A liquid chromatography/tandem mass spectrometry method for the simultaneous quantification of isoniazid and ethambutol in human plasma

Natural deep eutectic solvent for the simultaneous derivatization and microextraction of isoniazid from human plasma

BACKGROUND

Personalized medicine is a rapidly revolving field that offers new opportunities for tailoring disease treatment to individual patients. The main idea behind this approach is to carefully select safe and effective medications and treatment plant based on each patient's unique pharmacokinetic profile. Isoniazid is a first-line anti-tuberculosis drug that has interindividual variability in its metabolic processing, leading to significant differences in plasma concentrations among patients receiving equivalent doses. This variability necessitates the creation of individualized treatment regimens as part of personalized medicine to achieve more effective therapy.

RESULTS

In this work, a deep eutectic solvent-based liquid-liquid microextraction approach for the separation and determination of isoniazid in human plasma by high-performance liquid chromatography with UV-Vis detection was developed for the first time. A new natural deep eutectic solvent based on thymol as a hydrogen bond donor and 4-methoxybenzaldehyde as a hydrogen bond acceptor was proposed as the extraction solvent. The developed microextraction procedure assumed two simultaneous processes during the mixing of the sample and extraction solvent: the derivatization of the polar analyte in the presence of 4-methoxybenzaldehyde (component of the natural deep eutectic solvent) with the formation of a hydrophobic Schiff base (1); mass transfer of the Schiff base from the sample phase to the extraction solvent phase (2). Under optimal conditions, the limits of detection and quantification were 20 and 60 μg L-1, respectively. The RSD value was <10 %, the extraction recovery was 95 %.

SIGNIFICANCE

In this work, the possibility of isoniazid derivatization in the natural deep eutectic solvent phase with the formation of the Schiff base was presented for the first time. The approach provided the separation and preconcentration of polar isoniazid without the use of expensive derivatization agents and solid-phase extraction cartridges. The formation of the Schiff base was confirmed by mass spectrometry.

Rational tuning of binding properties of pillar [5] arene-based sensing material by synergistic effect and its application for fluorescent turn-on detection of isoniazid and controlled reversible morphology

Isoniazid (INH) is crucial in the treatment of tuberculosis; however, its overuse may induce significant gastrointestinal and hepatic side effects. On October 27, 2017, the International Agency for Research on Cancer, under the auspices of the World Health Organization, published a list of carcinogens for preliminary collation and reference. Isoniazid was categorized as a Group 3 carcinogen. The efficient detection of INH poses an important and challenging task. In this study, a "synergistic effect" is incorporated into the pillar (Yamagishi and Ogoshi, 2018) [5] arene-based macrocyclic host (DPA) by strategically attaching bis-p-hydroxybenzoic acid groups to the opposite ends of the pillar (Yamagishi and Ogoshi, 2018) [5] arene. This combination endows DPA with a reversible and selective fluorescence response to isoniazid. Additionally, DPA exhibits excellent analytical capabilities for isoniazid, including speed and selectivity, with a detection limit as low as 4.85 nM. Concurrently, DPA can self-assemble into a microsphere structure, which is convertible into micrometer-sized tubular structures through host-guest interactions with isoniazid. The introduction of a competitive guest, trimethylamine, enables the reversion to its microsphere structure. Consequently, this study presents an innovative and straightforward synthetic approach for smart materials that facilitates the reversible morphological transition between microspheres and microtubes in response to external chemical stimuli. This discovery provides a valuable strategy for designing "synergistic effects" in constructing trace-level isoniazid-responsive interfaces, with potential applications across various fields, such as controlled drug delivery.

Push forward LC-MS-based therapeutic drug monitoring and pharmacometabolomics for anti-tuberculosis precision dosing and comprehensive clinical management

The spread of tuberculosis (TB), especially multidrug-resistant TB and extensively drug-resistant TB, has strongly motivated the research and development of new anti-TB drugs. New strategies to facilitate drug combinations, including pharmacokinetics-guided dose optimization and toxicology studies of first- and second-line anti-TB drugs have also been introduced and recommended. Liquid chromatography-mass spectrometry (LC-MS) has arguably become the gold standard in the analysis of both endo- and exo-genous compounds. This technique has been applied successfully not only for therapeutic drug monitoring (TDM) but also for pharmacometabolomics analysis. TDM improves the effectiveness of treatment, reduces adverse drug reactions, and the likelihood of drug resistance development in TB patients by determining dosage regimens that produce concentrations within the therapeutic target window. Based on TDM, the dose would be optimized individually to achieve favorable outcomes. Pharmacometabolomics is essential in generating and validating hypotheses regarding the metabolism of anti-TB drugs, aiding in the discovery of potential biomarkers for TB diagnostics, treatment monitoring, and outcome evaluation. This article highlighted the current progresses in TDM of anti-TB drugs based on LC-MS bioassay in the last two decades. Besides, we discussed the advantages and disadvantages of this technique in practical use. The pressing need for non-invasive sampling approaches and stability studies of anti-TB drugs was highlighted. Lastly, we provided perspectives on the prospects of combining LC-MS-based TDM and pharmacometabolomics with other advanced strategies (pharmacometrics, drug and vaccine developments, machine learning/artificial intelligence, among others) to encapsulate in an all-inclusive approach to improve treatment outcomes of TB patients.

A high-throughput LC-MS/MS method for simultaneous determination of isoniazid, ethambutol and pyrazinamide in human plasma

RATIONALE

Tuberculosis (TB) remains a challenging global infectious disease, mainly affecting the lungs. First-line anti-TB drugs play a crucial role in slowing down the rapid spread of TB. In addition, the patient might benefit from therapeutic drug monitoring since it has become an accepted clinical tool for optimizing TB treatment.

METHODS

A simple and sensitive liquid chromatography/tandem mass spectrometry method was developed to monitor the plasma level of isoniazid, ethambutol and pyrazinamide in plasma samples. A one-step extraction procedure using an Ostro™ plate was applied, and extracts were analyzed by gradient elution followed by detection on a mass spectrometer by multiple reaction monitoring mode.

RESULTS

The analytes were separated within 4.2 min and over the concentration range of 0.2-10 μg/ml for isoniazid and ethambutol and 1-65 μg/ml for pyrazinamide. The method was successfully validated according to the European Medicine Agency guideline for the selectivity, linearity and lower limit of detection, precision and accuracy, matrix effect, extraction recovery, carryover, dilution integrity and stability, and applied for quantification of analytes in clinical samples from TB patients.

CONCLUSIONS

The presented method allows sensitive and reproducible determination of selected anti-TB drugs with advantages such as low sample volume requirement, short run time of analysis, one-step sample preparation procedure with capabilities for phospholipids removal, and a low quantification limit as well as a high degree of selectivity.

Chromatographic Methods for the Determination of Rifampicin, Isoniazid, Pyrazinamide, Ethambutol, and Main Metabolites in Biological Samples: A Review

Bioanalytical methods are used to quantify drugs and their metabolites in biological samples in order to determine bioequivalence, perform pharmacokinetic and bioavailability studies, and complete therapeutic drug monitoring. The objective of this review paper is to describe bioanalytical methods based on Liquid Chromatography that are used to quantify antitubercular drugs and their metabolites in different biological samples, utilizing scientific literature from 1992 to 2021.

A Simple and Sensitive UPLC–UV Method for Simultaneous Determination of Isoniazid, Pyrazinamide, and Rifampicin in Human Plasma and Its Application in Therapeutic Drug Monitoring

As the first-line clinical drugs for tuberculosis (TB), isoniazid (INH), pyrazinamide (PZA), and rifampicin (RMP) are playing important roles for preventing the rapid spread of TB. Precise quantification of these drugs in biological samples is crucial to evaluate or improve the efficacy of advanced TB drug delivery systems, which are designed for reducing drug resistance, minimizing side effects, etc. Herein, a simple and sensitive method based on UPLC–UV was established and investigated for simultaneous quantification of PZA, INH, and RMP in human plasma and was applied to anti-TB drug therapeutic drug monitoring. The analytes were implemented on an HSS T3 C18 column at 40°C. The separation was performed with a gradient elution with methanol–acetonitrile–water (3:3:94) at 0.1 ml/min. The analysis only involved plasma with a small volume of 100 µL and a rapid one-step protein precipitation with methanol–acetonitrile (1:1). The results showed that the calibration curves for INH, PZA, and RMP were linear in a range of 0.5–20 μg/ml, 5–60 μg/ml, and 5–60 μg/ml, respectively. The intra- and inter-day precisions were both smaller than 15%, and the lower limit of quantitation (LLOQ) was identifiable and reproducible at 0.5 μg/ml for INH and 5 μg/ml for both PZA and RMP, respectively. The target drugs in plasma were stable after 21 days of storage at −80°C. The results indicated that our developed method is suitable for the simultaneous monitoring of INH, PZA, and RMP in human plasma.

Simultaneous determination of three antituberculosis drugs in the serum of patients with spinal tuberculosis by capillary electrophoresis

The pharmacokinetic variations of a single drug in an antituberculosis regimen are associated with acquired drug resistance and therapy failure. This study aimed to develop a simple and effective method for monitoring the serum levels of isoniazid (INH), rifampicin (RFP), and pyrazinamide (PZA), three antibiotics used in patients with spinal tuberculosis using capillary electrophoresis (CE). A standard solution of INH, RFP, and PZA was prepared and mixed with serum to prepare the standard curve. The detection limit, quantification limit, precision, stability, repeatability, and sample recovery were determined. Then, INH, RFP, and PZA were measured from the leftover serum samples of all patients with spinal tuberculosis who were treated with 2SHRZ/2.5H2R2Z2 combined with surgery in a tertiary hospital in Qinghai from October 2015 to September 2017. A total of 107 patients with spinal tuberculosis treated using the 2SHRZ/2.5H2R2Z2 regimen combined with surgery were included in this study. All three antibiotics had linear standard curves with high correlation coefficients (R² = 0.9997, 0.9994, and 0.9986). The recovery rates were 98.1% for INH, 96.5% for PZA, and 97.2% for RFP. The results from the serum samples showed that the plasma concentrations of INH (4.989 ± 1.692 μg mL^-1) and RFP (9.400 ± 1.711 μg mL^-1) reached effective therapeutic concentrations in all patients, but not PZA (33.860 ± 1.830 μg mL^-1). The CE method for measuring INH, RFP, and PZA simultaneously in serum samples of patients with spinal tuberculosis is simple, rapid, and sensitive. This method is suitable for the routine monitoring of INH, RFP, and PZA concentrations in the serum of patients with spinal tuberculosis.

Rapid and Sensitive LC-MS/MS Method for Simultaneous Determination of Three First-Line Oral Antituberculosis Drug in Plasma

A bioanalytical method for simultaneous quantification of isoniazid (INH), pyrazinamide (PZA) and ethambutol (EMB) in plasma was developed and validated using high-performance liquid chromatography with tandem mass spectrometry. After extracted by protein precipitation with acetonitrile, the analytes were separated on a Waters XBridge Amide column by isocratic elution with acetonitrile and 5 mM ammonium acetate solution containing 0.3% formic acid (77:23, v/v) at a flow rate of 0.5 mL/min. The detection was carried out on a triple quadrupole tandem mass spectrometer equipped with an electrospray ionization source in positive mode by monitoring the selected ion transitions at m/z 205.2 → 116.1, m/z 137.9 → 121.2, m/z 124.3 → 78.9 and m/z 213.1 → 122.4 for EMB, INH, PZA and EMB-d8 Internal standard (IS), respectively. The calibration curves were linear over the range of 0.0125-2.00 μg/mL for EMB, 0.0625-10.0 μg/mL for INH and 0.250-40.0 μg/mL for PZA. Neither cross-analytes inter-conversion nor matrix effects were observed. The intra- and inter-assay precision (%RSD) values were within 8.80%, and accuracy (%RE) ranged from -11.13 to 13.49%, indicating that the precision and accuracy were well within the acceptable limits of variation. The method would be helpful for analysis of EMB, INH and PZA in plasma samples from clinical pharmacokinetics and therapeutic drug monitoring.

A simple and reliable analytical method for simultaneous quantification of first line antitubercular drugs in human plasma by LCMS/MS

The present study describes the optimization of a simple and reliable method for the determination of four first line antitubercular drugs in human plasma. The studied analytes were isoniazid (H), rifampicin (R), pyrazinamide (Z) and ethambutol (E) in fixed dose combination recommended to patients under the Revised National Tuberculosis Control Programme (RNTCP, India). The analytes were extracted from the human plasma (150 μL) using the single step liquid-liquid extraction approach and were analyzed by liquid chromatography (LC) coupled to tandem mass spectrometry (MS/MS). The method was fully validated, according to USFDA guidelines. A linear range of 0.05-10 μg mL^-1, 0.1-20 μg mL^-1, 0.5-100 μg mL^-1 and 0.05-10 μg mL^-1 for H, R, Z and E respectively was established, presenting determination coefficients above 0.99. Concerning imprecision, the CV was lower than 15% for all analytes. All tested analytes were found to be stable in the samples. Although the values obtained for recovery were above 85%, the method proved to be sensitive, since low detection limits of 0.05 μg mL^-1 for H and E, 0.1 μg mL^-1 for R and 0.5 μg mL^-1 for Z were obtained. The intra-day and inter-day accuracy and imprecision were within CV ±15%. The use of the conventional silica column in the extraction of these compounds through a single step protein precipitation method simplifies the analytical process. In addition due to its simplicity and sensitivity, it can be applied to carry out therapeutic drug monitoring and drug level assessment in human plasma samples. The results of analyte levels are comparable to other reported methods. The method had been successfully applied for simultaneous determination of first line anti-tubercular drugs in pulmonary tubercular patients. The method requires 150 μL of patient plasma and offers low volume for injection (10 μL) and blood sample collection (3 mL) which will be an added advantage for pediatric anti-TB drug level assessment and monitoring.

Longitudinal Pharmacokinetic-Pharmacodynamic Biomarkers Correlate With Treatment Outcome in Drug-Sensitive Pulmonary Tuberculosis: A Population Pharmacokinetic-Pharmacodynamic Analysis

Background

This study aims to explore relationships between baseline demographic covariates, plasma antibiotic exposure, sputum bacillary load, and clinical outcome data to help improve future tuberculosis (TB) treatment response predictions.

Methods

Data were available from a longitudinal cohort study in Malawian drug-sensitive TB patients on standard therapy, including steady-state plasma antibiotic exposure (154 patients), sputum bacillary load (102 patients), final outcome (95 patients), and clinical details. Population pharmacokinetic and pharmacokinetic-pharmacodynamic models were developed in the software package NONMEM. Outcome data were analyzed using univariate logistic regression and Cox proportional hazard models in R, a free software for statistical computing.

Results

Higher isoniazid exposure correlated with increased bacillary killing in sputum (P < .01). Bacillary killing in sputum remained fast, with later progression to biphasic decline, in patients with higher rifampicin area under the curve (AUC)_0-24 (P < .01). Serial sputum colony counting negativity at month 2 (P < .05), isoniazid C_MAX (P < .05), isoniazid C_MAX/minimum inhibitory concentration ([MIC] P < .01), and isoniazid AUC_0-24/MIC (P < .01) correlated with treatment success but not with remaining free of TB. Slower bacillary killing (P < .05) and earlier progression to biphasic bacillary decline (P < .01) both correlate with treatment failure. Posttreatment recurrence only correlated with slower bacillary killing (P < .05).

Conclusions

Patterns of early bacillary clearance matter. Static measurements such as month 2 sputum conversion and pharmacokinetic parameters such as C_MAX/MIC and AUC_0-24/MIC were predictive of treatment failure, but modeling of quantitative longitudinal data was required to assess the risk of recurrence. Pooled individual patient data analyses from larger datasets are needed to confirm these findings.

Development and Application of a LC-MS/MS Method for Simultaneous Quantification of Four First-Line Antituberculosis Drugs in Human Serum

A simple, rapid, and sensitive liquid chromatography (LC)/mass spectrometry (MS) method was established and validated for simultaneous quantitation of pyrazinamide, isoniazid, rifampicin, and ethambutol in human blood sample. Samples were pretreated by a single-step precipitation with acetonitrile. Chromatographic separation was achieved on XSelecT HSS T3 column by gradient elution with a total run time of 5.0 min. MS detection was performed by a triple quadrupole tandem mass spectrometer in the multiple reaction monitoring mode with a positive electrospray ionization source. Isotope-labeled internal standard, especially rifampicin-D8, was applied to adjust for the loss during sample treatment. The established LC-MS/MS method showed a wide analytical range (pyrazinamide: 1.02∼60.0 μg/mL, isoniazid: 0.152∼10.0 μg/mL, rifampicin: 0.500∼30.0 μg/mL, and ethambutol: 0.0998∼5.99 μg/mL) and a good linearity (r > 0.99 for the four analytes) with acceptable accuracy and precision (90.15%∼104.62% and 94.00%∼104.02% for intra- and interaccuracy, respectively; RSD%: <12.46% and <6.43% for intra- and interprecision, respectively). It also showed excellent recoveries (79.24%∼94.16% for all analytes) and absence of significant matrix effect. This method was successfully applied to the quantification of four first-line antituberculosis (anti-TB) drugs, suggesting its suitability for therapeutic drug monitoring in the clinical practices.

Optimization and Validation of a Chromatographic Method for the Quantification of Isoniazid in Urine of Tuberculosis Patients According to the European Medicines Agency Guideline

Isoniazid is a drug that is widely used against tuberculosis. However, it shows high interpatient variability in metabolism kinetics and clinical effect, which complicates the prescription of the medication and jeopardizes the success of the therapy. Therefore, in a specific patient, the pharmacokinetics of the drug must be elucidated to decide the proper dosage and intake frequency to make the drug suitable for therapeutic drug monitoring. This can be performed by the quantification of the drug in urine as this process is non-invasive and allows the effects of long-time exposure to be inferred. The paper describes the development of a micellar liquid chromatographic method to quantify isoniazid in urine samples. Extraction steps were avoided, making the procedure easy to handle and reducing the waste of toxic organic solvents. Isoniazid was eluted in less than 5 min without interference from other compounds of the urine using a mobile phase containing 0.15 SDS⁻12.5% 1-propanol (v/v)⁻Na₂HPO₄ 0.01 M buffered at pH 7, running at 1 mL/min under isocratic mode through a C18 column with the detection wavelength at 265 nm. The method was validated by following the requirements of the Guidelines on Bioanalytical Method Validation issued by the European Medicines Agency (EMA) in terms of selectivity, calibration curve (r² = 0.9998 in the calibration range (0.03⁻10.0 μg/mL), limit of detection and quantification (10 and 30 ng/mL respectively), precision (<16.0%), accuracy (-0.9 to +8.5%), carry-over, matrix effect, and robustness. The developed method was applied to quantify isoniazid in urine samples of patients of an Indian hospital with good results. The method was found to be useful for routine analysis to check the amount of isoniazid in these patients and could be used in its therapeutic monitoring.

Isoniazid: A Review of Characteristics, Properties and Analytical Methods

Isoniazid is a synthetic antimicrobial and one of the most important first-line drugs used in the treatment of tuberculosis. Since it was introduced in the therapy in 1952, the drug remains at the front line of the antituberculosis treatment mainly due to its potency and high selectivity against Mycobacterium tuberculosis. Pharmaceutical analysis and therapeutic drug monitoring of isoniazid in both, pharmaceuticals and biological samples, plays an important role to comprehend aspects regarding to bioavailability, bioequivalence and therapeutic monitoring during patients following-up. In the last case, validated and simple methods are extremely useful for Public Healthy in order to guarantee the drug efficacy, safety and reduce the tuberculosis resistance. Among the available analytical tools, HPLC-based methods coupled to ultraviolet or mass spectroscopy are the most widely used techniques to quantify isoniazid. Therefore, this review highlights the main analytical methods reported in the literature for determination of isoniazid focusing in HPLC-based methods.

Bioanalysis of antitubercular drugs using liquid chromatography

Tuberculosis is a life threatening disease and second to HIV in terms of deaths due to infectious diseases. Drug resistance development of the first-line drugs is a major concern in the treatment of this disease. There is no comprehensive and critical review in the literature of the bioanalytical methods for the determination of anti-tubercular agents from last two decades. This work offers a detailed account on the liquid chromatographic methods reported in the literature for the estimation of various anti-tubercular drugs. Major emphasis is given to sample preparation process, sensitivity of method, chromatographic separation conditions and detection systems used in their bioanalysis.

Simultaneous quantification of isoniazid, rifampicin, ethambutol and pyrazinamide by liquid chromatography/tandem mass spectrometry

A remediable cause of poor treatment response in drug-susceptible tuberculosis (TB) patients may be low plasma levels of one or more of the first-line anti-TB drugs. The aim of this work was to develop an accurate and precise LC-MS/MS method for simultaneous quantification of all four first-line anti-TB drugs in plasma suitable for therapeutic drug monitoring (TDM). To adjust for degradation and losses during sample preparation, isotopically labeled compounds were used as internal standards. Plasma samples spiked with internal standards were extracted using protein precipitation with methanol and acetonitrile. Simultaneous separation of all four drugs was accomplished with a Chromolith Reversed-Phase column and mobile phases consisting of water, methanol, ammonium acetate and formic acid with subsequent mass spectrometric quantification. The linear range of the calibration curve for isoniazid was 0.5-10 mg/L, for rifampicin 0.75-30 mg/L, for ethambutol 0.25-10 mg/L and for pyrazinamide 4-80 mg/L. The lower limit of quantification was 0.5 mg/L, 0.75 mg/L, 0.25 mg/L and 4.0 mg/L, respectively. Precision estimated by the coefficient of variation was <15% for all four drugs. The LC-MS/MS method can readily be used for simultaneous quantification of first-line anti-TB drugs in plasma and is well suited for TDM.

Quantifying Isoniazid Levels in Small Hair Samples: A Novel Method for Assessing Adherence during the Treatment of Latent and Active Tuberculosis

BACKGROUND

Tuberculosis (TB) is the leading cause of death from an infectious pathogen worldwide and the most prevalent opportunistic infection in people living with HIV. Isoniazid preventive therapy (IPT) reduces the incidence of active TB and reduces morbidity and mortality in HIV-infected patients independently of antiretroviral therapy. However, treatment of latent or active TB is lengthy and inter-patient variability in pharmacokinetics and adherence common. Current methods of assessing adherence to TB treatment using drug levels in plasma or urine assess short-term exposure and pose logistical challenges. Drug concentrations in hair assess long-term exposure and have demonstrated pharmacodynamic relevance in HIV.

METHODS

A large hair sample from a patient with active TB was obtained for assay development. Methods to pulverize hair and extract isoniazid were optimized and then the drug detected by liquid chromatography/ tandem mass spectrometry (LC/MS-MS). The method was validated for specificity, accuracy, precision, recovery, linearity and stability to establish the assay's suitability for therapeutic drug monitoring (TDM). Hair samples from patients on directly-observe isoniazid-based latent or active TB therapy from the San Francisco Department of Public Health TB clinic were then tested.

RESULTS

Our LC/MS-MS-based assay detected isoniazid in quantities as low as 0.02ng/mg using 10-25 strands hair. Concentrations in spiked samples demonstrated linearity from 0.05-50ng/mg. Assay precision and accuracy for spiked quality-control samples were high, with an overall recovery rate of 79.5%. In 18 patients with latent or active TB on treatment, isoniazid was detected across a wide linear dynamic range.

CONCLUSIONS

An LC-MS/MS-based assay to quantify isoniazid levels in hair with performance characteristics suitable for TDM was developed and validated. Hair concentrations of isoniazid assess long-term exposure and may be useful for monitoring adherence to latent or active TB treatment in the setting of HIV.

Development and validation of liquid chromatography tandem mass spectrometry method for simultaneous quantification of first line tuberculosis drugs and metabolites in human plasma and its application in clinical study

Rifampicin (RIF) and isoniazid (INH), first line drugs for the treatment of tuberculosis, are known to cause hepatotoxicity as a serious adverse side effect. To further understand the pharmacokinetic parameters of these two drugs, we have developed and validated a rapid, sensitive and selective LC-MS/MS method for simultaneous quantification of RIF, INH and their metabolites 25-desacetylrifampicin (DRIF), acetylisoniazid (AcINH) and isonicotinic acid (INA). Analytes were extracted from 20 μl of plasma using solid-phase extraction (SPE) followed by chromatographic separation on Zorbax SB-Aq column (50 mm × 4.6mm, particle size 5 μm) using stepwise gradient elution of 5mM ammonium acetate and 90% acetonitrile with 0.1% formic acid. Separation of all analytes was achieved in the total run time of 6 min. The analytes were detected under positive ionization mode by multiple reaction monitoring (MRM) and quantification of analytes was performed by using deuterium-labelled internal standard. Excellent linearity (r(2) ≥ 0.995) was achieved for the analytes at different concentration ranges. The method was accurate (90-115%), precise (CV %<14) and specific. Matrix effect was in the range of 93-111% except for INA (40-42%) while recovery from SPE was reproducible (CV %<7.4) in the range of 60-86%. Post-preparative stability (48 h, 6°C autosampler) and freeze-thaw stability (3 cycles) were assessed with mean recovered concentration of >85%. The method was successfully applied to a clinical study of 33 healthy subjects to evaluate the effect of concomitant of INH on the pharmacokinetic parameters of RIF as well as the segregation of the subjects into slow or fast acetylators of INH.

Development and validation of an UPLC method for the quantification of ethambutol in rat plasma

The method is applicable for pharmacokinetic studies after the oral administration of free EMB in rats, also with scope to extend the method to evaluate EMB-loaded solid lipid nanoparticles.

Development and validation of a hydrophilic interaction liquid chromatography-tandem mass spectrometry method for determination of isoniazid in human plasma

An LC-MS/MS method for the determination of isoniazid in human plasma was developed and validated. Human plasma aliquots of 100 microL were used for analysis. The assay used nialamide as the internal standard. The calibration curve concentration range was 50-10,000 ng/mL. Sample preparation utilized protein precipitation, and the supernatant was directly injected onto silica column without reconstitution. The recovery was over 90% and matrix effect was negligible. The method is simple and fast, which is advantageous in respect to instability of isoniazid in human plasma and loss on reconstitution due to its low molecular weight.

Simultaneous determination of first-line anti-tuberculosis drugs and their major metabolic ratios by liquid chromatography/tandem mass spectrometry

Monitoring of anti-tuberculosis drug concentrations and dose adjustment can be helpful in cases that show poor response to treatment. Here, we describe a method that can rapidly and simultaneously measure the blood concentrations of four anti-tuberculosis drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol) and two major metabolic ratios (acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin) using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). A C18 reversed-phase column and gradients of methanol in 0.3% formic acid and water were used for HPLC separation. The drug concentrations were determined by multiple reaction monitoring in positive ion mode and the assay performance was evaluated. We determined peak concentration ranges for each drug and acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin ratios by analyzing 2-h post-dose samples in patients treated with standard dosing as a first-line treatment. The preparation of 20 samples including two steps of deproteinization with 50% and 100% methanol was performed within 20 min and chromatographic separation was achieved within 4 min/sample. Interassay calibration variability data obtained over concentrations of 0-8 microg/mL for isoniazid and ethambutol and 0-80 microg/mL for rifampicin and pyrazinamide showed a linear and reproducible curve. Within-run and between-run imprecision (CVs) were 1.9-5.5% and 3.5-10.5% and the lower limits of detection and quantification were 0.01-0.5 microg/mL and 0.05-1.0 microg/mL, respectively. The isoniazid concentration was found to be inversely correlated to the acetylisoniazid/isoniazid ratio (R=-0.739, P<0.001). The devised method allows for the simple, rapid, sensitive and reproducible quantification of isoniazid, rifampicin, pyrazinamide, ethambutol and their two metabolic ratios and should be helpful for therapeutic drug monitoring in tuberculosis patients.

Quantification of isoniazid and acetylisoniazid in rat plasma and alveolar macrophages by liquid chromatography-tandem mass spectrometry with on-line extraction

To evaluate if pulmonary delivery of microparticles loaded with a prodrug of isoniazid (INH), isoniazid methanesulfonate (INHMS), can target alveolar macrophages (AM) and reduce metabolism of INH, an HPLC-MS/MS assay with automated online extraction for quantification of INH and its metabolite acetylisoniazid (AcINH) in plasma and AMs was developed and validated. Reproducibility in rat plasma and homogenate of a rat AM cell line, NR8383, for INH and AcINH showed excellent precision and accuracy with calibration curves exhibiting linearity within a range of 1-250ng/ml of INH and 0.05-50ng/ml of AcINH (r(2)>0.99). The validated methods were successfully applied to pharmacokinetic study of INHMS-loaded microparticles in rats, demonstrating efficient targeting of AMs and reduction of INH metabolism.