Association between PK/PD-involved gene polymorphisms and carbamazepine-individualized therapy

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.

Applying Physiologically Based Pharmacokinetic Modeling to Interpret Carbamazepine's Nonlinear Pharmacokinetics and Its Induction Potential on Cytochrome P450 3A4 and Cytochrome P450 2C9 Enzymes

Carbamazepine (CBZ) is commonly prescribed for epilepsy and frequently used in polypharmacy. However, concerns arise regarding its ability to induce the metabolism of other drugs, including itself, potentially leading to the undertreatment of co-administered drugs. Additionally, CBZ exhibits nonlinear pharmacokinetics (PK), but the root causes have not been fully studied. This study aims to investigate the mechanisms behind CBZ's nonlinear PK and its induction potential on CYP3A4 and CYP2C9 enzymes. To achieve this, we developed and validated a physiologically based pharmacokinetic (PBPK) parent-metabolite model of CBZ and its active metabolite Carbamazepine-10,11-epoxide in GastroPlus®. The model was utilized for Drug-Drug Interaction (DDI) prediction with CYP3A4 and CYP2C9 victim drugs and to further explore the underlying mechanisms behind CBZ's nonlinear PK. The model accurately recapitulated CBZ plasma PK. Good DDI performance was demonstrated by the prediction of CBZ DDIs with quinidine, dolutegravir, phenytoin, and tolbutamide; however, with midazolam, the predicted/observed DDI AUClast ratio was 0.49 (slightly outside of the two-fold range). CBZ's nonlinear PK can be attributed to its nonlinear metabolism caused by autoinduction, as well as nonlinear absorption due to poor solubility. In further applications, the model can help understand DDI potential when CBZ serves as a CYP3A4 and CYP2C9 inducer.

Physiologically based pharmacokinetic modeling to predict maternal pharmacokinetics and fetal carbamazepine exposure during pregnancy

Carbamazepine is an antiepileptic drug commonly used in pregnant women, during which the physiological changes may affect its efficacy. The aim of this study was to establish a physiologically based pharmacokinetic (PBPK) model of carbamazepine and its active metabolite carbamazepine-10,11-epoxide, and simulate maternal and fetal pharmacokinetic changes of carbamazepine and carbamazepine-10,11-epoxide in different trimesters and propose dose adjustment. We established pregnancy PBPK models for carbamazepine and carbamazepine-10,11-epoxide in PK-Sim® and Mobi® and validated the models with observed data from clinical reports. The placental transfer parameters obtained using different methods were also imported into the model and compared with the observed data to establish and validate fetal pharmacokinetic curves. The simulated results showed that mean steady-state trough plasma concentration of carbamazepine decreased by 27, 43.1, and 52 % during the first, second, and third trimesters, respectively. Therefore, to achieve an optimum therapeutic concentration, administering at least 1.4, 1.8, and 2.1 times the baseline dose of carbamazepine in the first, second, and third trimesters, respectively can be used as a dose reference. In conclusion, this study established and validated a pregnancy PBPK model of carbamazepine and carbamazepine-10,11-epoxide to assess exposure in pregnant women and fetuses, which provided a reference for the dosage adjustment of carbamazepine during pregnancy.

Genetic polymorphisms of microsomal epoxide hydrolase and UDP-glucuronosyltransferase (UGT) and its effects on plasma carbamazepine levels and metabolic ratio in persons with epilepsy of South India: A cross-sectional genetic association study

OBJECTIVES

Carbamazepine (CBZ), an anti-seizure drug, is widely prescribed for the management of focal seizures. At a given therapeutic dose, CBZ exhibits marked interindividual variation in the plasma CBZ levels. The aim wasto study the influence of EPHX1 c.337 T>C and UGT2B7*2 genetic polymorphisms on plasma carbamazepine (CBZ) levels in persons with epilepsy (PWE) from South India.

METHODS

115 PWE belong to South India origin who are on carbamazepine monotherapy were recruited. Genotyping of the two variants weredone using RT-PCR method. PWE who had seizure freedom for one year and their last dose which was not changed for one year duration were included and their plasma levels of CBZ and its active metabolite CBZ 10,11 epoxide were analysed by reverse phase HPLC.

RESULTS

In EPHX1 c. 337 (T>C) polymorphism, the PWE carrying CC had lower plasma CBZ levels when compared to CT genotype (2.45 μg/ml vs 3.15 μg/ml. In UGT2B7*2, PWE carrying homozygous mutant TT had higher levels when compared with CT (3.09 μg/ml vs 2.74 μg/ml) genotype but found no statistical significance. Mutant genotype of EPHX1 (CC) had higher metabolic ratio compared to TT genotype (1.33 vs 1.17) but not found to be statistically significant. Mutant genotype of UGT2B7*2 (TT) was found to be having lower metabolic ratio when compared with CC genotype (1.18 vs 1.35; p value =0.08).

CONCLUSION

PWE carrying EPHX1 c.337 T>C (rs1051740) and UGT2B7*2 (rs7439366) genetic polymorphisms did not affect the plasma CBZ levels and metabolic ratio of PWE of South Indian origin. However, this finding should be confirmed in a larger sample size which may help in optimization and personalized CBZ therapy in South Indians.

Influence of EPHX1 c.337 T>C and UGT2B7*2 genetic polymorphisms on the requirement of carbamazepine maintenance dose in person with epilepsy (PWE) of Southern part of India: a cross-sectional genetic association study

OBJECTIVES

Carbamazepine (CBZ) is a first-line antiseizure drug used for focal onset seizures. It exhibits inter-individual variability in plasma carbamazepine levels and there are both genetic and non-genetic factors having a role in the requirement of CBZ maintenance dose. The aim was to study the influence of EPHX1 c.337 T>C and UGT2B7*2 genetic polymorphisms on CBZ maintenance dose requirement in persons with epilepsy.

METHODS

Persons with epilepsy (PWE) of both gender of age 15-65 years on carbamazepine monotherapy who had been taking same maintenance dose for one year were eligible. Five milliliter of venous blood was collected in 10% EDTA under aseptic precautions. After centrifugation, the cellular component was used for DNA extraction and genotyping. For three genotypes of EPHX1 c.337 T>C and UGT2B7*2, the differences in mean carbamazepine dose were analyzed using Analysis of Variance (ANOVA). An unpaired t-test was used to draw a comparison between the genotypes and CBZ maintenance dose requirement for dominant and recessive models of EPHX1 c.337 T>C and UGT2B7*2. A value of p<0.05 was considered to be statistically significant.

RESULTS

For UGT2B7*2 (rs 7439366), CT required a higher dose (CT 626 mg/day and TT 523 mg/day) but not found to be significant (p-value 0.167). PWE carrying CT genotype of EPHX1 c.337 T>C had 62 mg higher dose when compared to homozygous mutant CC (590 mg/day for CT and 528 mg/day for CC) but p-value was not found to be significant (p-value 0.835).

CONCLUSIONS

The results of our study done in 115 PWE showed there was a lack of association between SNPs of EPHX1 c.337 T>C, UGT2B7*2 and CBZ maintenance dose requirement in Southern part of India and this finding has to be confirmed in a larger sample size.

ABCB1 c.3435C > T and EPHX1 c.416A > G polymorphisms influence plasma carbamazepine concentration, metabolism, and pharmacoresistance in epileptic patients

The gene polymorphisms of ABCB1, EPHX1, and SCN1A were found to influence carbamazepine (CBZ) metabolism and resistance in epilepsy patients, but the relevance remains controversial. To reveal the relationships among the gene polymorphisms of ABCB1, EPHX1, SCN1A and the metabolism and resistance of CBZ, the databases of PubMed, EMBASE, Cochrane Library, Chinese National Knowledge Infrastructure, Chinese Science and Technique Journals, China Biology medicine disc and Wan Fang were retrieved for suitable studies up to April 2021. 18 studies containing 3293 epilepsy patients were included. The result revealed the gene polymorphism of ABCB1 c.3435C > T is significantly associated with altered concentration-dose ratios of CBZ (CDR_CBZ) (CC vs. CT, OR = 0.25 (95% CI: 0.08-0.42), P = 0.004), and EPHX c.416A > G gene polymorphism may also significantly adjusted the concentration-dose ratios of carbamazepine-10, 11-trans dihydrodiol (CDR_CBZD) (AA vs. GG, OR = 0.48 (95% CI: 0.01-0.96), P = 0.045; AG vs. GG, OR = 0.68 (95% CI: 0.16-1.20), P = 0.010, respectively) and the ratio of CBZD:carbamazepine-10,11-epoxide (CBZE) (CDR_CBZD:CDR_CBZE) (AG vs GG, OR = 0.83 (95% CI: 0.31-1.36), P = 0.002). Furthermore, ABCB1 c.3435C > T polymorphism was also observed to be significantly influenced CBZ resistance (CC vs TT, OR = 1.78 (95% CI: 1.17-2.72), P = 0.008; CT vs TT, OR = 1.60 (95% CI: 1.12-2.30), P = 0.01; CC + CT vs TT, OR = 1.61 (95% CI: 1.15-2.26), P = 0.006, respectively). Therefore, CBZ metabolism and resistance in patients with epilepsy may be adjusted by the gene polymorphisms of ABCB1 c.3435C > T and EPHX1 c.416A > G which provides the further scientific basis for clinical individualized therapy of epilepsy. However, larger sample size studies are still needed to provide further conclusive evidence.

Relevance of NR1I2 variants on carbamazepine therapy in Mexican Mestizos with epilepsy at a tertiary-care hospital

Aim: We evaluated the potential influence of genetic (CYP3A5, EPHX1, NR1I2, HNF4A, ABCC2, RALBP1, SCN1A, SCN2A and GABRA1) and nongenetic factors on carbamazepine (CBZ) response, adverse drug reactions and CBZ plasma concentrations in 126 Mexican Mestizos (MM) with epilepsy. Subjects & methods: Patients were genotyped for 27 variants using TaqMan^® assays. Results: CBZ response was associated with NR1I2 variants and lamotrigine cotreatment. CBZ-induced adverse drug reactions were related to antiepileptic polytherapy and SCN1A rs2298771/rs3812718 haplotype. CBZ plasma concentrations were influenced by NR1I2-rs2276707 and -rs3814058, and by phenytoin cotreatment. CBZ daily dose was also influenced by NR1I2-rs3814055 and EPHX1-rs1051740. Conclusion: Interindividual variability in CBZ treatment was partly explained by NR1I2, EPHX1 and SCN1A variants, as well as antiepileptic cotreatment in MM with epilepsy.

Genetics and antiepileptic mood stabilizer treatment response in bipolar disorder: what do we know?

Antiepileptic mood stabilizers (AED-MS) are often used to treat bipolar disorder (BD). Similar to other mood disorder medications, AED-MS treatment response varies between patients. Identification of biomarkers associated with treatment response may ultimately help with the delivery of individualized treatment and lead to improved treatment efficacy. Here, we conducted a narrative review of the current knowledge of the pharmacogenomics of AED-MS (valproic acid, lamotrigine and carbamazepine) treatment response in BD, including genetic contributions to AED-MS pharmacokinetics. Genes involved in neurotransmitter systems and drug transport have been shown to be associated with AED-MS treatment response. As more studies are conducted, and experimental and analytical methods advance, knowledge of AED-MS pharmacogenomics is expected to grow and contribute to precision medicine in BD.

Genetic variants associated with severe cutaneous adverse drug reactions induced by carbamazepine

AIMS

Carbamazepine (CBZ) is one of the most common causative drugs of severe cutaneous adverse drug reactions (SCARs) including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reactions with eosinophilia and systemic symptoms. Although genetic polymorphisms of the human leucocyte antigens (HLA) are well recognized key elements for the susceptibility to CBZ-induced SCARs, some evidence suggest that polymorphisms of microsomal epoxide hydrolase 1 (EPHX1) may also contribute to the risk of these SCARs. This study investigated the association between the HLA and EPHX1 polymorphisms on CBZ-induced SCARs in large sample sizes and well-defined SCARs patients.

METHODS

Ninety-one CBZ-induced SCARs Thai patients and 144 CBZ-tolerant patients were enrolled in the study. The genotypes of HLA-A, HLA-B and EPHX1 were determined.

RESULTS

Only 2 HLA alleles including HLA-B*15:02 and HLA-A*24:07 were statistically significant association with CBZ-induced SJS/TEN. The highest risk was observed in patients with HLA-B*15:02 allele (OR = 44.33, 95% confidence interval = 20.24-97.09, corrected P-value = 6.80 × 10^-29 ). Moreover, HLA-B75 serotypes were significantly associated with CBZ-induced SJS/TEN groups with an odds ratio of 81.00 (95% confidence interval = 32.39-202.56, corrected P-value = 3.84 × 10^-34 ). There is no association between EPHX1 c.337 T > C polymorphism and all phenotypes of CBZ-induced SCARs.

CONCLUSION

The HLA-B*15:02 allele is the strongest genetic marker for the prediction of SJS/TEN induced by CBZ in Thai population. Screening for other alleles in the HLA-B75 serotype increases sensitivity for prediction of a life-threatening SCARs caused by CBZ.

Association of EPHX1 polymorphisms with plasma concentration of carbamazepine in epileptic patients: Systematic review and meta-analysis

BACKGROUND

Carbamazepine (CBZ) is a wildly used anti-epileptic drug (AED). Increasing evidence suggested that polymorphisms in Epoxide Hydrolase1 (EPHX1) gene are associated with the pharmacokinetics (PK) and pharmacodynamics (PD) of CBZ, albeit the results were inconsistent.

METHODS

A literature search on PubMed, Embase, and Cochrane Library was conducted to identify eligible studies published between 1974 and 2020. A meta-analysis was performed and the standardized mean difference (SMD) and 95% confidence interval (95% CI) were estimated using a random-effects model. The heterogeneity and leave-one-study-out sensitivity analyses of each article and the publication bias were also performed. All the statistical analyses were performed using STATA 14.0.

RESULTS

A total of 6 articles with 1746 subjects were included in this meta-analysis. A significant correlation was detected between EPHX1 rs1051740 T > C polymorphisms and decreased plasma concentration of CBZ (TT vs CC: SMD = 0.34, P < 0.001; TC vs CC: SMD = 0.35, P = 0.009). However, similar results were not detected in the comparison of TT vs. TC in the EPHX1 rs1051740 T > C variation (P = 0.637), while subgroup analyses showed an association with plasma CBZ concentration in the non-Asian group (P < 0.001, I² = 0.0%, Ph = 0.400). Although the association of EPHX1 rs2234922 A > G polymorphisms with plasma CBZ concentration was not detected (AA vs GG:SMD = 0.54, P = 0.102; AA vs AG:SMD = -0.05, P = 0.670; AG vs GG: SMD = 0.86, P = 0.107), subgroup analyses showed that the GG genotype EPHX1 rs2234922 was associated with increased plasma CBZ concentration in the Asian group (P = 0.005, I² = 48.6%, Ph = 0.143).

CONCLUSION

EPHX1 rs1051740 T > C and rs2234922 A > G are important genetic variants associated with plasma CBZ concentration. The role of EPHX1 polymorphisms in the interindividual variability of plasma CBZ concentration varied significantly among different ethnic groups, which should be considered during clinical validation and in future studies.

Associations between CYP3A4, CYP3A5 and SCN1A polymorphisms and carbamazepine metabolism in epilepsy: A meta-analysis

BACKGROUND AND OBJECTIVE

CYP3A4 (rs2242480), CYP3A5 (rs776746) and SCN1A (rs3812718 and rs2298771) gene polymorphisms were previously indicated to be associated with carbamazepine (CBZ) metabolism and resistance in epilepsy. However, previous studies regarding the effects of these polymorphisms still remain controversial. Therefore, we performed a meta-analysis to evaluate whether the four polymorphisms are associated with CBZ metabolism and resistance.

METHODS

The PubMed, EMBASE, Cochrane library, Chinese National Knowledge Infrastructure, Chinese Science and Technique Journals Database, China Biology Medicine disc and Wan Fang Database were searched up to January 2021 for appropriate studies regarding the association of rs2242480, rs776746, rs3812718 and rs2234922 polymorphisms with CBZ metabolism and resistance. The meta-analysis was conducted by Review Manager 5.3 software.

RESULTS

Eighteen studies involving 2546 related epilepsy patients were included. We found that the G allele of CYP3A4 rs2242480 markedly decreased the plasma CBZ concentration in epilepsy. For CYP3A5 rs776746 polymorphism, the GG genotype (homozygote codominant model: GG vs. AA) and GG + GA genotype (dominant model: GG + GA vs. AA and recessive model: GG vs. GA + AA) were respectively found to be significantly associated with increased CBZ plasma concentration. Additionally, it was also found that the SCN1A rs3812718 A allele was significantly associated with decreased CBZ plasma concentration and increased CBZ resistance. However, no association was observed between SCN1A rs2298771 polymorphism and CBZ metabolism and resistance.

CONCLUSION

The CYP3A4 rs2242480, CYP3A5 rs776746 and SCN1A rs3812718 polymorphisms may play important roles in CBZ metabolism and resistance, while SCN1A rs2298771 polymorphism is not associated with CBZ in epilepsy. These findings would improve the individualized therapy of epileptic patients in clinics.

Pharmacogenetics of Carbamazepine and Valproate: Focus on Polymorphisms of Drug Metabolizing Enzymes and Transporters

Pharmacogenomics can identify polymorphisms in genes involved in drug pharmacokinetics and pharmacodynamics determining differences in efficacy and safety and causing inter-individual variability in drug response. Therefore, pharmacogenomics can help clinicians in optimizing therapy based on patient's genotype, also in psychiatric and neurological settings. However, pharmacogenetic screenings for psychotropic drugs are not routinely employed in diagnosis and monitoring of patients treated with mood stabilizers, such as carbamazepine and valproate, because their benefit in clinical practice is still controversial. In this review, we summarize the current knowledge on pharmacogenetic biomarkers of these anticonvulsant drugs.

Evaluation of clinical and genetic factors in the population pharmacokinetics of carbamazepine

Aims

Carbamazepine can cause hypersensitivity reactions in ~10% of patients. An immunogenic effect can be produced by the electrophilic 10,11‐epoxide metabolite but not by carbamazepine. Hypothetically, certain single nucleotide polymorphisms might increase the formation of immunogenic metabolites, leading ultimately to hypersensitivity reactions. This study explores the role of clinical and genetic factors in the pharmacokinetics (PK) of carbamazepine and 3 metabolites known to be chemically reactive or formed through reactive intermediates.

Methods

A combination of rich and sparse PK samples were collected from healthy volunteers and epilepsy patients. All subjects were genotyped for 20 single nucleotide polymorphisms in 11 genes known to be involved in the metabolism or transport of carbamazepine and carbamazepine 10,11‐epoxide. Nonlinear mixed effects modelling was used to build a population‐PK model.

Results

In total, 248 observations were collected from 80 subjects. A 1‐compartment PK model with first‐order absorption and elimination best described the parent carbamazepine data, with a total clearance of 1.96 L/h, central distribution volume of 164 L and absorption rate constant of 0.45 h⁻¹. Total daily dose and coadministration of phenytoin were significant covariates for total clearance of carbamazepine. EPHX1‐416G/G genotype was a significant covariate for the clearance of carbamazepine 10,11‐epoxide.

Conclusion

Our data indicate that carbamazepine clearance was affected by total dose and phenytoin coadministration, but not by genetic factors, while carbamazepine 10,11‐epoxide clearance was affected by a variant in the microsomal epoxide hydrolase gene. A much larger sample size would be required to fully evaluate the role of genetic variation in carbamazepine pharmacokinetics, and thereby predisposition to carbamazepine hypersensitivity.

Pharmacogenomics of Cognitive Dysfunction and Neuropsychiatric Disorders in Dementia

Symptomatic interventions for patients with dementia involve anti-dementia drugs to improve cognition, psychotropic drugs for the treatment of behavioral disorders (BDs), and different categories of drugs for concomitant disorders. Demented patients may take >6-10 drugs/day with the consequent risk for drug-drug interactions and adverse drug reactions (ADRs >80%) which accelerate cognitive decline. The pharmacoepigenetic machinery is integrated by pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes redundantly and promiscuously regulated by epigenetic mechanisms. CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 geno-phenotypes are involved in the metabolism of over 90% of drugs currently used in patients with dementia, and only 20% of the population is an extensive metabolizer for this tetragenic cluster. ADRs associated with anti-dementia drugs, antipsychotics, antidepressants, anxiolytics, hypnotics, sedatives, and antiepileptic drugs can be minimized by means of pharmacogenetic screening prior to treatment. These drugs are substrates, inhibitors, or inducers of 58, 37, and 42 enzyme/protein gene products, respectively, and are transported by 40 different protein transporters. APOE is the reference gene in most pharmacogenetic studies. APOE-3 carriers are the best responders and APOE-4 carriers are the worst responders; likewise, CYP2D6-normal metabolizers are the best responders and CYP2D6-poor metabolizers are the worst responders. The incorporation of pharmacogenomic strategies for a personalized treatment in dementia is an effective option to optimize limited therapeutic resources and to reduce unwanted side-effects.

Effects of CYP3A5 and UGT2B7 variants on steady-state carbamazepine concentrations in Chinese epileptic patients

Carbamazepine (CBZ) is a widely used antiepileptic drug with large interindividual variability in serum concentrations. Previous studies found that CYP3A5*3 (rs776746), UGT2B7*2 (802C>T), and UGT2B7*3 (211G>T) variants could change the enzymes' activity, which may influence drug concentrations. Our study aims to investigate whether these variants affect steady-state CBZ concentrations in Chinese epileptic patients. In our study, 62 epileptic patients who received CBZ as monotherapy were monitored for steady-state CBZ concentrations. We used polymerase chain reaction (PCR)-based Sanger sequencing to assess the variants CYP3A5*3, UGT2B7*2, and UGT2B7*3. The results showed a positive correlation between dose and CBZ serum concentration in all patients and in patients with 3 different variants (all P < .05). After CBZ concentrations were normalized by the dose administered, negative correlations between dose-normalized CBZ concentrations and CBZ doses were observed in all patients, and in CYP3A5*3 and UGT2B7*3 patients (all P < .05), but not in UGT2B7*2 patients (P = .1080). UGT2B7*2 patients exhibited lower dose-normalized CBZ concentrations and larger CBZ dose requirements than UGT2B7*1/*1 patients (P = .0139, P = .032, respectively). There were no differences between UGT2B7*3, UGT2B7*1/*1 and CYP3A5*3, and CYP3A5*1/*1 patients with regard to steady-state CBZ concentration, dose-normalized concentration, required CBZ dose, and body weight-normalized dose (all P > .05). Moreover, a significant difference in body weight-normalized CBZ dose between UGT2B7 GC and TT haplotype patients was observed (P = .0154). In conclusion, our study found that the UGT2B7*2 variant, but not the CYP3A5*3 or UGT2B7*3 variant, could affect steady-state CBZ concentrations in epileptic patients.

Allele and genotype frequencies of genes relevant to anti-epileptic drug therapy in Mexican-Mestizo healthy volunteers

AIM

To determine allele and genotype frequencies of genes influencing anti-epileptic drug therapy in Mexican-Mestizo (MM) healthy volunteers, and to evaluate whether these are different from those reported for other populations.

SUBJECTS & METHODS

Thirty-nine variants of CYP3A5, EPHX1, NR1I2, HNF4A, UGT1A1, UGT2B7, ABCC2, RALBP1, SCN1A, SCN2A and GABRA1 were genotyped in 300 MM healthy volunteers.

RESULTS

All studied alleles were presented in MM, except for seven UGT1A1 variants (*6-8, 14, 15, 27 and 29). Allele and genotype frequencies showed interethnic variations when compared with European, Asian and African populations. Allele frequencies of greater than 30% were observed in ten genes.

CONCLUSION

The results presented regarding the frequencies and interethnic differences of these polymorphisms should be taken into account for future pharmacogenetic studies of anti-epileptic drugs in MM patients with epilepsy.

Evaluating the Role of Genetic Variants on first-line antiepileptic drug response in North India: Significance of SCN1A and GABRA1 Gene Variants in Phenytoin Monotherapy and its Serum Drug Levels

AIM

The present study aimed to evaluate association of genetic variants on drug response and therapy optimization parameters in patients treated with first-line antiepileptic drugs (AEDs). Genetic variants from ion channels, their functionally related genes, and synaptic vesicle cycle (SVC) genes with a potential role in epilepsy pathophysiology were thus prioritized.

METHODS

A total of 12 genes from ion channels and related gene set and seven genes from SVC comprising 155 SNPs were genotyped and evaluated with drug response, dose levels, and drug levels in 408 patients with epilepsy.

RESULTS

Both GABRA1 and SCN1A variants showed haplotypic and diplotypic associations in response to phenytoin (PHT). Diplotype analysis of GABRA1 variants revealed association of rs12658835|rs7735530 (AG/AG) (P-valuecorrected  = 0.034, OR = 3.75, 95% CI = 1.36-11.05) and rs12658835|rs7735530|rs7732641|rs2279020 (AGCA/AGCA) (P-valuecorrected  = 0.035, OR = 2.48, 95% CI = 0.96-6.41) with recurrent seizures. SCN1A haplotype rs6432860|rs3812718 (AC: P-valuecorrected  = 0.022, OR = 2.72, 95% CI = 1.39-5.35) and diplotype (AC/AC: P-valuecorrected  = 0.034, OR = 6.42, 95% CI = 1.10-65.76) were further observed to be associated with recurrent seizures. With respect to therapy optimization parameters, we observed significantly lower dose-adjusted drug levels at maximum dose of PHT in patients carrying AC/AC diplotype (P-value = 0.021).

CONCLUSION

The results further substantiate the role of GABRA1 in PHT mode of action and contribution of SCN1A in response and therapy optimization with PHT monotherapy.

Polymorphic Variants of SCN1A and EPHX1 Influence Plasma Carbamazepine Concentration, Metabolism and Pharmacoresistance in a Population of Kosovar Albanian Epileptic Patients

Aim

The present study aimed to evaluate the effects of gene variants in key genes influencing pharmacokinetic and pharmacodynamic of carbamazepine (CBZ) on the response in patients with epilepsy.

Materials & Methods

Five SNPs in two candidate genes influencing CBZ transport and metabolism, namely ABCB1 or EPHX1, and CBZ response SCN1A (sodium channel) were genotyped in 145 epileptic patients treated with CBZ as monotherapy and 100 age and sex matched healthy controls. Plasma concentrations of CBZ, carbamazepine-10,11-epoxide (CBZE) and carbamazepine-10,11-trans dihydrodiol (CBZD) were determined by HPLC-UV-DAD and adjusted for CBZ dosage/kg of body weight.

Results

The presence of the SCN1A IVS5-91G>A variant allele is associated with increased epilepsy susceptibility. Furthermore, carriers of the SCN1A IVS5-91G>A variant or of EPHX1 c.337T>C variant presented significantly lower levels of plasma CBZ compared to carriers of the common alleles (0.71±0.28 vs 1.11±0.69 μg/mL per mg/Kg for SCN1A IVS5-91 AA vs GG and 0.76±0.16 vs 0.94±0.49 μg/mL per mg/Kg for EPHX1 c.337 CC vs TT; P<0.05 for both). Carriers of the EPHX1 c.416A>G showed a reduced microsomal epoxide hydrolase activity as reflected by a significantly decreased ratio of CBZD to CBZ (0.13±0.08 to 0.26±0.17, p<0.05) also of CBZD to CBZE (1.74±1.06 to 3.08±2.90; P<0.05) and CDR_CBZD (0.13±0.08 vs 0.24±0.19 μg/mL per mg/Kg; P<0.05). ABCB1 3455C>T SNP and SCN1A 3148A>G variants were not associated with significant changes in CBZ pharmacokinetic. Patients resistant to CBZ treatment showed increased dosage of CBZ (657±285 vs 489±231 mg/day; P<0.001) but also increased plasma levels of CBZ (9.84±4.37 vs 7.41±3.43 μg/mL; P<0.001) compared to patients responsive to CBZ treatment. CBZ resistance was not related to any of the SNPs investigated.

Conclusions

The SCN1A IVS5-91G>A SNP is associated with susceptibility to epilepsy. SNPs in EPHX1 gene are influencing CBZ metabolism and disposition. CBZ plasma levels are not an indicator of resistance to the therapy.