Therapeutic drug monitoring of seven psychotropic drugs and four metabolites in human plasma by HPLC–MS

Simultaneous quantification of 55 psychotropic drugs and metabolites in human plasma with a fast UPLC-MS/MS method

OBJECTIVES

Therapeutic drug monitoring is strongly recommended for psychotropic drugs, which present a strong inter- and intra-individual variability due to multiple factors like inflammatory state, smoking, diet, drug interactions due to polypharmacy, and genetic profile. The aim of this study was to develop and validate a fast, simple, and sensitive method allowing the simultaneous quantification of a large number of psychotropic drugs.

METHODS

After a simple sample preparation with a one-step protein precipitation, a total of 55 compounds, including 22 antidepressants, 18 antipsychotics, 2 other psychotropic drugs (bupropion and nefopam), and their metabolites, was separated on a Waters Acquity HSS T3 ultra-performance liquid chromatography column, and subsequently detected and quantified by a triple quadrupole Quantis mass spectrometer with electrospray ionization operated in positive mode.

RESULTS

Total run time was only 5.7 min. Limits of detection ranged from 0.01 to 0.18 µg/L depending on compound. Measuring ranges were from 0.195 to 1000 µg/L depending on compound, and were defined according to therapeutic ranges. Inter- and intra-assay precisions values were less than 15 %. After validation, this method was successfully applied in daily practice for therapeutic drug monitoring of polymedicated psychiatric patients.

CONCLUSION

We developed and validated one of the most sensitive and complete UPLC-MS/MS methods in psychopharmacology, allowing the simultaneous determination of 55 psychotropic drugs in only 5.7 min after a simple sample preparation. This method has been successfully used in daily practice for therapeutic drug monitoring of psychiatric patients and is especially useful in polymedicated patients.

[Therapeutic drug monitoring of olanzapine]

Olanzapine, atypical antipsychotic, is used to treat schizophrenia and bipolar disorder. Its therapeutic drug monitoring (TDM) is quite commonly done. Olanzapine is well absorbed orally (bioavailability: 85 %), with peak plasma occurring between 4 and 6hours after oral administration. It is extensively metabolized by different hepatic enzymes (including CYP1A2 and CYP2D6 isoforms) to a large number of inactive metabolites, and its half-life is between 30 and 60hours. No specific therapeutic range, or threshold concentration could not be a consensus, but the higher intra- and interindividual variability, as well as the existence of studies suggesting a correlation between circulating concentrations of olanzapine and occurrence of therapeutic relapse or toxic phenomena appear to justify the STP for this molecule. Given these data, the interest of the STP was evaluated for this molecule to: recommended with therapeutic window of 20μg/L to 80μg/L.

[Therapeutic drug monitoring of clozapine]

Clozapine is a prototypical atypical antipsychotic used to treat severe schizophrenia and for which a therapeutic drug monitoring (TDM) is quite commonly proposed. Clozapine is rapidly absorbed (maximum concentration reached within 1 to 4hours), and is extensively metabolized in the liver by CYP1A2 to an active metabolite (and to a lesser extent, to inactive metabolites via other enzymes). Its half-life is 8 to 16h. A therapeutic range has been proposed for clozapine as some studies have reported both a relationship between low plasmatic concentrations and resistance to treatment (threshold level is likely between 250 and 400μg/L), and a relationship between high plasmatic concentrations and an increase in the occurrence of toxicity (alert level=1000μg/L). Given the data obtained in different studies, the TDM was evaluated for this molecule, to recommended.

Personalizing atomoxetine dosing in children with ADHD: what can we learn from current supporting evidence

PURPOSE

There is marked heterogeneity in treatment response of atomoxetine in patients with attention deficit/hyperactivity disorder (ADHD), especially for the pediatric population. This review aims to evaluate current evidence to characterize the dose-exposure relationship, establish clinically relevant metrics for systemic exposure to atomoxetine, define a therapeutic exposure range, and to provide a dose-adaptation strategy before implementing personalized dosing for atomoxetine in children with ADHD.

METHODS

A comprehensive search was performed across electronic databases (PubMed and Embase) covering the period of January 1, 1985 to July 10, 2022, to summarize recent advances in the pharmacokinetics, pharmacogenomics/pharmacogenetics (PGx), therapeutic drug monitoring (TDM), physiologically based pharmacokinetics (PBPK), and population pharmacokinetics (PPK) of atomoxetine in children with ADHD.

RESULTS

Some factors affecting the pharmacokinetics of atomoxetine were summarized, including food, CYP2D6 and CYP2C19 phenotypes, and drug‒drug interactions (DDIs). The association between treatment response and genetic polymorphisms of genes encoding pharmacological targets, such as norepinephrine transporter (NET/SLC6A2) and dopamine β hydroxylase (DBH), was also discussed. Based on well-developed and validated assays for monitoring plasma concentrations of atomoxetine, the therapeutic reference range in pediatric patients with ADHD proposed by several studies was summarized. However, supporting evidence on the relationship between systemic atomoxetine exposure levels and clinical response was far from sufficient.

CONCLUSION

Personalizing atomoxetine dosage may be even more complex than anticipated thus far, but elucidating the best way to tailor the non-stimulant to a patient's individual need will be achieved by combining two strategies: detailed research in linking the pharmacokinetics and pharmacodynamics in pediatric patients, and better understanding in nature and causes of ADHD, as well as environmental stressors.

A Small Footprint and Robust Interface for Solid Phase Microextraction and Mass Spectrometry Based on Vibrating Sharp-Edge Spray Ionization

Combining solid phase microextraction (SPME) and mass spectrometry (MS) analysis has become increasingly important to many bioanalytical, environmental, and forensic applications due to its simplicity, rapid analysis, and capability of reducing matrix effects for complex samples. To further promote the adoption of SPME-MS based analysis and expand its application scope calls for efficient and convenient interfaces that couple the SPME sample handling with the efficient analyte ionization for MS. Here, we report a novel interface that integrates both the desorption and the ionization steps in one device based on the capillary vibrating sharp-edge spray ionization (cVSSI) method. We demonstrated that the cVSSI is capable of nebulizing liquid samples in a pulled-tip glass capillary with a battery powered function generator. The cVSSI device allows the insertion of a SPME probe into the spray capillary for desorption and then direct nebulization of the desorption solvent in situ. With the integrated interface, we have demonstrated rapid MS analysis of drug compounds from serum samples. Quantitative determination of various drug compounds including metoprolol, pindolol, acebutolol, oxprenolol, capecitabine, and irinotecan was achieved with good linearity (R² = 0.97-0.99) and limit of detection ranging from 0.25 to 0.59 ng/mL without using a high voltage source. Only 3.5 μL of desorption solvent and 3 min desorption time were needed for the present method. Overall, we demonstrated a portable SPME-MS interface featuring high sensitivity, short analysis time, small footprint, and low cost, which makes it an attractive method for many applications requiring sample cleanup including drug compound monitoring, environmental sample analysis, and forensic sample analysis.

Determination of atomoxetine levels in human plasma using LC-MS/MS and clinical application to Chinese children with ADHD based on CPIC guidelines

The Clinical Pharmacogenetic Implementation Consortium (CPIC) guidelines for personalized atomoxetine therapy are based on the CYP2D6 genotype information and the peak plasma concentrations of atomoxetine. Therefore, a highly rapid, sensitive, and reproducible method is critical for the clinical implementation of the guidelines. In this study, an LC-MS/MS approach was developed and validated for the determination of atomoxetine levels in human plasma using atomoxetine-d3 as the internal standard. Samples were prepared by simple protein precipitation method with MeOH. The analyte was separated using a Kinetex C18 column (2.1 mm × 50 mm, 2.6 μm, Phenomenex) with a flow rate of 0.25 mL min^-1, using a gradient elution. A MeOH and water solution containing 5 mM ammonium acetate and 0.1 mM formic acid (pH 6.26) was used as the mobile phase and successfully solved the problem of inconsistent retention time between the plasma samples and the solution samples of atomoxetine. Detection was performed under positive-electrospray-ion multiple reaction-monitoring mode using the 256.4 → 43.8 and 259.3 → 47.0 transitions for atomoxetine and atomoxetine-d3, respectively. Linearity was achieved using an extremely wide range, from 0.500 to 2000 ng mL^-1 in plasma. The intra- and inter-batch precision and accuracy, dilution accuracy, recovery, and stability of the method were all within the acceptable limits and no matrix effect was observed. With a complex needle wash solution containing ACN : MeOH : isopropanol : H₂O (4 : 4:1 : 1, v/v/v/v), carryover contamination was eliminated successfully. This method was successfully implemented on pediatric patients with attention-deficit/hyperactivity disorder and provided valuable information to enable clinicians to do dose selection and titration.

Lab-in-a-pencil graphite: A 3D-printed microfluidic sensing platform for real-time measurement of antipsychotic clozapine level

A novel lab-in-a-pencil graphite microfluidic sensing electrode (μFSE) was fabricated for real-time flow injection measurement of the antipsychotic drug clozapine (Clz). A simple, low-cost, and reusable μFSE was obtained by using 3D printing of a microfluidic chamber integrated with a flat pencil graphite without the need to utilize complex technologies. The μFSE has tubular geometry with 800 μm diameter, where the solution continuously flows in the holes of flat pencil graphite electrodes. Under optimized conditions, this device offers fast and effective Clz detection with good analytical features. A linear calibration curve in the range of 0.5 to 10 μM Clz was obtained with good sensitivity (0.01275 μA μM^-1) and detection limit (24 nM). Finally, we demonstrate the applicability of our lab-fabricated microfluidic electrochemical device by monitoring Clz in serum samples at low concentrations.

Validation of a quick and simple chromatographic method for simultaneous quantification of sertraline, escitalopram, risperidone and paliperidone levels in the human plasma

Simultaneous quantification of multiple psychiatric drugs is important for the therapeutic drug monitoring of psychiatric patients. In addition, it would be highly advantageous if the method could be simple, straightforward, and not time-consuming. A 200 µl plasma sample was deproteinized, drugs were separated by a ZORBAX Eclipse XDB-Phenyl column with the mobile phase composed of acetonitrile and 0.1 % formic acid in water (60:40, v/v), and recorded in the MRM mode by using a positive electrospray source with tandem mass spectrometry detection. The dynamic range was 2-256 ng/ml for all the analyzed drugs, except escitalopram (8-256 ng/ml). Quality control samples were prepared in quintuplicates in three relevant concentrations for each drug. Coefficients of determination (R2 ) were higher than 0.99, while the relative difference between nominal and measured concentrations (RE) and CV were lower than 15% for all targets. High performance liquid chromatography coupled with the mass detector (HPLC-MS/MS) method for simultaneous determination of sertraline, escitalopram, risperidone and paliperidone in human plasma was validated with respect to selectivity, linearity, accuracy, precision, matrix effect and stability. This method has significant advantages in terms of low sample volume (200 µl), short preparation time (3 hours) and short runtime per sample (4 minutes).

A Comprehensive Review on Importance and Quantitation of Atypical Antipsychotic Drugs and their Active Metabolites in Commercial Dosage Forms

Background:

Schizophrenia is a severe mental illness that affects more than twenty-one million people throughout the world. Schizophrenia also causes early death. Schizophrenia and other related psychotic ailments are controlled by the prescription of antipsychotic drugs, which act by blocking certain chemical receptors in the brain and thus relieves the symptoms of psychotic disorder. These drugs are present in the different dosage forms in the market and provided in a certain amount as per the need of the patients.

Objective:

Since such medications treat mental disorders, it is very important to have a perfect and accurate dose so that the risk factor is not affected by a higher or lower dose, which is not sufficient for the treatment. For accurate assay of these kinds of drugs, different analytical methods were developed ranging from older spectrophotometric techniques to latest hyphenated methods.

Results:

The current review highlights the role of different analytical techniques that were employed in the determination and identification of antipsychotic drugs and their metabolites. Techniques such as spectrophotometry, fluorimetry, liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography, and gas chromatography-mass spectrometry employed in the method development of such antipsychotic drugs were reported in the review. Different metabolites, identified using the hyphenated techniques, were also mentioned in the review. The synthesis pathways of few of the metabolites were mentioned.

Conclusion:

The review summarizes the analyses of different antipsychotic drugs and their metabolites. A brief introduction of illnesses and their symptoms and possible medications were highlighted. Synthesis pathways of the associated metabolites were also mentioned.

Multiplexed therapeutic drug monitoring of antipsychotics in dried plasma spots by LC-MS/MS

In this work, a convenient method for the therapeutic monitoring of seven common antipsychotic drugs in "dried plasma spot" samples has been developed. It is based on the liquid chromatography tandem mass spectrometry technique, operating in multiple reaction monitoring mode, and a straightforward procedure for the simultaneous extraction of all antipsychotics in a single step, with high extraction yield. The method was fully validated with proper accuracy, precision, selectivity and sensitivity, for all the drugs. Limits of quantification were 0.12, 1.09, 1.46, 1.47, 5.70, 1.32, 1.33 µg/L for haloperidol, aripiprazole, olanzapine, quetiapine, clozapine, risperidone, and paliperidone, respectively. Accuracy, intra- and interday precision values were <10% for all drugs at all concentration levels examined. The method was tested in the analysis of 30 plasma samples from real patients for each drug. The proposed analytical approach, by combining practical and logistical advantages of microsampling with liquid chromatography tandem mass spectrometry analytical performance, could offer an ideal strategy for accurate and timely therapeutic drug monitoring of antipsychotic drugs in most clinical settings, even in remote centers and/or in out-patient settings, bringing so many potential improvements in psychiatric patient care.

High-sensitivity detection of therapeutic drugs in complex biofluids using a packed ballpoint-electrospray ionization technique

A simple and sensitive C₁₈ packed ballpoint-electrospray ionization (PBP-ESI) technique was developed for biofluid analysis. In this technique, the configuration of a commercial ballpoint consisting of a hollow chamber, an intermediate socket, and a metal ball was fully exploited. The rear-end hollow chamber was used for loading C₁₈ adsorbent and sample, and the front metal ball served as a spray emitter for online ionization. The good electrical conductivity of the metal body allowed high voltage to be conveniently applied to the ballpoint without inserting the electrode into the solution for electrical connection. Urine sample was directly analyzed with the C₁₈ packed ballpoint; plasma and whole blood samples were premixed with C₁₈ adsorbent before being packed into the ballpoint for detection. As a result of the sample cleanup by C₁₈ adsorbent, the salt matrix in the urine sample as well as the phospholipid and protein matrices in plasma and whole blood samples was significantly reduced. The lower limits of quantitation (LLOQs) for urine, plasma, and whole blood samples reached the subnanogram-per-milliliter level. Graphical abstract.

Optimization of chromatographic systems for analysis of selected psychotropic drugs and their metabolites in serum and saliva by HPLC in order to monitor therapeutic drugs

Retention, separation selectivity and system efficiency of selected basic psychotropic drugs (clozapine, aripiprazole, vortioxetine and zolpidem) and drug metabolites (desmethylclozapine, clozapine N-oxide and dehydroaripiprazole) on Hydro RP, Phenyl-Hexyl and Polar RP columns were studied. Mobile phases containing methanol or acetonitrile as organic modifiers, acetate buffer at pH 3.5 and addition of diethylamine (DEA) as a silanol blocker were applied. Significant differences in the retention, peak shapes and systems’ efficiency of the investigated compounds were obtained depending on the tested chemically bonded stationary phases with various ligands. Based on the obtained results the Phenyl-Hexyl column was selected for analysis of the drugs and their metabolites in human serum and saliva samples. Solid phase extraction (SPE) was applied for sample pre-treatment. The best SPE-HPLC-DAD procedure was used for simultaneous analysis of clozapine, aripiprazole and their metabolites in body fluids. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was applied for confirmation of the presence of the investigated compounds in biological samples. The lower limit of quantification (LLOQ) of clozapine obtained using the proposed method was 10 ng/mL. The validated method for determining the presence of clozapine and its main metabolite was successfully applied in therapeutic drug monitoring.

Photodegradation Study of Sertindole by UHPLC-ESI-Q-TOF and Influence of Some Metal Oxide Excipients on the Degradation Process

The evaluation of the influence of the excipients present in the pharmaceutical formulations on the drug stability is an important part of quality control of medicines. One of the most commonly applied group of excipients are pigments, such as titanium dioxide or various forms of iron oxides, which are well-known photocatalytic agents. Therefore, the photostability of an atypical antipsychotic drug sertindole and the influence of pigments commonly used in the pharmaceutical formulations (FeOOH, Fe₂O₃, and TiO₂) on this process were studied. The quantitative and qualitative analysis of the process was performed with the use of ultra high pressure liquid chromatography with diode array detection (UHPLC-DAD) system coupled with a high resolution hybrid electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer. Sertindole turned out to be a highly photolabile molecule. Overall 18 transformation products were found, mainly formed as a consequence of dechlorination, hydroxylation, and dehydrogenation. In all the experiments, except the TiO₂-mediated photocatalysis, the product of chlorine substitution with a hydroxyl group was the major product. The presence of Fe₂O₃ and TiO₂ accelerated the degradation process, while FeOOH served as its inhibitor. The experiments conducted with the use of the pharmaceutical formulations confirmed the catalytic activity of the used excipients. The exploration of the obtained phototransformation profiles with the use of principal component analysis (PCA) revealed that the presence of both iron oxides could influence the qualitative and quantitative aspect of the studied processes. In silico assessment of the properties showed that the transformation products are generally less toxic to rodents, possess lower hERG blocking potential, but could be more mutagenic than the parent molecule.

Simultaneous determination of six antipsychotics, two of their metabolites and caffeine in human plasma by LC-MS/MS using a phospholipid-removal microelution-solid phase extraction method for sample preparation

A simple and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated in human plasma for the simultaneous determination of aripiprazole (ARI) and its metabolite dehydro-aripiprazole (DARI); olanzapine (OLA), risperidone (RIS), paliperidone (PAL), quetiapine (QUE), clozapine (CLO) and caffeine (CAF). CAF is included to the method because it can have an influence on drug metabolism due to competitive inhibition. The above mentioned compounds and their isotope-labeled internal standards were extracted from 200 µL human plasma samples by both, effective phospholipids-eliminating three-step microelution-solid-phase extraction (µ-SPE) and protein precipitation (PPT) for comparison. A combination of formic acid (0.2%)-acetonitrile (pH 3.0; 65:35, v/v) was used as mobile phase and the chromatogram was run under gradient conditions at a flow rate of 0.6 mL/min. Run time lasted 6 min, followed by a re-equilibration time of 3 min. All analytes were monitored by mass spectrometric detection operating in multiple reaction monitoring mode and the method was validated covering the corresponding therapeutic ranges: 0.18-120 ng/mL for ARI, 0.25-80 ng/mL for DARI, 1.00-100 ng/mL for OLA, 0.70-60 ng/mL for RIS, 0.20-30 ng/mL for PAL, 0.50-160 ng/mL for QUE, 0.50-1000 ng/mL for CLO, and finally 1200-3700 ng/mL for CAF. The method was validated based on the recommendations of regulatory agencies through tests of precision, accuracy, extraction recovery, identity confirmation, trueness, matrix effect, process efficiency, stability, selectivity, linearity and carry-over effect fulfilling the guideline requirements. Our µ-SPE method results in the elimination of more than 99% of early eluting and more than 92% of late-eluting phospholipids compared to PPT. Additionally, the method was successfully applied for quantifying ARI and OLA plasma concentrations from healthy volunteers.

Use of high-pH (basic/alkaline) mobile phases for LC-MS or LC-MS/MS bioanalysis

High-pH or basic/alkaline mobile phases are not commonly used in LC-MS or LC-MS/MS bioanalysis because of the deeply rooted concern with column instability and reduced detection sensitivity for basic compounds in high-pH mobile phases owing to charge neutralization. With the advancement of LC column technology and the wide recognition of the "wrong-way-round" phenomena, high-pH mobile phases are more and more used in LC-MS or LC-MS/MS bioanalysis to improve chromatographic peak shape, retention, selectivity, resolution, and detection sensitivity, not only for basic compounds, but also for many other compounds. In this article, the benefits, practical considerations, application examples and cautions for using high-pH mobile phases in LC-MS or LC-MS/MS bioanalysis are reviewed, with a focus on quantification. Furthermore, the future trends in this field are also envisaged. A total of 84 references are cited in this review.

Spectroscopic methods to analyze drug metabolites

Drug metabolites have been monitored with various types of newly developed techniques and/or combination of common analytical methods, which could provide a great deal of information on metabolite profiling. Because it is not easy to analyze whole drug metabolites qualitatively and quantitatively, a single solution of analytical techniques is combined in a multilateral manner to cover the widest range of drug metabolites. Mass-based spectroscopic analysis of drug metabolites has been expanded with the help of other parameter-based methods. The current development of metabolism studies through contemporary pharmaceutical research are reviewed with an overview on conventionally used spectroscopic methods. Several technical approaches for conducting drug metabolic profiling through spectroscopic methods are discussed in depth.

Determination of antipsychotic drugs in hospital and wastewater treatment plant samples by gas chromatography/tandem mass spectrometry

The development and performance evaluation of a method for the simultaneous determination of six antipsychotic drugs in hospital effluents and wastewater treatment plants (WWTP) samples are herein presented. The method involves an off-line mixed mode (reversed-phase and strong cation exchange) solid phase extraction (SPE) with gas chromatography (GC) coupled to tandem mass spectrometry (MS/MS). The present methodology was validated following internationally accepted criteria, and the studied parameters included selectivity, linearity, limits of detection (LOD) and quantitation (LLOQ), instrumental limits, precision and accuracy, stability and recovery. The procedure was linear for concentrations ranging from 0.1 to 10μg/L (0.02 to 2μg/L for haloperidol), with determination coefficients higher than 0.99 for all analytes. Intra- and inter-day precision was lower than 15% for all analytes at the studied concentrations, while accuracy remained between a ±15% interval. Recoveries ranged from 31% to 83%. Low LODs were achieved, between 2 and 10ng/L, allowing a reliable identification of all analytes at trace levels, using only 50mL as sample volume. All studied parameters complied with the defined criteria and the method was successfully applied to gather preliminary results of the determination of antipsychotics on hospital effluents and on influent and effluent of WWTPs, opening perspectives for the study of their fate in the aquatic environment.

Micelle enhanced and native spectrofluorimetric methods for determination of sertindole using sodium dodecyl sulfate as sensitizing agent

Two stability indicating spectrofluorimetric methods were developed and validated for the determination of sertindole (SER) in the presence of its acid and oxidative degradates at λ(ex) 257 nm and λ(em) 335 nm. Method A was based on measuring the native fluorescence of SER using isopropanol as solvent. Method B was based on the enhancement of native fluorescence of SER quenched in aqueous media by using micellar microenvironment created by sodium dodecyl sulfate (SDS) anionic micelles using Britton Robinson Buffer (BRB) pH3.29 as solvent. Different factors affecting fluorescence intensity; both native and enhanced, were carefully studied to reach the optimum conditions of measurements. The proposed spectrofluorimetric methods were validated in accordance with ICH guidelines and were successfully applied for the determination of SER in bulk powder and pharmaceutical preparation with high sensitivity and stability indicating power. They were also statistically compared to the manufacturer methods with no significant difference in performance.

Electrically stimulated liquid phase microextraction combined with differential pulse voltammetry: a new and efficient design for in situ determination of clozapine from complicated matrices

Electromembrane extraction combined with differential pulse voltammetry for in situ determination of clozapine from complicated matrices.

Ultrasensitive label-free immunoassay for optical determination of amitriptyline and related tricyclic antidepressants in human serum

The present work focuses on the development of a label-free and ultrasensitive immunoassay for the detection of the drug amitriptyline in human serum. Reflectometric interference spectroscopy is used as the detection method, providing a simple, but highly sensitive optical setup. Amitriptyline is a common antidepressant; however, it has a small therapeutic window and can cause severe side effects in case of wrong dosage. Therefore, it is highly recommended for therapeutic drug monitoring to control the drug level. The limit of detection for this optical immunosensor was determined in buffer (0.3 μg/L) and in human serum (0.5 μg/L). It has become evident that this assay can compete with HPLC measurements. For drug concentrations at a normal level or above, the sample can be diluted up to 1:100. Especially for limited sample volumes, this is a great advantage. The sensor surface shows very high stability, and together with the regeneration solution 80 measurement cycles can be performed on each transducer chip. Cross-reactivity experiments indicate that a sum determination of several tricyclic antidepressants is possible.

Can valproic acid be an inducer of clozapine metabolism?

INTRODUCTION

Prior clozapine studies indicated no effects, mild inhibition or induction of valproic acid (VPA) on clozapine metabolism. The hypotheses that (i) VPA is a net inducer of clozapine metabolism, and (ii) smoking modifies this inductive effect were tested in a therapeutic drug monitoring study.

METHODS

After excluding strong inhibitors and inducers, 353 steady-state total clozapine (clozapine plus norclozapine) concentrations provided by 151 patients were analyzed using a random intercept linear model.

RESULTS

VPA appeared to be an inducer of clozapine metabolism since total plasma clozapine concentrations in subjects taking VPA were significantly lower (27% lower; 95% confidence interval, 14-39%) after controlling for confounding variables including smoking (35% lower, 28-56%).

DISCUSSION

Prospective studies are needed to definitively establish that VPA may (i) be an inducer of clozapine metabolism when induction prevails over competitive inhibition, and (ii) be an inducer even in smokers who are under the influence of smoking inductive effects on clozapine metabolism.

A novel approach to quantitative LC-MS/MS: therapeutic drug monitoring of clozapine and norclozapine using isotopic internal calibration

Therapeutic drug monitoring (TDM) requires timely results in order to be clinically helpful. Such assays, when carried out using mass spectrometry-based methods, typically involve a batched sample approach with multipoint calibration. Isotopic internal calibration offers the possibility of open-access mass spectrometric analysis with consequent shortening of turnaround times. We measured plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in (1) external quality assessment (EQA) samples (N = 22) and (2) patient samples (N = 100) using liquid chromatography-tandem mass spectrometry with isotopic internal calibration (ICAL-LC-MS/MS). Analyte concentrations were calculated from graphs of the response of three internal calibrators (clozapine-D4, norclozapine-D8, and clozapine-D8) against concentration. Precision (% RSD) and accuracy (% nominal concentrations) for the ICAL-LC-MS/MS method were <5 % and 104-112 %, respectively for both analytes. There was excellent agreement with consensus mean and with 'spiked' values on analysis of the EQA samples (R (2) = 0.98 and 0.97, respectively, inclusive of clozapine and norclozapine results). In the patient samples, comparison against traditionally calibrated HPLC-UV and LC-MS/MS methods showed excellent agreement (R (2) = 0.97 or better) with small albeit significant mean differences (<0.041 and <0.042 mg/L for clozapine and norclozapine, respectively). These differences probably reflect discrepancies in the in-house preparation of calibrators and/or interference in the UV method. Internal calibration offers a novel and attractive alternative to traditionally calibrated batch analysis in analytical toxicology. The method described has been validated for use in the high-throughput TDM of clozapine and norclozapine, and allows for (1) same-day reporting of results and (2) significant cost savings.

Stability-indicating chromatographic methods for the determination of sertindole

In this work, two chromatographic methods have been developed and validated for the determination of sertindole (an antipsychotic agent) in the presence of its oxidative degradation product. Sertindole was subjected to stress stability studies, including acid, alkali, oxidative, photolytic and thermal degradation. The chromatographic methods included the use of thin-layer chromatography (TLC-densitometry) and high-performance liquid chromatography (HPLC). The TLC method employed aluminum TLC plates precoated with silica gel G.F254 as the stationary phase and methanol-ethyl acetate-33% ammonia (1:9:0.1, by volume) as the mobile phase, and the chromatograms were scanned at 227 nm. The developed HPLC method used a reversed-phase C18 column with isocratic elution. The mobile phase was composed of phosphate buffer pH 3.0-acetonitrile-triethylamine (45:55:0.03, by volume) and run at a flow rate of 1.0 mL/min. Quantitation was achieved with ultraviolet detection at 256 nm. The linearity ranges were found to be 2-14 µg/band and 5-200 µg/mL for TLC and HPLC, respectively. The developed methods were validated according to the International Conference on Harmonization guidelines and were applied for bulk powder and dosage forms.

A rapid and sensitive liquid chromatography-tandem mass spectrometric assay for duloxetine in human plasma: Its pharmacokinetic application

This paper describes a simple, rapid and sensitive liquid chromatography–tandem mass spectrometry assay for the determination of duloxetine in human plasma. A duloxetine stable labeled isotope (duloxetine d₅) was used as an internal standard. Analyte and the internal standard were extracted from 100 μL of human plasma via solid phase extraction technique using Oasis HLB cartridges. The chromatographic separation was achieved on a C₁₈ column by using a mixture of acetonitrile–5 mM ammonium acetate buffer (83:17, v/v) as the mobile phase at a flow rate of 0.9 mL/min. The calibration curve obtained was linear (r²≥0.99) over the concentration range of 0.05–101 ng/mL. Multiple-reaction monitoring mode (MRM) was used for quantification of ion transitions at m/z 298.3/154.1 and 303.3/159.1 for the drug and the internal standard, respectively. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. A run time of 2.5 min for each sample made it possible to analyze more than 300 plasma samples per day. The proposed method was found to be applicable to clinical studies.

Aripiprazole

Aripiprazole is an atypical antipsychotic drug which belongs to the benzisoxazole derivatives. Aripiprazole is available in many salts and polymorphs forms. X-ray diffraction, IR spectroscopy, and DSC could be used for differentiating the polymorphs of aripiprazole. Some instrumental methods of analysis such as UV spectrophotometer, HPTLC, HPLC, and CE can be applied for analyzing aripiprazole and its impurities. Chromatography methods that have an MS/MS detector is the method of choice for analyzing aripiprazole and its metabolites. Bioavailability studies of the polymorphs of aripiprazole and their pharmaceutical preparations are very important to optimize the formulations of the dosage forms.