An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of carbamazepine-10,11-epoxide in human serum and plasma.

OBJECTIVES: A reference measurement procedure (RMP) using isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) was developed and validated with the aim of accurately measuring carbamazepine-10,11-epoxide concentrations in human serum and plasma. METHODS: To establish traceability to SI units, the absolute content of the reference material was determined using quantitative nuclear magnetic resonance (qNMR) spectroscopy. As sample preparation a protein precipitation protocol followed by a high dilution step was established. Chromatographic separation from carbamazepine and potential metabolites was achieved using a C18 stationary phase. Selectivity, specificity, matrix effects, precision and accuracy, inter-laboratory equivalence, and uncertainty of measurement were evaluated based on guidelines from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the Expression of Uncertainty in Measurement. RESULTS: The RMP demonstrated very good selectivity and specificity, showing no evidence of a matrix effect. This enabled accurate quantification of carbamazepine-epoxide in the concentration range of 0.0400-12.0 µg/mL. The intermediate precision was found to be less than 2.1 %, and the repeatability coefficient of variation (CV) ranged from 1.2 to 1.8 % across all concentration levels. Regarding accuracy, the relative mean bias varied from 1.4 to 2.5 % for native serum levels and from 1.4 to 3.5 % for Li-heparin plasma levels. The measurement uncertainty for single measurements ranged from 1.6 to 2.1 %. CONCLUSIONS: In this study, we introduce a new LC-MS/MS-based candidate RMP for accurately measuring carbamazepine-10,11-epoxide in human serum and plasma. This novel method offers a traceable and dependable platform, making it suitable for standardizing routine assays and assessing clinically relevant samples.

Evaluation of anti-seizure medications and their serum concentration with regard to cardiovascular risk parameters: A cross-sectional study.

OBJECTIVE: Epilepsy is a chronic disease that requires long-term monitoring and treatment. It is suspected that there is a interaction between the use of anti-seizure medications and the risk of cardiovascular disease. The aim of the study is to investigate the association between the intake of phenobarbital, carbamazepine and valproic acid and their serum drug concentrations (SDC) with various cardiovascular risk parameters (homocysteine, folic acid, vitamin B12, total cholesterol (TC), triglycerides, high- and low-density lipoprotein (LDL)). METHODS: This is a cross-sectional study. Data (demographic characteristics and laboratory results) of patients treated for epilepsy in a tertiary care hospital between January 2020 and February 2022 were analyzed retrospectively (n = 2014). Kruskal Wallis, Mann-Whitney U, correlation analysis was used, p < 0.05 was considered statistically significant. RESULTS: The median age of patients was 15 years (IQR:8-31) and 48.3 % were women. The highest homocysteine level was found in patients receiving valproic acid, but it was not statistically significant. Patients receiving phenobarbital had the highest levels of folic acid and B12 and the lowest levels of total cholesterol and low-density lipoprotein cholesterol, which was statistically significant. In patients receiving carbamazepine, a moderately negative significant association was found between serum drug concentration and folic acid levels and a moderately positive significant association was found between TC and LDL levels. CONCLUSION: In our study, the majority of patients were children and adolescents. Regular monitoring of drug serum concentrations and metabolic parameters may be useful to select the safest drug in terms of cardiovascular disease risk. Randomized controlled trials on the long-term effects of anti-seizure treatment are needed.

LC-MS3 Strategy for Quantification of Carbamazepine in Human Plasma and Its Application in Therapeutic Drug Monitoring.

This study developed a detection method based on the strategy of HPLC/MS3 and verified its suitability by quantifying carbamazepine in human plasma. The high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS3) system was performed using a Shimadzu UFLC XR liquid chromatography and a SCIEX QTRAP® 5500 linear ion trap triple quadrupole mass spectrometer. The specific operation was as follows: the sample protein was firstly precipitated using methanol, then carbamazepine and carbamazepine-D2N15 were separated on an ACQUITY UPLC HSS T3 column using the gradient elution with solvent A (0.1% formic acid) and solvent B (0.1% formic acid in acetonitrile) at a flow rate of 0.25 mL/min. Each sample was run for 7 min. This method was validated for various parameters including accuracy, precision, selectivity, linearity, LLOQ, etc. Only 5 µL of sample plasma could obtain the result of LLOD 0.5 µg/mL. The intra-day and inter-day precision was <8.23%, and accuracy was between -1.74% and 2.92%. This method was successfully used for monitoring the blood concentration of epilepsy patients after carbamazepine treatment.

Dried Blood Microsampling-Based Therapeutic Drug Monitoring of Antiepileptic Drugs in Children With Nodding Syndrome and Epilepsy in Uganda and the Democratic Republic of the Congo.

Nodding syndrome is a highly debilitating, generalized seizure disorder, affecting children in subregions of sub-Saharan Africa. Despite numerous efforts to uncover the etiology, the exact cause of this syndrome still remains obscure. Therefore, to date, patients only receive symptomatic care, including the administration of first-generation antiepileptic drugs for seizure control. As data on the efficacy of drugs within this population are completely lacking, the aim of this study was to explore how therapeutic drug monitoring could help to understand the differential response to therapy. Considering the challenging environment in which sampling had to be performed (remote areas, devoid of electricity, running water, etc), dried blood matrices [ie, dried blood spots (DBSs)] and volumetric absorptive microsampling (VAMS) were considered fit-for-purpose. In addition, owing to the similarities between the syndrome and other forms of epilepsy, samples originating from patients suffering from (onchocerciasis-associated) epilepsy were included. In total, 68 patients with Nodding syndrome from Uganda, 58 Ugandan patients with epilepsy, and 137 patients with onchocerciasis-associated epilepsy from the Democratic Republic of the Congo were included. VAMS samples and DBS were analyzed using validated methods, involving manual extraction or fully automated extraction, respectively, before quantification using liquid chromatography coupled with tandem mass spectrometry. Analysis revealed that serum concentrations (calculated from DBS) within the respective reference ranges were attained in only 52.9% of the 68 Nodding syndrome patients treated with valproic acid, in 21.4% of the 56 Ugandan epilepsy patients treated with carbamazepine, and in 65.7% of the 137 onchocerciasis-associated epilepsy patients from the Democratic Republic of the Congo treated with phenobarbital. In all other instances, concentrations were subtherapeutic. Furthermore, on comparing DBS with VAMS concentrations, an inexplicable overestimation was observed in the latter. Finally, no obvious link could be observed between the obtained drug concentrations and the number of seizures experienced during the last month before sampling, elaborating the fact that the level of improvement in some patients cannot simply be linked to reaching therapeutic concentrations.

Therapeutic drug monitoring of anti-epileptic drugs - a clinical verification of volumetric absorptive micro sampling.

Background Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) can serve as a valuable tool in optimising and individualising epilepsy treatment, especially in vulnerable groups such as pregnant women, the elderly and children. Unfortunately, TDM is often performed suboptimally due to limitations in blood collection. Therefore, we investigated volumetric absorptive micro sampling (VAMS) - a new home-sampling technique. We aimed to evaluate VAMS to determine and quantify the different AEDs and concentrations of 16 different AEDs in whole blood collected by VAMS. Methods Patient blood samples (n = 138) were collected via venepunctures at the Academic Centre for Epileptology Kempenhaeghe. AED concentrations were determined, and these concentrations were used to compare the VAMS method (whole blood) with the conventional method (serum). In addition, the recovery was examined as well as the impact of haematocrit. Finally, AED-spiked blood was used to test the stability of the AEDs inside the micro-sampler devices over a period of time and whether temperature had an effect on the stability. Results VAMS allows for an accurate detection of 16 different AEDs within 2 days after sampling. Deviation in recovery was less than 10% and high correlations were found between VAMS and conventional sampling. Moreover, haematocrit does not have an effect with values between 0.3 and 0.5 (L/L). Finally, although storage temperature of VAMS does affect some AEDs, most are unaffected. Conclusions VAMS enables an accurate detection of a wide variety of AEDs within 2 days after sampling.

Changes in perampanel levels during de-induction: Simulations following carbamazepine discontinuation.

OBJECTIVE: To evaluate the time course of changes in perampanel levels when co-administered with carbamazepine, and following carbamazepine discontinuation, using a physiologically based pharmacokinetic (PBPK) model. METHODS: The PBPK model was developed, verified using clinical PK data, and used to simulate the effect of abrupt discontinuation and down-titration (75 mg twice daily [bid]/wk) of co-administered carbamazepine 300 mg bid on the PK of perampanel once daily (qd). Perampanel dose tapering (8-4 mg) and up-titration (2-6 mg) were simulated during abrupt carbamazepine 300 mg bid discontinuation to identify a titration schedule that minimizes changes in perampanel plasma concentrations. RESULTS: The PBPK model accurately reproduced perampanel plasma concentration-time profiles from clinical studies in single- and multiple-dose regimen simulations, including multiple-dose carbamazepine co-administration. The time course of return to pre-induced perampanel levels occurred more slowly following carbamazepine down-titration (~48 days after first down-titration) vs abrupt discontinuation (~25 days). Perampanel dose tapering (8-4 mg) at abrupt carbamazepine discontinuation produced minimal changes in steady-state concentrations, which returned to the levels observed during carbamazepine co-administration in ~15 days from the time of carbamazepine discontinuation. When perampanel was up-titrated in the presence of carbamazepine, return to steady state occurred more slowly when carbamazepine was down-titrated weekly (~45 days) vs abrupt discontinuation (~24 days). CONCLUSION: This PBPK model simulated and predicted optimal perampanel dose tapering and up-titration schedules for maintaining perampanel levels during conversion to monotherapy. These results may guide physicians when managing conversion from perampanel polytherapy with concomitant enzyme-inducing anti-seizure medications to monotherapy.

Paper-based molecularly imprinted-interpenetrating polymer network for on-spot collection and microextraction of dried blood spots for capillary electrophoresis determination of carbamazepine.

Carbamazepine is an antiepileptic drug with a narrow therapeutic index, which requires an efficient method for blood level monitoring. Finger-prick dried blood spot (DBS) collection is an alternative microsampling technique, which is less invasive than conventional venipuncture. Paper-based molecularly imprinted-interpenetrating polymer networks (MI-IPN) were developed as blood collection devices, which allowed for selective on-spot microextraction of carbamazepine from DBS. A hybrid of homogeneous polystyrene and silica gel polymer was synthesized and coated on a Whatman® Grade 1 filter paper. Proteins and other interferences in the blood samples were eliminated by using the MI-IPN collection devices, and the resulting DBS extracts were suitable for direct injection into the capillary electrophoretic instrument. The lower limit of quantitation of 4 µg/mL in capillary blood was achieved by the sweeping-micellar electrokinetic chromatography method using a KCl-containing matrix, which was sufficient for the therapeutic drug monitoring purposes. Method accuracies were in the range of 88.4 ± 4.5% to 94.5 ± 2.7% with RSD values ≤ 5.1%. The developed paper-based MI-IPN provided superior extraction efficiencies (92.2 ± 2.5%) in comparison with commercially available DBS collection cards, i.e., Whatman® 903 protein saver card (59.8 ± 2.8%) and GenCollect™ 2.0 card (47.2 ± 1.4%). The paper-based MI-IPN devices for DBS collection and on-spot extraction were characterized by simple fabrication, low costs, disposability, and reduction in sample preparation steps, and their further developments might open new perspectives in clinical applications, such as in therapeutic drug monitoring. Graphical abstract.

Synthesis of bifunctional cabbage flower-like Ho3+/NiO nanostructures as a modifier for simultaneous determination of methotrexate and carbamazepine.

Cabbage flower-like Ho3+/NiO nanostructure (CFL-Ho3+/NiO NSs) with significant electrocatalytic oxidation has been published for the first time. First, structure and morphology of CFL-Ho3+/NiO-NSs have been described by XRD, SEM, and EDX methods. Then, CFL-Ho3+/NiO-NSs have been applied as a modifier for simultaneous electrochemical detection of methotrexate (MTX) and carbamazepine (CBZ). Functions of the modified electrode have been dealt with through electrochemical impedance spectroscopy (EIS). It has been demonstrated that the electrode response has been linear from 0.001-310.0 µM with a limit of detection of 5.2 nM and 4.5 nM (3 s/m) through DPV for MTX and CBZ. Diffusion coefficient (D) and heterogeneous rate constant (kh) have been detected for MTX and CBZ oxidation at the surface of the modified electrode. Moreover, CFL-Ho3+/NiO-NS/GCE has been employed for determining MTX and CBZ in urine and drug specimens. Outputs showed the analyte acceptable recovery. Therefore, the electrode could be applied to analyze both analytes in drug prescription and clinical laboratories. Graphical abstract Electrochemical sensor based on bifunctional cabbage flower-like Ho3+/NiO nanostructures modified glassy carbon electrode for simultaneous detecting methotrexate and carbamazepine was fabricated.

Population pharmacokinetics of oxcarbazepine active metabolite in Chinese paediatric epilepsy patients and its application in individualised dosage regimens.

PURPOSE: Oxcarbazepine (OXC) is an antiepileptic drug metabolised to active 10-monohydroxy derivative (MHD) following oral administration. There are no MHD population pharmacokinetic (PPK) models that describe the influence of genetic factors on MHD pharmacokinetics (PK). We developed a PPK model of MHD to investigate gene polymorphism of enzymes associated with MHD PK in Chinese paediatric epilepsy patients and evaluated its utility for dose individualisation. METHODS: Data were prospectively collected from 141 paediatric epilepsy patients (aged ≤ 14 years) who received OXC therapy at the First Affiliated Hospital of Fujian Medical University. The trough concentrations at steady state were determined by enzyme-multiplied immunoassay. Patients were genotyped for four single nucleotide polymorphisms (UGT2B7 802T>C, UGT1A9 I399C>T, ABCB1 3435C>T, and ABCB2 1249G>A). Patient gender, age, body weight (BW), hepatorenal function, and co-administrations were recorded. The PPK model was developed using nonlinear mixed-effects modelling software. The clinical performance of the final model was evaluated by including additional paediatric patients (n = 20) in the validation group. RESULTS: Oral clearance of MHD was significantly influenced by BW. The MHD PK was unrelated to the other covariates, such as the four single nucleotide polymorphisms and co-administration with new-generation antiepileptic drugs. The final BW-dependent exponent model showed the best fit with our data and predicted the trough concentrations in the validation group more accurately than the basic model. A new dosing strategy combining the dosage guideline and Bayesian method is proposed to individualise OXC regimens. CONCLUSION: A PPK model was established to estimate individual MHD clearance in paediatric patients taking OXC to develop individualised OXC dosing regimens for Chinese paediatric epilepsy patients.

Effects of semi-solidification of enteral nutrients on the pharmacokinetic behavior of orally administered carbamazepine in rats.

The use of semi-solid enteral nutrients plays an extremely important role in accurate nutrition management. In the present study, we compared the pharmacokinetic profile of orally administered carbamazepine (CBZ) in rats treated with liquid RACOL®, semi-solid RACOL®, and HINE E-gel®, which are enteral nutrients marketed in Japan. Since liquid and semi-solid formulations are both marketed in Japan for RACOL®, liquid RACOL® was orally administered to control rats. The serum concentration of CBZ at each sampling point was lower in the semi-solid RACOL®-treated group than in the liquid RACOL®-treated group. No significant differences were observed in the pharmacokinetic behavior of CBZ between the semi-solid RACOL®-treated and HINE E-gel®-treated groups. Regarding pharmacokinetic parameters, the impact of the area under the curve (AUC0→5h) was the liquid RACOL® group > the semi-solid RACOL® group ≈ the HINE E-gel® group. Therefore, we concluded that serum concentrations of CBZ were lower when concurrently treating with semi-solid enteral nutrients than when simultaneously processing liquid enteral nutrients.

Comparison of CYP3A4-Inducing Capacity of Enzyme-Inducing Antiepileptic Drugs Using 4ß-Hydroxycholesterol as Biomarker.

BACKGROUND: Enzyme-inducing antiepileptic drugs (EIAEDs) are among the clinically most important inducers of cytochrome P450 (CYP) 3A4, but there is limited evidence regarding the comparative potency of each EIAED in raising CYP3A4 activity. The aim of this study was to estimate CYP3A4-inductive potency of EIAEDs by comparing CYP3A4 activity in patients treated with carbamazepine, phenobarbital, or phenytoin. METHODS: Residual serum samples from patients treated with EIAEDs or levetiracetam were collected from a therapeutic drug monitoring service for analysis of 4ß-hydroxycholesterol (4ßOHC), which is an indicator of CYP3A4 activity. The samples were collected between January and September 2016 at Diakonhjemmet Hospital, Oslo, Norway. Concentration of 4ßOHC, EIAEDs, and levetiracetam was measured by ultra-performance liquid chromatography tandem mass spectrometry. Kruskal-Wallis and Mann-Whitney tests were used for comparison of 4ßOHC levels between the subgroups. RESULTS: In total, 4ßOHC measurements for 343 and 339 patients treated with EIAEDs and levetiracetam, respectively, were included in the study. Compared with levetiracetam-treated patients, the median 4ßOHC concentration was 3.3-fold, 5.8-fold, and 6.9-fold higher in patients using phenobarbital, phenytoin, or carbamazepine, respectively (P < 0.0001). Phenytoin users (n = 65) and carbamazepine users (n = 225) had 1.8- and 2.1-fold higher median 4ßOHC concentration than phenobarbital users (n = 28), respectively (P ≤ 0.0001). CONCLUSIONS: This study shows that phenytoin and carbamazepine have approximately twice the CYP3A4-inducing potency of phenobarbital. The results indicate that 2-fold higher doses of CYP3A4-metabolized drugs may generally be required during concurrent treatment with phenytoin or carbamazepine compared with phenobarbital.

Obstetric outcomes and effects on babies born to women treated for epilepsy during pregnancy in a resource limited setting: a comparative cohort study.

BACKGROUND: Management of epilepsy during pregnancy in a resource-limited setting (RLS) is challenging. This study aimed to assess obstetric outcomes and effects on babies of women with epilepsy (WWE) exposed to Anti-epileptic drugs (AEDs) compared to non-exposed controls in a RLS. METHODS: Pregnant WWE were recruited from antenatal and neurology clinics of a tertiary care hospitals in Sri Lanka. Patients were reviewed in each trimester and post-partum. Medication adherence, adverse effects, seizure control and carbamazepine blood levels were monitored. Post-partum, measurements for anthropometric and dysmorphic features of the babies and congenital abnormalities were recorded. Age and sex matched babies not exposed to AED recruited as controls were also examined. RESULTS: Ninety-six pregnant WWE were recruited (mean period of gestation 22.9 weeks). Mean age was 28 years and 48(50%) were primigravidae. Fifty percent (48) were on monotherapy, while 23.8, 15.9 and 4.1% were on two, three and four AEDs respectively. AEDs in first trimester (TM1) were carbamazepine (71%), valproate (25.8%) clobazam (29.5%), lamotrigine (7%) topiramate (5%) and others (3.4%). Sodium valproate use reduced significantly from T1 to T2(p < 0.05). Sub-therapeutic carbamazepine levels correlated positively (r = 0.547) with poor medication adherence (p = 0.009) and negatively (r = 0.306) with adverse effects (p = 0.002). Seventy-six WWE completed follow-up reporting w 75 (98.6%) live births and one T1 miscarriage (1.3%). Three (4.3%) were preterm. Majority (73.33%) were normal vaginal deliveries. Cesarean sections were not increased in WWE. Fifty-nine (61.45%) babies were examined. For those examined during infancy, 53 age and sex matched controls were recruited and examined.. Congenital abnormalities occurred in 5 (9.43%) babies of WWE [atrio-ventricular septal defect (2), renal hypoplasia (1), cryptorchidism (1), microcephaly (1)] compared to 2 (3.77%) in controls (2 microcephaly; p = 0.24). Fetal exposure to AEDs increased a risk of low birth weight (RR 2.8; p = 0.049). Anthropometric parameters of AED exposed babies were lower at birth but not statistically significant between the two groups (weight p = 0.263, length p = 0.363, occipito-frontal circumference (OFC) p = 0.307). However, weight (p = 0.009), length (p = 0.016) and OFC (p = 0.002) were significantly lower compared to controls at an average of 3.52 months. CONCLUSION: Most pregnancies are unplanned in the RLS studied, and AEDs were altered during pregnancy. Congenital anomalies occurred at rates comparable to previous reports. Fetal exposure to AED had growth retardation in infancy compared to non-exposed babies.

Mass Spectrometric Characterization of Circulating Covalent Protein Adducts Derived from Epoxide Metabolites of Carbamazepine in Patients.

Carbamazepine (CBZ) is an effective antiepileptic drug that has been associated with hypersensitivity reactions. The pathogenesis of those reactions is incompletely understood but is postulated to involve a complex interplay between the drug's metabolism, genetic variation in human leukocyte antigens, and adverse activation of the immune system. Multiple T-cell activation mechanisms have been hypothesized including activation by drug-peptide conjugates derived from proteins haptenated by reactive metabolites. However, definitive evidence of the drug-protein adducts in patients has been lacking. In this study, mass spectrometry was used to characterize protein modifications by microsomally-generated metabolites of CBZ and in patients taking CBZ therapy. CBZ 10,11-epoxide (CBZE), a major electrophilic plasma metabolite of CBZ, formed adducts with glutathione-S-transferase pi (GSTP; Cys47) and human serum albumin (HSA; His146 and His338, but not Cys34) in vitro via notably divergent side-chain selectivity. Both proteins were adducted at the same residues by undefined monoxygenated metabolites ([O]CBZ) when they were incubated with human liver microsomes, NADPH and CBZ. There was also evidence for formation of a CBZ adduct at His146 and His338 of HSA derived via dehydration from an intermediate arene oxide adduct. Glutathione trapping of reactive metabolites confirmed microsomal production of CBZE and indicated simultaneous production of arene oxides. In 15 patients prescribed CBZ therapy, [O]CBZ-modified HSA (His146) was detected in all subjects. The relative amount of adduct was moderately positively correlated with plasma concentrations of CBZ (r2 = 0.44, p = 0.002) and CBZE (r2 = 0.35, p = 0.006). Our results have provided the first chemical evidence for microsomal production of [O]CBZ species that are able to escape the microsomal domain to react covalently with soluble proteins. This study has also demonstrated the presence of circulating [O]CBZ-modified HSA in patients without hypersensitivity reactions who were receiving standard CBZ therapy. The implications of those circulating adducts for susceptibility to CBZ hypersensitivity merit further immunological investigation in hypersensitive patients.

Striking the Optimal Solubility-Permeability Balance in Oral Formulation Development for Lipophilic Drugs: Maximizing Carbamazepine Blood Levels.

The purpose of this research was to investigate the performance of cosolvent based solubility-enabling formulations in oral delivery of lipophilic drugs, accounting for the gastrointestinal tract (GIT) luminal solubilization processes, the solubility-permeability interplay, and the overall in vivo systemic absorption. The poorly soluble antiepileptic agent carbamazepine was formulated in three cosolvent-based formulations: 20%, 60%, and 100% PEG-400, and the apparent solubility and rat permeability of the drug in these formulations were evaluated. The performance of the formulations in the dynamic GIT environment was assessed utilizing the biorelevant pH-dilution method. Then, the overall in vivo drug exposure was investigated following oral administration to rats. The three formulations showed dramatic solubility and permeability differences; the 100% PEG-400 provided the highest solubility enhancement and the 20% the poorest, while the exact opposite was evident from the permeability point of view. The dissolution results indicated that the 20% PEG-400 formulation crashes quickly following oral administration, but both the 60% and the 100% PEG-400 formulations allowed full solubilization of the dose throughout the entire GIT-like journey. The best in vivo performing formulation was the 60% PEG-400 (Fsys > 90%), followed by the 100% PEG-400 (Fsys = 76%), and the 20% PEG-400 formulation (Fsys ≈ 60%). In conclusion, this work demonstrates the in vivo solubility-permeability trade-off in oral delivery of lipophilic drugs; when a solubility-enabling formulation is developed, minimal threshold solubility should be targeted, that is just enough to allow solubilization of the drug dose throughout the GIT, while excess solubilizer should be avoided.

Population pharmacokinetics of oxcarbazepine and its monohydroxy derivative in epileptic children.

AIMS: Oxcarbazepine is an antiepileptic drug with an activity mostly due to its monohydroxy derivative metabolite (MHD). A parent-metabolite population pharmacokinetic model in children was developed to evaluate the consistency between the recommended paediatric doses and the reference range for trough concentration (Ctrough ) of MHD (3-35 mg l-1 ). METHODS: A total of 279 plasma samples were obtained from 31 epileptic children (age 2-12 years) after a single dose of oxcarbazepine. Concentration-time data were analysed with Monolix 4.3.2. The probability to obtain Ctrough between 3-35 mg l-1 was determined by Monte Carlo simulations for doses ranging from 10 to 90 mg kg-1  day-1 . RESULTS: A parent-metabolite model with two compartments for oxcarbazepine and one compartment for MHD best described the data. Typical values for oxcarbazepine clearance, central and peripheral distribution volume and distribution clearance were 140 l h-1  70 kg-1 , 337 l 70 kg-1 , 60.7 l and 62.5 l h-1 , respectively. Typical values for MHD clearance and distribution volume were 4.11 l h-1  70 kg-1 and 54.8 l 70 kg-1 respectively. Clearances and distribution volumes of oxcarbazepine and MHD were related to body weight via empirical allometric models. Enzyme-inducing antiepileptic drugs (EIAEDs) increased MHD clearance by 29.3%. Fifty-kg children without EIAEDs may need 20-30 mg kg-1  day-1 instead of the recommended target maintenance dose (30-45 mg kg-1  day-1 ) to obtain Ctrough within the reference range. By contrast, 10-kg children with EIAEDs would need 90 mg kg-1  day-1 instead of the maximum recommended dose of 60 mg kg-1  day-1 . CONCLUSION: This population pharmacokinetic model of oxcarbazepine supports current dose recommendations, except for 10-kg children with concomitant EIAEDs and 50-kg children without EIAEDs.

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.

Development and validation of a reversed-phase HPLC method for licarbazepine monitoring in serum of patients under oxcarbazepine treatment.

Licarbazepine is the pharmacologically active metabolite of oxcarbazepine, a drug indicated for the treatment of partial seizures and bipolar disorders. Several HPLC methods have been developed thus far but there is lack of control for interferences from antipsychotic drugs. The aim of the present study was to develop a simple, low-cost and reliable HPLC-UV method for the determination of licarbazepine in human serum in the presence of co-administered antiepileptic, antipsychotic and commonly prescribed drugs. Sample preparation consisted of a single protein precipitation step with methanol. Separation lasted ~9 min on a reversed-phase C18 column using a mobile phase composed of 50 mm sodium-dihydrogen-phosphate-monohydrate/acetonitrile (70:30, v/v) delivered isocratically at 0.9 mL/min and 30°C. Wavelength was 210 nm and calibration curve was linear with r2 0.998 over the range 0.2-50.0 µg/mL. Coefficient of variation was <5.03% and bias <-4.92%. Recovery ranged from 99.49 to 104.52% and the limit of detection was 0.0182 µg/mL. No interferences from the matrix or from antiepileptic, antipsychotic and commonly prescribed drugs were observed. The method was applied to serum samples of patients under oxcarbazepine treatment and proved to be a useful tool for the therapeutic drug monitoring of licarbazepine during monotherapy or adjunctive treatment of seizures or affective disorders.

How long does the pharmacokinetic interaction between carbamazepine and quetiapine last after carbamazepine withdrawal?

OBJECTIVES: Carbamazepine and quetiapine are drugs that are used as mood stabilizers in the treatment of bipolar disorders. A series of studies has shown that concurrent use of carbamazepine decreases quetiapine serum level due to induction of CYP3A enzymes by carbamazepine. METHODS: In a 30-year-old bipolar patient with mania treated with quetiapine 1200 mg and carbamazepine 900 mg per day, we measured quetiapine serum level before and after carbamazepine withdrawal. RESULTS: No serum quetiapine was detected during concurrent use of carbamazepine and was lower than the therapeutic range almost 2 weeks after carbamazepine withdrawal. The patient suffered from sedation when her serum level of quetiapine was 181 ng/ml and because she was quiet we started slowly to decrease to a quetiapine dose of 600 mg. Her serum level (45 ng/ml) was again below therapeutic levels after 3 weeks of carbamazepine withdrawal. CONCLUSION: We hypothesize that induction of CYP3A lasts even after carbamazepine withdrawal. Our hypothesis was confirmed during the next treatment of mania. The patient had been off carbamazepine for 1 year and her serum level was four times higher (210 ng/ml) on 600 mg of quetiapine than 3 weeks after carbamazepine withdrawal. The influence of carbamazepine on CYP3A enzymes lasted at least 3 weeks after carbamazepine withdrawal which is in accordance with CYP3A de-induction lasting 3 weeks. This could be important information for psychiatrists to know that in some patients it is better to use a minimum washout period of 3 weeks for carbamazepine before new treatment with quetiapine.

4ß-hydroxycholesterol correlates with dose but not steady-state concentration of carbamazepine: indication of intestinal CYP3A in biomarker formation?

AIM: 4ß-hydroxycholesterol (4ßOHC) is an endogenous CYP3A(4) biomarker, which is elevated by use of the CYP3A4 inducer carbamazepine. Our aim was to compare to what extent serum concentration of 4ßOHC correlates with dose (presystemic exposure) and steady-state concentration (systemic exposure) of carbamazepine. METHODS: The study was based on a therapeutic drug monitoring material, including information about daily doses and steady-state concentrations (Css ) of carbamazepine. 4ßOHC concentrations were determined in residual serum samples of 55 randomly selected carbamazepine-treated patients and 54 levetiracetam-treated patients (negative controls) by UPLC-APCI-MS/MS after liquid-liquid extraction. Correlation analyses between 4ßOHC concentration and daily dose and Css of carbamazepine, respectively, were performed by Spearman's tests. In addition, 4ßOHC concentrations in females vs. males were compared in induced and non-induced patients. RESULTS: Median 4ßOHC concentration was ~10-fold higher in carbamazepine- vs. levetiracetam-treated patients (650 vs. 54 nmol l(-1) , P < 0.0001). There was a significant, positive correlation between carbamazepine dose and 4ßOHC concentration (Spearman r = 0.53, 95% confidence interval [CI] 0.27, 0.72, P < 0.001). No significant correlation between carbamazepine Css and 4ßOHC concentration was found (Spearman r = 0.14; 95% CI -0.14, 0.40, P = 0.3). Enzyme-induced females had significantly higher 4ßOHC concentrations than males (P < 0.001), while no significant gender difference was found in non-induced patients (P = 0.52). CONCLUSION: Serum concentrations of 4ßOHC correlate with presystemic, but not systemic exposure of the CYP3A4 inducer carbamazepine. This suggests a stronger inductive effect of carbamazepine on presystemic than systemic CYP3A4 phenotype and might indicate a role of the intestine in 4ßOHC formation. Moreover, CYP3A4 inducibility seems to be higher in females than males.

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.