Simultaneous screening and quantitation of alpidem, zolpidem, buspirone and benzodiazepines by dual-channel gas chromatography using electron-capture and nitrogen-phosphorus detection after solid-phase extraction

Development and evaluation of a simple and easy HPLC-UV system simultaneously suitable for determination of 24 anti-epileptic drugs in plasma

This paper aims to establish a simple and easy HPLC system coupled with UV detector suitable for simultaneous determination of 24 antiepileptic drugs in human plasma. Optimized chromatographic separation was performed on a ZORBAX Eclipse Plus-C18 (4.6 mm×150 mm, 3.5 μm) column with acetonitrile and 5 mM potassium dihydrogen phosphate water solution as mobile phase. 24 antiepileptic drugs were divided into three groups and eluted with different gradient procedures, respectively. The column temperature was maintained at 35 °C and the detection wavelength was set at 210 nm. Plasma was processed with ethyl acetate or acetonitrile. The calibration curves of 24 antiepileptic drugs demonstrated good linearity within the test range (r > 0.996). The intra- and inter-batch precision and accuracy were all less than 15%, while extraction recoveries were in the range of 74.57%∼90.89% with the RSD values less than 15%. The validated methods have been successfully applied to determination of some antiepileptic drugs in rat or patient plasma. Those results indicated that the developed methods were simple and easy, and could be suitable for the determination of 24 antiepileptic drugs in plasma just by changing the gradient elution procedures of mobile phase. This article is protected by copyright. All rights reserved.

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.

Development and Validation of a Reversed-Phase HPLC Method for the Estimation of Zolpidem in Bulk Drug and Tablets

In the present study an isocratic reversed-phase high-performance liquid chromatography method was developed for the estimation of zolpidem in bulk drug and pharmaceutical dosage forms. The quantification was carried out on C18columns. A mixture of acetonitrile-ammonium acetate (pH=8.0, 0.02 M) (60 : 40 v/v) was used as the mobile phase, at flow rate of 1.0 mL/min and the determination wavelength at 245 nm. The retention time of zolpidem was found to be 3–5 min. The validation of the proposed method was carried out for specificity, linearity, accuracy, precision, limit of detection, limit of quantification, and robustness. The linear dynamic range was from 2.5 to 30 μg mL−1. Regression equation was found to bey=0.1416x+0.0183with correlation coefficientr=0.9996. The percentage recovery obtained for zolpidem was greater than 96.5%. Limit of quantification and limit of detection were found to be 2.5 μg mL−1and 0.83 μg mL−1, respectively. The developed method can be used for routine quality control analysis of zolpidem in tablet formulations.

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.

Mass spectrometric investigation of buspirone drug in comparison with thermal analyses and MO-calculations

The buspirone drug is usually present as hydrochloride form of general formula C(21)H(31)N(5)O(2).HCl, and of molecular weight (MW)=421.96. It is an analgesic anxiolytic drug, which does not cause sedative or depression of central nervous system. In the present work it is investigated using electron impact mass spectral (EI-MS) fragmentation at 70 eV, in comparison with thermal analyses (TA) measurements (TG/DTG and DTA) and molecular orbital calculation (MOC). Semi-empirical MO calculation, PM3 procedure, has been carried out on buspirone both as neutral molecule (in TA) and the corresponding positively charged species (in MS). The calculated MOC parameters include bond length, bond order, particle charge distribution on different atoms and heats of formation. The fragmentation pathways of buspirone in EI-MS lead to the formation of important primary and secondary fragment ions. The mechanism of formation of some important daughter ions can be illuminated from comparing with that obtained using electrospray ESIMS/MS mode mass spectrometer through the accurate mass measurement determination. The losses of the intermediate aliphatic part (CH2)4 due to cleavage of N-C bond from both sides is the primary cleavage in both techniques (MS and TA). The PM3 provides a base for fine distinction among sites of initial bond cleavage and subsequent fragmentation of drug molecule in both TA and MS techniques; consequently the choice of the correct pathway of such fragmentation knowing this structural session of bonds can be used to decide the active sites of this drug responsible for its chemical, biological and medical reactivity.

HPLC determination of midazolam and its three hydroxy metabolites in perfusion medium and plasma from rats

A new, simple, rapid, sensitive, and repeatable isocratic reverse-phase HPLC method was developed and validated for simultaneous determination of midazolam and its main three hydroxylated metabolites, i.e. 1'-hydroxymidazolam, 4-hydroxymidazolam, and 1',4-dihydroxymidazolam in rat liver perfusate and also plasma. Diazepam was used as an internal standard to ensure precision and accuracy of this method. Analytes were extracted from alkalinized samples into diethyl ether using single-step liquid-liquid extraction. A C18 analytical column and a mobile phase composed of acetonitrile and sodium acetate buffer were used for the chromatographic separation with UV detection. Limits of detection varied between 7.9 and 19.6 microg/L for midazolam and its hydroxy metabolites. The overall recovery for the analytes exceeded 92%, for concentrations twice the limits of detection. The intra- and inter-day precision at three different concentrations never exceeded 8 and 11% variation, respectively. This method is applicable for modeling and description of possible pharmacological interactions on rat (CYP3A1/2) or human (CYP3A4/5) cytochrome P450 enzymes.

Flow injection analysis with tubular membrane ion-selective electrode and coated wires for buspirone hydrochloride

New Plastic membrane ion-selective electrode for buspirone hydrochloride based on buspironium tetraphenylborate was prepared. The electrode exhibited mean slope of calibration graph of 58.4 mV per decade of BusCl concentration at 25 degrees C. The electrode can be used within the concentration range 6.3 x 10(-5) - 10(-2) M BusCl at a pH range of 2.5-7.0. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal temperature coefficient of the electrode, amounting to 0.00056 V degrees C(-1). The electrode showed a very good selectivity for BusCl with respect to a number of inorganic cations, sugars and amino acids. The electrode was applied to the potentiometric determination of the buspirone ion and its pharmaceutical preparation under batch and flow injection conditions. Also, buspirone was determined by conductimetric titrations. Graphite rod, copper and silver coated wire electrodes were prepared and characterized as sensors for the drug under investigation.

Gas chromatography nitrogen phosphorous detection (GC-NPD) assay of tofisopam in human plasma for pharmacokinetic evaluation

Tofisopam (1-(3,4-dimethoxyphenyl)-4-methyl-5-ethyl-7,8-dimethoxy-5H-2,3-benzodiazepine) has been shown to be an effective anxiolytic agent in the wide-ranging clinical practice. A high sensitive gas chromatography nitrogen phosphorous detection (GC-NPD) bioanalytical method was developed and validated for the purpose of pharmacokinetic study of tofisopam. A liquid-liquid extraction method was used for the sample preparation. The mean recovery for tofisopam was 69.8% and the inter- and intra-day precision values were well below the 15% limit established for bioanalytical methods. A similar compound, girizopam was used as internal standard. The assay was linear in the 5-500 ng/ml range corresponding to therapeutically relevant plasma levels. The concentrations of the compound were measured in the plasma samples of 12 healthy male volunteers and the pharmacokinetic parameters were determined from the plasma concentration-time data. A rapid absorption and distribution, relatively short biological half-life and considerable inter-individual variation in the plasma concentration levels of parent compound were the main characteristics of the pharmacokinetics of tofisopam. According to these results, the new (GC-NPD) bioanalytical method proved to be capable of measuring concentration of tofisopam in human plasma and was successfully applied in a single dose pharmacokinetic study.

Quantification of clotiazepam in human plasma by gas chromatography–mass spectrometry

An analytical procedure was developed and validated for the quantification of clotiazepam in human plasma. After subjecting plasma samples to solid-phase extraction, the extract was evaporated and the residue re-constituted. An aliquot of the mixture was injected onto a gas chromatography-mass spectrometry system. The detector response was linear for clotiazepam concentrations in the range of 5-200 ng/ml. Intra- and inter-day precision for the assay over the concentration range was below 13.1 and 13.5%, and the accuracy ranged between 99.0-107.9% and 92.4-101.3%, respectively. The drug was found to be stable under various processing conditions used. The method is applicable to human pharmacokinetic studies of clotiazepam.

Quantification of zolpidem in human plasma by liquid chromatography–electrospray ionization tandem mass spectrometry

A simple and robust method for quantification of zolpidem in human plasma has been established using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS). Es-citalopram was used as an internal standard. Zolpidem and internal standard in plasma sample were extracted using solid-phase extraction cartridges (Oasis HLB, 1 cm3/30 mg). The samples were injected into a C8 reversed-phase column and the mobile phase used was acetonitrile-ammonium acetate (pH 4.6; 10 mm) (80:20, v/v) at a flow rate of 0.7 mL/min. Using MS/MS in the selected reaction-monitoring (SRM) mode, zolpidem and Es-citalopram were detected without any interference from human plasma matrix. Zolpidem produced a protonated precursor ion ([M+H]+) at m/z 308.1 and a corresponding product ion at m/z 235.1. The internal standard produced a protonated precursor ion ([M+H]+) at m/z 325.1 and a corresponding product ion at m/z 262.1. Detection of zolpidem in human plasma by the LC-ESI MS/MS method was accurate and precise with a quantification limit of 2.5 ng/mL. The proposed method was validated in the linear range 2.5-300 ng/mL. Reproducibility, recovery and stability of the method were evaluated. The method has been successfully applied to bioequivalence studies of zolpidem.

Rapid and highly sensitive liquid chromatography/electrospray ionization tandem mass spectrometry method for the quantitation of buspirone in human plasma: application to a pharmacokinetic study

A rapid and sensitive method for the quantitation of buspirone in human plasma by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was developed. Plasma samples were treated by liquid-liquid extraction with methyl tert-butyl ether (MTBE). The chromatographic separation was performed isocratically on a reversed-phase Shiseido C18 column (50 mm x 2.0 mm, 3 microm) with a mobile phase of acetonitrile/0.1% acetic acid (1:1, v/v). The acquisition was performed in multiple reaction monitoring (MRM) mode, monitoring the transitions m/z 386 --> 122 for buspirone and m/z 409 --> 238 for amlodipine (the internal standard). The method was validated to determine its specificity, recovery, limit of quantitation, accuracy and precision. The lower limit of quantitation was 0.02 ng/mL with a relative standard deviation of less than 10%. The present method provides an accurate, precise and sensitive tool for buspirone and was successfully applied to a pharmacokinetic study in eight subjects.

Quantification of zolpidem in human plasma by high-performance liquid chromatography with fluorescence detection

A simple, reliable HPLC method with fluorescence detection (excitation 320 and emission 388 nm) was developed and validated for quantitation of zolpidem in human plasma. Following a single-step liquid-liquid extraction, the analyte and internal standard (quinine) were separated using an isocratic mobile phase on a reversed-phase C(18) column. The lower limit of quantitation was 1.8 ng/mL, with a relative standard deviation of less than 5%. A linear dynamic range of 1.8-288 ng/mL was established. This HPLC method was validated with between-batch and within-batch precision of 1.7-4.8 and 1.2-2.3%, respectively. The between-batch and within-batch accuracy was 95.3-100.4 and 95.5-102.7%, respectively. Frequently coadministered drugs did not interfere with the described methodology. Stability of zolpidem in plasma was excellent, with no evidence of degradation during sample processing (autosampler) and 30 days storage in a freezer. This validated method is simple and repeatable enough to be used in pharmacokinetic studies.

Simultaneous determination of clobazam and its major metabolite in human plasma by a rapid HPLC method

A rapid and specific HPLC method has been developed and validated for simultaneous determination of clobazam, the anticonvulsant agent, and its major metabolite in human plasma. The sample preparation was a liquid-liquid extraction with tuloene yielding almost near 100% recoveries of two compounds. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6mm column, using a mixture of a phosphate buffer (pH 3.5; 10mM)-acetonitrile (70:30, v/v), in isocratic mode at 2 ml/min at a detection wave-length of 228 nm. The calibration curves were linear (r(2)>0.998) in the concentration range of 5-450 ng ml(-1). The lower limit of quantification was 5 ng ml(-1) for two compounds studied. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 0.89-9.1% and 2.1-10.1% R.S.D., respectively. The developed procedure was applied to assess the pharmacokinetics of clobazam and its major metabolite following administration of a single 10mg oral dose of clobazam to healthy volunteers.

Determination and in-process control of zolpidem synthesis by high-performance liquid chromatography

A high-performance liquid chromatographic assay with diode-array detection has been developed for the in-process control of zolpidem synthesis and for the analysis of the drug and its synthetic intermediates. The separation uses a 4.6mm i.d. reversed-phase Kromasil C(18) (150 mm) column, 5 microm particle size with a gradient elution mode of acetonitrile and 0.02 M NH(4)OAc (adjusted to pH 8.0) as the mobile phase (flow rate 1.0 mlmin(-1)). The analysis is performed in 12 min. The method is simple, rapid and highly specific.

Direct injection HPLC method for the determination of selected benzodiazepines in plasma using a Hisep column

A direct plasma injection HPLC method has been developed for the determination of selected benzodiazepines (nitrazepam, clobazam, oxazepam, lorazepam). The method uses an analytical hydrophobic shielded phase (Hisep) column equipped with a Hisep guard column, are easy to perform and requires 20 ul of a filtered plasma sample. The chromatographic run time is less than 15 min using a mobile phase of 15:85 v/v acetonitrile-0.18 M ammonium acetate pH 2.5. The method is good for 175 injections before replacement of the guard column. The method was linear in the range 0.5-18 ug ml(-1) (r>0.99, n=6) for the analytes with R.S.D. less than 10.82%. Interday and intraday variability were found to be less than 14%. The limits of detection and quantitation were 0.16 (s/n>3) and 0.5 ug ml(-1) (s/n>10), respectively, for each of the four benzodiazepines.

Automated solid-phase extraction and liquid chromatography-electrospray ionization-mass spectrometry for the determination of flunitrazepam and its metabolites in human urine and plasma samples

A sensitive and specific method using reversed-phase liquid chromatography coupled with electrospray ionization-mass spectrometry (LC-ESI-MS) has been developed for the quantitative determination of flunitrazepam (F) and its metabolites 7-aminoflunitrazepam (7-AF), N-desmethylflunitrazepam (N-DMF) and 3-hydroxyflunitrazepam (3-OHF) in biological fluids. After the addition of deuterium labelled standards of F,7-AF and N-DMF, the drugs were isolated from urine or plasma by automated solid-phase extraction, then chromatographed in an isocratic elution mode with a salt-free eluent. The quantification was performed using selected ion monitoring of protonated molecular ions (M+H(+)). Experiments were carried out to improve the extraction recovery (81-100%) and the sensitivity (limit of detection 0.025 ng/ml for F and 7-AF, 0.040 ng/ml for N-DMF and 0.200 ng/ml for 3-OHF). The method was applied to the determination of F and metabolites in drug addicts including withdrawal urine samples and in one date-rape plasma and urine sample.

Application of liquid chromatography-tandem mass spectrometry to the analysis of benzodiazepines in blood

A sensitive and selective high-performance liquid chromatography/atmospheric pressure chemical ionisation tandem mass spectrometry (HPLC/APCI-MS/MS) method for the simultaneous detection of 18 benzodiazepines and metabolites in human blood is described. The procedure utilises butyl chloride extraction at alkaline pH followed by reversed-phase liquid chromatography. The technique is suitable for screening analyses and confirmation of identity of the benzodiazepines at their lowest reported therapeutic concentrations using 500 microL of blood. The method has been successfully applied in forensic cases involving low concentrations of benzodiazepines.

Analysis of tofisopam in human serum by column-switching semi-micro high-performance liquid chromatography and evaluation of tofisopam bioequivalency

A rapid and sensitive column-switching semi-micro HPLC method is described for the direct analysis of tofisopam in human serum. The sample (100 microL) was directly injected onto the precolumn (Capcell Pak MF Ph-1), where unretained proteins were eluted to waste. Tofisopam was then eluted into an enrichment column using 13% acetonitrile in 50 mM phosphate buffer (pH 7.0) containing 5 mM sodium octanesulfonate and subsequently into the analytical column using 43% acetonitrile in 0.1% phosphoric acid containing 5 mM sodium octanesulfonate. The detection limit (2 ng/mL), good precision (CV < or = 4.2%) and speed (total analysis time 24 min) of the present method were sufficient for drug monitoring. This method was successfully applied to a bioequivalence test of two commercial tofisopam tablets.

Determination of antiepileptic drugs in biological material

Current analytical methodologies applied to the determination of antiepileptic drugs in biological material are reviewed. The role of chromatographic techniques is emphasized. Special attention is focused on new chemical entities as well as current trends such as high-speed liquid chromatographic techniques, hyphenated techniques and electrochromatography techniques. A review with 542 references.

Simultaneous determination of fifteen low-dosed benzodiazepines in human urine by solid-phase extraction and gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric method was developed for the simultaneous analysis of 15 low-dosed benzodiazepines, both parent compounds and their corresponding metabolites, in human urine. The target compounds are alprazolam, alpha-hydroxyalprazolam, 4-hydroxyalprazolam, flunitrazepam, 7-aminoflunitrazepam, desmethylflunitrazepam, flurazepam, hydroxyethylflurazepam, nitrogen-desalkylflurazepam, ketazolam, oxazepam, lormetazepam, lorazepam, triazolam and alpha-hydroxytriazolam. Nitrogen-methylclonazepam is used as the internal standard. The urine sample preparation involves enzymatic hydrolysis of the conjugated metabolites with Helix pomatia beta-glucuronidase for 1 h at 56 degrees C followed by solid-phase extraction on a phenyl-type column. The extracted benzodiazepines are subsequently analyzed on a polydimethylsiloxane column using on-column injection to enhance sensitivity. The extraction efficiency exceeded 80% for all compounds except for oxazepam, lorazepam and 4-hydroxyalprazolam which had recoveries of about 60%. The LODs ranged from 13 to 30 ng/ml in the scan mode and from 1.0 to 1.7 ng/ml in the selected ion monitoring (SIM) mode. Linear calibration curves were obtained in the concentration ranges from 50 to 1000 ng/ml in the scan mode and from 5 to 100 ng/ml in the SIM mode. The within-day and day-to-day relative standard deviations at three different concentrations never exceeded 15%.

Simple and sensitive high-performance liquid chromatographic method for the determination of 1,5-benzodiazepine clobazam and its active metabolite N-desmethylclobazam in human serum and urine with application to 1,4-benzodiazepines analysis

A HPLC-UV determination of clobazam and N-desmethylclobazam in human serum and urine is presented. After simple liquid-liquid extraction with dichloromethane the compounds and an internal standard diazepam were separated on a Supelcosil LC-8-DB column at ambient temperature under isocratic conditions using the mobile phase: CH3CN-water-0.5 M KH2PO4-H3PO4 (440:540:20:0.4, v/v and 360:580:60:0.4, v/v for serum and urine, respectively). The detection was performed at 228 nm with limits of quantification of 2 ng/ml for serum and 1 ng/ml for urine. Relative standard deviations for intra- and inter-assay precision were found below 8% for both compounds for all the tested concentrations. The described procedure may be easily adapted for several 1,4-benzodiazepines.

Chromatographic separation of 2,3-benzodiazepines

A review of chromatographic methods for the determination of 2,3-benzodiazepines (2,3-BZs) is presented. The determinations are performed to investigate the presence of potential impurities in drug substances and to study their pharmacokinetic profile in biological samples, either in animals or in humans. Several methods dealt with a pretreatment of samples, i.e., liquid-liquid extraction by using a variety of solvents, solid-phase extraction, direct injection of specimens into the chromatographic apparatus. Different chromatographic techniques have been used. High-performance liquid chromatography allows optimal sensitivity and specificity by using ultraviolet or diode array detection methods. Gas chromatography-mass spectrometry and gas chromatography with nitrogen-phosphorous or electron-capture detectors have been also reported. Suitable methods for the separation of enantiomers of 2,3-BZs have been described. Thin-layer chromatography has been shown to be capable to isolate analytes from biological samples as urine or faeces. The reported chromatographic techniques are currently applied to define the metabolic pathways of 2,3-BZs in experimental and clinical studies.

Benzodiazepine findings in blood and urine by gas chromatography and immunoassay

Gas chromatography (GC) and immunoassay techniques applied to blood and urine specimens were compared for the screening of benzodiazepines in postmortem forensic toxicology. Five hundred and six such successive postmortem cases in which both urine and peripheral blood was sent for toxicological analysis by the medical examiners were selected. The urine specimens were tested by the Emit((R)) d.a.u. Benzodiazepine Assay, and in parallel, the blood and urine specimens were screened for benzodiazepine drugs and their metabolites by an established automated dual-column GC method. The lowest number of positives (153) was obtained when immunoassay was performed without enzyme hydrolysis. When urine samples were hydrolysed before immunoassay, the number of positives increased to 175. The highest number of positives (200) was obtained in urine by GC, and the screening of blood by GC yielded 185 quantitative results. Despite the urine GC screening produced the most positives, the quantitative screening of the blood by GC appears to be the most efficient approach in postmortem forensic toxicology, considering the fact that although urine findings confirm the presence of the drug, quantitative results in urine are irrelevant to acute toxicity.

Equine metabolism of buspirone studied by high-performance liquid chromatography/mass spectrometry

The metabolism and urinary excretion of a 100 mg dose of the non-sedating anxiolytic drug buspirone was examined using high-performance liquid chromatography/electrospray ionization mass spectrometry in the positive ion mode. In addition to a significant proportion of unchanged buspirone we were able to detect three major metabolite classes. These were identified as monohydroxy, dihydroxy and dihydroxymethoxy products. Detection of the metabolites and the parent drug was possible in all the urine samples collected (1-12 h) post-administration.

GC/MS determination of zolpidem in postmortem specimens in a voluntary intoxication

An ingestion of an unknown quantity of Ivadal (zolpidem) tablets in a case of drug abuse is described. The authors report a new and fast method of analysing and determining the zolpidem concentration in postmortem specimens. Quantitation of zolpidem was performed by ethyl acetate extraction from alkalinized body fluids before GC/MS analysis. The analyses were performed without any complex sample clean-up steps and with little sample material. Postmortem concentrations of zolpidem in body fluids are given. The proposed method is a rapid procedure of analysis in cases of deliberate poisoning with the sedative-hypnotic drug, zolpidem.

Determination of zolpidem in serum microsamples by high-performance liquid chromatography and its application to pharmacokinetics in rats

A single-solvent extraction step high-performance liquid chromatographic method is described for quantitating zolpidem in rat serum microsamples (50 microl). The separation used a 2.1 mm I.D. reversed-phase OD-5-100 C18 column, 5 microm particle size with an isocratic mobile phase consisting of methanol-acetonitrile-26 mM sodium acetate buffer (adjusted to pH 2.0 with 40% phosphoric acid) containing 0.26 mM tetrabutylammonium phosphate (13:10:77, v/v/v). The detection limit was 3 ng/ml for zolpidem using an ultraviolet detector operated at 240 nm. The recovery was greater than 87% with analysis performed in 12 min. The method is simple, rapid, and applicable to pharmacokinetic studies of zolpidem after administering two intravenous bolus doses (1 and 4 mg/kg) in rats.

Effect of activated charcoal alone or given after gastric lavage in reducing the absorption of diazepam, ibuprofen and citalopram

AIMS

The efficacy of activated charcoal alone, and gastric lavage followed by charcoal in reducing the absorption of diazepam, ibuprofen and citalopram was studied in healthy volunteers.

METHODS

In a randomized cross-over study with three phases, nine healthy volunteers were administered single oral doses of 5 mg diazepam, 400 mg ibuprofen and 20 mg citalopram, taken simultaneously after an overnight fast. Thirty minutes later, the subjects were assigned to one of the following treatments: 200 ml water (control), 25 g activated charcoal as a suspension in 200 ml water or gastric lavage followed by 25 g charcoal in suspension given through the lavage tube. Plasma concentrations of diazepam, ibuprofen and citalopram were determined up to 10 h.

RESULTS

The AUC(0,10 h) of diazepam was reduced by 27% (P<0.05) by both charcoal alone and charcoal combined with lavage. The increase in plasma diazepam concentration from 0.5 h onwards was prevented by both interventions (P</=0.05), whereas the Cmax of diazepam was not significantly affected by either treatment. The AUC(0, 10 h) of ibuprofen was reduced by 49% (P<0.05) after the combination treatment and by 30% (P<0.05) after charcoal alone, but there was no significant difference between these two treatments. Both charcoal alone and the combination treatment were equally effective in preventing the increase in plasma ibuprofen from 0.5 h onwards (P<0.01). The Cmax of ibuprofen was reduced by 45% (P<0.05) and by 21% (P=NS), respectively. The AUC(0,10 h) of citalopram was reduced by 51% (P<0.05) after both charcoal alone and charcoal combined with lavage, and the Cmax by 52% (P<0.05) and 54% (P<0.05), respectively. The increase in plasma citalopram concentration from 0.5 h onwards was reduced by about 50% (P<0.01) by both interventions.

CONCLUSIONS

Activated charcoal alone and charcoal combined with lavage showed similar efficacy in preventing the absorption of diazepam, ibuprofen and citalopram. These results suggest that gastric lavage needs not be routinely performed before administration of charcoal.

Determination of benzodiazepine in tablets studied by thermal desorption gas chromatography

Thermal desorption gas chromatography (TDGC) was applied to the analysis of 13 kinds of tablets containing different benzodiazepines (BZDs). An aliquot of ground tablet sample (0.1-1 mg), weighed into a platinum sample cup, was placed in a furnace pyrolyzer where the sample was heated up to a suitable temperature (150-500 degrees C) so that BZD was desorbed from the sample powder. The desorbed components of BZDs were immediately transferred into a separation column by a helium carrier gas without using any trapping techniques. The desorbed components were identified by TDGC-mass spectrometry. Among various BZDs, fludiazepam, nimetazepam and mexazolam in tablet samples were determined by the present method. Thus, the results obtained were in good agreement with the specified values. Correlation coefficients of the calibration lines for the three BZDs' ranged from 0.997 to 0.999 for several micrograms to about 10 microg of the components. Relative standard deviations of this method were < 4.1% for 4 or 5 runs.

Determination of buspirone and 1-(2-pyrimidinyl)-piperazine (1-PP) in human plasma by capillary gas chromatography

Two separate gas chromatographic methods for the determination of buspirone and its active metabolite, 1-(2-pyrimidinyl)-piperazine (1-PP) in human plasma are described. Both procedures involve solid-phase extraction (the packing material of the cartridges used was C8 for buspirone and a mixed-mode sorbent for 1-PP), injection of the sample into a gas chromatograph equipped with a fused-silica capillary column and a nitrogen-phosphorus detector, and analysis with temperature programming (from 220 degrees C to 285 degrees C for buspirone and from 138 degrees C to 285 degrees C for 1-PP). The coating material of the analytical column was 5% diphenyl dimethyl silicone for buspirone and 50% diphenyl dimethyl silicone for 1-PP. Zolpidem was used as an internal standard in the buspirone assay and 1-phenylpiperazine in the 1-PP assay. Recovery of buspirone and 1-PP averaged 98% and 89%, respectively, and the limit of quantification was 0.2 ng/mL for both compounds. The between-run coefficients of variation ranged from 3.2% to 9.4% and from 2.9% to 8.6% for samples spiked with three different concentrations of buspirone and 1-PP, respectively. The suitability of these assays for pharmacokinetic studies was shown by analyzing timed plasma samples from volunteers after ingestion of a single therapeutic dose of buspirone (10 mg).

Clinical pharmacokinetics and pharmacodynamics of buspirone, an anxiolytic drug

Buspirone is an anxiolytic drug given at a dosage of 15 mg/day. The mechanism of action of the drug is not well characterised, but it may exert its effect by acting on the dopaminergic system in the central nervous system or by binding to serotonin (5-hydroxytryptamine) receptors. Following a oral dose of buspirone 20 mg, the drug is rapidly absorbed. The mean peak plasma concentration (Cmax) is approximately 2.5 micrograms/L, and the time to reach the peak is under 1 hour. The absolute bioavailability of buspirone is approximately 4%. Buspirone is extensively metabolised. One of the major metabolites of buspirone is 1-pyrimidinylpiperazine (1-PP), which may contribute to the pharmacological activity of buspirone. Buspirone has a volume of distribution of 5.3 L/kg, a systemic clearance of about 1.7 L/h/kg, an elimination half-life of about 2.5 hours and the pharmacokinetics are linear over the dose range 10 to 40 mg. After multiple-dose administration of buspirone 10 mg/day for 9 days, there was no accumulation of either parent compound or metabolite (1-PP). Administration with food increased the Cmax and area under the plasma concentration-time curve (AUC) of buspirone 2-fold. After a single 20 mg dose, the Cmax and AUC increased 2-fold in patients with renal impairment as compared with healthy volunteers. The Cmax and AUC were 15-fold higher for the same dose in patients with hepatic impairment compared with healthy individuals. The half-life of buspirone in patients with hepatic impairment was twice that in healthy individuals. The pharmacokinetics of buspirone were not affected by age or gender. Coadministration of buspirone with verapamil, diltiazem, erythromycin and itraconazole substantially increased the plasma concentration of buspirone, whereas cimetidine and alprazolam had negligible effects. Rifampicin (rifampin) decreased the plasma concentrations of buspirone almost 10-fold.

Lack of effect of terfenadine on the pharmacokinetics of the CYP3A4 substrate buspirone

The effects of terfenadine, a non-sedating antihistamine on the pharmacokinetics and pharmacodynamics of buspirone, a CYP3A4 substrate, were investigated in a randomised, placebo-controlled, two-phase cross-over study. Ten healthy volunteers took either 120 mg terfenadine or matched placebo orally once daily for 3 days. On day 3, 10 mg buspirone was taken orally. Plasma concentrations of buspirone were measured up to 18 hr and its pharmacodynamic effects up to 8 hr. Terfenadine slightly but not significantly increased plasma concentrations of buspirone. No psychomotor deterioration was observed during the terfenadine phase. In conclusion, terfenadine did not significantly affect the pharmacokinetics of buspirone, a CYP3A4 substrate shown to be very susceptible to interactions with CYP3A4 inhibitors. Thus, terfenadine is expected to have little effect on the pharmacokinetics of CYP3A4 substrates in general.

Interactions of buspirone with itraconazole and rifampicin: effects on the pharmacokinetics of the active 1-(2-pyrimidinyl)-piperazine metabolite of buspirone

The effects of inhibition and induction of the metabolism of buspirone on the plasma concentrations of 1-(2-pyrimidinyl)-piperazine (a piperazine metabolite), the principal active metabolite of buspirone, were investigated. Two separate randomized, placebo-controlled cross-over studies with two phases were carried out in healthy volunteers. In Study I, six subjects took itraconazole 200 mg daily or matched placebo orally for 4 days. On day 4, 10 mg buspirone was administered orally. In study II, six subjects took rifampicin 600 mg daily or matched placebo orally for 5 days. On day 6, 30 mg buspirone was administered orally. Buspirone and piperazine metabolite concentrations in plasma were determined by gas chromatography. Itraconazole decreased the mean AUC of the piperazine metabolite by 50% (P<0.05) and the Cmax by 57% (P<0.05) compared with placebo, whereas the mean AUC and Cmax of unchanged buspirone were increased 14.5-fold (P<0.05) and 10.5-fold (P<0.05), respectively, by itraconazole. Rifampicin had no significant effect on the AUC of the piperazine metabolite, but it increased the mean Cmax of the piperazine metabolite by 35% (P=0.08). The mean AUC and Cmax of parent buspirone were reduced by 91% (P<0.05) and 85% (P<0.05), respectively, by rifampicin. The mean ratio of the AUC of the piperazine metabolite to that of buspirone was decreased 34-fold (P<0.05) by itraconazole and increased 7.6-fold (P<0.05) by rifampicin. In conclusion, itraconazole and rifampicin caused only relatively minor changes in the plasma concentrations of the active piperazine metabolite of buspirone, although they had drastic effects on the concentrations of parent buspirone.

Grapefruit juice substantially increases plasma concentrations of buspirone

BACKGROUND

Buspirone has a low oral bioavailability because of extensive first-pass metabolism. The effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of orally administered buspirone is not known.

METHODS

In a randomized, 2-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water 3 times a day for 2 days. On day 3, each subject ingested 10 mg buspirone with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 hour and 1 1/2 hours after buspirone administration. Timed blood samples were collected up to 12 hours after ingestion, and the effects of buspirone were measured with 6 psychomotor tests up to 8 hours after ingestion.

RESULTS

Grapefruit juice increased the mean peak plasma concentration of buspirone 4.3-fold (range, 2-fold to 15.6-fold; P < .01) and the mean area under the plasma buspirone concentration-time curve 9.2-fold (range, 3-fold to 20.4-fold; P < .01). The time of the peak concentration (tmax) of buspirone increased from 0.75 to 3 hours (P < .01), and the elimination half-life (t1/2) was slightly increased (P < .01) by grapefruit juice. A significant increase in the pharmacodynamic effects of buspirone by grapefruit juice was seen only in subjective overall drug effect (P < .01).

CONCLUSIONS

Grapefruit juice considerably increased plasma buspirone concentrations. The probable mechanism of this interaction is delayed gastric emptying and inhibition of the cytochrome P450 3A4-mediated first-pass metabolism of buspirone caused by grapefruit juice. Concomitant use of buspirone and at least large amounts of grapefruit juice should be avoided.