Determination of Carbamazepine and its Main Metabolite Carbamazepine-10,11-Epoxide in Rat Brain Microdialysate and Blood Using ESI–LC–MS (Ion Trap)

Quantitative bioanalytical and analytical method development of dibenzazepine derivative, carbamazepine: A review

Bioanalytical methods are widely used for quantitative estimation of drugs and their metabolites in physiological matrices. These methods could be applied to studies in areas of human clinical pharmacology and toxicology. The major bioanalytical services are method development, method validation and sample analysis (method application). Various methods such as GC, LC-MS/MS, HPLC, HPTLC, micellar electrokinetic chromatography, and UFLC have been used in laboratories for the qualitative and quantitative analysis of carbamazepine in biological samples throughout all phases of clinical research and quality control. The article incorporates various reported methods developed to help analysts in choosing crucial parameters for new method development of carbamazepine and its derivatives and also enumerates metabolites, and impurities reported so far.

Optimization and validation of bioanalytical SPE – HPLC method for the simultaneous determination of carbamazepine and its main metabolite, carbamazepine-10, 11-epoxide, in plasma

Carbamazepine is widely used as an antiepileptic drug in the treatment of partial and generalized tonic-clonic seizures. Carbamazepine 10,11-epoxide is the most important metabolite of carbamazepine, because it is a pharmacologically active compound with anticonvulsant properties. According to that, the routine analysis of carbamazepine 10,11-epoxide along with carbamazepine may provide optimal therapeutic monitoring of carbamazepine treatment. The aim of this study was to optimize and validate a simple and reliable solid - phase extraction method followed by RP-HPLC for the simultaneous determination of plasma levels of carbamazepine and carbamazepine-10,11-epoxide, in order to assure the implementation of the method for therapeutic monitoring. The extraction of the analytes from the plasma samples was performed by means of a solid-phase extraction procedure. The separation was carried out on a reversed-phase column using isocratic elution with acetonitrile and water (35:65, v/v) as a mobile phase. The temperature was 30°C and UV detection was set at 220 nm. The extraction yield values were more than 98% for all analytes, measured at four concentration levels of the linear concentration range. The method displayed excellent selectivity, sensitivity, linearity, precision and accuracy. Stability studies indicate that stock solutions and plasma samples were stabile under different storage conditions at least during the observed period. The method was successfully applied to determine the carbamazepine and carbamazepine-10,11-epoxide in plasma of epileptic patients treated with carbamazepine as monotherapy and in polytherapy. In conclusion, the proposed method is suitable for application in therapeutic drug monitoring of epileptic patients undergoing treatment with carbamazepine.

Metabolite identification in rat brain microdialysates by direct infusion nanoelectrospray ionization after desalting on a ZipTip and LTQ/Orbitrap mass spectrometry

Analyzing brain microdialysate samples by mass spectrometry is challenging due to the high salt content of the artificial cerebral spinal fluid (aCSF), low analyte concentrations and small sample volumes collected. A drug and its major metabolites can be examined in brain microdialysates by targeted approaches such as selected reaction monitoring (SRM) which provides selectivity and high sensitivity. However, this approach is not well suited for metabolite profiling in the brain which aims to determine biotransformation pathways. Identifying minor metabolites, or metabolites that arise from brain metabolism, remains a challenge and, for a drug in early discovery, identification of metabolites present in the brain can provide useful information for understanding the pharmacological activity and potential toxicological liabilities of the drug. A method is described here for rapid metabolite profiling in brain microdialysates that involves sample clean-up using C18 ZipTips to remove salts followed by direct infusion nanoelectrospray with an LTQ/Orbitrap mass spectrometer using real-time internal recalibration. Full scan mass spectra acquired at high resolving power (100 K at m/z 400) were examined manually and with mass defect filtering. Metabolite identification was aided by sub-parts-per-million mass accuracy and structural characterization was accomplished by tandem mass spectrometry (MS/MS) experiments in the Orbitrap or LTQ depending on the abundance of the metabolite. Using this approach, brain microdialysate samples from rats dosed with one of four CNS drugs (imipramine, reboxetine, citalopram or trazodone) were examined for metabolites. For each drug investigated, metabolites, some of which not previously reported in rat brain, were identified and characterized.

Metabolite profiling of Calvin cycle intermediates by HPLC-MS using mixed-mode stationary phases

SUMMARY

A sensitive and robust mixed-mode high performance liquid chromatography-tandem mass spectrometry method was developed for the qualitative and quantitative determination of sugar phosphates, which are notoriously difficult to separate using reversed-phase materials. Sugar phosphates were separated on a Primesep SB column by gradient elution using aqueous ammonium formate and acetonitrile as mobile phases. Target analytes were identified by their precursor/product ions and retention times. Quantitative analysis was performed in negative ionization/multiple reaction monitoring mode with five different time segments. The method was validated by spiking authentic sugar phosphate standards into complex plant tissue extracts. Standard curves of neat authentic standards and spiked extracts were generated for concentrations in the low picomole to nanomole range, with correlation coefficients of R(2) > 0.991, and the degree of ion suppression in the presence of a plant matrix was calculated for each analyte. Analyte recoveries, which were determined by including known quantities of authentic standards in the sugar phosphate extraction protocol, ranged from 40.0% to 57.4%. The analytical reproducibility was assessed by determining the coefficient of variance based on repeated extractions/measurements (<20%). The utility of our method is demonstrated with two types of applications: profiling of Calvin cycle intermediates in (i) dark-adapted and light-treated tobacco leaves, and in (ii) antisense plants expressing reduced levels of the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase or ribulose-1,5-bisphosphate carboxylase/oxygenase (comparison with wild-type controls). The broader applicability of our method is illustrated by profiling sugar phosphates extracted from the leaves of five taxonomically diverse plants.