Serum Carbamazepine Concentration Research Articles

An Retrospective Study of Commonly Prescribed Antiepileptic Drugs and it’s Interaction with Other Drugs which are Already in use Respect to Other Disease

Antiepileptic drugs (AED) are increasingly used in the treatment of some non-epileptic neurological diseases and psychiatric diseases. Most of the available data on the use of these agents in clinical conditions other than epilepsy are from case series, uncontrolled studies, or small randomized clinical trials, and their apparent efficacy requires confirmation in well-designed large phase III trials. Interactions between antiepileptic drugs or between antiepileptic drugs and other drugs can be pharmacokinetic or pharmacodynamic. Pharmacokinetic interactions include changes in absorption, distribution ,or eliminate , while pharmacodynamic interactions include synergism and antagonism at the site ,of action. Most clinically significant antiepileptic drug interactions are due to induction or inhibition of drug metabolism. Carbamazepine, phenytoin, phenobarbital and primidone are strong inducers of cytochrome P450 and glucuronide enzymes (as well as P-glycoprotein) and may reduce the effectiveness of concomitantly administered drugs such as oral anticoagulants, calcium antagonists, antimicrobial steroids. Mechanism Oxcarbazepine, eslicarbazepine acetate, felbamate, rufinamide, topiramate (at doses ≥ 200 mg/day) and perampanel (at doses ≥ 8 mg/day) have weaker inducing properties and less tendency to produce interactions mediated by enzyme induction. In contrast to enzyme induction, enzyme inhibition results in decreased metabolic clearance of the affected drug, which can increase serum concentrations leading to toxic effects. Examples of important interactions mediated by enzyme inhibition include valproic-induced increases in serum concentrations of phenobarbital and lamotrigine. There are also interactions where other drugs induce or inhibit the metabolism of antiepileptic drugs. Examples include an increase in serum carbamazepine concentration due to erythromycin and a decrease in serum lamotrigine concentration due to estrogen-containing contraceptives. Pharmacodynamic interactions between antiepileptic drugs may also be clinically important. These interactions can have potentially beneficial effects, such as the combined therapeutic synergy of valproic acid and lamotrigine, or adverse effects, such as the mutual potentiation of neurotoxicity in patients treated with a combination of sodium channel blocking antiepileptic drugs. AEDs are also used to treat psychiatric conditions, particularly bipolar disorder. To date, the AEDs most commonly used to treat this disorder have been carbamazepine and valproic acid, which have shown manic efficacy and likely long-term mood-stabilizing effects in many bipolar patients, including those who are lithium-intolerant. . The availability of new generation AEDs has expanded treatment options for bipolar disorder. Lamotrigine, oxcarbazepine, gabapentin, and topiramate appear to show promise in the treatment of bipolar disorder, both as monotherapy and in combination with traditional mood stabilizers. In addition, newer AEDs appear to have a more favorable tolerability and drug interaction profile than older compounds, thus improving compliance

Effect of glycation-induced concentration-dependent change in albumin structure and alteration in its binding capacity

Reducing sugars causes confirmatory alterations in albumin structure by the nonenzymatic glycation of the amino group of serum albumin. In this study, glucose and its hazardous metabolic products like glyoxal and methylglyoxal were incubated with bovine serum albumin (BSA). The confirmational changes in BSA molecule’s structure by glycating substances was investigated using a variety of spectroscopic methods, including deconvolutionFourier Transform Infra-red (FT-IR) spectroscopy, fluorescence spectroscopy, UV spectroscopy and circular dichroism (CD) spectroscopy. Dynamic fluorescence quenching was observed in the case of glucose, while static quenching was observed in the case of methyl glyoxal and glyoxal. Similarly, employing deconvolution FT-IR spectroscopy and CD spectroscopy for determination of change in secondary structures in terms signature of α-helix, β-turn, β-sheet and random coil modifications. Destabilization or unfolding of the albumin structure, due to the disruption of the hydrogen bonding pattern that stabilizes the albumin manifold, causes a 25-50% reduction in α-helix and a 2-fold increase in β-sheet and turns in glycated BSA. The competitive displacement interaction studies with warfarin were performed using the ultrafiltration technique and quantitative determination of free drug in ultrafiltrate using LC-MS/MS. The binding of carbamazepine (CBZ) or its active metabolite to proteins was unaffected by the glycation of BSA with glucose and methyl glyoxal. Nevertheless, with glyoxal-modified BSA, it changed the binding of selected analytes significantly. Based on in vitro observations and results, it could be anticipated that the serum CBZ concentration variation may be worsened in uncontrolled diabetes circumstances, with an overall variance of 30–40% possible. Communicated by Ramaswamy H. Sarma

A prospective study of drug-drug interaction between antiepileptic drugs and meropenem in patients in a tertiary hospital in China from January 2020 to March 2023.

This study aimed to determine the minimum interaction between different antiepileptic drugs (AEDs) and meropenem (MEPM) for clinical treatment. The data of 91 patients enrolled in the neurology department from January 2020 to March 2023 for clinical trials were measured and observed. Self-controlled studies were conducted to monitor the trough concentrations of valproic acid (VPA), carbamazepine (CBZ) and levotiracetam (LEV) before and after MEPM usage. Relevant indicators of liver and kidney function were also monitored. The serum VPA trough concentrations were 36.25±8.22 μg/ml at 24±12 h and 34.99±11.17 μg/ml at 96±12 h after MEPM use; the difference was significant (p<0.05). Decreased CBZ trough concentrations were also identified after MEPM usage (96±12 h), whereas LEV trough concentrations were not affected. An increased liver injury rate (χ2 =8.744, p<0.05) and a decreased kidney injury rate (χ2 =5.393, p<0.05) were found in the VPA group only. The interaction between VPA and MEPM decreased serum VPA concentrations, increased liver injury rates, and decreased kidney injury rates. In addition, the co-administration of MEPM and CBZ reduced serum CBZ concentrations. Clinicians should be aware of this potential interaction and closely monitor the relevant biochemical indices and number of seizures.

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

An isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) was developed and validated to accurately measure serum and plasma concentrations of carbamazepine. Quantitative nuclear magnetic resonance (qNMR) spectroscopy was used to determine the absolute content of the reference material, ensuring its traceability to SI units. The separation of carbamazepine from potential interferences, whether known or unknown, was achieved using a C18 column. A protein precipitation protocol followed by a high dilution step was established for sample preparation. Assay validation and determination of measurement uncertainty were performed in accordance with the guidelines of the Clinical and Laboratory Standards Institute, the International Conference on Harmonization (ICH), and the Guide to the Expression of Uncertainty in Measurement (GUM). In order to demonstrate equivalence to the already existing RMP a method comparison study was performed. The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of carbamazepine within the range of 0.800-18.0 μg/mL. Intermediate precision and repeatability (n=60 measurements) was found to be <1.6 % and <1.3 % over all concentration levels and independent from the matrix. The relative mean bias ranged from-0.1 to 0.6 % for native serum and from-0.3 to-0.1 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment were found to be <1.8 % and <1.3 %, respectively. Method comparison showed a good agreement between the Joint Committee of Traceability in Laboratory Medicine (JCTLM) listed RMP and the candidate RMP resulting in a Passing-Bablok regression equation with a slope of 1.01 and an intercept of-0.01. The bias in the patient cohort was found to be 0.9 %. We present a novel LC-MS/MS-based candidate RMP for carbamazepine in human serum and plasma which provides a traceable and reliable platform for the standardization of routine assays and evaluation of clinically relevant samples.

Application of Teeth in Toxicological Analysis of Decomposed Cadavers Using a Carbamazepine-Administered Rat Model.

In a regular autopsy, blood and organs are used to quantify drug and toxicant concentrations; however, specimens such as blood cannot be collected from highly decomposed corpses, making the quantification of drug and toxicants impossible. This study aimed to estimate the blood carbamazepine (CBZ) concentration from teeth, a part of the human body that is best preserved after death. We sampled teeth and blood of rats administered CBZ. The correlation between the tooth and serum CBZ concentrations was analyzed. Rats were euthanized after CBZ administration and kept at 22 °C for 0 to 15 days before sampling the teeth and measuring the CBZ concentration. Undecalcified, fresh, frozen sections of rat teeth were prepared, and CBZ localization was evaluated. CBZ concentrations in both teeth and cardiac blood peaked at 60 min after administration and increased in a dose-dependent manner. CBZ concentration in teeth did not substantially change after death, with high CBZ distribution being observed in the pulp cavity. The tooth and serum CBZ concentrations were highly correlated, suggesting that the measurement of toxicant concentration in sampled teeth would allow for the estimation of blood toxicant concentration in highly decomposed corpses.

Treatment of Canine Idiopathic Epilepsy - Clinical Picture after Drug Interaction

Background: The large number of diseases demand perennial development of the pharmaceutical industry. The drug-testing phase is essential to make them available safely. Awareness of pharmacological properties, adverse effects and drug interactions is required. Drug interactions are common in veterinary medicine and should be avoided. At times, epileptic seizures require polydrug therapy, predisposing patients to drug interactions. The interaction between carbamazepine and phenobarbital reported in the literature is an example. The aim of this paper is to report a clinical picture of drug interaction in the treatment of idiopathic epilepsy. Case: A 1-year-old Border Collie male dog, was admitted at the Veterinary Hospital of the Federal University of Lavras in post-ictal. The tutor reported that a year ago the animal had epileptic seizures and clusters with intervals of 21 to 25 days. Despite the continued use of previously prescribed phenobarbital (7.4 mg/kg, v.o., BID, until new recommendations) and carbamazepine (7.5 mg/kg, v.o., BID, until new recommendations), seizure control was not achieved. The physical examination indicated, tachypnea, ptialism, mydriasis, intense fatigue, and alienation from the environment. The patient did not respond to the threat-reflex test. Blood count, hepatic and renal blood chemistry, serum electrolyte (potassium, sodium, calcium and phosphorus), and phenobarbital dosages were requested. Based on the animal's history, breed characteristics, and alterations in the physical examination associated with normal results in complementary exams, idiopathic epilepsy was diagnosed. After analyzing the case, it was observed that the inefficiency in the control of seizures was possibly due to the drug interaction between phenobarbital and carbamazepine. Carbamazepine and phenobarbital reciprocally reduce their half-lives. To confirm the raised hypothesis, the serum concentration of carbamazepine was gradually reduced through weaning from its dose administered to the patient. Serial dosage of the concentration of phenobarbital in the bloodstream was performed. As a result, the serum phenobarbital, previously dosed at a concentration of 13.3 mg/dL with concomitant administration of carbamazepine, increased to 22 mg/dL 40 days after the beginning of weaning from carbamazepine (T0), and then to 36 mg/dL 100 days after T0. There was an increase in the concentration of phenobarbital in the bloodstream while the serum concentration of carbamazepine declined. The patient spaced out his seizures to every 50 to 60 days with phenobarbital monotherapy at a dose of 6 mg/kg. Discussion: Efficient control of clusters, such as the reduction of seizures by 50%, was only possible due to the meticulous perception of the possible interaction reported in medicine. Carbamazepine and phenobarbital are P450 isoenzyme inducers. The concomitant administration of both drugs potentiated the action of isoenzymes in the hepatic microsomal system, which led to an accelerated metabolic processing of the drugs. After weaning from carbamazepine, that is, reducing the action of carbamazepine on the isoenzymes of the P450 enzyme system, the concentration of phenobarbital normalized at 36 mg/dL. Such concentration is within the reference range reported in the literature: 25 mg/dL to 35 mg/dL of serum phenobarbital for treatment efficacy. Therefore, the control of convulsive crises was achieved. The increase in the concentration of phenobarbital due only to weaning from carbamazepine, even after decreasing the daily dose of barbiturate prescribed to the animal, contributed to evidence of the interaction of these drugs. It is noted that prior knowledge of pharmacological properties, careful study of the patient's history, and the cooperation of the tutor were essential for the therapeutic success and practice of evidence-based veterinary medicine. Keywords: drug interaction, carbamazepine, phenobarbital, P450 enzyme. Título: Tratamento da epilepsia idiopática canina - quadro clínico após interação medicamentosa. Descritores: interação medicamentosa, carbamazepina, fenobarbital, enzima P450.

Carbamazepine and carbamazepine-epoxide concentrations in mothers, colostrum, and breastfed newborns: Comparison with concentrations determined during delivery and in the mature milk period

ObjectiveTo obtain information on the transport of carbamazepine and its active metabolite carbamazepine-epoxide from mother to colostrum and breastfed newborns. MethodsIn this cohort study, carbamazepine and carbamazepine-epoxide concentrations in maternal serum (162 women), milk (i.e., colostrum) and breastfed newborn serum were analysed between the 1st and 5th days after delivery from November 1990 to February 2021. The measured concentrations were compared with the delivery and mature milk periods. The effect of the combination with both enzyme-inducing antiseizure medication and valproic acid was also evaluated. ResultsCarbamazepine concentrations varied from 1.0 to 11.2 mg/L (epoxide 0.3–4.4 mg/L) in maternal serum, from 0.5 to 6.8 mg/L (epoxide 0.3–2.4 mg/L) in milk and from 0.5 to 4.7 mg/L (epoxide 0.3–1.7 mg/L) in newborn serum. The median milk/maternal serum concentration ratio of carbamazepine was 0.45 (epoxide 0.71), the median newborn/maternal serum concentration ratio of carbamazepine was 0.20 (epoxide 0.41), and the median newborn serum/milk concentration ratio of carbamazepine was 0.38 (epoxide 0.50). A highly significant correlation was found between the milk and maternal serum concentrations of both carbamazepine and carbamazepine-epoxide and between the milk and newborn serum concentrations of carbamazepine. ConclusionsIn the serum of breastfed newborns, only one concentration of carbamazepine reached the reference range used for the general epileptic population, and more than half was below the lower limit of quantification. Routine monitoring of serum carbamazepine concentrations is not required in breastfed newborns. However, observation of newborns is desirable, and if signs of potential adverse reactions are noted, the serum concentrations in newborns should be measured.

Serum monitoring of carbamazepine in patients with epilepsy and clinical implications

Carbamazepine is a drug with a narrow therapeutic range that requires clinical monitoring, since its toxic effects are not easily predictable, and the therapeutic level can vary. Our study aimed to monitor the serum level and determine the concentration/dose relationship of carbamazepine in people with epilepsy, analyzing its clinical implication. It is observed that 90.48% of the study volunteers present serum level values (4.3–10.4 mg/L) within the therapeutic range (4–12 mg/L); 7.14% present supratherapeutic levels (12.7–14.4 mg/L), 2.38% subtherapeutic (0.93 mg/L). The findings indicate a negative correlation (r = -0.616; r2 = 0.379; p = 0.001), between the dose (mg/day) and the dose ratio (mg/L/mg/day); and a positive correlation (r = 0.544; r2 = 0.296; p = 0.002), between the dose (mg/day)-serum concentration (mg/L). ANOVA and Tukey’s test mean difference is significant (p&amp;lt;0.05). It is concluded that there is a positive and significant linear correlation between daily doses and serum carbamazepine concentrations, which should be considered to individualize the dose and optimize clinical results.

Influence of concurrent and staggered dosing of semi-solid nutrients on the pharmacokinetics of orally administered carbamazepine in rats.

In the present study, we examined the effects of concurrent and staggered dosing of PG-soft ace-MP TM (PG), novel semi-solid enteral nutrients, on the pharmacokinetics of orally administered carbamazepine (CBZ) in rats due to the high possibility of drug interaction during the absorption process. The pharmacokinetic behavior of CBZ was considerably altered when administered concurrently with PG. The maximum serum CBZ concentration (Cmax) significantly decreased and the mean residence time (MRT) significantly increased. The elimination constant (ke) also significantly increased, but there were no significant changes in the area under the serum CBZ concentration versus time curve (AUC) and the time to reach Cmax (Tmax). However, these changes in the pharmacokinetic parameters were eliminated by waiting 20 min, the time interval equivalent to the Tmax described above, between CBZ administration and PG dosing. This study suggested that PG interferes with CBZ absorption from the digestive tract, although staggered administration of CBZ and PG prevented their interaction.

Study on the relationship between adverse drug reactions of carbamazepine and HLA-B*1502 genetic polymorphism and blood concentration

Objective： To study the relationship between genetic polymorphism，blood concentration and adverse drug reactions（ADRs） of carbamazepine（CBZ），so as to promote clinical safety and reasonable use of CBZ.Methods： Clinical medical data of the inpatients treated in Ruijin Hospital Affiliated to School of Medicine，Shanghai Jiao Tong University from 2017 to 2019 were collected retrospectively.Data concerning HLA-B*1502 gene detection and serum concentration of CBZ were collected to analyze the relationship between HLA-B*1502 genotype and ADRs of CBZ in the patients.Results： A total of 148 patients were enrolled for study，of whom 101 patients received HLA-B*1502 genotypes detection，with the genotype of 34 patients being positive，accounting for 33.66%.In the 148 patients，78 were treated with CBZ（53.79%），among whom 60 patients（86 case times） received serum drug concentration detection of CBZ.The serum drug concentration in 53 case times was within the recommended concentration range，accounting for 61.63% of the detected case times，and the serum drug concentration in 32 case times（37.21%） was lower than that of the recommended data.CBZ-related ADRs occurred in 12 cases（15.38%），of which one patient with HLA-B*1502 homozygous mutation developed severe skin ADRs after taking CBZ.Conclusion： There is close association between HLA-B*1502 genotype and skin ADRs induced by CBZ.The treatment window of CBZ is narrow，and the rate of ADRs might be associated with blood concentration of CBZ.Gene detection and blood concentration detection are of great significance to the improvement of the safety of CBZ in clinical practice.

Effect of CYP3A5 genotypes on serum carbamazepine concentrations at steady-state in Vietnamese epileptic patients

Effect of CYP3A5 genotypes on serum carbamazepine concentrations at steady-state in Vietnamese epileptic patients

Pharmacokinetic interaction between modified Atkins diet and antiepileptic drugs in adults with drug-resistant epilepsy.

The aim was to examine the influence of modified Atkins diet on serum concentration of antiepileptic drugs (AEDs). Prospective data from 63 adult patients with either focal or generalized drug-resistant epilepsy recruited to 12-week dietary treatment as add-on to AEDs are analyzed. AED serum concentrations, ketones, glucose, and hemoglobin A1c were measured before and after the dietary intervention. Paired t test was used and Spearman correlation coefficient, r, was estimated. Mean age was 37years (range 16-65years). Mean serum concentrations of carbamazepine, clobazam, and valproate were significantly reduced after 4 and 12weeks of the diet period (<.001≤P≤.02). Levels of lacosamide, lamotrigine, and topiramate were less reduced (.02≤P≤.08), whereas the serum concentrations of oxcarbazepine, zonisamide, and levetiracetam were unchanged (.06≤P≤.90). The largest reduction in serum concentration was found for clobazam: mean reduction after 12weeks was 1.5μmol/L (34%). Percent change in serum concentration after 4 and 12weeks of all drugs analyzed was -10.5% (95% confidence interval [CI] -14.1 to -6.8; n=60; P<.001) and -13.5% (95% CI -18.8 to -8.3; n=56; P<.001), respectively. Percent change in serum concentration of AEDs was not significantly correlated to percent change in seizure frequency after 12weeks of dietary treatment (r=.14, P=.33, n=53) but negatively correlated to urine ketosis (r=-.43; P=.003; n=46). A reduction in AED serum concentrations may counteract a seizure-reducing effect of the diet, and in patients without such an effect, it may cause seizure aggravation. Thus, we recommend that clinicians who are treating patients with ketogenic diets monitor serum concentrations of the concomitant AEDs.

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.

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.

Effect of ketogenic diet and other dietary therapies on anti-epileptic drug concentrations in patients with epilepsy.

The ketogenic diet (KD) is an effective high-fat, adequate-protein, low-carbohydrate diet for patients with refractory epilepsy. The aim of this study was to investigate the potential effects of the KD and other dietary therapies on the concentrations of anticonvulsants in patients with epilepsy. Patients with epilepsy who were treated with the KD and other dietary therapies for more than 30days with at least one measurement performed both before and during the diet were evaluated. The mean serum concentrations and the mean serum concentrations per weight per daily dose per bioavailability (F) of anti-epileptic drugs (AEDs) before and during the treatment were assessed. We also compared the rates of events out of reference ranges of the AEDs between before and during the KD and other dietary therapies. We compared the serum albumin, alanine transaminase and aspartate transaminase data of patients with valproic acid before and during the KD. One-hundred thirty-nine patients including 81 male patients were enrolled. The median age of the patients was 2.91 (0.15-15.46) years. The median duration of the dietary therapies was 153 (35-2307) days. After the dietary therapies, the serum concentrations of carbamazepine, lamotrigine, levetiracetam, topiramate and valproic acid decreased, whereas that of phenobarbital slightly increased. However, statistical significance was found only with valproic acid (67.07±25.89μg/mL vs 51.00±20.19μg/mL, P<.05). The serum concentrations per weight per daily dose per drug F significantly decreased for valproic acid (1.38±1.39×10-2 vs 0.82±0.82×10-2 μgdmL-1 F-1 ) and phenobarbital (6.66±7.20×10-2 vs 4.75±4.07×10-2 μgdmL-1 F-1 , P<.05). The rate of occurrence of events out of reference ranges significantly increased with valproic acid (36.08% vs 57.23%, P<.05). Most anti-epileptic drug serum concentrations remained stable during the KD and other related dietary therapies except those of valproic acid. Therefore, serum concentrations of valproic acid should be monitored when the KD and other dietary therapies are concomitantly administered.

Correlation Between Elimination Parameters of Phenytoin and Carbamazepine in Patients with Epilepsy Receiving Both Drugs Concomitantly: A Preliminary Study

An individualized dosage regimen is of importance for phenytoin and carbamazepine therapy. However, not all patients can afford the cost of therapeutic drug monitoring, particularly in rural areas. An approach used to assist individualized drug therapy is needed. The aim of the study was to determine the relationship between maximum rate of metabolism of phenytoin and carbamazepine clearance. Such information will be beneficial in aiding individualized drug therapy. Thirteen epileptic patients receiving phenytoin in combination with carbamazepine were included in the study. All patients were studied at steady-state conditions with no change in phenytoin and carbamazepine dosage for at least one month before the study commencement. Serum phenytoin and carbamazepine concentrations were determined by Fluorescence Polarization Technique (TDx® Analyzer System). The maximum rate of metabolism of phenytoin (V max) and carbamazepine clearance (CLCBZ ) was calculated based on measured drug levels at steady-state. Subsequently, their relationships were determined by simple linear regression. There was a high correlation coefficient between maximum rate of metabolism of phenytoin (V max) and carbamazepine clearance (CLCBZ) [r = 0.816; p = 0.001 and r = 0.818; p = 0.001 for V max (mg/day) vs. CLCBZ (L/day) and V max (mg/kg/day) vs. CLCBZ (L/kg/day), respectively]. This high positive correlation can be of use in predicting V max from CLCBZ and vice versa, particularly in rural hospitals in Thailand where therapeutic drug monitoring for either one of the drugs is not available. Elimination parameters of phenytoin and carbamazepine can be predicted by their respective relationships. The proposed equations used to determine maximum rate of metabolism of phenytoin and carbamazepine clearance are of benefit in reducing the cost for drug concentration measurements.

Determination of serum carbamazepine concentration using dried blood spot specimens for resource-limited settings

ABSTRACTObjectives: Carbamazepine (CBZ) is a commonly used anti-epileptic in rural hospitals in India. These hospitals lack the facilities to measure CBZ concentration; however, in larger hospitals this is performed using high performance liquid chromatography (HPLC). Dried blood spot (DBS) represents a feasible matrix for safe transportation by post/courier. This study was to determine whether the concentration of CBZ in serum can be predicted from that measured in DBS using an inexpensive HPLC method and inexpensive standard filter paper.Methods: CBZ in serum and DBS from 80 epileptic patients were measured using a validated HPLC assay. The data was then randomly divided into two groups; simple Deming regression was performed with the first group and validation was performed using the second.Results: There was a good correlation between the serum and DBS concentrations (r = 0.932) in the first group. The regression equation obtained was: predicted serum concentration = DBS concentration x 0.83 + 1.09. In the validation group, the correlation between the predicted and actual serum concentrations was also good (r = 0.958), and the mean difference between them was only 0.28 μg/ml (p = 0.8062). The imprecision and bias in both the groups were acceptable.Conclusion: Using inexpensive materials, serum CBZ concentrations can be accurately predicted from DBS specimens. This method can be recommended for the therapeutic drug monitoring of CBZ in resource-limited settings.

The influence of CYP2C8*3 on carbamazepine serum concentration in epileptic pediatric patients.

The aim of the present study was to investigate the distribution of CYP2C8 variants *3 and *5, as well as their effect on carbamazepine pharmacokinetic properties, in 40 epileptic pediatric patients on carbamazepine treatment. Genotyping was conducted using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and allele-specific (AS)-PCR methods, and steady-state carbamazepine plasma concentrations were determined by high performance liquid chromatography (HPLC). The CYP2C8 *3 and *5 polymorphisms were found at frequencies of 17.5 and 0.0%, respectively. After dose adjustment, there was a difference in daily dose in CYP2C8*3 carriers compared to non carriers [mean ± standard deviation (SD): 14.19 ± 5.39 vs. 15.46 ± 4.35 mg/kg; p = 0.5]. Dose-normalized serum concentration of carbamazepine was higher in CYP2C8*3 (mean ± SD: 0.54 ± 0.18 vs. 0.43 ± 0.11 mg/mL, p = 0.04), and the observed correlation between weight-adjusted carbamazepine dose and carbamazepine concentration after dose adjustment was significant only in CYP2C8*3 non carriers (r = 0.52, p = 0.002). However, the population pharmacokinetic analysis failed to demonstrate any significant effect of CYP2C8 *3 polymorphism on carbamazepine clearance [CL L/h = 0.215 + 0.0696*SEX+ 0.000183*DD]. The results indicated that the CYP2C8*3 polymorphism might not be of clinical importance for epilepsy treatment in pediatric populations.

SCN1A and SCN1B gene polymorphisms and their association with plasma concentrations of carbamazepine and carbamazepine 10, 11 epoxide in Iranian epileptic patients.

From a genetic point of view, epilepsy is a polygenic multifactorial syndrome. The SCN1A and B genes belong to a family of genes that provide instructions for making sodium channels. Understanding the relevance of SCN1A and SCN1B gene polymorphisms to plasma concentration of carbamazepine (CBZ) and 'its active metabolite carbamazepine 10, 11 epoxide (CBZE), may shed more light on inter-individual variations in response to CBZ. In this cross-sectional study, genotype distribution and allele frequency of six non-synonymous exonic single nucleotide polymorphisms (SNPs) of the SCN1A and B genes were selected and determined using PCR-RFLP in 70 epileptic patients treated with CBZ for at least 6 months. The patients had no hepatic or renal diseases and received no medications known to have a major interaction with CBZ. Serum concentrations of CBZ and CBZE were measured using High-Performance Liquid Chromatography (HPLC). The AA, AG and GG alleles of SCN1A were found in 23, 37 and 10 patients, respectively. There were no statistically significant differences in the mean (± standard deviation) of plasma concentrations of CBZ (P=0.8) and CBZE (P=0.1) among these 3 groups. Likewise, there was no statistically significant relationship between SCN1A polymorphisms and CBZ concentration/dose ratio (P=0.7). A significant association was found between CBZ plasma level and CBZ concentration/dose with CBZ daily dose. All patients had the same genotype of SCN1B gene(CC). and no statistical analysis was performed. No significant association between SCN1A gene polymorphisms and plasma levels of CBZ and CBZE were found[u1].

Interactions between antiepileptic drugs, and between antiepileptic drugs and other drugs.

Interactions between antiepileptic drugs, or between antiepileptic drugs and other drugs, can be pharmacokinetic or pharmacodynamic in nature. Pharmacokinetic interactions involve changes in absorption, distribution or elimination, whereas pharmacodynamic interactions involve synergism and antagonism at the site of action. Most clinically important interactions of antiepileptic drugs result from induction or inhibition of drug metabolism. Carbamazepine, phenytoin, phenobarbital and primidone are strong inducers of cytochrome P450 and glucuronizing enzymes (as well as P-glycoprotein) and can reduce the efficacy of co-administered medications such as oral anticoagulants, calcium antagonists, steroids, antimicrobial and antineoplastic drugs through this mechanism. Oxcarbazepine, eslicarbazepine acetate, felbamate, rufinamide, topiramate (at doses ≥ 200 mg/day) and perampanel (at doses ≥ 8 mg/day) have weaker inducing properties, and a lower propensity to cause interactions mediated by enzyme induction. Unlike enzyme induction, enzyme inhibition results in decreased metabolic clearance of the affected drug, the serum concentration of which may increase leading to toxic effects. Examples of important interactions mediated by enzyme inhibition include the increase in the serum concentration of phenobarbital and lamotrigine caused by valproic acid. There are also interactions whereby other drugs induce or inhibit the metabolism of antiepileptic drugs, examples being the increase in serum carbamazepine concentration by erythromycin, and the decrease in serum lamotrigine concentration by oestrogen-containing contraceptives. Pharmacodynamic interactions between antiepileptic drugs may also be clinically important. These interactions can have potentially beneficial effects, such as the therapeutic synergism of valproic acid combined with lamotrigine, or adverse effects, such as the reciprocal potentiation of neurotoxicity observed in patients treated with a combination of sodium channel blocking antiepileptic drugs.