Effects of dosage and CYP2D6-mutated allele on plasma concentration of paroxetine

Dose adjustment of paroxetine based on CYP2D6 activity score inferred metabolizer status in Chinese Han patients with depressive or anxiety disorders: a prospective study and cross-ethnic meta-analysis

BACKGROUND

Understanding the impact of CYP2D6 metabolism on paroxetine, a widely used antidepressant, is essential for precision dosing.

METHODS

We conducted an 8-week, multi-center, single-drug, 2-week wash period prospective cohort study in 921 Chinese Han patients with depressive or anxiety disorders (ChiCTR2000038462). We performed CYP2D6 genotyping (single nucleotide variant and copy number variant) to derive the CYP2D6 activity score and evaluated paroxetine treatment outcomes including steady-state concentration, treatment efficacy, and adverse reaction. CYP2D6 metabolizer status was categorized into poor metabolizers (PMs), intermediate metabolizers (IMs), extensive metabolizers (EMs), and ultrarapid metabolizers (UMs). The influence of CYP2D6 metabolic phenotype on paroxetine treatment outcomes was examined using multiple regression analysis and cross-ethnic meta-analysis. The therapeutic reference range of paroxetine was estimated by receiver operating characteristic (ROC) analyses.

FINDINGS

After adjusting for demographic factors, the steady-state concentrations of paroxetine in PMs, IMs, and UMs were 2.50, 1.12, and 0.39 times that of EMs, with PM and UM effects being statistically significant (multiple linear regression, P = 0.03 and P = 0.04). Sex and ethnicity influenced the comparison between IMs and EMs. Moreover, poor efficacy of paroxetine was associated with UM, and a higher risk of developing adverse reactions was associated with lower CYP2D6 activity score. Lastly, cross-ethnic meta-analysis suggested dose adjustments for PMs, IMs, EMs, and UMs in the East Asian population to be 35%, 40%, 143%, and 241% of the manufacturer's recommended dose, and 62%, 68%, 131%, and 159% in the non-East Asian population.

INTERPRETATION

Our findings advocate for precision dosing based on the CYP2D6 metabolic phenotype, with sex and ethnicity being crucial considerations in this approach.

FUNDING

National Natural Science Foundation of China; Academy of Medical Sciences Research Unit.

Impact of CYP2D6 Genotype on Paroxetine Serum Concentration

BACKGROUND

Paroxetine is a selective serotonin reuptake inhibitor metabolized by cytochrome P450 (CYP)2D6. Only small-scale studies have reported the impact of CYP2D6 genotype on paroxetine exposure, and international guidelines differ in their recommendations on whether paroxetine should be administered according to CYP2D6 genotype. To clarify this issue, the aim of the present study was to investigate the impact of CYP2D6 genotype on paroxetine serum concentration in a large population of patients after adjusting for CYP2C19 genotype, age, and sex.

METHODS

Patients from a therapeutic drug monitoring database with records on their paroxetine serum concentrations and CYP2D6 and CYP2C19 genotyping between 2010 and 2021 were included in the study. The impact of CYP2D6 and CYP2C19 genotypes, age, and sex on the paroxetine concentration-to-dose (C/D) ratio was investigated by multiple linear regression analysis. Patients treated with relevant CYP inhibitors or inducers were excluded.

RESULTS

In total, 304 patients were included in the study: 17 CYP2D6 poor metabolizers (PMs), 114 intermediate metabolizers (IMs), 168 extensive metabolizers (EMs), and 5 ultrarapid metabolizers. Multiple linear regression analysis showed that CYP2D6 IMs and PMs had 2.2-fold and 3.8-fold higher paroxetine C/D-ratios than extensive metabolizers, respectively ( P < 0.001). Patients who were CYP2C19 IMs (n = 70) or PMs (n = 13) had 1.6-fold higher paroxetine C/D ratio than extensive metabolizers ( P = 0.04). An age ≥65 years was associated with a 2.9-fold increased C/D ratio ( P < 0.001), whereas sex was not significantly associated with paroxetine exposure.

CONCLUSIONS

The present study showed that CYP2D6 genotype is of significant importance for paroxetine dose adjustments. For CYP2D6 PMs, 25% of the regular paroxetine starting dose may be sufficient, whereas CYP2D6 IMs could receive 50% of the regular dosage. This well-powered study shows that the guidelines should consider the importance of CYP2D6 genotype for personalized dosing of paroxetine.

The Antidepressant Paroxetine Reduces the Cardiac Sodium Current

A considerable amount of literature has been published on antidepressants and cardiac ion channel dysfunction. The antidepressant paroxetine has been associated with Brugada syndrome and long QT syndrome, albeit on the basis of conflicting findings. The cardiac voltage-gated sodium channel (Na_V1.5) is related to both of these syndromes, suggesting that paroxetine may have an effect on this channel. In the present study, we therefore carried out patch clamp experiments to examine the effect of paroxetine on human Na_V1.5 channels stably expressed in human embryonic kidney 293 (HEK-293) cells as well as on action potentials of isolated rabbit left ventricular cardiomyocytes. Additionally, computer simulations were conducted to test the functional effects of the experimentally observed paroxetine-induced changes in the Na_V1.5 current. We found that paroxetine led to a decrease in peak Na_V1.5 current in a concentration-dependent manner with an IC₅₀ of 6.8 ± 1.1 µM. In addition, paroxetine caused a significant hyperpolarizing shift in the steady-state inactivation of the Na_V1.5 current as well as a significant increase in its rate of inactivation. Paroxetine (3 µM) affected the action potential of the left ventricular cardiomyocytes, significantly decreasing its maximum upstroke velocity and amplitude, both of which are mainly regulated by the Na_V1.5 current. Our computer simulations demonstrated that paroxetine substantially reduces the fast sodium current of human left ventricular cardiomyocytes, thereby slowing conduction and reducing excitability in strands of cells, in particular if conduction and excitability are already inhibited by a loss-of-function mutation in the Na_V1.5 encoding SCN5A gene. In conclusion, paroxetine acts as an inhibitor of Na_V1.5 channels, which may enhance the effects of loss-of-function mutations in SCN5A.

Precision Medicine in Antidepressants Treatment

Precision medicine uses innovative approaches to improve disease prevention and treatment outcomes by taking into account people's genetic backgrounds, environments, and lifestyles. Treatment of depression is particularly challenging, given that 30-50% of patients do not respond adequately to antidepressants, while those who respond may experience unpleasant adverse drug reactions (ADRs) that decrease their quality of life and compliance. This chapter aims to present the available scientific data that focus on the impact of genetic variants on the efficacy and toxicity of antidepressants. We compiled data from candidate gene and genome-wide association studies that investigated associations between pharmacodynamic and pharmacokinetic genes and response to antidepressants regarding symptom improvement and ADRs. We also summarized the existing pharmacogenetic-based treatment guidelines for antidepressants, used to guide the selection of the right antidepressant and its dose based on the patient's genetic profile, aiming to achieve maximum efficacy and minimum toxicity. Finally, we reviewed the clinical implementation of pharmacogenomics studies focusing on patients on antidepressants. The available data demonstrate that precision medicine can increase the efficacy of antidepressants and reduce the occurrence of ADRs and ultimately improve patients' quality of life.

CYP2D6 pharmacogenetics and phenoconversion in personalized medicine

INTRODUCTION

CYP2D6 contributes to the metabolism of approximately 20-25% of drugs. However, CYP2D6 is highly polymorphic and different alleles can lead to impacts ranging from null to increase in activity. Moreover, there are commonly used drugs that potently inhibit the CYP2D6, thus causing 'phenoconversion' which can convert the genotypic normal metabolizer into phenotypic poor metabolizer. Despite growing literature on the clinical implications of non-normal CYP2D6 genotype and phenoconversion on patient-related outcomes, implementation of CYP2D6 pharmacogenetics and phenoconversion to guide prescribing is rare. This review focuses on providing the clinical importance of CYP2D6 pharmacogenetics and phenoconversion in precision medicine and summarizes the challenges and approaches to implement these into clinical practice.

AREAS COVERED

A literature search was performed using PubMed and clinical studies documenting the effects of CYP2D6 genotypes and/or CYP2D6 inhibitors on pharmacokinetics, pharmacodynamics or treatment outcomes of CYP2D6-metabolized drugs, and studies on implementation challenges and approaches.

EXPERT OPINION

Considering the extent and impact of genetic polymorphisms of CYP2D6, phenoconversion by the comedications, and contribution of CYP2D6 in drug metabolism, CYP2D6 pharmacogenetics is essential to ensure drug safety and efficacy. Utilization of proper guidelines incorporating both CYP2D6 pharmacogenetics and phenoconversion in clinical care assists in optimizing drug therapy.

Pharmacokinetics of immediate and sustained-release formulations of paroxetine: Population pharmacokinetic approach to guide paroxetine personalized therapy in chinese psychotic patients

Paroxetine is one of the most potent selective serotonin reuptake inhibitors (SSRIs) approved for treating depression, panic disorder, and obsessive-compulsive disorder. There is evidence linking genetic polymorphisms and nonlinear metabolism to the Paroxetine’s pharmacokinetic (PK) variability. The purpose of the present study was to develop a population PK (PPK) model of paroxetine in Chinese patients, which was used to define the paroxetine’s PK parameters and quantify the effect of clinical and baseline demographic factors on these PK characteristics. The study included 184 inpatients with psychosis (103 females and 81 males), with a total of 372 serum concentrations of paroxetine for PPK analyses. The total daily dosage ranged from 20 to 75 mg. One compartment model could fit the PKs characterize of paroxetine. Covariate analysis revealed that dose, formulation, and sex had a significant effect on the PK parameters of paroxetine; however, there was no evident genetic influence of CYP2D6 enzymes on paroxetine concentrations in Chinese patients. The study determined that the population’s apparent distribution volume (V/F) and apparent clearance (CL/F), respectively, were 8850 and 21.2 L/h. The CL/F decreased 1-2-fold for each 10 mg dose increase, whereas the different formulations caused a decrease in V/F of 66.6%. Sex was found to affect bioavailability (F), which decreased F by 47.5%. Females had higher F values than males. This PPK model described data from patients with psychosis who received paroxetine immediate-release tablets (IR-T) and/or sustained-release tablets (SR-T). Paroxetine trough concentrations and relative bioavailability were different between formulations and sex. The altered serum concentrations of paroxetine resulting from individual variants and additive effects need to be considered, to optimize the dosage regimen for individual patients.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Therapy response prediction in major depressive disorder: current and novel genomic markers influencing pharmacokinetics and pharmacodynamics

Major depressive disorder is connected with high rates of functional disability and mortality. About a third of the patients are at risk of therapy failure. Several pharmacogenetic markers especially located in CYP450 genes such as CYP2D6 or CYP2C19 are of relevance for therapy outcome prediction in major depressive disorder but a further optimization of predictive tools is warranted. The article summarizes the current knowledge on pharmacogenetic variants, therapy effects and side effects of important antidepressive therapeutics, and sheds light on new methodological approaches for therapy response estimation based on genetic markers with relevance for pharmacokinetics, pharmacodynamics and disease pathology identified in genome-wide association study analyses, highlighting polygenic risk score analysis as a tool for further optimization of individualized therapy outcome prediction.

The role of sex, age and genetic polymorphisms of CYP enzymes on the pharmacokinetics of anticholinergic drugs

There is evidence that use of drugs with anticholinergic properties increases the risk of cognitive impairment, and increased exposure to these drugs potentiates this risk. Anticholinergic drugs are commonly used even with associated risk of adverse events. Aging, sex, and genetic polymorphisms of cytochrome P450 (CYP) enzymes are associated with alterations in pharmacokinetic processes, which increase drug exposure and may further increase the risk of adverse drug events. Due to the increasing burden of cognitive impairment in our aging population and the future of personalized medicine, the objective of this review was to provide a critical clinical perspective on age, sex, and CYP genetic polymorphisms and their role in the metabolism and exposure to anticholinergic drugs. Age-related changes that may increase anticholinergic drug exposure include pseudocapillarization of liver sinusoidal endothelial cells, an approximate 3.5% decline in CYP content for each decade of life, and a reduction in kidney function. Sex-related differences that may be influenced by anticholinergic drug exposure include women having delayed gastric and colonic emptying, higher gastric pH, reduced catechol-O-methyl transferase activity, reduced glucuronidation, and reduced renal clearance and men having larger stomachs which may affect medication absorption. The overlay of poor metabolism phenotypes for CYP2D6 and CYP2C19 may further modify anticholinergic drug exposure in a significant proportion of the population. These factors help explain findings of clinical trials that show older adults and specifically older women achieve higher plasma concentrations of anticholinergic drugs and that poor metabolizers of CYP2D6 experience increased drug exposure. Despite this knowledge neither age, sex nor CYP phenotype are routinely considered when making decisions about the use or dosing of anticholinergic medications. Future study of anticholinergic medication needs to account for age, sex and CYP polymorphisms so that we may better approach personalized medicine for optimal outcomes and avoidance of medication-related cognitive impairment.

Association of CYP2C19 and CYP2D6 Poor and Intermediate Metabolizer Status With Antidepressant and Antipsychotic Exposure: A Systematic Review and Meta-analysis

IMPORTANCE

Precise estimation of the drug metabolism capacity for individual patients is crucial for adequate dose personalization.

OBJECTIVE

To quantify the difference in the antipsychotic and antidepressant exposure among patients with genetically associated CYP2C19 and CYP2D6 poor (PM), intermediate (IM), and normal (NM) metabolizers.

DATA SOURCES

PubMed, Clinicaltrialsregister.eu, ClinicalTrials.gov, International Clinical Trials Registry Platform, and CENTRAL databases were screened for studies from January 1, 1990, to June 30, 2020, with no language restrictions.

STUDY SELECTION

Two independent reviewers performed study screening and assessed the following inclusion criteria: (1) appropriate CYP2C19 or CYP2D6 genotyping was performed, (2) genotype-based classification into CYP2C19 or CYP2D6 NM, IM, and PM categories was possible, and (3) 3 patients per metabolizer category were available.

DATA EXTRACTION AND SYNTHESIS

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines were followed for extracting data and quality, validity, and risk of bias assessments. A fixed-effects model was used for pooling the effect sizes of the included studies.

MAIN OUTCOMES AND MEASURES

Drug exposure was measured as (1) dose-normalized area under the plasma level (time) curve, (2) dose-normalized steady-state plasma level, or (3) reciprocal apparent total drug clearance. The ratio of means (RoM) was calculated by dividing the mean drug exposure for PM, IM, or pooled PM plus IM categories by the mean drug exposure for the NM category.

RESULTS

Based on the data derived from 94 unique studies and 8379 unique individuals, the most profound differences were observed in the patients treated with aripiprazole (CYP2D6 PM plus IM vs NM RoM, 1.48; 95% CI, 1.41-1.57; 12 studies; 1038 patients), haloperidol lactate (CYP2D6 PM vs NM RoM, 1.68; 95% CI, 1.40-2.02; 9 studies; 423 patients), risperidone (CYP2D6 PM plus IM vs NM RoM, 1.36; 95% CI, 1.28-1.44; 23 studies; 1492 patients), escitalopram oxalate (CYP2C19 PM vs NM, RoM, 2.63; 95% CI, 2.40-2.89; 4 studies; 1262 patients), and sertraline hydrochloride (CYP2C19 IM vs NM RoM, 1.38; 95% CI, 1.27-1.51; 3 studies; 917 patients). Exposure differences were also observed for clozapine, quetiapine fumarate, amitriptyline hydrochloride, mirtazapine, nortriptyline hydrochloride, fluoxetine hydrochloride, fluvoxamine maleate, paroxetine hydrochloride, and venlafaxine hydrochloride; however, these differences were marginal, ambiguous, or based on less than 3 independent studies.

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, the association between CYP2C19/CYP2D6 genotype and drug levels of several psychiatric drugs was quantified with sufficient precision as to be useful as a scientific foundation for CYP2D6/CYP2C19 genotype-based dosing recommendations.

Pharmacogenetic/Pharmacogenomic Tests for Treatment Prediction in Depression

Genetic factors play a significant but complex role in antidepressant (AD) response and tolerability. During recent years, there is growing enthusiasm in the promise of pharmacogenetic/pharmacogenomic (PGx) tools for optimizing and personalizing treatment outcomes for patients with major depressive disorder (MDD). The influence of pharmacokinetic and pharmacodynamic genes on response and tolerability has been investigated, including those encoding the cytochrome P450 superfamily, P-glycoprotein, monoaminergic transporters and receptors, intracellular signal transduction pathways, and the stress hormone system. Genome-wide association studies are also identifying new genetic variants associated with AD response phenotypes, which, combined with methods such as polygenic risk scores (PRS), is opening up new avenues for novel personalized treatment approaches for MDD. This chapter describes the basic concepts in PGx of AD response, reviews the major pharmacokinetic and pharmacodynamic genes involved in AD outcome, discusses PRS as a promising approach for predicting AD efficacy and tolerability, and addresses key challenges to the development and application of PGx tests.

Non-Linear Pharmacokinetics of Atomoxetine in Adult Japanese Patients With ADHD

Objective: The objective was to reveal the relationship between dose and concentration of atomoxetine. Method: Fifty-five blood samples of 33 patients with ADHD were examined using high-performance liquid chromatography. Results: The plasma concentrations were 53.2 ± 67.0, 298.0 ± 390.5, and 639.3 ± 831.9 ng/mL at doses of 40 mg, 80 mg, and 120 mg, and the concentration/dose were 1.33 ± 1.67, 3.73 ± 4.88, and 5.33 ± 6.93 ng/mL/mg, respectively. Statistical analyses revealed a significant correlation between the concentration and the dose of atomoxetine (p = .004), and a trending toward significance in the difference in the concentration/dose in the three dosage groups (p = .064). The concentration/dose at 40 and 80 + 120 mg/day were 1.33 ± 1.67 and 4.22 ± 5.53 ng/mL/mg, the latter was significantly higher than the former (p = .006), which suggested non-linear pharmacokinetics. Conclusion: Clinicians should carefully titrate in high dose atomoxetine treatment.

Sex differences in the pharmacology of itch therapies-a narrative review

BACKGROUND

Chronic itch is the most common skin-related condition, associated with a high psychosocial and economic burden. In recent years, increasing evidence of sex differences in the perception, clinical presentation and treatment requirements of itch points towards potential benefits when using sex-adapted therapies. It is well-known that body composition, absorption, metabolism, elimination and adverse drug reactions (ADRs) differ between sexes, but only little is known about the impact of sex in the pharmacology of itch treatments, which could help to rationalise sex-adapted treatment strategies.

AIM

To evaluate and review sex effects in the pharmacokinetics and /-dynamics of drugs used to treat itch.

METHODS

In this narrative review we performed a PubMed and MEDLINE (Ovid) search using the terms (itch OR pruritus) AND (gender OR sex) AND (drug OR medication OR pharmacokinetics OR pharmacodynamics). Additional searches were performed for the topical and systemic drugs recommended by the European Guideline on Chronic Pruritus.

RESULTS

We found numerous reports with variable levels of evidence of sex effects with respect to the pharmacokinetics and/or pharmacodynamics of 14 drug classes used for the treatment of itch, including a total of 19 systemic and 3 topical drugs. Women seem to present higher plasma levels of several drugs used in itch treatment, including tri- and tetracyclic antidepressants (e.g. doxepin, amitriptyline, mirtazapine), serotonin reuptake inhibitors (e.g. paroxetine, sertraline, fluoxetine), immunosuppressive drugs (e.g. cyclosporine, mycophenolate mofetil), serotonin receptor antagonists (e.g. ondansetron) and betablockers (e.g. propranolol). Adverse drug reactions (ADRs) were generally more common in women. Being female was reported to be an independent risk factor for QTc-prolongation associated with antihistamines and tetracyclic antidepressants. Additionally, women seem to be more prone to sedative effects of antihistamines, and to suffer from a higher frequency as well as severity of side effects with systemic calcineurin inhibitors, opioid agonists, and opioid antagonists. Women were also sensitised more often to topically applied drugs. Of note, apart from only one experimental study with capsaicin, none of these reports were designed specifically to assess the effect of sex (and gender) in the treatment of itch.

DISCUSSION/CONCLUSION

Our review supports previous reports that sex is of importance in the pharmacokinetics and /-dynamics of several drugs used to treat itch although those drugs were mostly evaluated for non-itch indications. However, the results are limited by methodological limitations evident in most studies such as underrepresentation of women in clinical trials. This emphasises the need to study the impact of sex (and gender) in future itch trials to yield better outcomes and prevent ADRs in both sexes.

Effects of CYP2D6 activity on the efficacy and safety of mirtazapine in patients with depressive disorders and comorbid alcohol use disorder

The objective of the study was to investigate the effects of CYP2D6 activity on the efficacy and safety of mirtazapine in patients with depressive disorders and comorbid alcohol use disorder who received mirtazapine. The study included 109 Russian patients who received mirtazapine at a dose of 30.0 [15.0; 45.0] mg per day. Genotyping of CYP2D6*4 (1846G > A, rs3892097) was performed using real-time polymerase chain reaction with allele-specific hybridization. The activity of CYP2D6 was evaluated by determining the concentration of endogenous substrate of the enzyme and its urinary metabolite - pinoline to 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline ratio, using high-performance liquid chromatography - mass spectrometry. The statistically significant differences between the scores on the Hamilton Depression Rating Scale (HAMD) in patients with different genotypes were revealed by day 16: (GG) 5.0 [3.0; 6.0], (GA) 1.5 [1.0; 3.2] (p < 0.001), and for the The UKU Side Effects Rating Scale (UKU): (GG) 6.0 [6.0; 7.0], (GA) 8.5 [8.0; 10.0] (p < 0.001). The calculation of correlation coefficients between the differences in scale scores and metabolic rate showed the presence of statistically significant weak inverse correlation with the efficacy indicator evaluated by HAMD (r = -0.278, p < 0.05), but not by UKU (r = 0.274, p > 0.05). This study demonstrated that an increased CYP2D6 activity reduces the efficacy of treatment with mirtazapine.

Effects of CYP2D6 genetic polymorphisms on the efficacy and safety of fluvoxamine in patients with depressive disorder and comorbid alcohol use disorder

Background

Fluvoxamine therapy is used for treatment of patients with depressive disorder, but it is often ineffective, and some patients suffer from dose-dependent undesirable side effects such as vertigo, headache, indigestion, xerostomia, increased anxiety, etc. CYP2D6 is involved in the biotransformation of fluvoxamine. Meanwhile, the genes encoding these isoenzymes have a high level of polymorphism, which may affect the protein synthesis.

Objective

The primary objective of our study was to investigate the effects of CYP2D6 genetic polymorphisms on the efficacy and safety of fluvoxamine in patients with depressive disorder and comorbid alcohol use disorder, in order to develop the algorithms of optimization of fluvoxamine therapy for reducing the risk of dose-dependent undesirable side effects and pharmacoresistance.

Methods

The study involved 45 male patients (average age: 36.44±9.96 years) with depressive disorder and comorbid alcohol use disorder. A series of psychometric scales was used in the research. Genotyping of CYP2D6 (1846G>A) was performed using real-time polymerase chain reaction.

Results

According to results of Mann–Whitney U-test, statistically significant differences between the efficacy and safety of fluvoxamine were obtained on 9th and 16th days of therapy in patients with GG and GA genotypes (The Hamilton Rating Scale for Depression: 10.0 [10.0; 23.0] vs 25.0 [24.0; 16.0] (P<0.001) on the 9th day and 4.0 [2.0; 5.0] vs 6.0 [6.0; 7.0] on the 16th day; The UKU Side Effect Rating Scale: 6.0 [4.0; 6.0] vs 9.0 [9.0; 10.0] (P<0.001) on the 9th day and 5.0 [1.0; 9.0] vs 19.0 [18.0; 22.0] on the 16th day).

Conclusion

This study demonstrated the lower efficacy and safety of fluvoxamine in patients with depressive disorder and comorbid alcohol use disorders with GA genotype in CYP2D6 1846G>A polymorphic marker.

The Risk of Congenital Heart Anomalies Following Prenatal Exposure to Serotonin Reuptake Inhibitors-Is Pharmacogenetics the Key?

Serotonin reuptake inhibitors (SRIs) are often prescribed during pregnancy. Previous studies that found an increased risk of congenital anomalies, particularly congenital heart anomalies (CHA), with SRI use during pregnancy have created concern among pregnant women and healthcare professionals about the safety of these drugs. However, subsequent studies have reported conflicting results on the association between CHA and SRI use during pregnancy. These discrepancies in the risk estimates can potentially be explained by genetic differences among exposed individuals. In this review, we explore the potential pharmacogenetic predictors involved in the pharmacokinetics and mechanism of action of SRIs, and their relation to the risk of CHA. In general, the risk is dependent on the maternal concentration of SRIs and the foetal serotonin level/effect, which can be modulated by the alteration in the expression and/or function of the metabolic enzymes, transporter proteins and serotonin receptors involved in the serotonin signalling of the foetal heart development. Pharmacogenetics might be the key to understanding why some children exposed to SRIs develop a congenital heart anomaly and others do not.

Influence of the cytochrome P450 2D6 *10/*10 genotype on the pharmacokinetics of paroxetine in Japanese patients with major depressive disorder: a population pharmacokinetic analysis

OBJECTIVE

Although the reduced function of the cytochrome P450 2D6*10 (CYP2D6*10) allele is common among Asian populations, existing evidence does not support paroxetine therapy adjustments for patients who have the CYP2D6*10 allele. In this study, we attempted to evaluate the degree of the impact of different CYP2D6 genotypes on the pharmacokinetic (PK) variability of paroxetine in a Japanese population using a population PK approach.

METHODS

This retrospective study included 179 Japanese patients with major depressive disorder who were being treated with paroxetine. CYP2D6*1, *2, *5, *10, and *41 polymorphisms were observed. A total of 306 steady-state concentrations for paroxetine were collected from the patients. A nonlinear mixed-effects model identified the apparent Michaelis-Menten constant (Km) and the maximum velocity (Vmax) of paroxetine; the covariates included CYP2D6 genotypes, patient age, body weight, sex, and daily paroxetine dose.

RESULTS

The allele frequencies of CYP2D6*1, *2, *5, *10, and *41 were 39.4, 14.5, 4.5, 41.1, and 0.6%, respectively. There was no poor metabolizer who had two nonfunctional CYP2D6*5 alleles. A one-compartment model showed that the apparent Km value was decreased by 20.6% in patients with the CYP2D6*10/*10 genotype in comparison with the other CYP2D6 genotypes. Female sex also influenced the apparent Km values. No PK parameters were affected by the presence of one CYP2D6*5 allele.

CONCLUSION

Unexpectedly, elimination was accelerated in individuals with the CYP2D6*10/*10 genotype. Our results show that the presence of one CYP2D6*5 allele or that of any CYP2D6*10 allele may have no major effect on paroxetine PKs in the steady state.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Selective Serotonin Reuptake Inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are primary treatment options for major depressive and anxiety disorders. CYP2D6 and CYP2C19 polymorphisms can influence the metabolism of SSRIs, thereby affecting drug efficacy and safety. We summarize evidence from the published literature supporting these associations and provide dosing recommendations for fluvoxamine, paroxetine, citalopram, escitalopram, and sertraline based on CYP2D6 and/or CYP2C19 genotype (updates at www.pharmgkb.org).

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.

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.

Paroxetine markedly increases plasma concentrations of ophthalmic timolol; CYP2D6 inhibitors may increase the risk of cardiovascular adverse effects of 0.5% timolol eye drops

Although ophthalmic timolol is generally well tolerated, a significant fraction of topically administered timolol can be systemically absorbed. We investigated the effect of the strong CYP2D6 inhibitor paroxetine on the pharmacokinetics of timolol after ophthalmic administration. In a four-phase crossover study, 12 healthy volunteers ingested either paroxetine (20 mg) or placebo daily for 3 days. In phases 1-2, timolol 0.1% gel, and in phases 3-4, timolol 0.5% drops were administered to both eyes. Paroxetine increased the plasma concentrations of timolol with both timolol formulations to a similar degree. The geometric mean ratio (95% confidence interval) of timolol peak concentration was 1.53-fold (1.23-1.91) with 0.1% timolol and 1.49-fold (0.94-2.36) with 0.5% timolol, and that of timolol area under the plasma concentration-time curve (AUC) from time 0 to 12 hours was 1.61-fold (1.26- to 2.06-fold) and 1.78-fold (1.21-2.62), respectively. During paroxetine administration, six subjects on 0.5% timolol drops, but none on 0.1% timolol gel, had plasma timolol concentrations exceeding 0.7 ng/ml, which can cause systemic adverse effects in patients at risk. There was a positive correlation between the AUC from time 0 to 13 hours of paroxetine and the placebo phase AUC from time 0 to infinity of timolol after timolol 0.5% drops (P < 0.05), and a nonsignificant trend after timolol 0.1% gel, consistent with the role of CYP2D6 in the metabolism of both agents. In the orthostatic test, heart rate immediately after upright standing was significantly lower (P < 0.05) during the paroxetine phase than during the placebo phase at 1 and 3 hours after 0.5% timolol dosing. In conclusion, paroxetine and other CYP2D6 inhibitors can have a clinically important interaction with ophthalmic timolol, particularly when patients are using 0.5% timolol formulations.

Possible impact of the CYP2D6*10 polymorphism on the nonlinear pharmacokinetic parameter estimates of paroxetine in Japanese patients with major depressive disorders

It has been suggested that the reduced function allele with reduced cytochrome P450 (CYP) 2D6 activity, CYP2D6*10, is associated with the interindividual differences in the plasma paroxetine concentrations, but there is no data presently available regarding the influence of the CYP2D6*10 polymorphism on the pharmacokinetic parameters, eg, Michaelis–Menten constant (K_m) and maximum velocity (V_max), in Asian populations. The present study investigated the effects of the CYP2D6 polymorphisms, including CYP2D6*10, on the pharmacokinetic parameters of paroxetine in Japanese patients with major depressive disorders. This retrospective study included 15 Japanese patients with major depressive disorders (four males and eleven females) who were treated with paroxetine. The CYP2D6*2, CYP2D6*4, CYP2D6*5, CYP2D6*10, CYP2D6*18, CYP2D6*39, and CYP2D6*41 polymorphisms were evaluated. A total of 56 blood samples were collected from the patients. The K_m and V_max values of paroxetine were estimated for each patient. The allele frequencies of CYP2D6*2, CYP2D6*4, CYP2D6*5, CYP2D6*10, CYP2D6*18, CYP2D6*39, and CYP2D6*41 were 6.7%, 0%, 10.0%, 56.7%, 0%, 26.7%, and 0%, respectively. The mean values of K_m and V_max were 50.5±68.4 ng/mL and 50.6±18.8 mg/day, respectively. Both the K_m and V_max values were significantly smaller in CYP2D6*10 allele carriers than in the noncarriers (24.2±18.3 ng/mL versus 122.5±106.3 ng/mL, P=0.008; 44.2±16.1 mg/day versus 68.3±15.0 mg/day, P=0.022, respectively). This is the first study to demonstrate that the CYP2D6*10 polymorphism could affect the nonlinear pharmacokinetic parameter estimates of paroxetine in Asian populations. The findings of this study suggest that the CYP2D6*10 polymorphism may be associated with the smaller values of both the K_m and V_max in Japanese patients with major depressive disorders, and these results need to be confirmed in further investigations with a larger number of patients.

Factors affecting discontinuation of initial treatment with paroxetine in panic disorder and major depressive disorder

OBJECTIVE

The aims of the present study were to analyze the association between discontinuation of paroxetine (PAX) and the genetic variants of the polymorphism in the serotonin transporter gene-linked polymorphic region (5-HTTLPR) in Japanese patients with panic disorder (PD) and major depressive disorder (MDD).

METHODS

The 5-HTTLPR genotype was determined by polymerase chain reaction method. PAX plasma concentration was measured by high-performance liquid chromatography to confirm adherence.

RESULTS

When comparing between the PD and MDD patients with the chi-square test and Fisher's exact test, the PD patients had a significant and higher discontinuation rate due to non-adherence than did the MDD patients (13.5% [7/52] versus 0% [0/88], respectively; P<0.001). MDD patients had a significant and higher discontinuation rate due to untraceability than PD patients (12.5% [11/88] versus 1.9% [1/52]; P=0.032). Multilogistic regression revealed a tendency for the long/short and short/short genotypes to affect discontinuation due to adverse effects in PD patients (25.0% versus 6.3%, respectively; P=0.054).

CONCLUSION

The results indicate that the 5-HTTLPR genotype might contribute to the discontinuation of initial PAX treatment due to adverse effects in PD patients.

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.

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.

Pharmacokinetic properties of once-daily oral low-dose mesylate salt of paroxetine (LDMP 7.5 mg) following single and multiple doses in healthy postmenopausal women

BACKGROUND

Low-dose mesylate salt of paroxetine (LDMP 7.5 mg) is being investigated for the treatment of vasomotor symptoms associated with menopause.

OBJECTIVE

This Phase I, open-label, single- and multiple-dose study evaluated the pharmacokinetic properties, safety and tolerability of LDMP in postmenopausal, nonsmoking women aged ≥40 years.

METHODS

After a 3-week screening period, subjects received LDMP 7.5-mg capsules as a single dose on day 1 and then as multiple doses (once daily for 14 days) on Days 6-19. Blood samples were collected predose and up to 120 hours postdose on day 1 (single-dose pharmacokinetic profile), at predose (after 12 doses) on day 18, and at predose and up to 24 hours postdose on day 19 (multiple-dose pharmacokinetic profile). Capsules were taken with 240 mL of water while subjects were fasted. Safety was evaluated throughout the study.

RESULTS

Twenty-four women (mean age, 56 years) completed the study. On day 1, median Tmax was ~6 hours, and mean t1/2 was 17.30 hours. Mean plasma concentrations attained predose on days 18 and 19 (days 13 and 14 of multiple dosing) and at 24 hours postdose (day 20) were similar, suggesting that steady state was achieved by day 13 of multiple dosing after 12 daily doses. Mean AUC0-24 h at steady state (day 14 of multiple dosing) was ~3-fold greater than AUC0-∞ on day 1, indicating nonlinear pharmacokinetics. Mean Cmax on day 14 of multiple dosing was ~5-fold greater than that attained on day 1, and the accumulation index (AUCday 19/AUCday 1) at steady state was 9.71. Fluctuation index (calculated as [(Cmax - Cmin)/Cavg ss] × 100) was 75.8%. Most subjects (23/24 [95.8%]) experienced at least 1 treatment-emergent adverse event (AE); however, most AEs (67 events in 22/24 subjects [91.7%]) were mild, and the remainder were moderate. Seventeen subjects experienced 33 AEs that were deemed possibly or probably related to LDMP. No serious AEs were reported, and no clinically meaningful changes in laboratory values, vital signs, or ECGs were observed.

CONCLUSIONS

On multiple dosing, LDMP exhibited nonlinear pharmacokinetics and was well tolerated in these healthy postmenopausal women; the extent of accumulation was consistent with data from the published literature.

Influence of CYP2D6 and CYP2C19 gene variants on antidepressant response in obsessive-compulsive disorder

Numerous studies have reported on pharmacogenetics of antidepressant response in depression. In contrast, little is known of response predictors in obsessive-compulsive disorder (OCD), a disorder with among the lowest proportion of responders to medication (40-60%). Our study is the largest investigation to date (N=184) of treatment response and side effects to antidepressants in OCD based on metabolizer status for CYP2D6 and CYP2C19. We observed significantly more failed medication trials in CYP2D6 non-extensive compared with extensive metabolizers (P=0.007). CYP2D6 metabolizer status was associated with side effects to venlafaxine (P=0.022). There were nonsignificant trends for association of CYP2D6 metabolizer status with response to fluoxetine (P=0.056) and of CYP2C19 metabolizer status with response to sertraline (P=0.064). Our study is the first to indicate that CYP genes may have a role in antidepressant response in OCD. More research is required for a future clinical application of genetic testing, which could lead to improved treatment outcomes.

Construction of a drug safety assurance information system based on clinical genotyping

To capitalize on the vast potential of patient genetic information to aid in assuring drug safety, a substantial effort is needed in both the training of healthcare professionals and the operational enablement of clinical environments. Our research aims to satisfy these needs through the development of a drug safety assurance information system (GeneScription) based on clinical genotyping that utilizes patient-specific genetic information to predict and prevent adverse drug responses. In this paper, we present the motivations for this work, the algorithms at the heart of GeneScription, and a discussion of our system and its uses. We also describe our efforts to validate GeneScription through its evaluation by practicing pharmacists and pharmacy professors and its repeated use in training pharmacists. The positive assessment of the GeneScription software tool by these domain experts provides strong validation of the importance, accuracy, and effectiveness of GeneScription.

Antidepressant-induced akathisia-related homicides associated with diminishing mutations in metabolizing genes of the CYP450 family

PURPOSE

To examine the relation between variant alleles in 3 CYP450 genes (CYP2D6, CYP2C9 and CYP2C19), interacting drugs and akathisia in subjects referred to a forensic psychiatry practice in Sydney, Australia.

PATIENTS AND METHODS

This paper concerns 10/129 subjects who had been referred to the first author's practice for expert opinion or treatment. More than 120 subjects were diagnosed with akathisia/serotonin toxicity after taking psychiatric medication that had been prescribed for psychosocial distress. They were tested for variant alleles in CYP450 genes, which play a major role in Phase I metabolism of all antidepressant and many other medications. Eight had committed homicide and many more became extremely violent while on antidepressants. Ten representative case histories involving serious violence are presented in detail.

RESULTS

Variant CYP450 allele frequencies were higher in akathisia subjects compared with random primary care patients tested at the same facility. Ten subjects described in detail had variant alleles for one or more of their tested CYP450 genes. All but two were also on interacting drugs, herbals or illicit substances, impairing metabolism further. All those described were able to stop taking antidepressants and return to their previously normal personalities.

CONCLUSION

THE PERSONAL, MEDICAL, AND LEGAL PROBLEMS ARISING FROM OVERUSE OF ANTIDEPRESSANT MEDICATIONS AND RESULTING TOXICITY RAISE THE QUESTION: how can such toxicity events be understood and prevented? The authors suggest that the key lies in understanding the interplay between the subject's CYP450 genotype, substrate drugs and doses, co-prescribed inhibitors and inducers and the age of the subject. The results presented here concerning a sample of persons given antidepressants for psychosocial distress demonstrate the extent to which the psychopharmacology industry has expanded its influence beyond its ability to cure. The roles of both regulatory agencies and drug safety "pharmacovigilantes" in ensuring quality and transparency of industry information is highlighted.

Pharmacogenetics of drug-induced birth defects: what is known so far?

A literature review was performed to collect information on the role of pharmacogenetics in six proposed teratogenic mechanisms associated with drug use during pregnancy: folate antagonism, oxidative stress, angiotensin-converting enzyme inhibition and angiotensin II receptor antagonism, cyclooxygenase-1 and -2 inhibition, 5-hydroxytryptamine-reuptake inhibition and drug transporters in the placenta. Data on the direct relationship between pharmacogenetics and drug-induced birth defects were found for folate metabolism, oxidative stress caused by phenytoin exposure and drug transporters in the placenta. Although no specific data to support pharmacogenetic-related birth defects were found for the NSAIDs, paroxetine and fluoxetine, it might be expected that polymorphisms modify their teratogenic effects. The usually low prevalence of drug-induced malformations impedes the demonstration of the contribution of pharmacogenetics. Large-scale studies, preferably case-control studies, are needed.

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.

5-HT2B receptors are expressed on astrocytes from brain and in culture and are a chronic target for all five conventional ‘serotonin-specific reuptake inhibitors’

In well-differentiated primary cultures of mouse astrocytes, which express no serotonin transporter (SERT), the ‘serotonin-specific reuptake inhibitor’ (SSRI) fluoxetine leads acutely to 5-HT2B receptor-mediated, transactivation-dependent phosphorylation of extracellular regulated kinases 1/2 (ERK1/2) with an EC50 of ~5 μM, and chronically to ERK1/2 phosphorylation-dependent upregulation of mRNA and protein expression of calcium-dependent phospholipase A2 (cPLA2) with ten-fold higher affinity. This affinity is high enough that fluoxetine given therapeutically may activate astrocytic 5-HT2B receptors (Li et al., 2008, 2009). We now confirm the expression of 5-HT2B receptors in astrocytes freshly dissociated from mouse brain and isolated by fluorescence-activated cell sorting (FACS) and investigate in cultured cells if the effects of fluoxetine are shared by all five conventional SSRIs with sufficiently high affinity to be relevant for mechanism(s) of action of SSRIs. Phosphorylated and total ERK1/2 and mRNA and protein expression of cPLA2a were determined by Western blot and reverse transcription polymerase chain reaction (RT-PCR). Paroxetine, which differs widely from fluoxetine in affinity for SERT and for another 5-HT2 receptor, the 5-HT2C receptor, acted acutely and chronically like fluoxetine. One micromolar of paroxetine, fluvoxamine or sertraline increased cPLA2a expression during chronic treatment; citalopram had a similar effect at 0.1–0.5 μM; these are therapeutically relevant concentrations.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

CYP2D6 and ABCB1 genetic variability: influence on paroxetine plasma level and therapeutic response

Paroxetine is characterized by large interindividual pharmacokinetic variability and heterogeneous response patterns. The present study investigates plasma concentration and therapeutic response to paroxetine for the influence of age, sex, and CYP2D6 and ABCB1 polymorphisms, the latter gene encoding for the permeability glycoprotein. Genotyping for CYP2D6 (alleles *3, *4, *5, *6, and *xN) and ABCB1 polymorphisms (61A>G, 2677G>T, and 3435C>T) was performed in 71 depressed patients who started 20 mg paroxetine per day and had plasma concentration measured after 2 weeks at a fixed dose. A dose increase to 30 mg per day was possible starting at week 2. For 63 patients, severity of depression (Montgomery-Asberg Depression Rating Scale) was assessed at weeks 0, 2, and 4 and every 2 weeks thereafter until discontinuation. Persistent response was defined as 50% improvement from baseline score sustained from the first occurrence to study end point. Paroxetine concentration significantly differed between female and male patients (median, 28 versus 16 ng/mL; P = 0.001). Differences were not significant between CYP2D6 heterozygous and homozygous extensive metabolizers (median, 27 versus 22 ng/mL; P = 0.074) and between ABCB1 genotypes (P > 0.10). When considered in a multivariate model, CYP2D6 heterozygous extensive metabolizer phenotype (P = 0.062) and female gender (P = 0.001) predicted 1.3-fold and 1.6-fold higher paroxetine concentration, respectively, but fraction of explained variability was modest (21%). Frequency of persistent response at study end point did not significantly differ according to CYP2D6 heterozygous extensive metabolizer versus homozygous extensive metabolizer phenotype and ABCB1 polymorphisms in univariate analyses. After adjusting for age, sex, paroxetine concentration at week 2, and daily dose at study end point, ABCB1 genotype contributed to improving the model significantly for 61A>G (P = 0.043), but not 2677G>T (P = 0.068) and 3435C>T (P = 0.11). None of two poor metabolizers and four ultrarapid metabolizers showed persistent response to paroxetine. The hypothesis that permeability glycoprotein activity might be a relevant predictor of therapeutic response deserves to be further investigated while controlling for pharmacokinetic variability.

Dose-Dependent Effects of the 3435 C>T Genotype of ABCB1 Gene on the Steady-State Plasma Concentration of Fluvoxamine in Psychiatric Patients

This study investigated effects of the 3435 C>T genotype of the adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1, MDR1) gene on the steady-state plasma concentration of fluvoxamine (FLV).

METHODS

Sixty-two psychiatric patients were treated with different doses (50, 100, 150, and 200 mg/d) of FLV. Blood samples were collected after at least 2 weeks of treatment with the same daily dose to obtain steady-state concentrations of FLV, and 3435 C>T genotype was determined by polymerase chain reaction.

RESULTS

FLV concentration-to-dose ratio was significantly different among 3435 C>T genotype groups at the 200 mg/d dose (P = 0.019). A post-hoc analysis revealed that FLV concentration-to-dose ratio was significantly higher in the TT genotype group as compared with the CC genotype group at the 200 mg/d dose (median value of concentration-to-dose ratio (ng/mL)/(mg/d), 0.861 vs 0.434, P = 0.026). FLV concentration-to-dose ratio was significantly higher in the CT + TT genotype group than the CC genotype group at the 200 mg/d dose (median value of concentration-to-dose ratio (ng/mL)/(mg/d), 0.618 vs 0.434, P = 0.031). At 50, 100, and 150 mg/d dose, FLV concentration-to-dose ratios were not significantly different among 3435 C>T genotype groups. At 50, 100, and 150 mg/d dose, no significant differences were found in FLV concentration-to-dose ratios between the CT + TT genotype group and CC genotype group.

CONCLUSIONS

This study suggests that pharmacokinetics of FLV depend on ABCB1 gene polymorphism only at the 200 mg/d dose.

High Plasma Concentrations of Paroxetine Impede Clinical Response in Patients With Panic Disorder

Selective serotonin reuptake inhibitors are thought to interact with serotonergic neurons and be effective for treatment of panic disorder. In the present study, the authors investigated an association between plasma concentrations of paroxetine in patients with panic disorder and clinical response to initial treatment with paroxetine. Subjects were 21 unrelated Japanese patients who fulfilled DSM-IV-TR criteria for a diagnosis of panic disorder (6 males, 15 females, mean age 35.9 +/- 11.3 years). Subjects were administered 10 mg/day of paroxetine for 2 weeks as initial treatment. Improvement of the symptoms of the disorder was assessed with the Panic and Agoraphobia Scale (PAS). In the range of plasma levels >20 ng/mL, none of the subjects showed the reduction ratio in PAS score >0.2. The subjects whose plasma concentrations of paroxetine were less than 20 ng/mL had a significantly higher mean reduction ratio in PAS score than the subjects whose plasma concentrations of paroxetine were >20 ng/mL. Multiple regression analysis showed that the plasma concentration of paroxetine was the only significant factor and accounted for 28.0% of the variability in the reduction ratio of PAS score of the subjects. The final model of correlation was: reduction ratio in PAS score = 0.423 - 0.009 x (plasma concentrations of paroxetine) (R = 0.529, P = 0.014, coefficient of determination (R2) = 0.280). Assuming that the reduction ratio in PAS score was 0.2 in the equation above, plasma concentration of paroxetine is calculated to be about 25 ng/mL, which is suggested to be the upper end of the therapeutic window for the initial phase of the treatment with paroxetine for panic disorder.

Terbinafine increases the plasma concentration of paroxetine after a single oral administration of paroxetine in healthy subjects

OBJECTIVE

Paroxetine is believed to be a substrate of CYP2D6. However, no information was available indicating drug interaction between paroxetine and inhibitors of CYP2D6. The aim of this study was to examine the effects of terbinafine, a potent inhibitor of CYP2D6, on pharmacokinetics of paroxetine.

METHODS

Two 6-day courses of either a daily 150-mg of terbinafine or a placebo, with at least a 4-week washout period, were conducted. Twelve volunteers took a single oral 20-mg dose of paroxetine on day 6 of both courses. Plasma concentrations of paroxetine were monitored up to 48 h after dosing.

RESULTS

Compared with the placebo, terbinafine treatment significantly increased the peak plasma concentration (C(max)) of paroxetine, by 1.9-fold (6.4 +/- 2.4 versus 12.1 +/- 2.9 ng/ml, p < 0.001), and the area under the plasma concentration-time curve from zero to 48 h [AUC (0-48)] of paroxetine by 2.5-fold (127 +/- 67 vs 318 +/- 102 ng/ml, p < 0.001). Elimination half-life differed significantly (15.3 +/- 2.4 vs 22.7 +/- 8.8 h, p < 0.05), although the magnitude of alteration (1.4-fold) was smaller than C(max )or AUC.

CONCLUSION

The present study demonstrated that the metabolism of paroxetine after a single oral dose was inhibited by terbinafine, suggesting that inhibition of CYP2D6 activity may lead to a change in the pharmacokinetics of paroxetine. However, further study is required to confirm this phenomenon at steady state.

Serotonin syndrome caused by minimum doses of SSRIS in a patient with spinal cord injury

There have been only a few reports of serotonin syndrome developing after mono-therapy with a selective serotonin reuptake inhibitor (SSRI). We report a case of serotonin syndrome caused by long-term therapy with fluvoxamine prior to treatment with paroxetine. An 18-year-old man with spinal cord injury (SCI) at thoracic level 2-3 presented with onset of serotonin syndrome after taking fluvoxamine (50 mg per day) for 8 weeks prior to treatment with paroxetine (10 mg per day) for 6 days. He had confusion, agitation, severe headache, tachycardia (124 beats/minute), hypertension (165/118 mmHg), high fever (39.1 degrees C), and myoclonus. All of the symptoms disappeared within 24 hours after discontinuation of administration of paroxetine. This is an interesting case of serotonin syndrome that developed after minimum doses of single therapy with an SSRI in a patient with SCI.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effect of the CYP2D6*10 C188T polymorphism on postoperative tramadol analgesia in a Chinese population

OBJECTIVE

The CYP2D6*10 allele is the most common allele with a frequency ranging from 51.3 to 70% and correlated with a significantly reduced metabolic activity in a Chinese population. The aim of the present study was to investigate whether the CYP2D6*10 allele has an impact on the postoperative analgesia effect of tramadol in Chinese patients recovering from major abdominal surgery.

METHODS

A prospective study design was used and 70 gastric cancer patients recovering from gastrectomy were enrolled. After receiving a loading dose i.v., patients could self-administer doses of the drug combination (10 mg/ml tramadol plus 0.3 mg/ml metoclopramide) via patient-controlled analgesia (PCA). Blood samples were collected after induction of anesthesia. The CYP2D6*10 C188T polymorphism was analyzed by means of polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP). Demographic data among groups with different genotypes were analyzed using analysis of variance. The total consumption of tramadol between the three genotype groups for 48 h was compared.

RESULTS

The allele frequency of CYP2D6*10 is 52.4%; patients were categorized into three groups according to the CYP2D6 genotype: patients without CYP2D6*10 (group I, n=17), patients heterozygous for CYP2D6*10 (group II, n=26), and patients homozygous for CYP2D6*10 (group III, n=20). The demographic data among the three groups were comparable. The total consumption of tramadol for 48 h in group III was significantly higher than that in groups I and II, while it did not differ between groups I and II.

CONCLUSIONS

This study indicates that the CYP2D6*10 allele has significant impact on analgesia with tramadol in a Chinese population. Pharmacogenetics may explain some of the varying responses to pain medication in postoperative patients.