Genetic Polymorphisms Of CYP2D6 Research Articles

Tramadol intoxication in children: An emerging issue

Background: Prescribing tramadol in children raises safety concerns. In Europe, tramadol is still approved and licensed for use in children over 1-3 years of age, depending on the country. In this context, the authors report a case of a tramadol overdose in a 5-year-old-child with a medical history of homozygous sickle cell disease.Methods: Tramadol and M1 were quantified using liquid chromatography with a diode array detection method. CYP2D6 genotype was determined using a Next Generation Sequencing platform (MISeq, Illumina).Results: Tramadol and M1 were quantified in blood respectively at 5.48 and 1.32 µg/mL at admission, at 0.77 and 0.35 µg/mL 12 hours later, and at 0.32 and 0.18 µg/mL 20 hours later. The patient was predicted as a CYP2D6 normal metabolizer (*35/*29).Conclusion: One of the most important difficulties with the use of tramadol in children relates to its pharmacokinetic (PK) properties. Indeed, tramadol’s PK is characterized by a great variability related to: i) anatomical/physiological factors that impact the volume of distribution (Vd); ii) CYP2D6 genetic polymorphisms. Considering such an issue is particularly relevant to prevent poisoning. In the reported case, the plasma elimination half-life was estimated at 6.3 h, significantly more than those reported in 2-8 year-old children (about 3 h). This discrepancy does not seem related to genetic polymorphisms but rather to the Vd. Indeed, the patient was predicted to be a CYP2D6 normal metabolizer (*35/*29). The case presented here highlights the risk associated with the tramadol use in children and emphasizes the importance of considering PK variability among this population. Such variability necessitates greater caution in prescribing tramadol in children and highlights the importance of therapeutic education for families of children treated with this painkiller.

Physiologically based pharmacokinetic modeling to predict the pharmacokinetics of codeine in different CYP2D6 phenotypes.

Codeine, a prodrug used as an opioid agonist, is metabolized to the active product morphine by CYP2D6. This study aimed to establish physiologically based pharmacokinetic (PBPK) models of codeine and morphine and explore the influence of CYP2D6 genetic polymorphisms on the pharmacokinetics of codeine and morphine. An initial PBPK modeling of codeine in healthy adults was established using PK-Sim® software and subsequently extrapolated to CYP2D6 phenotype-related PBPK modeling based on the turnover frequency (Kcat) of CYP2D6 for different phenotype populations (UM, EM, IM, and PM). The mean fold error (MFE) and geometric mean fold error (GMFE) methods were used to compare the differences between the predicted and observed values of the pharmacokinetic parameters to evaluate the accuracy of PBPK modeling. The validated models were then used to support dose safety for different CYP2D6 phenotypes. The developed and validated CYP2D6 phenotype-related PBPK model successfully predicted codeine and morphine dispositions in different CYP2D6 phenotypes. Compared with EMs, the predicted AUC0-∞ value of morphine was 98.6% lower in PMs, 60.84% lower in IMs, and 73.43% higher in UMs. Morphine plasma exposure in IMs administered 80mg of codeine was roughly comparable to that in EMs administered 30mg of codeine. CYP2D6 UMs may start dose titration to achieve an optimal individual regimen and avoid a single dose of over 20mg. Codeine should not be used in PMs for pain relief, considering its insufficient efficacy. PBPK modeling can be applied to explore the dosing safety of codeine and can be helpful in predicting the effect of CYP2D6 genetic polymorphisms on drug-drug interactions (DDIs) with codeine in the future.

The impacts of natural product miltirone and the CYP2D6 pharmacogenetic phenotype on fluoxetine metabolism.

Introduction: To study the effects of drug-induced CYP2D6 activity inhibition and genetic polymorphisms on fluoxetine metabolism, rat liver microsomes (RLMs) and SD rats were used to investigate the potential drug‒drug interactions (DDIs), and CYP2D6 http://muchong.com/t-10728934-1 recombinant baculosomes were prepared and subjected to catalytic reactivity studies. Methods and Results: All analytes were detected by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC‒MS/MS). After screening for 27 targeted natural products, miltirone was identified as having obvious inhibitory effect on fluoxetine metabolism in RLMs. In vivo, the concentration of fluoxetine in rat blood increased markedly after miltirone administration. The molecular docking results showed that miltirone bound more strongly to CYP2D6 than fluoxetine, and PHE120 may be the key residue leading to the inhibition of CYP2D6-mediated fluoxetine N-demethylation by miltirone. In terms of the genetic polymorphism of CYP2D6 on fluoxetine metabolism, the intrinsic clearance values of most variants were significantly altered. Among these variants, CYP2D6*92 and CYP2D6*96/Q424X were found to be catalytically inactive for fluoxetine metabolism, five variants (CYP2D6*89/L142S, *97/F457L, *R497, *V342M and *R344Q) exhibited markedly increased clearance values (>125.07%) and seven variants (CYP2D6*2, *10, *87/A5V, *93/T249P, *E215K, *R25Q and *R440C) exhibited significantly decreased clearance values (from 6.62% to 66.79%) compared to those of the wild-type. Conclusion: Our results suggest that more attention should be given to subjects in the clinic who take fluoxetine and also carry one of these infrequent CYP2D6 alleles or are coadministered drugs containing miltirone.

PBPK modeling to predict the pharmacokinetics of venlafaxine and its active metabolite in different CYP2D6 genotypes and drug-drug interactions with clarithromycin and paroxetine.

Venlafaxine, a serotonin-norepinephrine reuptake inhibitor (SNRI), is indicated for the treatment of major depressive disorder, social anxiety disorder, generalized anxiety disorder, and panic disorder. Venlafaxine is metabolized to the active metabolite desvenlafaxine mainly by CYP2D6. Genetic polymorphism of CYP2D6 and coadministration with other medications can significantly affect the pharmacokinetics and/or pharmacodynamics of venlafaxine and its active metabolite. This study aimed to establish the PBPK models of venlafaxine and its active metabolite related to CYP2D6 genetic polymorphism and to predict drug-drug interactions (DDIs) with clarithromycin and paroxetine in different CYP2D6 genotypes. Clinical pharmacogenomic data for venlafaxine and desvenlafaxine were collected to build the PBPK model. Physicochemical and absorption, distribution, metabolism, and excretion (ADME) characteristics of respective compounds were obtained from previously reported data, predicted by the PK-Sim® software, or optimized to capture the plasma concentration-time profiles. Model evaluation was performed by comparing the predicted pharmacokinetic parameters and plasma concentration-time profiles to the observed data. Predicted plasma concentration-time profiles of venlafaxine and its active metabolite were visually similar to the observed profiles and all predicted AUC and Cmax values for respective compounds were included in the twofold error range of observed values in non-genotyped populations and different CYP2D6 genotypes. When clarithromycin or clarithromycin plus paroxetine was concomitantly administered, predicted plasma concentration-time profiles of venlafaxine properly captured the observed profiles in two different CYP2D6 genotypes and all predicted DDI ratios for AUC and Cmax were included within the acceptance range. Consequently, the present model successfully captured the pharmacokinetic alterations of venlafaxine and its active metabolite according to CYP2D6 genetic polymorphism as well as the DDIs between venlafaxine and two CYP inhibitors. The present model can be used to predict the pharmacokinetics of venlafaxine and its active metabolite considering different races, ages, coadministered drugs, and CYP2D6 activity of individuals and it can contribute to individualized pharmacotherapy of venlafaxine.

Impact of Viloxazine Extended-Release Capsules (Qelbree®) on Select Cytochrome P450 Enzyme Activity and Evaluation of CYP2D6 Genetic Polymorphisms on Viloxazine Pharmacokinetics.

Viloxazine extended-release (ER) [Qelbree®] is a nonstimulant attention-deficit/hyperactivity disorder (ADHD) treatment. In vitro studies suggested potential for viloxazine to inhibit cytochrome450 (CYP) enzymes 1A2, 2B6, 2D6 and 3A4. This clinical study therefore evaluated viloxazine ER effects on index substrates for CYP1A2, 2D6, and 3A4, and secondarily evaluated the impact of CYP2D6 polymorphisms on viloxazine pharmacokinetics. Thirty-seven healthy subjects received a modified Cooperstown cocktail (MCC; caffeine 200mg, dextromethorphan 30mg, midazolam 0.025 mg/kg) on Day 1, viloxazine ER 900 mg/day on Days 3-5, and a combination of viloxazine ER 900 mg and MCC on Day 6. Viloxazine ER effects on MCC substrates were evaluated using analysis of variance. The impact of CYP2D6 genetic polymorphisms on steady-state viloxazine plasma concentrations was evaluated using Student's t test assessing pharmacokinetic parameter differences between poor versus extensive metabolizers. The least squares geometric mean ratio [GMR%] (90% CI) of MCC substrate + viloxazine ER/MCC substrate alone for caffeine maximum concentration (Cmax), area under the plasma concentration-time curve from time 0 to the last quantifiable concentration (AUCt), and area under the plasma concentration-time curve from time 0 extrapolated to infinity (AUC∞) was 99.11 (95.84-102.49), 436.15 (398.87-476.92), and 583.35 (262.41-1296.80), respectively; 150.76 (126.03-180.35), 185.76 (155.01-222.61), and 189.71 (160.37-224.42) for dextromethorphan Cmax, AUCt, and AUC∞, respectively; and 112.81 (104.71-121.54), 167.56 (153.05-183.45), and 168.91 (154.38-184.80) for midazolam Cmax, AUCt, and AUC∞, respectively. At steady state, viloxazine least squares GMR (90% CI) for poor/extensive CYP2D6 metabolizers were Cmax 120.70 (102.33-142.37) and area under the plasme concentration-time curve from time 0 to 24 hours (AUC0-24 125.66 (105.36-149.87)). Viloxazine ER is a strong CYP1A2 inhibitor and a weak CYP2D6 and CYP3A4 inhibitor. CYP2D6 polymorphisms did not meaningfully alter the viloxazine ER pharmacokinetic profile.

Genetic Polymorphisms in CYP2 Gene Family in Bulgarian Individuals and their Clinical Implications

Abstract The cytochrome P450 superfamily consists of hemeproteins involved in the detoxication of different xenobiotics, including drugs. The CYP2 gene family is responsible for the metabolism of 80% of the drugs in clinical use. There are considerable interindividual and interethnic variabilities in the rate of drug metabolism as a result of genetic polymorphisms. The goal of our study was to determine the frequency of 10 genetic polymorphisms in CYP2 family genes to give light on the pharmacogenetic defects of the main CYPs, involved in drug metabolism, in Bulgarian individuals. We detected high allele frequency for CYP2D6*10 (0.27), CYP2D6*4 (0.22), and CYP2B6*9 (0.24), followed by CYP2C19*2 (0.14), CYP2C9*3 (0.11) and CYP2C9*2 (0.09). The genotype frequencies were also determined for all investigated variants. In total 47.2% of the analyzed individuals carried CYP2D6 genetic polymorphisms – 5.6% carried a single variant and 41.6% were found to have two or more such variants. Homozygotes for CYP2D6 variants were established among 14% of Bulgarian individuals. Determination of the prevailing pharmacogenetic polymorphisms of the CYPs, most responsible for drug metabolism, will lead to a lower risk of drug toxicity, increased drug efficacy, and drug dose optimization.

Risperidone plasma level, and its correlation with CYP2D6 gene polymorphism, clinical response and side effects in chronic schizophrenia patients

BackgroundTo explore the influence of CYP2D6 genetic polymorphism on risperidone metabolism, thereby affecting risperidone’s effects and safeties in patients with chronic schizophrenia.MethodsSixty-nine subjects with chronic schizophrenia treated with risperidone were recruited. CYP2D6 genotypes was determined using targeted sequencing and translated into phenotype using activity system. Risperidone plasma concentrations were measured using HPLC. Positive and Negative Symptom Scale (PANSS) and Brief Psychiatric Rating Scale (BPRS) were used to evaluate the existence and severity of psychiatric symptoms, Barnes Akathisia Scale (BAS) and Extrapyramidal Symptom Rating Scale (ESRS) for neurological side effects. Metabolic and endocrine status assess were also included.ResultsThe plasma drug concentrations varied hugely among individuals. Intermediate metabolizer (IM) group had higher plasma levels of RIP and dose corrected RIP concentration, RIP/9-OH-RIP ratio and C/D ratio than normal metabolizer (NM) group (p < 0.01). There was no statistic difference between responders and non-responders in dose-adjusted plasma concentrations and ratios of RIP/9-OH-RIP and C/D. The occurrence of EPS was related to active moiety levels in 4th week (p < 0.05). The prolactin (PRL) levels in two follow-ups were both significantly higher than baseline (p < 0.01). PRL change from baseline to week 4 and week 8 were both positively associated with active moiety concentration detected in week 4 (p < 0.05).ConclusionsThe risperidone plasma levels have great inter- and intraindividual variations, and are associated with the CYP2D6 phenotypes, as well as the changes in serum prolactin in patients diagnosed with chronic schizophrenia.

Impact of CYP2D6 polymorphisms on the efficacy of tamoxifen in Iraqi women with breast cancer

Objectives: The aim of the present study was to investigate the impact of the CYP2D6 genetic polymorphism on clinical outcome in Iraqi breast cancer patients who were candidates for Tamoxifen therapy. Methods: Comprehensive CYP2D6 genotyping was performed in 140 Iraqi women with breast cancer who were women on adjuvant treatment with tamoxifen. Breast cancer patients recruited into the study were divided into two groups: seventy breast cancer women who had no history of recurrence at the time of sampling and had a long time on tamoxifen without recurrence and seventy breast cancer women who had recurrence at the time of sampling after one year of treatment with tamoxifen therapy. Recurrence free survival (RFS) was determined in the recruited patients. Results: Multiple genetic variants of the gene encoding the CYP2D6 enzyme were detected with significant differences in their frequencies and percentages in both recurrent and non-recurrent groups of breast cancer patients. The findings of this study suggest that interindividual variation in clinical outcome may be related to genetic variation in CYP2D6 enzyme, which is characterized by variable RFS periods. Conclusions: This study revealed that the CYP2D6 enzyme of breast cancer patients who participated in this study is highly polymorphic. The CYP2D6 gene of study participants exhibited different allelic combinations with variable frequencies. The multiple genetic variants (alleles) of the gene encoding the CYP2D6 enzyme exhibited significant differences in their frequencies and percentages in both recurrent and non-recurrent groups of breast cancer patients. .The study revealed variable Recurrence free survival (RFS) with highly polymorphic gene. Our study quotes the presence of increased CYP2D6 enzyme polymorphism is associated with variable clinical response.

Screening and validation of double allele-specific binding F-primers for the measurement of antihypertensive pharmacogenomics.

Previous studies have proposed that genetic polymorphisms of CYP2D6*10, ADRB1, NPPA, CYP3A5*3, ACE, CYP2C9*3, and AGTR1 are involved in antihypertensive pharmacogenomics. The purpose of this study is to develop an amplification analysis using double allele-specific (AS) binding primers for accurate measurement of antihypertensive pharmacogenomics. To establish a quadruplex quantitative PCR (qPCR) analysis for genotyping of CYP2D6*10, ADRB1 (1165 G>C), NPPA (2238 T>C) and CYP3A5*3, and a triplex qPCR analysis for genotyping of ACE (I/D), CYP2C9*3 and AGTR1 (1166 A>C), mismatch AS F-primers were screened by detection of plasmid/gDNA, and were validated by agreement analysis/reproducibility evaluation, in which the ΔCq (differences in threshold cycles between the wild-type F-primer-based amplification assay and the mutant-type F-primer-based amplification assay) was employed to determine genotypes. Seven pairs of primers were successfully selected through three rounds of F-primers screening. Except for ADRB1, the robustness assessment showed the amplification efficiency ranging from 0.9 to 1.1. In agreement analysis, two specimens in the training set (n = 203) were defined by the triplex analysis rather than NGS as heterozygotes for ACE, which was evidenced by gel electrophoresis. Reproducibility evaluation demonstrated that the coefficient of variation (CV) was <5%. Multiplex amplification analysis using screened AS binding primers is a simple, reliable, and accurate tool to guide drug delivery in antihypertensive personalized treatment.

Genotype-guided new approach for dose optimisation of hydroxychloroquine administration in Chinese patients with SLE

ObjectivesThe study aims to investigate the impact of gene polymorphisms on blood hydroxychloroquine (HCQ) concentrations in patients with SLE and provide guidelines for individualised care.Methods489 Chinese patients with SLE taking...

CYP1A2 expression rather than genotype is associated with olanzapine concentration in psychiatric patients

Olanzapine is a commonly prescribed atypical antipsychotic agent for treatment of patients with schizophrenia and bipolar disorders. Previous in vitro studies using human liver microsomes identified CYP1A2 and CYP2D6 enzymes being responsible for CYP-mediated metabolism of olanzapine. The present work focused on the impact of CYP1A2 and CYP2D6 genetic polymorphisms as well as of CYP1A2 metabolizing capacity influenced by non-genetic factors (sex, age, smoking) on olanzapine blood concentration in patients with psychiatric disorders (N = 139). CYP2D6 genotype-based phenotype appeared to have negligible contribution to olanzapine metabolism, whereas a dominant role of CYP1A2 in olanzapine exposure was confirmed. However, CYP1A2 expression rather than CYP1A2 genetic variability was demonstrated to be associated with olanzapine concentration in patients. Significant contribution of − 163C > A (rs762551), the most common SNP (single nucleotide polymorphism) in CYP1A2 gene, to enhanced inducibility was confirmed by an increase in CYP1A2 mRNA expression in smokers carrying − 163A, and smoking was found to have appreciable impact on olanzapine concentration normalized by the dose/bodyweight. Furthermore, patients’ olanzapine exposure was in strong association with CYP1A2 expression; therefore, assaying CYP1A2 mRNA level in leukocytes can be an appropriate tool for the estimation of patients’ olanzapine metabolizing capacity and may be relevant in optimizing olanzapine dosage.

Effects of CYP2D6 allelic variants on therapy with tamsulosin in patients with benign prostatic hyperplasia.

Tamsulosin is a first-line drug for the treatment of lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH). Despite its high ratings for efficacy and safety, these parameters may vary due togenetic polymorphisms of CYP2D6 enzyme, which is involved in the metabolism of the drug. This variability may have great impact on the therapy of LUTS associated with BPH and may require an individualized approach to drug selection. The aim of the study was to assess the impact of genetic polymorphisms in CYP2D6 on the efficacy and safety of tamsulosin therapy in patients with LUTS associated with BPH. The study included 106 patients with LUTS/BPH (N40 according to ICD-10). All patients received monotherapy with tamsulosin 0.4 mg/day for at least 8weeks. Depending on the severity of symptoms, all patients were divided into 2 groups based on the IPSS score: the first group of patients had moderate symptoms (n=57), and the second group of patients had severe symptoms (n=49). The results of treatment were assessed using the IPSS questionnaire with determination of quality of life (QoL), transrectal ultrasound of the prostate with determination of prostate volume andpostvoid residual urine volume, and uroflowmetry. The carriage of allelic variants of CYP2D6 (*3, *4, *9, *10, and *41) were determined by polymerase chain reaction in all patients. In patients with moderate symptoms who was classified as «intermediate» metabolizers by CYP2D6, a statistically significant greater reduction in symptoms according to the overall IPSS scale at 8weeks (p=0.046) and the obstructive symptom subscale starting from 4weeks of treatment (p<0.05) was shown. Allelic variants of the CYP2D6 gene did not affect the frequency of adverse reactions to tamsulosin. The results of the study show that in patients with moderate LUTS associated with BPH who are «intermediate» metabolizers by CYP2D6, there is a better therapeutic effect of tamsulosin.

Effects of CYP2D6 and CYP2C19 genetic polymorphisms and cigarette smoking on the pharmacokinetics of tolperisone.

Tolperisone, a muscle relaxant used for post-stroke spasticity, is metabolized to its main metabolite by CYP2D6 and to a lesser extent by CYP2C19 and CYP1A2. We investigated the effects of CYP2D6 and CYP2C19 genetic polymorphisms and cigarette smoking on tolperisone pharmacokinetics. A 150mg oral dose of tolperisone was given to 184 healthy Korean subjects and plasma concentrations of tolperisone were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A 3.14-fold significant increase in AUC0-∞ was observed in the CYP2D6*10/*10 group compared with the CYP2D6*wt/*wt group, whereas a 3.59-fold increasein AUC0-∞ was observed in CYP2C19PMs compared to CYP2C19EMs. Smokers had a 38.5% decrease in AUC0-∞ when compared to non-smokers. When these effects were combined, CYP2D6*10/*10-CYP2C19PM-Non-smokers had a 25.9-fold increase in AUC0-∞ compared to CYP2D6*wt/*wt-CYP2C19EM-Smokers. Genetic polymorphisms of CYP2D6 and CYP2C19 and cigarette smoking independently and significantly affected tolperisone pharmacokinetics and these effects combined resulted in a much greater impact on tolperisone pharmacokinetics.

Predictive modeling of adverse drug reactions to tamoxifen therapy for breast cancer on base of pharmacogenomic testing.

The present study investigated the analysis of adverse drug reactions (ADRs) to tamoxifen (TAM) in breast cancer patients in relation to the carriage of genetic polymorphisms of genes encoding enzymes of CYP system and transporters of P-glycoprotein (Pg) and predictive models based on it. A total of 120 women with breast cancer taking adjuvant TAM were examined for the gene polymorphisms such as CYP2D6*4, CYP3A5*3, CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C19*3 and ABCB1 (C3435T). Allelic variants were determined using the real-time polymerase chain reaction method. The research material was double sampling of buccal epithelium. Medical history data and extracts from case histories were used as sources of medical information, on the basis of which questionnaires specially created by us were filled out. An associative analysis showed association with the development of ADRs to TAM indicating their clinical significance from different genetic polymorphisms of CYP2D6, CYP3A5, CYP2C9 and ABCB1. The complex associative analysis performed using mathematical modeling made it possible to build predictive risk models for the development of ADRs such as hot flashes, dyspepsia, bone pain, and asthenia. Models that include both genetic and non-genetic determinants of ADRs of TAM may further improve the prediction of individual response to TAM.

Part I: Interactive case: Menopause

Part I: Interactive case: Menopause

Predictive modeling of adverse events of tamoxifen therapy for breast cancer (results of a cohort study)

Relevance. Endocrine therapy is the standard treatment for women with ER-positive breast cancer. The clinical response to Tamoxifen is variable. Approximately 30 % of patients with breast cancer will have a recurrence of the disease within 15 years after treatment, despite ongoing endocrine therapy. This article presents the results of a prospective pharmacogenetic cohort study. The study was conducted in 2018–2019. Aim. To analyze adverse drug reactions to Tamoxifen in the adjuvant regimen in breast cancer patients in relation to the carriage of genetic polymorphisms of genes encoding cytochrome P450 enzymes and drug transporter proteins and to build predictive models based on them. A comparative analysis of the relationship between genetic and non-genetic determinants with adverse events on tamoxifen therapy allowed us to build predictive models of their development. Materials and Methods. The study involved 120 women with pre- and postmenopausal breast cancer who underwent genetic testing for CYP and Pg enzyme gene polymorphisms. Entry criteria: a histologically confirmed diagnosis of breast cancer, taking Tamoxifen at the recommended doses, establishing a diagnosis not earlier than 2007, and obtaining informed voluntary consent to participate in the study. Allelic variants were determined using real-time polymerase chain reaction in the Research Institute for Molecular and Personalized Medicine of the Russian Medical Academy of Continuous Professional Education of the Ministry of Healthcare of the Russian Federation. Results. An associative analysis showed their association with the development of adverse drug reactions (ADR) to Tamoxifen, indicating the clinical significance of different genetic polymorphisms of CYP2D6, CYP3A5, CYP2C9 and ABCB1. The complex associative analysis performed using mathematical modeling made it possible to build predictive risk models for the development of such ADR, such as hot flashes, dyspepsia, bone pain, and asthenia. The resulting regression models were statistically significant (p &lt; 0,001) and demonstrated high diagnostic efficiency. This allows them to be implemented in clinical practice. Conclusion. Thus, models that include both genetic and non-genetic determinants of response may further improve the prediction of individual response to tamoxifen

Population Pharmacokinetic-Pharmacodynamic Modeling of Carvedilol to Evaluate the Effect of Cytochrome P450 2D6 Genotype on the Heart Rate Reduction.

Carvedilol is a beta-adrenergic receptor antagonist primarily metabolized by cytochromes P450 (CYP) 2D6. This study established a carvedilol population pharmacokinetic (PK)-pharmacodynamic (PD) model to describe the effects of CYP2D6 genetic polymorphisms on the inter-individual variability of PK and PD. The PK-PD model was developed from a clinical study conducted on 21 healthy subjects divided into three CYP2D6 phenotype groups, with six subjects in the extensive metabolizer (EM, *1/*1, *1/*2), seven in the intermediate metabolizer-1 (IM-1, *1/*10, *2/*10), and eight in the intermediate metabolizer-2 (IM-2, *10/*10) groups. The PK-PD model was sequentially developed, and the isoproterenol-induced heart rate changes were used to establish the PD model. A direct effect response and inhibitory Emax model were used to develop a carvedilol PK-PD model. The carvedilol PK was well described by a two-compartment model with zero-order absorption, lag time, and first-order elimination. The carvedilol clearance in the CYP2D6*10/*10 group decreased by 32.8% compared with the other groups. The inhibitory concentration of carvedilol estimated from the final PK-PD model was 16.5 ng/mL regardless of the CYP2D6 phenotype. The PK-PD model revealed that the CYP2D6 genetic polymorphisms were contributed to the inter-individual variability of carvedilol PK, but not PD.

Effects of CYP2C19 genetic polymorphism on the pharmacokinetics of tolperisone in healthy subjects

Tolperisone hydrochloride is a centrally-acting muscle relaxant used for relieving spasticities of neurological origin and muscle spasms associated with painful locomotor diseases. It is metabolized to the inactive metabolite mainly by CYP2D6 and, to a lesser extent, by CYP2C19 and CYP1A2. In our previous study, the pharmacokinetics of tolperisone was significantly affected by the genetic polymorphism of CYP2D6, but the wide interindividual variation of tolperisone pharmacokinetics was not explained by genetic polymorphism of CYP2D6 alone. Thus, we studied the effects of CYP2C19 genetic polymorphism on tolperisone pharmacokinetics. Eighty-one subjects with different CYP2C19 genotypes received a single oral dose of 150mg tolperisone with 240mL ofwater, and blood samples were collected up to 12h after dosing. The plasma concentration of tolperisone was measured by a liquid chromatography-tandem mass spectrometry system. The CYP2C19PM group had significantly higher Cmax and lower CL/F values than the CYP2C19EM and CYP2C19IM groups. The AUCinf of the CYP2C19PM group was 2.86-fold and 3.00-fold higher than the CYP2C19EM and CYP2C19IM groups, respectively. In conclusion, the genetic polymorphism of CYP2C19 significantly affected tolperisone pharmacokinetics.

Analysis of the complications of endocrine therapy with tamoxifen in breast cancer: clinical and pharmacogenetic aspects. Prospective pharmacogenetic cohort study

Background. Tamoxifen is the drug of choice in ER-positive breast cancer (BC) therapy for perimenopausal women and one of the endocrine therapy options for menopausal patients. The pharmacological effect of tamoxifen can be influenced by the activity of cytochrome P450 (CYP) enzymes and P-glycoprotein transporters (Pg), and the genes encoding them have broad polymorphism, affecting serum concentrations of active metabolites. This article presents the overall results of a prospective population-based study of the clinical significance of genetic polymorphism of tamoxifen metabolic enzymes and transporters in breast cancer patients after radical treatment receiving adjuvant endocrine therapy with tamoxifen in outpatient settings during 2018-2019. The study was approved by the Research Ethics Committee of the Russian Medical Academy of Continuing Professional Education.&#x0D; Aim. To analyze the clinical presentation of endocrine therapy with tamoxifen in the adjuvant regimen and to assess the association of polymorphisms of genes encoding cytochrome P450 enzymes and drug transporter proteins with adverse events in BC patients.&#x0D; Materials and methods. One hundred and four women with stage I-III luminal breast cancer receiving adjuvant tamoxifen were examined for the presence of CYP2D6, CYP2C, and the following CYP3A gene polymorphisms: CYP2D6*4, CYP3A5*3, CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C19*3, as well as the ABCB1 gene polymorphic marker (C3435T) encoding the P-glycoprotein. The allelic variants were identified using the real-time polymerase chain reaction; the test was performed in the Research Center of the Russian Medical Academy of Continuing Professional Education. The study material was buccal epithelium (double sampling) taken after informed consent signing.&#x0D; Results. Association analysis showed the association of different genetic polymorphisms of CYP2D6, CYP3A5, CYP2C9, and ABCB1 with tamoxifen adverse drug reactions, indicating the clinical significance of these polymorphisms.&#x0D; Conclusion. With the implementation of genetic testing of the studied polymorphisms into the routine clinical practice of oncologists prescribing tamoxifen and gynecologists involved in the follow-up of breast cancer patients receiving endocrine therapy in the adjuvant mode, there will be an opportunity for more effective and safer pharmacotherapy.

Physiologically based pharmacokinetic modelling to predict the pharmacokinetics of metoprolol in different CYP2D6 genotypes.

Metoprolol, a selective β1-adrenoreceptor blocking agentused in the treatment of hypertension, angina, and heart failure, is primarily metabolized by the CYP2D6 enzyme, which catalyzes α-hydroxylation and O-desmethylation. As CYP2D6 is genetically highly polymorphic and the enzymatic activity differs greatly depending on the presence of the mutant allele(s), the pharmacokinetic profile of metoprolol is highly variable depending on the genotype of CYP2D6. The aim of study was to develop the physiologically based pharmacokinetic (PBPK) model of metoprolol related to CYP2D6 genetic polymorphism for personalized therapy with metoprolol. For PBPK modelling, our previous pharmacogenomic data were used. To obtain kinetic parameters (Km, Vmax, and CLint) of each genotype, the recombinant CYP enzyme of each genotype was incubated with metoprolol and metabolic rates were assayed. Based on these data, the PBPK model of metoprolol was developed and validated in different CYP2D6 genotypes using PK-Sim® software. As a result, the input values for various parameters for the PBPK model were presented and the PBPK model successfully described the pharmacokinetics of metoprolol in each genotype group. The simulated values were within the acceptance criterion (99.998% confidence intervals) compared with observed values. The PBPK model developed in this study can be used for personalized pharmacotherapy with metoprolol in individuals of various races, ages, and CYP2D6 genotypes.