A sensitive gas chromatographic/mass spectrometric method for the resolution and quantification of ethosuximide enantiomers in biological fluids

A validated method for the separation of ethyl glucoside isomers by gas chromatography-tandem mass spectrometry and quantitation in human whole blood and urine

Ethyl glucoside (EG) is present in Japanese sake in high concentrations, and can be found in other alcoholic beverages like beer and wine in varying amounts. EG exists as alpha (α) and beta (β) isomers, and the concentrations and ratios of these isomers differ depending on the alcoholic beverage. Herein, we report a validated analysis method for the separation of EG isomers in human whole blood and urine, by GC-MS/MS. Whole blood and urine samples were deproteinized and interferences removed by weak cation exchange cartridges. The target analytes were acetylated using acetic anhydride and pyridine by microwave-accelerated derivatization. Separation was performed using tandem columns, with detection in the multiple reaction monitoring (MRM) mode. The MRM transitions for all compounds were m/z 157.0 > 115.1 for the quantifying transition, and m/z 157.0 > 73.1 and m/z 141.0 > 81.0 for the qualifying transitions. Assay validation included linearity, LOD and LLOQ, bias, within-run and between-run precision, stability, and dilution integrity. Baseline separation of the 2 isomers was achieved with linear calibration (r² > 0.99) across the calibration range 0.625 to 50 μg/mL for both α- and β-EG in both whole blood and urine. The validated method was then applied to actual human whole blood and urine samples collected at autopsy, as well as relevant alcoholic beverage samples. The quantitation of EG isomers could benefit the forensic toxicology community by acting as markers for recent alcoholic beverage consumption.

Microextraction combined with microderivatization for drug monitoring and protein modification analysis from limited blood volume using mass spectrometry

In the clinic, ethosuximide is commonly used to treat generalized absence seizures but has recently been repurposed for other diseases. Because of adverse effects and drug interactions, high-throughput therapeutic drug monitoring of ethosuximide is necessary. Microextraction is a simple, effective, rapid, and low consumption of organic solvents method for sample preparation. In this study, microderivatization-increased detection (MDID)-combined microextraction was used to detect ethosuximide by mass spectrometry. Ethosuximide is a difficult to retain and ionize compound in the C18 nano-flow column and ionization interface, respectively. Hence, we developed a fast method for detecting ethosuximide in human plasma by using the MDID strategy (within 2 min). Chemical microderivatization parameters were studied and optimized to increase the sensitivity of ethosuximide detection at trace levels. The linear range for the analysis of ethosuximide in 10 μL plasma was 5-500 μg/mL with a coefficient of determination (r²) ≥ 0.995. The precision and accuracy of intraday and interday analyses of ethosuximide were below 13.0%. Furthermore, modifications of major proteins in plasma and blood cells, induced by ethosuximide, were identified. The proposed method effectively utilizes microliter samples to detect drug plasma concentrations under suitable microextraction procedures toward the eco-friendly goal of low consumption of organic solvents. Graphical abstract ᅟ.

Chiral chromatographic resolution of antiepileptic drugs and their metabolites: a challenge from the optimization to the application

A large number of the antiepileptic drugs (AEDs) presently available for clinical practice are chiral compounds while others, although achiral, may originate pharmacologically active chiral metabolites in vivo. The well-known implications of chirality in pharmacokinetics and pharmacodynamics demand the investigation of pharmacological properties for a racemic mixture and each enantiomer. To achieve these objectives, appropriate chiral analytical methods must be available. This article provides the first review of the current state of the art in chiral chromatographic methods available for quantifying enantiomers of AEDs in distinct matrices. Particular attention is paid to the methodological aspects and optimization strategies that successfully allow enantiomeric chromatographic separation of chiral AEDs and/or metabolites. Furthermore, the relevance of these methods in supporting the discovery and development of chiral AEDs is emphasized. In parallel and whenever available, the principal validation parameters are herein considered and related to the stage of drug discovery and development. In an attempt to optimize anticonvulsant activity and simultaneously diminish toxic effects, many pharmaceutical companies have started to manufacture single enantiomers. Therefore, chiral chromatographic techniques will be essential and the information herein compiled can be used as a framework for developing them.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Analysis of antiepileptic drugs in biological fluids by means of electrokinetic chromatography

An overview of the electrokinetic chromatographic methods for the analysis of antiepileptic drug levels in biological samples is presented. In particular, micellar electrokinetic capillary chromatography is a very suitable method for the determination of these drugs, because it allows a rapid, selective, and accurate analysis. In addition to the electrokinetic chromatographic studies on the determination of antiepileptic drugs, some information regarding sample pretreatment will also be reported: this is a critical step when the analysis of biological fluids is concerned. The electrokinetic chromatographic methods for the determination of recent antiepileptic drugs (e.g., lamotrigine, levetiracetam) and classical anticonvulsants (e.g., carbamazepine, phenytoin, ethosuximide, valproic acid) will be discussed in depth, and their pharmacological profiles will be briefly described as well.