Evidence for involvement of polymorphic CYP2C19 and 2C9 in the N-demethylation of sertraline in human liver microsomes

Hyponatremic Cognitive Dysfunction Resulting from Drug-Drug-Gene Interaction between Sertraline and Cannabidiol in an Intermediate CYP2C19 Metabolizer Patient

Background: Pharmacogenomics (PGx) can provide more precision in determining causation of adverse drug reactions (ADRs) from drug-drug-gene interaction clinical application. Case Summary: Patient was an intermediate CYP2C19 metabolizer on stable therapy taking a low but therapeutic dose of sertraline for depression and anxiety over a period of 20 years. The patient then became hyponatremic and cognitively impaired after addition of cannabidiol (CBD) to this sertraline regimen. The proposed mechanism was drug-drug-gene interaction of CBD further inhibiting the CYP2C19 metabolism of sertraline and increasing drug exposure to produce moderate to severe hyponatremia and subsequent cognitive dysfunction. Practice Implications: Pharmacogenomics (PGx) testing may assist in etiology of patient symptoms from adverse drug reactions (ADRs) or drug-drug interactions by combining these with detection and application of drug-gene interactions. This case shows inhibition of CYP2C19 by CBD to further increase sertraline exposure, producing hyponatremia and subsequent cognitive dysfunction through CYP2C19 phenoconversion by CBD.

Pre-clinical drug-drug interactions (DDIs) of gefitinib with/without losartan and selective serotonin reuptake inhibitors (SSRIs): citalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, and venlafaxine

Objective

Methods

Results

Conclusion

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In vitro hepatocytes assays can predict relevant drug-drug interactions (DDIs).

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Proof-of concept data testing can provide a clear insight of multidrug regimen DDIs.

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Classifying drugs as inhibitors/inducers alone cannot successfully identify DDIs.

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Regimens requiring three or more drugs may cause significant DDIs (p-value < 0.05).

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SSRI metabolism by human hepatocytes can be affected by gefitinib and losartan.

Citalopram and Cannabidiol: In Vitro and In Vivo Evidence of Pharmacokinetic Interactions Relevant to the Treatment of Anxiety Disorders in Young People

BACKGROUND

Cannabidiol (CBD), a major nonintoxicating constituent of cannabis, exhibits anxiolytic properties in preclinical and human studies and is of interest as a novel intervention for treating anxiety disorders. Existing first-line pharmacotherapies for these disorders include selective serotonin reuptake inhibitor and other antidepressants. Cannabidiol has well-described inhibitory action on cytochrome P450 (CYP450) drug-metabolizing enzymes and significant drug-drug interactions (DDIs) between CBD and various anticonvulsant medications (eg, clobazam) have been described in the treatment of epilepsy. Here, we examined the likelihood of DDIs when CBD is added to medications prescribed in the treatment of anxiety.

METHODS

The effect of CBD on CYP450-mediated metabolism of the commonly used antidepressants fluoxetine, sertraline, citalopram, and mirtazapine were examined in vitro. Cannabidiol-citalopram interactions were also examined in vivo in patients (n = 6) with anxiety disorders on stable treatment with citalopram or escitalopram who received ascending daily doses of adjunctive CBD (200-800 mg) over 12 weeks in a recent clinical trial.

RESULTS

Cannabidiol minimally affected the metabolism of sertraline, fluoxetine, and mirtazapine in vitro. However, CBD significantly inhibited CYP3A4 and CYP2C19-mediated metabolism of citalopram and its stereoisomer escitalopram at physiologically relevant concentrations, suggesting a possible in vivo DDI. In patients on citalopram or escitalopram, the addition of CBD significantly increased citalopram plasma concentrations, although it was uncertain whether this also increased selective serotonin reuptake inhibitor-mediated adverse events.

CONCLUSIONS

Further pharmacokinetic examination of the interaction between CBD and citalopram/escitalopram is clearly warranted, and clinicians should be vigilant around the possibility of treatment-emergent adverse effects when CBD is introduced to patients taking these antidepressants.

The role of hepatic cytochrome P450s in the cytotoxicity of sertraline

Sertraline, an antidepressant, is commonly used to manage mental health symptoms related to depression, anxiety disorders, and obsessive-compulsive disorder. The use of sertraline has been associated with rare but severe hepatotoxicity. Previous research demonstrated that mitochondrial dysfunction, apoptosis, and endoplasmic reticulum stress were involved in sertraline-associated cytotoxicity. In this study, we reported that after a 24-h treatment in HepG2 cells, sertraline caused cytotoxicity, suppressed topoisomerase I and IIα, and damaged DNA in a concentration-dependent manner. We also investigated the role of cytochrome P450 (CYP)-mediated metabolism in sertraline-induced toxicity using our previously established HepG2 cell lines individually expressing 14 CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrated that CYP2D6, 2C19, 2B6, and 2C9 metabolize sertraline, and sertraline-induced cytotoxicity was significantly decreased in the cells expressing these CYPs. Western blot analysis demonstrated that the induction of ɣH2A.X (a hallmark of DNA damage) and topoisomerase inhibition were partially reversed in CYP2D6-, 2C19-, 2B6-, and 2C9-overexpressing HepG2 cells. These data indicate that DNA damage and topoisomerase inhibition are involved in sertraline-induced cytotoxicity and that CYPs-mediated metabolism plays a role in decreasing the toxicity of sertraline.

The impact of pregnancy on the pharmacokinetics of antidepressants: a systematic critical review and meta-analysis

Introduction: Pregnancy-related physiological changes exert a crucial impact on the pharmacokinetics of antidepressants; however, the current evidence presents inconsistencies. A clearer understanding of pregnancy-related effects on antidepressant disposition may facilitate the development of guidelines for appropriate dose adjustments during the course of pregnancy based on therapeutic drug monitoring.Areas covered: We systematically reviewed studies comparing antidepressant levels in the same individuals during pregnant and non-pregnant states. Using dose-adjusted plasma concentration measurements, we estimated alteration ratios between the 3rd trimester and baseline (before or after pregnancy). Additionally, we performed a meta-analysis for changes in dose-adjusted concentrations to estimate mean differences.Expert opinion: Data for several antidepressants display clear alteration patterns during pregnancy. On the basis of the alteration ratios trimipramine, fluvoxamine, and nortriptyline show a prominent decrease in dose-adjusted levels, especially in the 3rd trimester. Clomipramine, imipramine, citalopram, and paroxetine show smaller decreases in dose-adjusted concentrations in the third trimester. For escitalopram, venlafaxine and fluoxetine, changes are considered negligible. For sertraline, there was a tendency toward increased dose-adjusted concentrations in pregnancy. Available evidence suffers from major limitations and factors affecting pharmacokinetics have been insufficiently addressed. Further research is required to promote knowledge on pregnancy effects on antidepressant pharmacokinetics.

Pharmacokinetics of serotonergic drugs: focus on OCD

INTRODUCTION

Although the treatment of obsessive-compulsive disorder (OCD), a common, chronic, and disabling psychiatric condition, has significantly improved in the last decades, with the demonstration of the specific effectiveness of serotonin reuptake inhibitors (SRIs), a large proportion of patients still show high relapse rates. In addition, pharmacological treatments should be maintained for years, so that the clinicians should take into account the pharmacokinetic changes in the long-term, which may be responsible for dangerous side effects or interactions. Areas covered: The aim of this paper was to review the literature on the pharmacokinetics of SSRIs and clomipramine, and on their pharmacokinetic parameters in OCD patients. Expert opinion: Although the literature on the pharmacokinetics of both clomipramine and SSRIs is consistent, data on pharmacokinetic parameters in OCD patients are very few. Given the impact of OCD, its chronicity requiring long-term treatments, together with the need to increase the clinical response rate, more studies in this field are urgently required.

P450 Pharmacogenetics in Indigenous North American Populations

Indigenous North American populations, including American Indian and Alaska Native peoples in the United States, the First Nations, Métis and Inuit peoples in Canada and Amerindians in Mexico, are historically under-represented in biomedical research, including genomic research on drug disposition and response. Without adequate representation in pharmacogenetic studies establishing genotype-phenotype relationships, Indigenous populations may not benefit fully from new innovations in precision medicine testing to tailor and improve the safety and efficacy of drug treatment, resulting in health care disparities. The purpose of this review is to summarize and evaluate what is currently known about cytochrome P450 genetic variation in Indigenous populations in North America and to highlight the importance of including these groups in future pharmacogenetic studies for implementation of personalized drug therapy.

Sertraline in pregnancy - Therapeutic drug monitoring in maternal blood, amniotic fluid and cord blood

RATIONALE

This study is the first to measure and correlate sertraline concentrations in maternal blood, amniotic fluid and umbilical cord blood and account for distribution of the drug between these three compartments.

METHODS

Concentrations of sertraline were measured in six mother infant pairs at the time of delivery. Data are provided as median values, first and third quartiles as well as ranges. To account for the penetration ratio into amniotic fluid and cord blood, the concentration of sertraline in both environments was divided by the concentration in maternal serum. Daily doses were correlated with maternal serum- and umbilical cord blood-concentrations, and serum levels were correlated with levels in amniotic fluid.

RESULTS

The median daily dose of sertraline was 75mg (Q1: 43.75mg, Q3: 100mg; range 25-100mg). Amniotic fluid concentrations of sertraline strongly correlated with the daily dose (r=0.833, p=0.039) while neither maternal serum concentrations nor cord blood concentrations correlated with the daily dose (p>0.05). The median penetration ratio for sertraline into amniotic fluid was 0.57 (Q1: 0.28, Q3: 0.75; range: 0.22-0.88). The median penetration ratio into the fetal circulation, calculated on the basis of umbilical cord blood-concentrations, was found to be 0.36 (Q1: 0.28, Q3: 0.49; range: 0.17-0.65).

CONCLUSIONS

Sertraline concentrations in amniotic fluid gave evidence that maternally administered sertraline is constantly accessible to the fetus via amniotic fluid in a manner not previously appreciated. A relatively low penetration into fetal circulation may contribute to a sufficient safety profile of sertraline during pregnancy although in our study APGAR Scores were relatively low in three infants. Our data support the important role of therapeutic drug monitoring in maintaining the safety of pregnant women and exposed infants.

Influence of CYP2B6 and CYP2C19 polymorphisms on sertraline metabolism in major depression patients

BACKGROUND

Genetic polymorphisms in CYP2B6 and CYP2C19 may cause variability in the metabolism of sertraline, a widely used antidepressant in major depressive disorder treatment.

OBJECTIVE

This study investigates the impact of CYP2B6*4 (785A > G), CYP2B6*9 (516G > T), CYP2B6*6 (516G > T + 685G > A) CYP2C19*2 (685G > A), CYP2C19*17 (-3402C > T) polymorphisms on plasma concentrations of sertraline and N-desmethyl sertraline in major depression patients treated with sertraline [n = 50].

SETTING

Participants were patients who admitted to an adult psychiatry outpatient unit at a university hospital. These were DSM-IV major depression diagnosed patients with a stable sertraline medication regimen [for at least one month].

METHODS

CYP2B6*4 (rs 2279343; 785A > G), CYP2B6*9 (516G > T; rs 3745274), CYP2B6*6 (516G > T + 685G > A) CYP2C19*2 (rs 4244285; 685G > A), CYP2C19*17 (rs 11188072; -3402C > T), polymorphisms were analyzed by polymerase chain reaction and restriction fragment length polymorphism. Plasma concentrations were measured by high-performance liquid chromatography in patients treated with SERT.

MAIN OUTCOME MEASURE

The distribution of CYP2B6*4, *6, *9 and CYP2C19*2, *17 among patient group and the association between genotype and sertraline metabolism.

RESULTS

Sertraline, N-desmethyl sertraline, N-desmethyl sertraline/sertraline and dose-adjusted plasma concentrations were statistically compared between individuals with wild-type and variant alleles both for CYP2B6 and CYP2C19 enzymes. The mean N-desmethyl sertraline/sertraline value, was significantly lower in all subgroups with *6 and *9 variant alleles (p < 0.05). Sertraline/C values were significantly higher (p < 0.05) and N-desmethyl sertraline/C values were lower in all subgroups with *6 and *9 variant alleles compared to wild-type subgroup.

CONCLUSION

CYP2B6*6 and *9 variant alleles had a significant decreasing effect on sertraline metabolism in major depression patients which might result as variations in sertraline therapy.

Effect of Cytochrome P450 polymorphism on the action and metabolism of selective serotonin reuptake inhibitors

INTRODUCTION

The aim of this article is to review the field of clinically relevant pharmacogenetic effects of cytochrome P450 polymorphisms on metabolism, kinetics, and action of selective serotonin reuptake inhibitors (SSRIs).

AREAS COVERED

The relevant literature in humans on the implications of genetic variation on SSRI drug exposure, drug safety, and efficacy was systematically evaluated. There is a large amount of evidence on the influences of CYP polymorphisms on the pharmacokinetics of SSRIs. Regulatory agencies have issued warnings or advice considering dose adjustments in the presence of affected metabolic phenotypes for several SSRIs. Evidence-based dose adjustments for drugs dependent on CYP genotype are available to clinicians. However, few data on the relationship between genetically determined elevated plasma concentrations of SSRIs and specific side effects or therapeutic failure are currently available.

EXPERT OPINION

Genetic polymorphisms in CYP2D6 and CYP2C19 exert large influences on the individual exposure to SSRIs, leading to the aim to achieve similar concentration time courses in different metabolizer phenotypes. The implementation of a stratified approach to medication with SSRIs in different metabolic phenotypes on a rational basis will require new studies assessing the association between clinical outcomes (such as adverse reactions) and genetically determined elevated plasma concentrations.

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.

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.

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.

Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades

There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).

HPLC analysis of the second-generation antidepressant sertraline and its main metabolite N-desmethylsertraline in human plasma

A liquid chromatographic method with ultraviolet detection was developed for the analysis of the recent antidepressant sertraline and its main metabolite N-desmethylsertraline in human plasma. The analytes were separated on a C8 reversed phase column, using a mobile phase composed of acetonitrile and a 12.3 mM, pH 3.0 phosphate buffer containing 0.1% triethylamine (35:65, v/v). Clomipramine was used as the Internal Standard. Using a solid phase extraction procedure with C2 cartridges high extraction yields (>94%) and good purification from matrix interference were obtained. Good linearity was obtained in the 7.5-250.0 ng mL(-1) range for sertraline and in the 10-500 ng mL(-1) range for N-desmethylsertraline. The analytical method was validated in terms of precision, extraction yield and accuracy. These assays gave R.S.D.% values for precision always lower than 3.9% and mean accuracy higher than 90%. Thanks to its good selectivity, the method proved to be suitable for the analysis of plasma samples from patients treated with sertraline as either monotherapy or polypharmacy.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

SERTRALINE IS METABOLIZED BY MULTIPLE CYTOCHROME P450 ENZYMES, MONOAMINE OXIDASES, AND GLUCURONYL TRANSFERASES IN HUMAN: AN IN VITRO STUDY

The oxidative and conjugative metabolism of sertraline was examined in vitro to identify the enzymes involved in the generation of N-desmethyl, deaminated, and N-carbamoyl-glucuronidated metabolites in humans. In human liver microsomes, sertraline was N-demethylated and deaminated by cytochrome P450 (P450) enzymes with overall K(m) values of 98 and 114 microM, respectively, but the intrinsic clearance for N-demethylation was approximately 20-fold greater than for deamination. Using P450 isoform-selective inhibitors and recombinant heterologously expressed enzymes, it was demonstrated that several P450 enzymes catalyzed sertraline N-demethylation, with CYP2B6 contributing the greatest extent, and lesser contributions from CYP2C19, CYP2C9, CYP3A4, and CYP2D6. For deamination, data supported a role for CYP3A4 and CYP2C19. Purified human monoamine oxidases A and B also catalyzed sertraline deamination with comparable K(m) values (230-270 microM). Monoamine oxidase B catalyzed the reaction approximately 3-fold faster than did monoamine oxidase A. Sertraline N-carbamoyl glucuronidation was measured in human liver microsomes in bicarbonate buffer and under a CO2 atmosphere (K(m) = 50 microM) and was catalyzed at the fastest rate by recombinant human UGT2B7. The observation that multiple enzymes appear to be involved in sertraline metabolism suggests that there should be no single agent that could substantially alter the pharmacokinetics of sertraline, nor should there be any single drug-metabolizing enzyme genetic polymorphism (e.g., CYP2D6, CYP2C19, CYP2C9, UGT1A1) that could profoundly impact the pharmacokinetics of sertraline.

Characterization of the CYP2C8 Active Site by Homology Modeling

To compare the features of the active sites of CYP2C8, CYP2C9, and CYP2C19, homology modeling was performed based on the crystallographic coordinates of mammalian CYP2C5. It was found that CYP2C8 has a much larger pocket than the other forms due to the existence of an additional pocket. The approach to the additional pocket is comprised of Ile102, Ser114, Leu208, Val366, and Ile476, and the side chains of Ser114, Val366, and Ile476, which are smaller than the corresponding residues in the other CYPs, enable access to the pocket. The general features of the active site in the CYP2C8 model are similar to those of the previously constructed CYP3A4 model, which may account for the 2 CYPs sharing some of their substrates. The CYP2C8 model was validated by examining the bound orientation of paclitaxel and showing that it is consistent with the formation of the 6-beta hydroxylated derivative during metabolism. Docked paclitaxel was found to form a hydrogen bond with the side chain of Asn 99, which is a characteristic residue of CYP2C8 and is located in the additional pocket. Descriptors for CYP2C8 and CYP2C9 substrates were also examined with the molecular operating environment (MOE). The descriptor by which CYP2C8 and CYP2C9 substrates were classified most distinctly was found to be molar refractivity, which might be related to the longer shape and more polar nature of the active site of CYP2C8 in the CYP2C subfamily.

Clinical pharmacokinetics of sertraline

Sertraline is a naphthalenamine derivative with the predominant pharmacological action of inhibiting presynaptic reuptake of serotonin from the synaptic cleft. It was initially marketed for the treatment of major depressive disorder and is now approved for the management of panic disorder, obsessive-compulsive disorder and post-traumatic stress disorder. Sertraline is slowly absorbed following oral administration and undergoes extensive first-pass oxidation to form N-desmethyl-sertraline, a weakly active metabolite that accumulates to a greater concentration in plasma than the parent drug at steady state. Sertraline is eliminated from the body by other metabolic pathways to form a ketone and an alcohol, which are largely excreted renally as conjugates. The elimination half-life of sertraline ranges from 22-36 hours, and once-daily administration is therapeutically effective. Steady-state plasma concentrations vary widely, up to 15-fold, in patients receiving usual antidepressant dosages between 50 and 150 mg/day. However, only sparse data have been published that support useful correlations between sertraline plasma concentrations and therapeutic or adverse effects to justify therapeutic drug monitoring. Sertraline has minimal inhibitory effects on the major cytochrome P450 enzymes, and few drug-drug interactions of clinical significance have been documented. Like other selective serotonin reuptake inhibitors, sertraline is well tolerated in therapeutic dosages and relatively safe in overdosage.

Role of pharmacogenomics in individualising treatment with SSRIs

The introduction of the SSRIs has significantly transformed the pharmacological treatment of a range of psychiatric disorders. In particular, individuals affected by depression, panic disorder, obsessive-compulsive disorder and social phobia have benefited substantially from their use. Compared with the previous generation of psychotropic drugs, SSRIs offer an improved tolerability to therapy while maintaining a high level of efficacy. Nevertheless, despite these advantages, not all patients benefit from treatment; an appreciable proportion do not respond adequately, while others may react adversely. This necessitates a review of the initial treatment choice, often involving extended periods of illness while a more suitable therapy is sought. Such a scenario could be avoided were it possible to determine the most suitable drug prior to treatment. Several factors are postulated to influence outcome of drug therapy; most recently, pharmacogenetic studies have demonstrated a significant influence of genetic mechanisms on the efficacy of clinically prescribed drugs. This contribution, which is primarily a reflection of alterations in genes that encode drug-metabolising enzymes, drug receptors, transporters and second messengers, may be pertinent to the success of SSRI therapy. Attesting to this potential, studies to elucidate the influence of genetic processes on SSRI efficacy now represent a major focus of pharmacogenetics research. Current evidence emerging from the field suggests that gene variants within the serotonin transporter and cytochrome P450 drug-metabolising enzymes may bear a particular importance, though further corroboration of these findings is still warranted. At the same time, it appears likely that further key participating genes remain to be identified. By comprehensively delineating these genetic components, it is envisaged that this will eventually facilitate the development of highly sensitive protocols for individualising SSRI treatment.

Sertraline: a review of its use in the management of major depressive disorder in elderly patients

Sertraline is a selective serotonin reuptake inhibitor (SSRI) with well established antidepressant and anxiolytic activity. Results from several well designed trials show that sertraline (50 to 200 mg/day) is effective in the treatment of major depressive disorder in elderly patients (> or =60 years of age). Primary endpoints in most studies included the Hamilton Depression Rating Scale (HDRS), Clinical Global Impression (CGI) score and the Montgomery-Asberg Depression Rating Scale (MADRS). Sertraline was significantly more effective than placebo, and was as effective as fluoxetine, nortriptyline and imipramine in elderly patients. During one trial, amitriptyline was significantly more effective than sertraline [mean reduction from baseline on one of six primary outcomes (HDRS)], although no quantitative data were provided. Subgroup analysis of data from a randomised, double-blind trial in elderly patients with major depressive disorder suggests that vascular morbidity, diabetes mellitus or arthritis does not affect the antidepressant effect of sertraline. Secondary endpoints from these clinical trials suggest that sertraline has significant benefits over nortriptyline in terms of quality of life. In addition, significant differences favouring sertraline in comparison with nortriptyline and fluoxetine have been recorded for a number of cognitive functioning parameters. Sertraline is generally well tolerated in elderly patients with major depressive disorder, and lacks the marked anticholinergic effects that characterise the adverse event profiles of tricyclic antidepressants (TCAs). The most frequently reported adverse events in patients aged > or =60 years with major depressive disorder receiving sertraline 50 to 150 mg/day were dry mouth, headache, diarrhoea, nausea, insomnia, somnolence, constipation, dizziness, sweating and taste abnormalities. The tolerability profile of sertraline is generally similar in younger and elderly patients. Sertraline has a low potential for drug interactions at the level of the cytochrome P450 enzyme system. In addition, no dosage adjustments are warranted for elderly patients solely based on age.

CONCLUSION

Sertraline is an effective and well tolerated antidepressant for the treatment of major depressive disorder in patients aged > or =60 years. Since elderly patients are particularly prone to the anticholinergic effects of TCAs as a class, SSRIs such as sertraline are likely to be a better choice for the treatment of major depressive disorder in this age group. In addition, sertraline may have advantages over the SSRIs paroxetine, fluoxetine and fluvoxamine in elderly patients because of the drug's comparatively low potential for drug interactions, which is of importance in patient groups such as the elderly who are likely to receive more than one drug regimen.

Methylphenidate inhibits cytochrome P450 in the Swiss Webster mouse

Drug interactions have previously been reported following the co-administration of methylphenidate (MPH) and drugs metabolized by the cytochrome P450 (CYP450) system such as imipramine. Therefore, this study used the Swiss Webster mouse to determine the effect of MPH on CYP450 isozymes likely to be important in the interaction between MPH and imipramine. Single high doses of MPH (25, 50 and 100 mg/kg, i.p.) were administered to simulate the abuse of MPH. Under these conditions, MPH decreased total hepatic CYP450 to 50% of control. Additionally, MPH inhibited the catalytic activity of CYP1A and CYP2E1 by 50%, and decreased the polypeptide levels of CYP3A by 30%. In a second study designed to simulate more closely therapeutic use, MPH was administered orally for two weeks at 10-fold lower doses (2.5, 5 and 10 mg/kg/day). MPH decreased total hepatic CYP450 at both 5 and 10 mg/ kg/day (0.96 +/- 0.01 and 0.96 +/- 0.06 nmol/mg versus 1.34 +/- 0.01 nmol/mg for saline control, P<0.05). The catalytic activity and protein levels of CYP1A were diminished by up to 50% of control, while catalytic activity and polypeptide levels for CYP2E1 and CYP3A remained unchanged. These results indicate that MPH inhibits the CYP450 system following both abuse and therapeutic scenarios. However, this effect was dependent on both the isoform of CYP450 and the duration of MPH administration.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

O-Dealkylation of fluoxetine in relation to CYP2C19 gene dose and involvement of CYP3A4 in human liver microsomes

This work evaluated the kinetic behavior of fluoxetine O-dealkylation in human liver microsomes from different CYP2C19 genotypes and identified the isoenzymes of cytochrome P450 involved in this metabolic pathway. The kinetics of the rho-trifluoromethylphenol (TFMP) formation from fluoxetine was determined in human liver microsomes from three homozygous (wt/wt) and three heterozygous (wt/m1) extensive metabolizers (EMs) and three poor metabolizers (PMs) with m1 mutation (m1/m1) with respect to CYP2C19. The formation rate of TFMP was determined by gas chromatograph with electron-capture detection. The kinetics of TFMP formation was best described by the two-enzyme and single-enzyme Michaelis-Menten equation for liver microsomes from CYP2C19 EMs and PMs, respectively. The mean intrinsic clearance (V(max)/K(m)) for the high- and low-affinity component was 25.2 microl/min/nmol and 3.8 microl/min/nmol of cytochrome P450 in the homozygous EMs microsomes and 12.8 microl/min/nmol and 2.9 microl/min/nmol of cytochrome P450 in the heterozygous EMs microsomes, respectively. Omeprazole (a CYP2C19 substrate) at a high concentration and triacetyloleandomycin (a selective inhibitor of CYP3A4) substantially inhibited O-dealkylation of fluoxetine. Furthermore, fluoxetine O-dealkylation was correlated significantly with S-mephenytoin 4'-hydroxylation at a low substrate concentration and midazolam 1'-hydroxylation at a high substrate concentration in liver microsomes of 11 Chinese individuals, respectively. Moreover, there were obvious differences in the O-dealkylation of fluoxetine in liver microsomes from different CYP2C19 genotypes and in microsomal fractions of different human-expressed lymphoblast P450s. The results demonstrated that polymorphic CYP2C19 and CYP3A4 enzymes were the major cytochrome P450 isoforms responsible for fluoxetine O-dealkylation, whereas CYP2C19 catalyzed the high-affinity O-dealkylation of fluoxetine, and its contribution to this metabolic reaction was gene dose-dependent.

The xenobiotic inhibitor profile of cytochrome P4502C8

AIMS

To investigate inhibition of recombinant CYP2C8 by: (i) prototypic CYP isoform selective inhibitors (ii) imidazole/triazole antifungal agents (known inhibitors of CYP), and (iii) certain CYP3A substrates (given the apparent overlapping substrate specificity of CYP2C8 and CYP3A).

METHODS

CYP2C8 and NADPH-cytochrome P450 oxidoreductase were coexpressed in Spodoptera frugiperda (Sf21) cells using the baculovirus expression system. CYP isoform selective inhibitors, imidazole/triazole antifungal agents and CYP3A substrates were screened for their inhibitory effects on CYP2C8-catalysed torsemide tolylmethylhydroxylation and, where appropriate, the kinetics of inhibition were characterized. The conversion of torsemide to its tolylmethylhydroxy metabolite was measured using an h.p.l.c. procedure.

RESULTS

At concentrations of the CYP inhibitor 'probes' employed for isoform selectivity, only diethyldithiocarbamate and ketoconazole inhibited CYP2C8 by > 10%. Ketoconazole, at an added concentration of 10 microM, inhibited CYP2C8 by 89%. Another imidazole, clotrimazole, also potently inhibited CYP2C8. Ketoconazole and clotrimazole were both noncompetitive inhibitors of CYP2C8 with apparent Ki values of 2.5 microM. The CYP3A substrates amitriptyline, quinine, terfenadine and triazolam caused near complete inhibition (82-91% of control activity) of CYP2C8 at concentrations five-fold higher than the known CYP3A Km. Kinetic studies with selected CYP3A substrates demonstrated that most inhibited CYP2C8 noncompetitively. Apparent Ki values for midazolam, quinine, terfenadine and triazolam ranged from 5 to 25 microM.

CONCLUSIONS

Inhibition of CYP2C8 occurred at concentrations of ketoconazole and diethyldithiocarbamate normally employed for selective inhibition of CYP3A and CYP2E1, respectively. Some CYP3A substrates have the capacity to inhibit CYP2C8 activity and this may have implications for inhibitory drug interactions in vivo.