Frequencies of UGT1A4*2 (P24T) and *3 (L48V) and their effects on serum concentrations of lamotrigine

Development of a PBPK Model for Lamotrigine which Incorporates Metabolism by UGT2B10: Impact of UGT2B10 Poor Metabolizer Phenotype and Pregnancy

An updated physiologically based pharmacokinetic (PBPK) model was developed for lamotrigine by incorporating a component of metabolism due to a UDP-glucuronyltransferase (UGT) 2B isozyme. This was assigned to UGT2B10 based on recent in vitro data in our laboratory demonstrating metabolism of lamotrigine by this isozyme (Tang et al. AAPS J 26:107, 2024). The PBPK model developed in this work was able to reasonably recapitulate the exposure of lamotrigine after single (IV and Oral) and multiple (Oral) doses. The predicted/observed maximal plasma concentration (Cmax) ratio ranged from 0.8 to 1.4 across all simulated studies and for 16 out of 18 simulated studies was between 0.8 and 1.25. Similarly, the predicted/observed area under the curve (AUC) ratio ranged from 0.6 to 1.44 across all simulated studies and for 18 out of 26 of the simulated studies the ratio was between 0.8 and 1.25. There was a slight tendency to overpredict the lamotrigine AUC on multiple dosing. The median predicted fraction metabolised (fm) by UGT2B10 in the model was 60%. With this fm value, the in vivo clinical DDI between lamotrigine and valproate was reasonably recapitulated considering only UGT2B10 inhibition (Predicted/Observed AUC ratios ranged from 0.65 - 1.2). Information on the prevalence of UGT2B10 poor metabolizer phenotypes and longitudinal changes in UGT1A4 and UGT2B10 expression during pregnancy were incorporated into the PBPK model and the plasma concentrations in subjects with different UGT2B10 phenotypes and in different trimesters of pregnancy were simulated. The simulated concentrations in pregnant subjects were in line with those reported during pregnancy.

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: Focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialised tools are used. Three tools have been proven useful to personalise drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 45 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimise treatment effects, minimise side effects and ultimately reduce the global burden of diseases, personalised drug treatment has not yet become the standard of care in psychiatry.

Pharmacogenetic Variants and Plasma Concentrations of Antiseizure Drugs: A Systematic Review and Meta-Analysis

Importance

Precise estimation of a patient's drug metabolism capacity is important for antiseizure dose personalization.

Objective

To quantify the differences in plasma concentrations for antiseizure drugs associated with variants of genes encoding drug metabolizing enzymes.

Data Sources

PubMed, Clinicaltrialsregister.eu, ClinicalTrials.gov, International Clinical Trials Registry Platform, and CENTRAL databases were screened for studies from January 1, 1990, to September 30, 2023, without language restrictions.

Study Selection

Two reviewers performed independent study screening and assessed the following inclusion criteria: appropriate genotyping was performed, genotype-based categorization into subgroups was possible, and each subgroup contained at least 3 participants.

Data Extraction and Synthesis

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines were followed for data extraction and subsequent quality, validity, and risk-of-bias assessments. The results from the included studies were pooled with random-effect meta-analysis.

Main Outcomes and Measures

Plasma concentrations of antiseizure drugs were quantified with the dose-normalized area under the concentration-time curve, the dose-normalized steady state concentration, or the concentrations after a single dose at standardized dose and sampling time. The ratio of the means was calculated by dividing the mean drug plasma concentrations of carriers and noncarriers of the pharmacogenetic variant.

Results

Data from 98 studies involving 12 543 adult participants treated with phenytoin, valproate, lamotrigine, or carbamazepine were analyzed. Studies were mainly conducted within East Asian (69 studies) or White or European (15 studies) cohorts. Significant increases of plasma concentrations compared with the reference subgroup were observed for phenytoin, by 46% (95% CI, 33%-61%) in CYP2C9 intermediate metabolizers, 20% (95% CI, 17%-30%) in CYP2C19 intermediate metabolizers, and 39% (95% CI, 24%-56%) in CYP2C19 poor metabolizers; for valproate, by 12% (95% CI, 4%-20%) in CYP2C9 intermediate metabolizers, 12% (95% CI, 2%-24%) in CYP2C19 intermediate metabolizers, and 20% (95% CI, 2%-41%) in CYP2C19 poor metabolizers; and for carbamazepine, by 12% (95% CI, 3%-22%) in CYP3A5 poor metabolizers.

Conclusions and Relevance

This systematic review and meta-analysis found that CYP2C9 and CYP2C19 genotypes encoding low enzymatic capacity were associated with a clinically relevant increase in phenytoin plasma concentrations, several pharmacogenetic variants were associated with statistically significant but only marginally clinically relevant changes in valproate and carbamazepine plasma concentrations, and numerous pharmacogenetic variants were not associated with statistically significant differences in plasma concentrations of antiseizure drugs.

UGT1A4*3 polymorphism influences serum concentration and therapeutic effect of lamotrigine for epilepsy treatment: A meta-analysis

BACKGROUND

Lamotrigine as a broad-spectrum antiepileptic drug, is widely applied and its clinical efficacy is highly recognized. However, significant differences are observed in blood drug concentration of lamotrigine among individuals, which may have an impact on its efficacy. UGT1A4 is the main metabolic enzyme. However, it was inconsistent for the influence of UGT1A4 genetic polymorphism on concentration and efficacy of lamotrigine therapy. This study aimed to evaluate the influences of UGT1A4*3 genetic polymorphisms on lamotrigine concentration and therapeutic effect through meta-analysis.

METHODS

The literature search was conducted in Medline, Embase, PubMed, Web of Science, Wan Fang Database, China National Knowledge Infrastructure, China Science and Technology Journal Database until January 2024. The primary outcome included the mean serum concentration, concentration-to-dose-ratio by body weight (CDR), or efficacy related to different UGT1A4*3 genotype for lamotrigine therapy. Data were collected to access the Mean Difference or odds ratio with 95% confidence interval. Meta-analysis was performed by RevMan 5.2.

RESULTS

A total of eleven studies were enrolled. The meta-analysis for mean serum concentration of lamotrigine showed no significant difference between patients carrying TT genotypes and TG and GG genotypes group (MD: 0.12, 95% [-0.35, 0.58], P = 0.62). There was significant difference in CDR (MD: 0.49, 95% [0.03, 0.94], P = 0.04) and therapeutic efficacy (OR: 7.18, 95% [4.01, 12.83], P<0.00001) of lamotrigine, however no significant difference was found in subgroup analysis of CDR of children (MD: 0.03, 95% [-0.35, 0.42], P = 0.87) between patients carrying TT genotypes and TG and GG genotypes group.

CONCLUSIONS

Polymorphism of UGT1A4*3 influenced the CDR and therapeutic efficacy of lamotrigine for antiepileptic therapy. Genotype analysis provided reference for personalized medication in the future. However, more high-quality evidences are necessary for precise and definitive conclusion.

UGT1A4 Polymorphism is not Associated with a Clinically Relevant Change in Giredestrant Exposure

PURPOSE

Giredestrant is a potent, orally bioavailable, small-molecule selective estrogen receptor antagonist and degrader (SERD) that is being developed for the treatment of patients with estrogen receptor (ER)-positive breast cancer. In vitro, giredestrant was primarily metabolized by UGT1A4. The goal of this study was to investigate if UGT1A4 polymorphism had a clinically relevant impact on giredestrant exposure.

METHODS

Genotyping and pharmacokinetic data were obtained from 118 and 61 patients in two clinical studies, GO39932 [NCT03332797] and acelERA Breast Cancer [NCT04576455], respectively.

RESULTS

The overall allelic frequencies of UGT1A4*2 and UGT1A4*3 were 3.3% and 11%, respectively. Giredestrant exposure was consistent between patients with wild-type UGT1A4 and UGT1A4*2 and *3 polymorphisms, with no clinically relevant difference observed. In addition, haplotype analysis indicated that no other UGT1A4 variants were significantly associated with giredestrant exposure.

CONCLUSION

Therefore, this study indicates that UGT1A4 polymorphism status is unlikely a clinically relevant factor to impact giredestrant exposure and giredestrant can be administered at the same dose level regardless of patients' UGT1A4 polymorphism status.

Pharmacokinetics, Pharmacodynamics, and Side Effects of Midazolam: A Review and Case Example

Midazolam, a short-acting benzodiazepine, is widely used to alleviate patient anxiety, enhance compliance, and aid in anesthesia. While its side effects are typically dose-dependent and manageable with vigilant perioperative monitoring, serious cardiorespiratory complications, including fatalities and permanent neurological impairment, have been documented. Prolonged exposure to benzodiazepines, such as midazolam, has been associated with neurological changes in infants. Despite attempts to employ therapeutic drug monitoring for optimal sedation dosing, its efficacy has been limited. Consequently, efforts are underway to identify alternative predictive markers to guide individualized dosing and mitigate adverse effects. Understanding these factors is crucial for determining midazolam's suitability for future administration, particularly after a severe adverse reaction. This article aims to elucidate the factors influencing midazolam's pharmacokinetics and pharmacodynamics, potentially leading to adverse events. Finally, a case study is presented to exemplify the complex investigation into the causative factors of midazolam-related adverse events.

Bearing variant alleles at uridine glucuronosyltransferase polymorphisms UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) has no relevant consequences for lamotrigine troughs in adults with epilepsy

PURPOSE

To estimate whether epilepsy patients with variant UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) alleles differ from their wild-type (wt) peers in exposure to lamotrigine.

METHODS

Consecutive adults on lamotrigine monotherapy or lamotrigine + valproate co-treatment undergoing routine therapeutic drug monitoring, otherwise generally healthy and free of interacting drugs, were genotyped for UGT2B7 -161C > T and UGT1A4*3 c.142 T > G. Heterozygous, variant homozygous, or combined heterozygous/variant homozygous subjects were compared to their wt controls for dose-adjusted lamotrigine troughs with adjustment for age, sex, body weight, rs7668258/rs2011425, polymorphisms of efflux transporter proteins ABCG2 c.421C > A (rs2231142) and ABCB1 1236C > T (rs1128503), and level of exposure to valproate using covariate entropy balancing.

RESULTS

Of the 471 included patients, 328 (69.6%) were on monotherapy and 143 were co-treated with valproate. Dose-adjusted lamotrigine troughs in UGT2B7 -161C > T heterozygous (CT, n = 237) or variant homozygous (TT, n = 115) subjects were closely similar to those in their wt controls (CC, n = 119): geometric means ratios (GMRs) (frequentist and Bayes) 1.00 (95%CI 0.86-1.16) and 1.00 (95%CrI 0.83-1.22) for CT vs. CC; and 0.97 (0.81-1.17) and 0.97 (0.80-1.20) for TT vs. CC subjects. Lamotrigine troughs were also closely similar in UGT1A4*3 c.142 T > G variant carriers (n = 106: 102 TG + 4 GG subjects) and wt controls (TT, n = 365): GMR = 0.95 (0.81-1.12) frequentist, 0.96 (0.80-1.16) Bayes. GMRs for variant carriers vs. wt controls were around unity also at different levels of exposure to valproate.

CONCLUSION

Dose-adjusted lamotrigine troughs in epilepsy patients with variant UGT2B7 -161C > T or UGT1A4*3 c.142 T > G alleles are equivalent to those in their respective wt peers.

Polymorphisms Affecting the Response to Novel Antiepileptic Drugs

Epilepsy is one of the most frequent chronic neurologic disorders that affects nearly 1% of the population worldwide, especially in developing countries. Currently, several antiepileptic drugs (AEDs) are available for its therapy, and although the prognosis is good for most patients, 20%-30% amongst them do not reach seizure freedom. Numerous factors may explain AED-resistance such as sex, age, ethnicity, type of seizure, early epilepsy onset, suboptimal dosing, poor drug compliance, alcohol abuse, and in particular, genetic factors. Specifically, the interindividual differences in drug response can be caused by single nucleotide polymorphisms (SNPs) in genes encoding for drug efflux transporters, for the brain targets of AEDs, and for enzymes involved in drug metabolism. In this review, we used the PubMed database to retrieve studies that assessed the influence of SNPs on the pharmacokinetic (PK), pharmacodynamic (PD), and efficacy of new antiepileptic drugs. Our results showed that polymorphisms in the ABCB1, ABCC2, UGT1A4, UGT2B7, UGT2B15, CYP2C9, and CYP2C19 genes have an influence on the PK and efficacy of AEDs, suggesting that a genetic pre-evaluation of epileptic patients could help clinicians in prescribing a personalized treatment to improve the efficacy and the safety of the therapy.

Transcriptional Regulation of Drug Metabolizing CYP Enzymes by Proinflammatory Wnt5A Signaling in Human Coronary Artery Endothelial Cells

Downregulation of drug metabolizing enzymes and transporters by proinflammatory mediators in hepatocytes, enterocytes and renal tubular epithelium is an established mechanism affecting pharmacokinetics. Emerging evidences indicate that vascular endothelial cell expression of drug metabolizing enzymes and transporters may regulate pharmacokinetic pathways in heart to modulate local drug bioavailability and toxicity. However, whether inflammation regulates pharmacokinetic pathways in human cardiac vascular endothelial cells remains largely unknown. The lipid modified protein Wnt5A is emerging as a critical mediator of proinflammatory responses and disease severity in sepsis, hypertension and COVID-19. In the present study, we employed transcriptome profiling and gene ontology analyses to investigate the regulation of expression of drug metabolizing enzymes and transporters by Wnt5A in human coronary artery endothelial cells. Our study shows for the first time that Wnt5A induces the gene expression of CYP1A1 and CYP1B1 enzymes involved in phase I metabolism of a broad spectrum of drugs including chloroquine (the controversial drug for COVID-19) that is known to cause toxicity in myocardium. Further, the upregulation of CYP1A1 and CYP1B1 expression is preserved even during inflammatory crosstalk between Wnt5A and the prototypic proinflammatory IL-1β in human coronary artery endothelial cells. These findings stimulate further studies to test the critical roles of vascular endothelial cell CYP1A1 and CYP1B1, and the potential of vascular-targeted therapy with CYP1A1/CYP1B1 inhibitors in modulating myocardial pharmacokinetics in Wnt5A-associated inflammatory and cardiovascular diseases.

Precision medicine in women with epilepsy: The challenge, systematic review, and future direction

Epilepsy is one of the most prevalent neurologic conditions, affecting almost 70 million people worldwide. In the United States, 1.3 million women with epilepsy (WWE) are in their active reproductive years. Women with epilepsy (WWE) face gender-specific challenges such as pregnancy, seizure exacerbation with hormonal pattern fluctuations, contraception, fertility, and menopause. Precision medicine, which applies state-of-the art molecular profiling to diagnostic, prognostic, and therapeutic problems, has the potential to advance the care of WWE by precisely tailoring individualized management to each patient's needs. For example, antiseizure medications (ASMs) are among the most common teratogens prescribed to women of childbearing potential. Teratogens act in a dose-dependent manner on a susceptible genotype. However, the genotypes at risk for ASM-induced teratogenic deficits are unknown. Here we summarize current challenging issues for WWE, review the state-of-art tools for clinical precision medicine approaches, perform a systematic review of pharmacogenomic approaches in management for WWE, and discuss potential future directions in this field. We envision a future in which precision medicine enables a new practice style that puts focus on early detection, prediction, and targeted therapies for WWE.

Possible interplay between the theories of pharmacoresistant epilepsy

Epilepsy is one of the oldest known neurological disorders and is characterized by recurrent seizure activity. It has a high incidence rate, affecting a broad demographic in both developed and developing countries. Comorbid conditions are frequent in patients with epilepsy and have detrimental effects on their quality of life. Current management options for epilepsy include the use of anti-epileptic drugs, surgery, or a ketogenic diet. However, more than 30% of patients diagnosed with epilepsy exhibit drug resistance to anti-epileptic drugs. Further, surgery and ketogenic diets do little to alleviate the symptoms of patients with pharmacoresistant epilepsy. Thus, there is an urgent need to understand the underlying mechanisms of pharmacoresistant epilepsy to design newer and more effective anti-epileptic drugs. Several theories of pharmacoresistant epilepsy have been suggested over the years, the most common being the gene variant hypothesis, network hypothesis, multidrug transporter hypothesis, and target hypothesis. In our review, we discuss the main theories of pharmacoresistant epilepsy and highlight a possible interconnection between their mechanisms that could lead to the development of novel therapies for pharmacoresistant epilepsy.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Influence of genetic variants and antiepileptic drug co-treatment on lamotrigine plasma concentration in Mexican Mestizo patients with epilepsy

Genetic and nongenetic factors may contribute to lamotrigine (LTG) plasma concentration variability among patients. We simultaneously investigated the association of UGT1A1, UGT1A4, UGT2B7, ABCB1, ABCG2, and SLC22A1 variants, as well as antiepileptic drug co-treatment, on LTG plasma concentration in 97 Mexican Mestizo (MM) patients with epilepsy. UGT1A4*1b was associated with lower LTG dose-corrected concentrations. Patients with the UGT2B7-161T allele were treated with 21.22% higher LTG daily dose than those with CC genotype. Two novel UGT1A4 variants (c.526A>T; p.Thr185= and c.496T>C; p.Ser166Leu) were identified in one patient. Patients treated with LTG + valproic acid (VPA) showed higher LTG plasma concentration than patients did on LTG monotherapy or LTG + inducer. Despite the numerous drug-metabolizing enzymes and transporter genetic variants analyzed, our results revealed that co-treatment with VPA was the most significant factor influencing LTG plasma concentration, followed by UGT1A4*1b, and that patients carrying UGT2B7 c.-161T required higher LTG daily doses. These data provide valuable information for the clinical use of LTG in MM patients with epilepsy.

Representation of CYP3A4, CYP3A5 and UGT1A4 Polymorphisms within Croatian Breast Cancer Patients' Population

Single nucleotide polymorphism (SNP) in genes encoding drug-metabolizing enzymes (DME) could have a critical role in individual responses to anastrozole. Frequency of CYP3A4*1B, CYP3A5*3 and UGT1A4*2 SNPs in 126 Croatian breast cancer (BC) patients and possible association with anastrozole-induced undesirable side effects were analyzed. Eighty-two postmenopausal patients with estrogen receptor (ER)-positive BC treated with anastrozole and 44 postmenopausal ER-positive BC patients before hormonal adjuvant therapy were included in the study. Genomic DNA was genotyped by TaqMan Real-Time PCR. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry. The homozygotes for the variant G allele of CYP3A5*3 were predominant (88%), and the homozygotes for the reference A allele were not detected. While homozygotes for the variant G allele of CYP3A4*1B were not detected, predominantly wild type homozygotes for A allele (94%) were present. CYP3A4*1B and CYP3A5*3 SNPs were in 84.3% linkage disequilibrium (D’ = 0.843) and 95.1% (D’ = 0.951) in group treated with anastrozole and w/o treatment, respectively. Homozygotes for the A allele of UGT1A4*2 were not detected in our study groups. Although the variant CYP3A5*3 allele, which might result in poor metabolizer phenotype and more pronounced side effects, was predominant, significant association with BMD changes induced by anastrozole were not confirmed.

The Ontogeny of UDP-glucuronosyltransferase Enzymes, Recommendations for Future Profiling Studies and Application Through Physiologically Based Pharmacokinetic Modelling

Limited understanding of drug pharmacokinetics in children is one of the major challenges in paediatric drug development. This is most critical in neonates and infants owing to rapid changes in physiological functions, especially in the activity of drug-metabolising enzymes. Paediatric physiologically based pharmacokinetic models that integrate ontogeny functions for cytochrome P450 enzymes have aided our understanding of drug exposure in children, including those under the age of 2 years. Paediatric physiologically based pharmacokinetic models have consequently been recognised by the European Medicines Agency and the US Food and Drug Administration as innovative tools in paediatric drug development and regulatory decision making. However, little is currently known about age-related changes in UDP-glucuronosyltransferase-mediated metabolism, which represents the most important conjugation reaction for xenobiotics. Therefore, the objective of the review was to conduct a thorough literature survey to summarise our current understanding of age-related changes in UDP-glucuronosyltransferases as well as associated clinical and experimental sources of variance. Our findings indicate that there are distinct differences in UDP-glucuronosyltransferase expression and activity between isoforms for different age groups. In addition, there is substantial variability between individuals and laboratories reported for human liver microsomes, which results in part from a lack of standardised experimental conditions. Therefore, we provide a number of best practice recommendations for experimental conditions, which ultimately may help improve the quality of data used for quantitative clinical pharmacology approaches, and thus for safe and effective pharmacotherapy in children.

Psychotropic drug use in perinatal women with bipolar disorder

Optimal dose management of psychotropic drugs during the perinatal period reduces the risk for recurrence of mood episodes in women with Bipolar Disorder. Physiological changes during pregnancy are associated with decreases in the plasma concentrations of the majority of mood stabilizing medications. Regular symptom and drug concentration monitoring for lithium and anticonvulsants with reflexive dose adjustment improves the probability of sustained symptom remission across pregnancy. The elimination clearance trajectory across pregnancy for psychotropics dictates the frequency of laboratory monitoring and dose adjustment. The literature on the pharmacokinetics of lithium, lamotrigine, carbamazepine and atypical antipsychotics during pregnancy and postpartum are reviewed, recommendations for symptom and laboratory monitoring are proposed and recommendations for dose adjustments are presented.

Lack of Association of Generic Brittle Status with Genetics and Physiologic Measures in Patients with Epilepsy

PURPOSE

A patient was denoted to be generic brittle (GB) if they had a negative opinion about generics (e.g. prior history of a switch problem) or took the innovator brand of their most problematic anti-epileptic drug (AED) when generic was available. The aim of this hypothesis-generating study was to assess possible genetic and physiologic differences between GB and not GB patients with epilepsy.

METHODS

Patients (n = 148) with epilepsy were previously characterized as being either GB or not GB. Blood was collected from each subject for genotyping and physiologic testing. Genotyping for 24 single nucleotide polymorphisms (SNPs) and two copy number variants (CNVs) was performed across 12 genes in each patient. Forty-four physiologic tests were conducted in each patient. Chi square analysis was performed to assess for associations between genotyping results and GB status, as well as between physiologic test results and GB status.

RESULTS

No SNP or CNV discriminated GB status in genetic analysis (genotype or allele frequency). Physiologic test results in this study were not associated with GB status.

CONCLUSIONS

Questions from neurologists and patients about generics is frequently based on applicability of generic drug standards to individual subjects. However, findings here in patients with epilepsy did not uncover genetic or physiologic reasons that explained which patients were GB and which were not GB.

Genetic variations associated with pharmacoresistant epilepsy (Review)

Epilepsy is a common, serious neurological disorder worldwide. Although this disease can be successfully treated in most cases, not all patients respond favorably to medical treatments, which can lead to pharmacoresistant epilepsy. Drug-resistant epilepsy can be caused by a number of mechanisms that may involve environmental and genetic factors, as well as disease- and drug-related factors. In recent years, numerous studies have demonstrated that genetic variation is involved in the drug resistance of epilepsy, especially genetic variations found in drug resistance-related genes, including the voltage-dependent sodium and potassium channels genes, and the metabolizer of endogenous and xenobiotic substances genes. The present review aimed to highlight the genetic variants that are involved in the regulation of drug resistance in epilepsy; a comprehensive understanding of the role of genetic variation in drug resistance will help us develop improved strategies to regulate drug resistance efficiently and determine the pathophysiological processes that underlie this common human neurological disease.

Glucuronidation of Abiraterone and Its Pharmacologically Active Metabolites by UGT1A4, Influence of Polymorphic Variants and Their Potential as Inhibitors of Steroid Glucuronidation

Abiraterone (Abi) acetate (AA) is a prodrug of Abi, a CYP17A1 inhibitor used to treat patients with advanced prostate cancer. Abi is a selective steroidal inhibitor that blocks the biosynthesis of androgens. It undergoes extensive biotransformation by steroid pathways, leading to the formation of pharmacologically active Δ4-Abi (D4A) and 5α-Abi. This study aimed to characterize the glucuronidation pathway of Abi and its two active metabolites. We show that Abi, its metabolites, and another steroidal inhibitor galeterone (Gal) undergo secondary metabolism to form glucuronides (G) in human liver microsomes with minor formation by intestine and kidney microsomal preparations. The potential clinical relevance of this pathway is supported by the detection by liquid chromatography-tandem mass spectrometry of Abi-G, D4A-G, and 5α-Abi-G in patients under AA therapy. A screening of UGT enzymes reveals that UGT1A4 is the main enzyme involved. This is supported by inhibition experiments using a selective UGT1A4 inhibitor hecogenin. A number of common and rare nonsynonymous variants significantly abrogate the UGT1A4-mediated formation of Abi-G, D4A-G, and 5α-Abi-G in vitro. We also identify Gal, Abi, and its metabolites as highly potent inhibitors of steroid inactivation by the UGT pathway with submicromolar inhibitor constant values. They reduce the glucuronidation of both the adrenal precursors and potent androgens in human liver, prostate cancer cells, and by recombinant UGTs involved in their inactivation. In conclusion, tested CYP17A1 inhibitors are metabolized through UGT1A4, and germline variations affecting this metabolic pathway may also influence drug metabolism. SIGNIFICANCE STATEMENT: The antiandrogen abiraterone (Abi) is a selective steroidal inhibitor of the cytochrome P450 17α-hydroxy/17,20-lyase, an enzyme involved in the biosynthesis of androgens. Abi is metabolized to pharmacologically active metabolites by steroidogenic enzymes. We demonstrate that Abi and its metabolites are glucuronidated in the liver and that their glucuronide derivatives are detected at variable levels in circulation of treated prostate cancer patients. UDP-glucuronosyltransferase (UGT)1A4 is the primary enzyme involved, and nonsynonymous germline variations affect this metabolic pathway in vitro, suggesting a potential influence of drug metabolism and action in patients. Their inhibitory effect on drug and steroid glucuronidation raises the possibility that these pharmacological compounds might affect the UGT-associated drug-metabolizing system and pre-receptor control of androgen metabolism in patients.

A repository of protein abundance data of drug metabolizing enzymes and transporters for applications in physiologically based pharmacokinetic (PBPK) modelling and simulation

Population factors such as age, gender, ethnicity, genotype and disease state can cause inter-individual variability in pharmacokinetic (PK) profile of drugs. Primarily, this variability arises from differences in abundance of drug metabolizing enzymes and transporters (DMET) among individuals and/or groups. Hence, availability of compiled data on abundance of DMET proteins in different populations can be useful for developing physiologically based pharmacokinetic (PBPK) models. The latter are routinely employed for prediction of PK profiles and drug interactions during drug development and in case of special populations, where clinical studies either are not feasible or have ethical concerns. Therefore, the main aim of this work was to develop a repository of literature-reported DMET abundance data in various human tissues, which included compilation of information on sample size, technique(s) involved, and the demographic factors. The collation of literature reported data revealed high inter-laboratory variability in abundance of DMET proteins. We carried out unbiased meta-analysis to obtain weighted mean and percent coefficient of variation (%CV) values. The obtained %CV values were then integrated into a PBPK model to highlight the variability in drug PK in healthy adults, taking lamotrigine as a model drug. The validated PBPK model was extrapolated to predict PK of lamotrigine in paediatric and hepatic impaired populations. This study thus exemplifies importance of the DMET protein abundance database, and use of determined values of weighted mean and %CV after meta-analysis in PBPK modelling for the prediction of PK of drugs in healthy and special populations.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

The influence of concomitant antiepileptic drugs on lamotrigine serum concentrations in Northwest Chinese Han population with epilepsy

Objective

The aims of this study were to identify the influencing factors such as gender, age, dose and combinations of other antiepileptic drugs (AEDs), especially in triple combinations on the pharmacokinetic of Lamotrigine (LTG) in epilepsy patients of Northwest Chinese Han population.

Methods

Data of the LTG concentration and clinical information were analyzed retrospectively from a therapeutic drug monitoring (TDM) database at the Clinical Pharmacy Laboratory of Xi’an Central Hospital between January 1, 2016 and January 1, 2018. The independent-sample t-test, one-way ANOVA analysis and Bonferroni and Tamhane T3 post-hoc test, the stepwise multivariate regression analysis were adopted by IBM SPSS, version 22.0.

Results

226 serum samples met the inclusion criteria and were evaluated. The mean LTG serum concentration was 5.48±3.83 μg/mL. There were no gender differences (P = 0.64), and there were no significant effects by age on LTG serum concentration after age stratification (3–14 years old, 14-45 years old, 45–59 years old) (P = 0.05). Multiple regression analysis showed that the daily LTG dose and co-administration of other AEDs significantly affected LTG serum concentrations. Combination with enzyme-inducer AEDs, the mean steady-state LTG concentration could be decreased by 30.73% compared with LTG monotherapy. Among enzyme-inducer AEDs, particularly strong inducer Carbamazepine (CBZ) could decrease the mean LTG concentration by 53.65%, but weak inducer AEDs such as Oxcarbazepine (OXC) and Topiramate (TPM) had no effect, Valproic acid (VPA) could increase the mean LTG concentration by 93.95%, and the inducer only partially compensated for the inhibitory effect of VPA in triple combination.

Conclusions

There were no significant gender and age effects, but the LTG daily dose and co-administration of other AEDs significantly affected LTG serum concentration. Combination with enzyme-inducer AEDs, especially CBZ could significantly decrease LTG serum concentrations, VPA could significantly increase LTG serum concentrations, and the inducer only partially compensated for the inhibitory effect of VPA in triple combination. In the clinical setting, these findings can help to estimate LTG concentrations and adjust dosage and evaluate adverse drug reactions.

Meta-analysis of the Influence of UGT Genetic Polymorphisms on Lamotrigine Concentration

Uridine 5'-diphospho-glucuronosyltransferases (UGTs) are involved in the metabolism of lamotrigine, but whether the UGT1A4 and UGT2B7 genetic polymorphisms affect lamotrigine concentration remains controversial. Thus, the objective of this meta-analysis was to analyse the influence of UGT1A4 and UGT2B7 genetic polymorphisms on lamotrigine concentration. Through searching, screening, selection, data extraction and quantitative analyses, the influence of UGT1A4 and UGT2B7 genetic polymorphisms on lamotrigine concentration-to-dose ratio (CDR) was assessed by meta-analysis of nine studies. Neither UGT1A4 70C>A nor 142T>G significantly affected lamotrigine CDR values (standardized difference in means [SDM] = 0.433, 95% confidence interval [CI] = -0.380-1.302; SDM = -0.458, 95% CI = -1.141-0.224, respectively). Only the UGT2B7 -161C>T homozygous variant had significantly higher CDR values than the wild-type (WT) and heterozygous variant (SDM = 0.634, 95% CI = 0.056-1.222). In conclusion, CDR of lamotrigine was significantly higher for the UGT2B7 -161C>T homozygous variant than for the WT and heterozygous variant. Thus, UGT2B7 -161C>T homozygous variant needs to receive reduced dose.

Interaction between ABCG2 421C>A polymorphism and valproate in their effects on steady-state disposition of lamotrigine in adults with epilepsy

AIMS

To investigate the impact of glucuronidation enzyme (UGT1A4*3 142T>G, UGT1A4*2 70C>A, UGT2B7 -161C>T) and transporter (MDR1/ABCB1 1236C>T, ABCG2 421C>A) polymorphisms on steady-state disposition of lamotrigine and on the lamotrigine-valproate interaction.

METHODS

Adults with epilepsy on lamotrigine monotherapy (n = 131) or lamotrigine + valproate treatment (n = 74) were genotyped and steady-state lamotrigine and valproate morning troughs were determined as a part of routine therapeutic drug monitoring.

RESULTS

No effect of UGT and MDR1/ABCB1 polymorphisms was observed. In the entire cohort, ABCG2 421A allele had no effect however an interaction between the variant allele and valproate was observed: (i) in lamotrigine-only patients, variant allele (vs. wild type homozygosity) was independently (adjustments: age, sex, body mass index, lamotrigine dose, other polymorphisms) associated with mildly lower lamotrigine troughs [geometric means ratio (GMR) = 0.76, 95% confidence interval (CI) 0.59-0.98], whereas in lamotrigine + valproate patients it was associated with higher troughs (GMR = 1.72, 95%CI 1.14-2.62); (ii) valproate cotreatment was overall associated with markedly higher troughs vs. lamotrigine monotherapy (GMR = 3.49, 95%CI 2.73-4.44), but more so in variant allele carriers (GMR = 5.24, 95%CI 3.38-8.15) than in wild type homozygotes (GMR = 2.32, 95%CI 1.89-2.83); (iii) variant allele effects in two treatment subsets and valproate effects in two genotype subsets differed by 2.36-fold (95%CI 1.39-3.67); (iv) increase in lamotrigine troughs associated with increasing valproate troughs was greater in variant allele carriers than in wild type homozygotes, i.e. variant allele effect increased with increasing valproate troughs.

CONCLUSION

This study is first to indicate a potentially relevant interaction between ABCG2 421C>A polymorphism and valproate in their effects on lamotrigine disposition.

Physiologically-based pharmacokinetic modelling of a CYP2C19 substrate, BMS-823778, utilizing pharmacogenetic data

AIMS

Previous studies demonstrated direct correlation between CYP2C19 genotype and BMS-823778 clearance in healthy volunteers. The objective of the present study was to develop a physiologically-based pharmacokinetic (PBPK) model for BMS-823778 and use the model to predict PK and drug-drug interaction (DDI) in virtual populations with multiple polymorphic genes.

METHODS

The PBPK model was built and verified using existing clinical data. The verified model was simulated to predict PK of BMS-823778 and significance of DDI with a strong CYP3A4 inhibitor in subjects with various CYP2C19 and UGT1A4 genotypes.

RESULTS

The verified PBPK model of BMS-823778 accurately recovered observed PK in different populations. In addition, the model was able to capture the exposure differences between subjects with different CYP2C19 genotypes. PK simulation indicated higher exposures of BMS-823778 in CYP2C19 poor metabolizers who were also devoid of UGT1A4 activity, compared to those with normal UGT1A4 functionality. Moderate DDI with itraconazole was predicted in subjects with wild-type CYP2C19 or UGT1A4. However, in subjects without CYP2C19 or UGT1A4 functionality, significant DDI was predicted when BMS-823778 was coadministered with itraconazole.

CONCLUSIONS

A PBPK model was developed using clinical data that accurately predicted human PK in different population with various CYP2C19 phenotypes. Simulations with the verified PBPK model indicated that UGT1A4 was probably an important clearance pathway in CYP2C19 poor metabolizers. DDI with itraconazole is likely to be dependent on the genotypes of CYP2C19 and UGT1A4.

Clinical Pharmacokinetics and the Impact of Genetic Polymorphism on a CYP2C19 Substrate, BMS-823778, in Healthy Subjects

BMS-823778 is a potent and selective inhibitor of 11β-HSD1, an enzyme that regulates tissue-specific intracellular glucocorticoid metabolism and is a compelling target for the treatment of metabolic diseases. Metabolism of BMS-823778 was mediated mainly by polymorphic CYP2C19, with minor contributions from CYP3A4/5 and UGT1A4. The clinical pharmacokinetics (PK) of BMS-823778 was first investigated in healthy volunteers after single and multiple ascending doses. BMS-823778 was rapidly absorbed after the oral dose, and systemic exposure at steady state increased proportionally to the dose. Large intersubject variability in BMS-823778 exposure was likely because of the polymorphism of metabolic enzymes. The impact of genetic polymorphism of CYP2C19, UGT1A4, and CYP3A5 on BMS-823778 PK was assessed in healthy Chinese and Japanese subjects, as well as in a human absorption, distribution, metabolism, and excretion study in which all subjects were genotyped either before or after treatment. A clear trend of high exposure and low clearance was seen in poor metabolizers (PMs) of CYP2C19 compared with extensive (EM) and intermediate metabolizer (IM) subjects. The impact of UGT1A4 or CYP3A5 polymorphism on BMS-823778 PK was statistically not significant in CYP2C19 EM and IM subjects; however, in a subject with predicted CYP2C19 PM phenotype, the PK of BMS-823778 was affected significantly by UGT1A4 polymorphism. Overall, BMS-823778 was safe and well tolerated in healthy subjects after single or multiple oral doses. The PK of BMS-823778 was characterized by rapid absorption, and the systemic clearance directly correlated with the genetic polymorphism of CYP2C19.

The Impact of Pharmacokinetic Interactions With Eslicarbazepine Acetate Versus Oxcarbazepine and Carbamazepine in Clinical Practice

BACKGROUND

Eslicarbazepine acetate (ESL) is a new anti-epileptic drug (AED) chemically related to oxcarbazepine (OXC) and carbamazepine (CBZ) and is increasingly used in clinical practice. The purpose of the study was to investigate 2-way pharmacokinetic interactions between ESL and other AEDs as compared to OXC and CBZ.

METHODS

Anonymous data regarding age, gender, use of AEDs, daily doses and serum concentration measurements of ESL, OXC, CBZ and lamotrigine (LTG) and other AEDs were retrieved from 2 therapeutic drug monitoring (TDM) databases in Norway. Drugs were categorized according to their known potential for interactions. Concentration/dose (C/D) ratios were calculated.

RESULTS

Data from 1100 patients were available. The C/D ratios of ESL and OXC were unchanged in combination with enzyme-inducing AEDs or valproate (VPA). The C/D ratio of CBZ decreased by 40% and 22% in combination with other enzyme-inducing AEDs or VPA, respectively, pointing to an increased clearance. ESL demonstrated no significant enzyme-inducing effect on LTG metabolism although there was a 20% and 34% decrease in the C/D ratio of LTG in combination with OXC and CBZ, respectively.

CONCLUSIONS

Possible pharmacokinetic interactions have been studied for ESL as compared to OXC and CBZ. The pharmacokinetics of ESL is not affected by enzyme-inducing AEDs or VPA and does not affect the metabolism of LTG in contrast to OXC and CBZ. The study demonstrates the value of using TDM databases to explore the potential for pharmacokinetic interactions of new AEDs.

No association between non-bullous skin reactions from lamotrigine and heterozygosity of UGT1A4 genetic variants *2(P24T) or *3(L48V) in Norwegian patients

PURPOSE

High initial serum concentrations increase the risk of cutaneous adverse reactions. Genetic variants of the main metabolizing isoenzyme, uridine diphosphate glucuronosyltransferase (UGT) 1A4 influence the elimination of lamotrigine (LTG). Our aim was to investigate the potential association between the two best studied variants, *2 (P24T) and *3 (L48V), and the occurrence non-bullous skin reactions from LTG.

METHOD

The study included 29 patients of Caucasian ethnicity with a history of non-bullous skin reactions from LTG. 184 subjects tolerant to LTG for at least three months were used as controls. UGT1A4 genotyping was performed in all patients and controls by sequencing of the first part of exon 1. Six controls were excluded due to rare genetic variants.

RESULTS

Two of 29 subjects (7%) with rash from LTG were heterozygous for UGT1A4 *2, compared to 23 of 178 (13%) tolerant controls (p=0.54). Four of 29 subjects (14%) with rash from LTG were heterozygous for UGT1A4 *3 compared to 25 of 178 (14%) tolerant controls (p=0.97).

CONCLUSION

It is unlikely that heterozygosity of the UGT1A4 genetic variants *2(P24T) or *3(L48V) influences the risk of non-bullous skin reactions in patients treated with LTG.

Effects of UGT1A9 genetic polymorphisms on monohydroxylated derivative of oxcarbazepine concentrations and oxcarbazepine monotherapeutic efficacy in Chinese patients with epilepsy

AIM

The human UDP-glucuronosyltransferase which is genetically polymorphic catalyzes glucuronidations of various drugs. The interactions among UGT1A4, UGT1A6, UGT1A9, and UGT2B15 genetic polymorphisms, monohydroxylated derivative (MHD) of oxcarbazepine (OXC) plasma concentrations, and OXC monotherapeutic efficacy were explored in 124 Chinese patients with epilepsy receiving OXC monotherapy.

METHOD

MHD is the major active metabolite of OXC, and its plasma concentration was measured using high-performance liquid chromatography when patients reached their maintenance dose of OXC. Genomic DNA was extracted from whole blood and SNP genotyping performed using PCR followed by dideoxy chain termination sequencing. We followed the patients for at least 1 year to evaluate the OXC monotherapy efficacy. Patients were divided into two groups according to their therapeutic outcome: group 1, seizure free; group 2, not seizure free. The data were analyzed using T test, one-way analysis of variance (ANOVA), Kruskal-Wallis test, chi-square test, Fisher's exact test, correlation analysis, and multivariate regression analysis.

RESULT

T test analysis showed that MHD plasma concentrations were significantly different between the two groups (p = 0.002). One-way ANOVA followed by Bonferroni post hoc testing of four candidate SNPs revealed that carriers of the UGT1A9 variant allele I399 C > T (TT 13.28 ± 7.44 mg/L, TC 16.41 ± 6.53 mg/L) had significantly lower MHD plasma concentrations and poorer seizure control than noncarriers (CC 22.24 ± 8.49 mg/L, p < 0.05).

CONCLUSION

In our study, we have demonstrated the effects of UGT1A9 genetic polymorphisms on MHD plasma concentrations and OXC therapeutic efficacy. Through MHD monitoring, we can predict OXC therapeutic efficacy, which may be useful for the personalization of OXC therapy in epileptic patients.

An investigation of the influence of patient-related factors and comedications on lamotrigine clearance in patients with epilepsy

Lamotrigine (LTG) is one of the most widely used antiepileptic drugs. Confusion still exists in the literature as to the relative influence of age, body weight, and concomitant drug therapy on LTG pharmacokinetics. So, the objective of this study is to evaluate the influence of patient-related factors and comedication on LTG apparent oral clearance (CL/F). A therapeutic drug-monitoring database was used to identify steady-state plasma LTG concentrations in 210 patients. LTG CL/F values were calculated for each patient according to the equation CL/F (L/h per kg) = LTG daily dose (mg/kg)/Css (steady state concentration) (mg/L) × 24 h. A linear-regression model was used to assess the influence of gender, dose, age, and body weight in LTG CL/F. The influence of comedication on LTG CL/F was investigated by applying the Bonferroni post-test. The lowest LTG CL/F was found in patients comedicated with valproate (VPA) (mean, 0.0183 L/h per kg), followed by patients receiving VPA + enzyme inducers (0.0271 L/h per kg), patients on LTG monotherapy (0.0298 L/h per kg) and patients comedicated with enzyme inducers (0.056 L/h per kg) LTG CL/F correlated significantly with LTG dose (P < 0.01), but showed no significant relationship with gender, weight, and age. LTG CL/F is influenced by the type of antiepileptic comedication. The correlation with dose may be a spurious finding related to the fact that physicians, in adjusting dosage according to clinical response, are more likely to use larger doses in patients with high clearance values.