produces sufficiently accurate results to be useful in a clinical context, particularly in instances in which reference standards are not readily accessible.

Venlafaxine in the treatment of children and adolescents with attention-deficit/hyperactivity disorder

OBJECTIVE

The objectives of this pilot study were to explore the changes in symptom severity, tolerability, and the pharmacodynamics of venlafaxine treatment in youths with attention-deficit/hyperactivity disorder (ADHD).

METHODS

This was a 2-week, open-label, outpatient trial of venlafaxine in children and adolescents, ages 5-17 years, with ADHD. Three dosing strata, 0.5, 1.0, and 2.0 mg/kg per day, were examined. ADHD symptom severity and improvement assessments included the ADHD Rating Scale (ARS-IV) and the Clinical Global Impressions Scale (CGI). During this study, venlafaxine, O-desmethylvenlafaxine (ODV), norepinephrine, and serotonin concentrations were obtained.

RESULTS

Thirty-eight participants (33 males) were treated in this trial. Overall, parent-completed and teacher-completed ARS-IV total scores showed a statistically significant positive change at the end of the study when compared to baseline (p < 0.05). Significant increases in plasma venlafaxine concentrations were observed at day 15 when compared to day 8 (p = 0.04). In addition, plasma norepinephrine and serotonin concentrations were found to be significantly decreased from baseline at end of study (p < 0.05). Four patients ended participation in the study prematurely: lost to follow up (n = 2), withdrawal of consent (n = 1), and worsening of ADHD symptoms after 8 days of treatment (n = 1). There were no discontinuations due to other adverse events.

CONCLUSIONS

Venlafaxine appeared to offer some benefit and appears to be relatively safe for the short-term treatment of ADHD in this open-label trial. The pharmacodynamics of venlafaxine in youths are consistent with serotonergic and neuradrenergic modulation.

Pharmacogenetics of antipsychotics: useful for the clinician?

PURPOSE OF REVIEW

The concept of individualized drug therapy on the basis of pharmacogenetics has become a central focus in psychopharmacology of schizophrenia. This article reviews recent advances in this field with respect to their importance for the clinician.

RECENT FINDINGS

First, there is an increasing agreement about the importance of polymorphisms in cytochrome P450 enzymes and the effects of drug-drug interactions in relation to the incidence of adverse effects. Secondly, prediction of response on the basis of variants in candidate genes is incipient and remains elusive. Thirdly, some advances have been made in understanding the pharmacogenetics of weight gain.

SUMMARY

Despite much effort, only a few of the results are now ready for translation into clinical practice. Cytochrome P450 genotyping would be a big step forward towards a more individualized drug treatment based on molecular diagnostics and could improve treatment, reduce adverse effects and increase compliance of the patients. Another promising field may be that of predicting the antipsychotic-induced weight gain and it is hoped that commercially available DNA tests may be available within the next few years. Prediction of response is still hampered by many methodological and clinical problems and is not yet available to the clinician.