Simultaneous determination of lamotrigine, phenobarbitone, carbamazepine and phenytoin in human serum by high-performance liquid chromatography

Application of a Small Protein-Coated Column to Trap, Extract and Enrich Carbamazepine Directly from Human Serum for Direct Chromatographic Analysis

An automated solid phase extraction (SPE) protocol to determine carbamazepine in human serum has been developed and validated using a simple, rabid and sensitive liquid chromatography-based bio-analytical method. Extraction of carbamazepine was carried out using an on-line SPE tool of a short protein-coated (PC) ODS silica pre-column (PC-ODS-pre-column) and phosphate buffer saline (PBS) with a pH of 7.4 as an extraction solvent. There are two distinct chromatographic modes used by PC-ODS-pre-column. While carbamazepine trapping required reversed-phase liquid chromatography, proteins were extracted from serum samples using PBS by size-exclusion liquid chromatography. Then, carbamazepine was eluted from the PC-ODS-pre-column onto the quantification position using a mixture of methanol-distilled deionized water (50:50, v/v) as an eluent and ODS analytical column. At room temperature (22 ± 1 °C), carbamazepine was completely separated from the co-eluted matrix components and detected at 230 nm. Carbamazepine’s linearity was obtained at concentrations ranging from 50 to 10,000 ng/mL. With good accuracy and precision, carbamazepine recoveries in serum samples ranged from 86.14 to 97.82%. The extraction step was conducted using PBS as a safe and green extraction solvent, making this protocol both cost-effective and ecologically safe.

Development of a useful single-reference HPLC method for therapeutic drug monitoring of phenytoin and carbamazepine in human plasma

A single reference high-performance liquid chromatographic (SR-HPLC) method was developed and validated for the therapeutic drug monitoring (TDM) of phenytoin (PHT) and carbamazepine (CBZ) in plasma from patients. The analytical parameters evaluated were linearity, limit of quantification (LOQ), selectivity, accuracy, and stability according to the US Food and Drug Administration (FDA) guideline. The developed method shows good linearity (r2 > 0.999; LOQ-50 µg/mL), and LOQ values were 1.56 µg/mL for PHT and 0.40 µg/mL for CBZ at 254 nm. For the development of SR-HPLC method, we evaluated to improve the detection wavelength, stirred retention time, and stability for SR, and selected 5-(p-methylphenyl)-5-phenylhydantoin for PHT (relative molar sensitivity, RMS = 0.848) and 10-methoxyiminostilbene for CBZ (RMS = 0.263). The established differential definite quantities of PHT and CBZ in plasma samples were similar using the RMS and absolute calibration methods based on RSD < 5.10%. A preliminary application was performed using chemiluminescent immunoassay and SR-HPLC method, in which the detectable values of the correlation coefficient and the slope of the intercept were PHT: 0.964 and 0.992647, and CBZ: 0.969 and 1.072089, respectively. Based on these results, we propose that the SR-HPLC method with RMS would be offered to the useful and accurate TDM of various medicines in plasma/serum samples.

A sensitive LC-MS/MS method for quantification of phenytoin and its major metabolite with application to in vivo investigations of intravenous and intranasal phenytoin delivery

Phenytoin is a powerful antiseizure drug with complex pharmacokinetic properties, making it an interesting model drug to use in preclinical in vivo investigations, especially with regards to formulations aiming to improve drug delivery to the brain. Moreover, it has a major metabolite, 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin, which can be simultaneously studied to achieve a better assessment of its behaviour in the body. Here, we describe the development and validation of a sensitive LCMS/MS method for quantification of phenytoin and 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin in rat plasma and brain which can be used in such preclinical studies. Calibration curves produced covered a range of 7.81 to 250 ng/mL (plasma) and 23.4 to 750 ng/g (brain tissue) for both analytes. The method was validated for specificity, sensitivity, accuracy, and precision and found to be within the acceptable limits of ±15% over this range in both tissue types. The method when applied in two in vivo investigations: validation of a seizure model and to study the behaviour of a solution of intranasally administered phenytoin as a foundation for future studies into direct nose‐to‐brain delivery of phenytoin using specifically developed particulate systems, was highly sensitive for detecting phenytoin and 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin in rat plasma and brain.

High performance liquid chromatography: A versatile tool for assaying antiepileptic drugs in biological matrices

Epilepsy is a recurrent long-term illness occurring in approximately 1.0% of the world's population. There are currently about 29 approved antiepileptic drugs for the management of epilepsy. Due to narrow therapeutic indices of most antiepileptic drugs, clinical pharmacokinetic characteristics and therapeutic drug monitoring of these drugs are imperative. The objectives of this review were to identify common chromatographic principles, requirements and/or conditions for high-performance liquid chromatography as applied to assay of antiepileptic drugs in biological matrices. The review was conducted using 66 peer reviewed articles (1990 to 2020) from 29 journals that were sought via PubMed, Science Direct and Google Scholar. In all, 29 antiepileptic drugs were assayed from 6 different biological matrices. Forty-three of the reviewed articles estimated the concentration of only one antiepileptic drug, whilst 23 articles focused on simultaneous determination of two or more antiepileptic drugs. Thirty-four, 20, and 14 articles reported using liquid-liquid extraction, protein precipitation, or solid phase extraction for sample clean up, respectively. The ratio of reversed-phase to normal phase, LC-UV to LC-MS and isocratic elution to gradient elution were 61:3, 43:7 and 55:11, respectively. With the exception of one article the reported recoveries ranged from 60.3% to 109.6%. It is noteworthy, that, the performance metrics of high-performance liquid chromatography are better compared to other assays of antiepileptic drugs in biological matrices. This review describes the relevant liquid chromatographic method conditions over the past 30 years for the analysis of this class of drugs, which provides a basis for further method development and optimization.

Pharmacodynamic and pharmacokinetic interactions of hydroalcoholic leaf extract of Centella asiatica with valproate and phenytoin in experimental models of epilepsy in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Centella asiatica (CA) is commonly used herbal medicine for treatment of epilepsy. CA has CYP2C9, CYP2D6 and CYP3A4 enzymes inhibition property and used as an adjuvant therapy with conventional antiepileptic drugs (AEDs). That may be responsible for herb-drug interaction.

AIM OF THE STUDY

The present study was planned to evaluate interactions profile of hydroalcoholic extract Centella asiatica (HECA) with antiepileptic drugs in experimental models of epilepsy in rats.

MATERIALS AND METHODS

Wistar rats (175-200 g) were used. In the pharmacodynamic interaction study, seizures were induced using pentylenetetrazole (PTZ) (60 mg/kg, i.p.) and maximal electroshock seizure (MES) (70 mA for 0.2 s). The therapeutic and sub-therapeutic doses of valproate (VPA) and phenytoin (PHT) were co-administrated with HECA in PTZ and MES model of seizures respectively. Behavioural parameters were assessed using elevated plus maze test and passive avoidance paradigm. Rat brain oxidative stress parameters were also assessed. In the pharmacokinetic interaction study, the serum levels of the VPA and PHT were estimated at different time intervals by HPLC and pharmacokinetic parameters were analyzed by WinNonlin software.

RESULTS

The VPA and PHT produced complete protection against seizures in their therapeutic doses but not with sub-therapeutic doses. However, co-administration of HECA with a sub-therapeutic dose of VPA and PHT enhanced the protection of seizures and significantly (p < 0.001) attenuated the seizure induced oxidative stress and cognitive impairment. It also significantly increased (p < 0.001) serum levels of VPA and PHT. The alterations in pharmacokinetic parameters (maximum serum concentration, area under the curve, clearance) of AEDs were also found with co-administration of HECA.

CONCLUSION

The results suggested that co-administration of HECA could improve the therapeutic efficacy of VPA and PHT. But, alteration in pharmacokinetic parameters revel that needs critical medical supervision to avoid any toxic reactions.

Meloxicam quantification in rabbit plasma by RP-HPLC: optimization and application to pharmacokinetic study

Background

The goal of the proposed study was to validate a rapid, simple, an accurate, robust, and sensitive bioanalytical method for quantifying Meloxicam and Lornoxicam (as internal standard) in rabbit plasma.

Result

Limit of detection and limit of quantification for Meloxicam were found to be 0.0081 and 0.1035 μg mL−1, respectively. The bioanalysis was continued according to standard guidelines and successfully used for bioavailability studies of meloxicam after single dose administration of pure drug and the formulation in rabbit plasma. Finally, obtained results proved its simplicity and an efficiency to be applied for the therapeutic drug monitoring and bioequivalence studies.

Conclusion

Therefore, the set RP-HPLC bioanalysis is simple, convenient, and acceptable to analyze meloxicam in bulk and pharmaceutical formulations in rabbit plasma.

Graphical abstract

Carbon based nanomaterials for the detection of narrow therapeutic index pharmaceuticals

Precise detection of important pharmaceuticals with narrow therapeutic index (NTI) is very critical as there is a small window between their effective dose and the doses at which the adverse reactions are very likely to appear. Regarding the fact that various pharmacokinetics will be plausible while considering pharmacogenetic factors and also differences between generic and brand name drugs, accurate detection of NTI will be more important. Current routine analytical techniques suffer from many drawbacks while using novel biosensors can bring up many advantages including fast detection, accuracy, low cost with simple and repeatable measurements. Recently the well-known carbon Nano-allotropes including carbon nanotubes and graphenes have been widely used for development of different Nano-biosensors for a diverse list of analytes because of their great physiochemical features such as high tensile strength, ultra-light weight, unique electronic construction, high thermo-chemical stability, and an appropriate capacity for electron transfer. Because of these exceptional properties, scientists have developed an immense interest in these nanomaterials. In this case, there are important reports to show the effective Nano-carbon based biosensors in the detection of NTI drugs and the present review will critically summarize the available data in this field.

Validated RP-HPLC method for quantification of felodipine in rabbit plasma: Application in a bioequivalence study

OBJECTIVE

The aim of present study was to develop a simple, rapid, selective, sensitive and robust reverse phase high performance liquid chromatographic method for quantification of felodipine in rabbit plasma at the wavelength of 360nm.

METHOD

Protein was precipitated from rabbit plasma sample by addition of acetonitrile as a vehicle. An isocratic elution of samples was performed on capcell pak C₈ DD S5 column (4.6mm×250mm particle size 5μm) column with mobile phase consisting 5mM Phosphate Buffer (pH 4.8 adjusted with dilute ortho-phosphoric acid solution): acetonitrile (25:75:v/v) delivered at flow rate 1.0mLmin^-1.

RESULT

A good linear response was achieved over the range of 0.25-20.00μgmL^-1. LODs and LOQs for felodipine were found to be 0.055 and 0.201μgmL^-1, respectively. The method was quantitatively evaluated in terms of linearity, precision, accuracy (recovery), selectivity robustness and stability study as per standard guidelines. The validated RP-HPLC method was successfully applied for the bioavailability studies of felodipine. The pharmacokinetic parameters were calculated for all the investigated drugs in rabbit after single-dose administrations of pure drug and formulation of felodipine. Finally, the obtained results for the application of the proposed RP-HPLC method proved its efficiency to be applied to the therapeutic drug monitoring (TDM) and bioequivalence (BE) studies.

CONCLUSION

Thus, developed method is simple, convenient and suitable for the analysis of felodipine in bulk and pharmaceutical formulations.

Sensitive inexpensive HPLC determination of four antiepileptic drugs in human plasma: application to PK studies

Aim: Recently, polytherapy regimen has been introduced for the treatment of epileptic patients for better seizure control with lesser side effects and better control of multiple seizure types. Methodology: A simple, sensitive and highly specific reversed-phase HPLC method was developed for simultaneous determination of four antiepileptic drugs (AEDs), levetiracetam, lamotrigine, oxcarbazepine and carbamazepine, in real human plasma without interference from endogenous components of plasma. Conclusion: The method was proved to be linear in the range of 0.5–50 µg/ml for all drugs. It was successfully applied for clinical PK study of the AEDs in healthy volunteers following single administration. Also, this method was applied for simultaneous determination of the studied drugs in volunteers’ plasma receiving synergistic binary combinations from the four AEDs when used as add-on therapy. The good precision and selectivity of the developed method allow it to be used for routine therapeutic drug monitoring of such drugs as a useful tool in epilepsy management.

Pharmacodynamic and pharmacokinetic interaction of Panchagavya Ghrita with phenytoin and carbamazepine in maximal electroshock induced seizures in rats

Introduction:

Traditionally, Panchagavya Ghrita (PG) has been used for the management of epilepsy, anxiety, fever and jaundice. It consists of five components of cow products namely, cow milk, clarified butter from cow milk, cow urine, curd from cow milk, and cow dung juice.

Aim:

To evaluate the effect of PG in maximal electroshock (MES) induced seizures model and its pharmacodynamic and pharmacokinetic interaction with phenytoin (PHT) and carbamazepine (CBZ) in rats.

Materials and Methods:

Male Wistar rats were administered PG 500, 1000, 2000, and 4000 mg/kg orally for 7 days and seizures were induced by MES. For interaction studies, PG (4000 mg/kg) was administered along with a sub-therapeutic dose of PHT (20 mg/kg, p.o.) and CBZ (10 mg/kg, p.o.). Behavioral parameters were assessed. Oxidative stress markers and serum levels of PHT and CBZ were estimated.

Results:

Tonic hind limb extension, cognitive impairment, and oxidative stress produced by MES were reversed by PG (4000 mg/kg). Co-administration of PG (4000 mg/kg) with a sub-therapeutic dose of PHT and CBZ potentiated antiepileptic effect and ameliorated cognitive impairment as well as oxidative stress. Although, there was a slight increase in serum levels of PHT and CBZ on co-administration with PG, it was statistically insignificant.

Conclusion:

Co-administration of PG with low doses of PHT and CBZ caused complete seizure protection. This suggests the potential of PG as an adjunct in epilepsy with improved efficacy and tolerability.

Influence of organic surface coatings on the sorption of anticonvulsants on mineral surfaces

Here, we explore the role that sorption to mineral surfaces plays in the fate of two commonly encountered effluent-derived pharmaceuticals, the anticonvulsants phenytoin and carbamazepine. Adsorption isotherms and pH-edge experiments are consistent with electrostatics governing anticonvulsant uptake on metal oxides typically found in soil and aquifer material (e.g., Si, Al, Fe, Mn, and Ti). Appreciable, albeit limited, adsorption was observed only for phenytoin, which is anionic above pH 8.3, on the iron oxides hematite and ferrihydrite. Adsorption increased substantially in the presence of cationic and anionic surfactants, species also commonly encountered in wastewater effluent. For carbamazepine, we propose the enhanced uptake results entirely from hydrophobic interactions with apolar tails of surfactant surface coatings. For phenytoin, adsorption also arises from the ability of surfactants to alter the net charge of the mineral surface and thereby further enhance favorable electrostatic interactions with its anionic form. Collectively, our results demonstrate that although pristine mineral surfaces are likely not major sinks for phenytoin and carbamazepine in the environment, their alteration with organic matter, particularly surfactants, can considerably increase their ability to retain these emerging pollutants in subsurface systems.

Interaction profile of Zizyphus jujuba with phenytoin, phenobarbitone, and carbamazepine in maximal electroshock-induced seizures in rats

The antiepileptic effect of hydroalcoholic extract of Zizyphus jujuba (HEZJ) in experimental seizures was demonstrated earlier. The present study aimed to evaluate the pharmacokinetic and pharmacodynamic interactions of HEZJ with phenytoin (PHT), phenobarbitone (PB), and carbamazepine (CBZ) in maximal electroshock (MES)-induced seizures in male Wistar rats. Maximal electroshock (70 mA, 9 ms pulse width, 0.2 s) was used to induce seizures. Blood samples were collected at two time points for estimation of serum PHT, PB, and CBZ levels using high-pressure liquid chromatography (HPLC). Co-administration of HEZJ with the sub-therapeutic doses of PHT, PB, and CBZ exhibited 66.7, 66.7, and 50.0% protection against tonic hind limb extension as compared to 33.3, 33.3, and 50% protection respectively, in the groups treated with PHT, PB, and CBZ alone in their sub-therapeutic doses. Co-administration of HEZJ with the sub-therapeutic doses of these antiepileptic drugs (AEDs) showed significant improvement in cognitive functions as compared to MES group as well as these AEDs alone. A significant increase in glutathione levels and decrease in malondialdehyde levels were observed with pretreatment of HEZJ with the sub-therapeutic doses of these AEDs. Co-administration of HEZJ with PHT, PB, and CBZ did not cause any significant changes in the serum concentrations of these AEDs. The results of the present study indicate that the co-administration of HEZJ with sub-therapeutic doses of PHT and PB potentiated the antiepileptic effect of PHT and PB in MES-induced seizures with no change found in the antiepileptic effect of CBZ.

Overexpression of multidrug resistance-associated protein 2 in the brain of pentylenetetrazole-kindled rats

Clinical studies and animal models have shown that pharmacoresistant epilepsy is partly due to the overexpression of ATP-binding cassette transporters at the brain. The purposes of the study were to investigate the function and expression of multidrug resistance-associated protein 2 (Mrp2) in the brain of pentylenetetrazole (PTZ)-kindled rats, and the effect of the altered Mrp2 function and expression on phenytoin (PHT) distribution in the brain. Kindled rats were developed by sub-convulsive dose of PTZ (33 mg/kg, every day, intraperitoneal (i.p.)) for 28 days. Mrp2 expression and function were measured by western blot and bromosulfophthalein (BSP) distribution in the brain. PHT concentrations in the brain of PTZ-kindled rats were measured alone or with co-administration of probenecid (50mg/kg). Further experiment was designed to investigate whether PHT treatment prevented the up-regulated brain Mrp2 expression and function induced by PTZ-kindling. The results showed that PTZ-kindling resulted in an increase of Mrp2 level in the hippocampus and cortex of rats, accompanied by significant decreases in the brain-to-plasma concentration ratio of BSP. PTZ-kindling also decreased PHT levels in the hippocampus and cortex without altering PHT concentrations in plasma, resulting in a lower brain-to-plasma concentration ratio of PHT. Co-administration of probenecid increased the brain-to-plasma ratio of BSP and PHT in the brain of both normal and PTZ-kindled rats. A 14-day PHT treatment prevented the up-regulation of Mrp2 expression and function induced by PTZ-kindling, accompanied by increases of PHT concentrations in the brain and good anticonvulsive effects. The present study demonstrated that chronic PTZ-kindling increased Mrp2 expression and function in the rat brain, and the up-regulation partly came from epileptic seizure.

Liquid chromatography tandem mass spectrometry method for the estimation of lamotrigine in human plasma: Application to a pharmacokinetic study

A reliable, selective and sensitive liquid chromatography tandem mass spectrometry method was developed and validated for the quantification of lamotrigine in human plasma using lamotrigine-¹³C3, d3 as an internal standard. Analyte and internal standard were extracted from human plasma by solid-phase extraction and detected in positive ion mode by tandem mass spectrometry with electrospray ionization (ESI) interface. Chromatographic separation was performed on a Chromolith^® SpeedROD; RP-18e column (50−4.6 mm i.d.) using acetonitrile: 5±0.1 mM ammonium formate solution (90:10, v/v) as the mobile phase at a flow rate of 0.500 mL/min. The calibration curves were linear over the range of 5.02–1226.47 ng/mL with the lower limit of quantitation validated at 5.02 ng/mL. The analytes were found stable in human plasma through three freeze (−20 °C)-thaw (ice-cold water bath) cycles and under storage on bench-top in ice-cold water bath for at least 6.8 h, and also in the mobile phase at 10 °C for at least 57 h. The method has shown good reproducibility, as the intra- and inter-day precisions were within 3.0%, while the accuracies were within ±6.0% of nominal values. The validated LC–MS/MS method was applied for the evaluation of pharmacokinetic and bioequivalence parameters of lamotrigine after an oral administration of 50 mg lamotrigine tablet to thirty-two healthy adult male volunteers.

Highly sensitive voltammetric determination of lamotrigine at highly oriented pyrolytic graphite electrode

The electrochemical behavior of lamotrigine (LMT) at the pyrolytic graphite electrode (PGE) is investigated in detail by the means of cyclic voltammetry. During the electrochemical reduction of LMT, an irreversible cathodic peak appeared. Cyclic voltammetric studies indicated that the reduction process has an irreversible and adsorption-like behavior. The observed reduction peak is attributed to a two-electron process referring to the reduction of azo group. The electrode showed an excellent electrochemical activity toward the electro-reduction of LMT, leading to a significant improvement in sensitivity as compared to the glassy carbon electrode. The results of electrochemical impedance spectroscopy and cyclic voltammetry showed that edge-plane pyrolytic graphite electrode has excellent electrochemical response properties toward LMTs with respect to glassy carbon electrode modified with carbon nanotubes. High sensitivity, low detection limit and very good repeatability together with excellent recovery make the electrode as a powerful devise for accurate determination of LMT in pharmaceutical and biological samples.

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.

Comparison of dissolution profiles and serum concentrations of two lamotrigine tablet formulations

Objective: The aim of this study was to investigate the extent of variations in lamotrigine serum concentrations between two immediate-release tablet formulations. Data were compared with in vitro difference and similarity tests on dissolution profiles of the two formulations.

Methods: Dissolution characteristics of formulations A (reference) and B (test) were evaluated at three points spanning the physiologic pH range (pH 1.2, pH 4.5, pH 6.8). A model-independent approach of difference (f1) and similarity (f2) tests were applied to dissolution data. A clinical study was performed with 16 patients who were divided into two groups — one group received formulation A (n=9) and the other received formulation B (n=7). Lamotrigine steady-state concentrations were determined by high-performance liquid chromatography on a reverse-phase column.

Results: There were no statistically significant differences in lamotrigine serum concentrations between the two groups, although formulation B had slightly higher mean concentration values (formulation A: 3.97±4.1 μg/mL; formulation B: 5.78±2.7 μg/mL). Dissolution profiles of the two formulations were similar in the pH 1.2 dissolution medium; however, the dissolution profiles of formulation B were outside the dissolution limit (≥85% at 15 minutes) in the pH 4.5 and 6.8 dissolution media.

Conclusions: No significant changes in the serum concentrations of lamotrigine were seen between the two investigated formulations. There is no evidence to suggest that the differences in dissolution profiles at pH 4.5 and pH 6.8 affect the therapeutic efficacy of the formulations. It is evident that the doses of test formulation given to the patients were higher as a consequence of common assumption that generic products have a lower absorption rate, which is proven unnecessary in this study. This investigation was a pilot study and thus further investigations with a larger sample size are necessary to determine if there is a connection between dissolution profiles and the therapeutic effect of investigated formulations.

Pattern of P450 expression at the human blood-brain barrier: roles of epileptic condition and laminar flow

PURPOSE

P450 enzymes (CYPs) play a major role in hepatic drug metabolism. It is unclear whether these enzymes are functionally expressed by the diseased human blood-brain barrier (BBB) and are involved in local drug metabolism or response. We have evaluated the cerebrovascular CYP expression and function, hypothesizing possible implication in drug-resistant epilepsy.

METHODS

CYP P450 transcript levels were assessed by cDNA microarray in primary endothelial cultures established from a cohort of brain resections (n = 12, drug-resistant epilepsy EPI-EC and aneurism domes ANE-EC). A human brain endothelial cell line (HBMEC) and non-brain endothelial cell line (HUVEC) were used as controls. The effect of exposure to shear stress on CYP expression was evaluated. Results were confirmed by Western blot and immunohistochemistry on brain specimens. Endothelial drug metabolism was assessed by high performance liquid chromatography (HPLC-UV).

RESULTS

cDNA microarray showed the presence of CYP enzymes in isolated human primary brain endothelial cells. Using EPI-EC and HBMEC we found that CYP mRNA levels were significantly affected by exposure to shear stress. CYP3A4 protein was overexpressed in EPI-EC (290 ± 30%) compared to HBMEC and further upregulated by shear stress exposure. CYP3A4 was increased in the vascular compartment at regions of reactive gliosis in the drug-resistant epileptic brain. Metabolism of carbamazepine was significantly elevated in EPI-EC compared to HBMEC.

DISCUSSION

These results support the hypothesis of local drug metabolism at the diseased BBB. The direct association between BBB CYP enzymes and the drug-resistant phenotype needs to be further investigated.

Development of a dissolution test for lamotrigine in tablet form using an ultraviolet method

A dissolution test for tablets containing 100 mg of lamotrigine was developed and validated. The dissolution test was applied to compare the dissolution profile of Neural® with the reference product Lamictal®. The analysis procedure was carried out using a simple ultraviolet method at 267 nm. After the determination of solubility and sink conditions, the parameters selected were paddles at 50 rpm, 900 mL of 0.01 M hydrochloric acid, and 30 minutes duration (single point). This method was validated for specificity, linearity, accuracy, precision and robustness. Lamotrigine stability was also evaluated in dissolution medium.

Bioanalytical applications using supercritical fluid techniques

The bioanalytical applications of supercritical fluid techniques, such as supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC), are of increasing interest. The main role of these techniques is in the sample preparation and separation of biologically active compounds, particularly drugs and their metabolites, as well as endogenous compounds. An insight is given into the different types of extracting fluids and modifiers, detectors, stationary phases, mobile phases and collection strategies. A critical discussion is presented on the existing state of the art concerning the applications of SFC and SFE with a specific focus on its advantages and limitations in the bioanalytical field. New developments and the possibilities for routine work in the near future are also covered.