Development and validation of a liquid chromatography-tandem mass spectrometry assay for the simultaneous quantitation of 5 azole antifungals and 1 active metabolite

A general and rapid LC-MS/MS method for simultaneous determination of voriconazole, posaconazole, fluconazole, itraconazole and hydroxyitraconazole in IFI patients

OBJECTIVE

To establish a rapid and universal quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS) method for measuring the exposure levels of five triazole antifungal drugs in human plasma, including voriconazole, fluconazole, posaconazole, itraconazole, and hydroxyitraconazole.

METHODS

A triple quadrupole mass spectrometer operating in positive ionization mode was used to detect the analyte, and multiple reaction monitoring mode was employed to gather data. The mobile phase included 0.05 % formic acid in water (phase A) and acetonitrile (phase B). The analytes were separated on an Agilent EclipsePlusC18 RRHD column (30 × 50 mm, 1.8 μm) using gradient elution. The flow rate was 0.3 mL/min with the column temperature set at 35 °C. The acetonitrile was used to pretreat the plasma sample, and the itraconazole-D5 and hydroxyitraconazole-D5 were utilized as the internal standards.

RESULTS

The calibration range was from 100 to 10,000 ng/mL for posaconazole, itraconazole, and hydroxyitraconazole, from 200 to 20,000 ng/mL for fluconazole and from 50 to 5000 ng/mL for voriconazole, with linear correlation coefficients more than 0.99 for all regression curves. The intra- and inter-day accuracy and precision of the method were within ±15 %. The mean extraction recovery of all the analytes ranged from 74.32 % to 117.83 %, and the matrix effect was from 72.54 % to 111.2 %. The results of stability fell into the scope of ±15 % deviation.

CONCLUSION

This newly developed method is sensitive, simple, and robust, and successfully applied in determining triazole antifungal drugs in plasma from 66 IFI patients to provide reference for safe and effective drug administration in clinical practice.

UPLC-MS/MS method for fluconazole determination in plasma and its application in Mexican patients with candidaemia

Aim: An accurate and fast ultra-high performance liquid chromatography coupled with tandem mass spectrometry analytical method was developed and validated for quantifying fluconazole levels in human plasma according to the US FDA guidelines.Materials & methods: A simple protein precipitation by acetonitrile was employed for the sample preparation. The chromatographic separation was carried out using isocratic elution of water (0.1% formic acid) and acetonitrile on an Acquity ultra-high performance liquid chromatography HSS T3 column. Samples from ten adult patients diagnosed with candidemia who received fluconazole treatment were analyzed.Results & conclusion: The method demonstrated excellent linearity and stability within the 1-50 μg/ml range (r2 >0.999). The intraday and interday precision were determined with coefficient of variation values ranging from 1.4 to 4.38% and 2.8 to 6.6%, respectively. This rapid and selective method has successfully analyzed 27 plasma samples. The straightforward sample preparation in a single step and the reduced analysis time make this method suitable for adult patients with candidemia, leading to improved clinical outcomes.

Therapeutic drug monitoring of mycophenolic acid and azole antifungals on two distinct LC-MS/MS instruments

Background

As an active metabolite of a commonly prescribed immunosuppressant, mycophenolic acid (MPA) levels are often monitored to prevent organ rejection following a transplant. Triazoles are often prescribed for treatment of invasive fungal infections in immunocompromised patients. Due to the variability in individual pharmacokinetics and drug-drug interactions, therapeutic drug monitoring is recommended for triazole antifungals. A multiplex LC-MS/MS assay has been developed that can quantify both MPA and triazole drugs in serum.

Methods

A sample preparation procedure was established to spike in internal standard compounds and precipitate proteins. Reversed-phase chromatographic separation was performed on a C18 column with an analysis time of five minutes per sample. The mass spectrometer was operated in multiple reaction monitoring mode. The method was validated on two HPLC systems interfaced with either a Triple Quad 6500 or an API 4000 instrument.

Results

The multiplex assay was linear over a wide dynamic range with analyte measurable ranges of 0.4-48 μg/mL for MPA, 0.1-12 μg/mL for posaconazole, and 0.2-24 μg/mL for voriconazole, itraconazole, hydroxyitraconazole, and isavuconazole. The between-day and intraday imprecisions were less than 10 %. Limits of detection were below 0.04 ug/mL with limits of quantitation below 0.2 μg/mL. Method comparison studies against the current in-house method met acceptance criteria. The instrument comparison study demonstrated a strong correlation between data collected from the two systems.

Conclusion

A robust multiplex LC-MS/MS assay was developed and validated for monitoring MPA and triazoles drug levels in a clinical laboratory. The assay performance on two distinct instruments was acceptable and comparable.

A rapid and simple HPLC-MS/MS method for the therapeutic drug monitoring of six special-grade antimicrobials in pediatric patients

Meropenem, linezolid, fluconazole, voriconazole, posaconazole, and vancomycin are six important antimicrobials used for severe infections in critically ill patients listed in special-grade antimicrobials in China. The six antimicrobials' highly variable pharmacodynamics and pharmacokinetics in critically ill pediatric patients present significant challenges to clinicians in ensuring optimal therapeutic targets. Therefore, therapeutic drug monitoring of these antimicrobials in human plasma is necessary to obtain their plasma concentration. A rapid, simple, and sample-saving high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed, which could simultaneously determine all six antimicrobials. It required only 10 μL of plasma and a one-step protein precipitation process. Chromatographic separation was achieved on a reversed-phase column (C18, 30 × 2.1 mm, 2.6 μm) via gradient elution using water and acetonitrile containing 0.1 % formic acid as mobile phase. The injection volume was 2 μL, and the total run time was only 2.5 min. Detection was done using a Triple Quad™ 4500MD tandem mass spectrometer coupled with an electrospray ionization (ESI) source in positive mode. The calibration curves ranged from 0.5 to 64 μg/mL for meropenem and fluconazole, 0.2-25.6 μg/mL for linezolid and voriconazole, 0.1-12.8 μg/mL for posaconazole and 1-128 μg/mL for vancomycin, with the coefficients of correlation all greater than 0.996. Furthermore, the method was validated rigorously according to the European Medicines Agency (EMA) guidelines, demonstrating excellent accuracy (from 93.0 % to 110.6 %) and precision (from 2.0 % to 12.8 %). Moreover, its applicability to various matrices (including serum, hemolytic plasma, and hyperlipidemic plasma) was evaluated. Thus, this method was successfully applied to routine therapeutic drug monitoring for critically ill pediatric patients and other patients in need.

Overview of therapeutic drug monitoring and clinical practice

With the rapid development of clinical pharmacy in China, therapeutic drug monitoring (TDM) has become an essential tool for guiding rational clinical drug use and is widely concerned. TDM is a tool that combines pharmacokinetic and pharmacodynamic knowledge to optimize personalized drug therapy, which can improve treatment outcomes, reduce drug-drug toxicity, and avoid the risk of developing drug resistance. To effectively implement TDM, accurate and sophisticated analytical methods are required. By researching the literature published in recent years, we summarize the types of commonly monitored drugs, therapeutic windows, and clinical assays and track the trends and hot spots of therapeutic drug monitoring. The purpose is to provide guidelines for clinical blood drug concentration monitoring, to implement individualized drug delivery programs better, to ensure the rational use of drugs for patients, and to provide a reference for the group to carry out related topics in the future.

Advancing posaconazole quantification analysis with a new reverse-phase HPLC method in its bulk and marketed dosage form

Introduction: Posaconazole is a widely used antifungal drug, and its accurate quantification is essential for quality control and assessment of its pharmaceutical products. This study aimed to develop and validate a reverse-phase high-performance liquid chromatography (HPLC) analytical method for quantifying Posaconazole in bulk and dosage form. Methods: The HPLC method was developed and validated based on International Conference on Harmonisation (ICH) guidelines. The developed method was then applied to quantify Posaconazole in a marketed tablet formulation. The method's specificity, linearity, precision, accuracy, robustness, and stability were evaluated. Results: The developed HPLC method showed good linearity over a 2-20 μg/mL concentration range. The percentage recovery of Posaconazole from the bulk and marketed formulations was found to be 99.01% and 99.05%, respectively. The intra-day and inter-day precisions were less than 1%, and the method was stable under different conditions. The HPLC method was successfully applied to quantify Posaconazole in the marketed formulation. Conclusion: The developed and validated HPLC method is reliable and efficient for analyzing Posaconazole in bulk and dosage forms. The method's accuracy, precision, specificity, linearity, robustness, and stability demonstrate its effectiveness. The method can be used for the quality control and assessment of Posaconazole-containing pharmaceutical products.

Simultaneous determination of four antibiotics in human plasma by high-performance LC-MS/MS: application to therapeutic drug monitoring

Background: Aimed to simultaneously measure linezolid, voriconazole, cefoperazone and fluconazole in human plasma suitable for therapeutic drug monitoring applications, a robust, rapid and easy-to-use HPLC-MS/MS approach was developed and validated. Materials & methods: Protein precipitation was used to prepare analytes from 100 μl plasma. HPLC was employed for analyte separation, and quantification was conducted via multiple reaction monitoring in positive ion mode. The methodology was fully validated. Results & conclusion: All four antibiotics were found to be stable under the tested conditions, and accuracy values ranged from 90.96 to 113.25% and CV values were <14.0%. This HPLC-MS/MS method can be used for routine clinical therapeutic drug monitoring of linezolid, voriconazole, cefoperazone and fluconazole simultaneously.

Progress of triazole antifungal agent posaconazole in individualized therapy

WHAT IS KNOWN AND OBJECTIVE

Posaconazole is the second-generation triazole antifungal agent with widespread clinical application. Posaconazole exposure is influenced by various factors such as drug interactions, disease state and diet, resulting in a high interindividual variability in many patients and failure to ensure therapeutic efficacy. Therefore, it is necessary to conduct individualized therapy on posaconazole to ensure the efficacy and safety of treatment.

METHODS

Articles were identified through PubMed using the keywords such as "posaconazole," "therapeutic drug monitoring" and "Population pharmacokinetics" from 1 January 2001 to 30 April 2022.

RESULTS AND DISCUSSION

In this paper, we review the individualized treatment studies of posaconazole from the three aspects of therapeutic drug monitoring, population pharmacokinetic study and Monte Carlo simulation to provide reference for in-depth individualized posaconazole dosing studies.

WHAT IS NEW AND CONCLUSION

This review suggests that therapeutic drug monitoring should be performed in patients taking posaconazole to adjust the dosage and assess the efficacy and cost-effectiveness of posaconazole under different clinical conditions and different dosing regimens through Monte Carlo simulations. In the future, a more detailed delineation and comprehensive examination of posaconazole PPK for specific populations requires further study.

A versatile high-performance LC-MS/MS assay for the quantification of voriconazole and its N-oxide metabolite in small sample volumes of multiple human matrices for biomedical applications

Voriconazole (VRC) pharmacokinetics, in particular its complex metabolism, is still not fully understood which challenges its optimal therapeutic use. To increase knowledge on the pharmacokinetics of this antifungal drug, it is essential to broaden the perspective and expand in vitro and clinical in vivo investigations in particular to aspects such as unbound plasma, target-site and metabolite concentrations. Innovative sampling approaches such as microdialysis, a minimally-invasive technique for the analysis of compound concentrations in target-site human tissue fluids, are associated with bioanalytical challenges, i.e. small sample volumes and low concentrations. Thus, a bioanalytical LC-MS/MS assay for the simultaneous quantification of VRC and its main N-oxide (NO) metabolite in human plasma, ultrafiltrate and microdialysate was developed and validated according to the European Medicines Agency guideline. Quantification was rapid, simple and feasible for clinically relevant concentrations from 5 to 5000 ng/mL in plasma and ultrafiltrate as well as from 4 to 4000 ng/mL in microdialysate. Due to the high sensitivity of the assay, only 20 µL of plasma or ultrafiltrate and 5 µL of microdialysate were required. For VRC and NO in all matrices, between-run accuracy was high with a maximum mean deviation of 7.0% from the nominal value and between-run precision was demonstrated by ≤ 11.8% coefficient of variation. Both compounds proved stable under various conditions. The assay suitability was demonstrated by the application to a clinical study quantifying simultaneously VRC and NO concentrations in plasma, ultrafiltrate and microdialysate. Additionally, the assay was successfully adapted for pharmacokinetic analyses in human tissue-derived in vitro experiments. Overall, by reducing the required sample volume, the bioanalytical method allows for an increased number of plasma samples in vulnerable populations, e.g. infants, and enables the generation of concentration-time profiles with a higher temporal resolution in microdialysis studies. Consequently, the developed assay is apt to elucidate the complex pharmacokinetics of VRC in clinical settings as prerequisite for therapy optimisation.

Bio-analytical liquid chromatographic-based method with a mixed mode online solid phase extraction for drug monitoring of fluconazole in human serum

A simple, cost-effective and sensitive liquid chromatography-based bio-analytical method has been developed and validated for therapeutic drug monitoring of fluconazole (FLUC) in human serum. Integration of online mixed-mode solid-phase extraction (SPE) into the analytical system was the key for direct injection of untreated serum samples. A short protein-coated (PC) µBondapak CN silica column (PC-µB-CN-column) as a SPE tool and phosphate buffer saline (PBS) (pH 7.4) as an eluent were applied in the extraction step. PC-µB-CN-column operates in two different chromatographic modes. Using PBS, proteins were extracted from serum samples by size-exclusion liquid chromatography, while FLUC trapping was reversed-phase liquid chromatography dependent. FLUC was then eluted from the PC-µB-CN-column onto the quantification position using a mixture of acetonitrile-distilled deionized water (20:80, v/v) as an eluent and ODS analytical column. FLUC was separated at ambient temperature (22 ± 1 °C) and detected at 260 nm. The method was linear over the range of 200-10000 ng/mL. FLUC recovery in untreated serum samples ranged from 97.8 to 98.8% and showed good accuracy and precision. The reliability of the developed method was evaluated by studying the pharmacokinetic profile of FLUC in humans after an oral administration of a single 150 mg tablet.

High-throughput simultaneousquantification offive azole anti-fungal agents and one active metabolite in human plasma using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry

OBJECTIVES

For patients with hematological malignancy, triazole antifungal agents such as fluconazole (FLCZ), itraconazole (ITCZ), voriconazole (VRCZ), posaconazole (PSCZ) and isavuconazole (ISCZ) are often used for prophylaxis of deep mycosis. Since these azoles exhibit large pharmacokinetic variability, dose adjustment by therapeutic drug monitoring is recommended for some azoles. This study aimed to develop and validate a novel method for simultaneous determination of plasma concentrations of FLCZ, ITCZ, VRCZ, PSCZ, ISCZ and ITCZ-OH, an active metabolite of ITCZ, using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS).

DESIGN & METHODS

A high-throughput solid-phase extraction method using 96-well MCX µElution Plate was selected as the pretreatment procedure.

RESULTS

The calibration curves for FLCZ, ITCZ, ITCZ-OH, VRCZ, PSCZ and ISCZ showed good linearity (back-calculation of calibrators: relative error ≤ 15% [LLOQ: ≤ 20%]) over wide ranges of 100-100000, 20-20000, 40-40000, 20-20000, 5-5000 and 50-50000 ng/mL, respectively. The validation results of all six drugs fulfilled the criteria of the guidance for bioanalytical method validation of the US Food and Drug Administration for within-batch and batch-to-batch precision and accuracy. The extraction recovery rates were good at ≥ 74.9%, and almost no matrix effects were found for all the drugs. The trough (10 h post-dose in 1 patient on PSCZ) drug concentrations in patients with hematologic malignancy who received oral FLCZ, ITCZ, VRCZ or PSCZ were quantified using the method developed. The measurements for all samples were within the ranges of the calibration curves, demonstrating the feasibility of clinical application of the novel method.

CONCLUSIONS

We have succeeded in developing a novel high-throughput method using UHPLC-MS/MS for simultaneous quantification of plasma concentrations of FLCZ, ITCZ, ITCZ-OH, VRCZ, PSCZ and ISCZ.

Implementation of a Dual-Column Liquid Chromatography-Tandem Mass-Spectrometry Method for the Quantification of Isavuconazole in Clinical Practice

Objectives  Therapeutic drug monitoring (TDM) of isavuconazole, which is a novel broad-spectrum antimycoticum against invasive fungal infections, ensures an effective exposure of the drug and minimizes the risk of toxicity. This study is aimed at evaluating the analytical performance of a dual-column liquid chromatography-tandem mass-spectrometry (LC-MS/MS) method for isavuconazole quantification.

Materials and Methods  The method was performed on a Voyager TSQ Quantum triple quadrupole instrument equipped with an Ultimate 3000 chromatography system (Thermo Fisher Scientific, San Jose, California, United States). Analytical and preanalytical requirements of the isavuconazole LC-MS/MS method were evaluated. Sample stability measurements were performed at room temperature (RT) and in serum tubes with separator gel.

Results  The isavuconazole LC-MS/MS method was linear over the concentration range of 0.2 to 12.8 mg/L. The coefficient of determination ( r² ) always exceeded 0.999. Within- and between-run precision ranged between 1.4 to 2.9% and 1.5 to 3.0%, the recovery between 93.9 and 102.7%. At RT, serum samples were stable for 3 days. Isavuconazole serum concentrations were significantly lower after incubation (18 hours) in serum tubes with separator gel at RT.

Conclusion  The dual-column isavuconazole LC-MS/MS is a reliable tool for the TDM of isavuconazole. Serum samples are stable for at least 3 days and should be collected in tubes without separator gel.

Application of HPTLC, spectrofluorimetry and differential pulse voltammetry for determination of the antifungal drug posaconazole in suspension dosage form

This work presents the development, validation and application of three simple and direct analytical methods for determination of posaconazole (PSZ) in its pure form and in suspension dosage form. Method I is based on high performance thin layer chromatography (HPTLC) where effective separation of PSZ and the internal standard (itraconazole) was achieved using Merck HPTLC plates (20×10cm aluminium plates with 250μm layer thickness precoated with silicagel 60 F₂₅₄) and a mobile phase composed of acetone and chloroform (1:2, by volume), followed by densitometric measurement of the drugs' spots at 262nm. Method II involves measurement of the native fluorescence of PSZ in 0.1M H₂SO₄ at excitation and emission wavelengths of 260 and 365nm, respectively. Method III depends on the voltammetric analysis of PSZ. A well-defined cathodic wave was obtained for PSZ in Britton-Robinson buffer pH 6.5 using the differential-pulse mode at the hanging mercury drop electrode (HMDE). The developed methods were validated according to the International Conference on Harmonization (ICH) guidelines regarding linearity, ranges, accuracy, precision, robustness and limits of detection and quantification. The proposed methods showed good linearity over the concentration ranges 5-50, 0.05-0.3, 0.005-0.05μg/mL PSZ for methods I, II, and III respectively. Intra and inter-day precision were verified by the RSD% values which were less than 2%. The proposed methods were successfully applied for the quantification of PSZ in suspension dosage form with no observable interferences. Assay methods were favorably compared with those obtained by previously reported HPLC method.

Advances in antifungal drug measurement by liquid chromatography-mass spectrometry

Fungal infections, especially invasive types, have become a serious healthcare problem as the immunocompromised population increases. There are five main classes of antifungal drugs: polyenes, flucytosine, allylamines, azoles, and echinocandins. Therapeutic drug monitoring (TDM) is justified for flucytosine and triazoles due to their large inter- and intra-individual pharmacokinetic variability and their high tendency for drug-drug interactions. Available methods for measuring these drugs include bioassay, liquid chromatography and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The LC-MS/MS approach is preferred due to its superior analytic sensitivity and specificity. In this review, we highlight TDM methods by LC-MS/MS for these antifungal drugs searchable in PubMed by December 1, 2018. LC-MS/MS methods that were developed for other purposes such as pharmacokinetics or toxicokinetics were also included. We have critically analyzed these methods with an emphasis on sensitivity, specificity, simplicity, throughput and robustness.

Development and validation of a volumetric absorptive microsampling assay for analysis of voriconazole and voriconazole N-oxide in human whole blood

Voriconazole is a broad-spectrum antifungal triazole drug for the treatment of invasive fungal infections. It is extensively metabolized by hepatic drug metabolizing enzymes cytochrome (CYP) 2C19 and CYP3A4. Selective inhibition of intestinal CYP3A4 by grapefruit juice may increase the oral bioavailability of voriconazole in children. To test this hypothesis it is necessary to develop a sensitive assay for measuring voriconazole and its major metabolites in a small volume of blood. Mitra® devices from Neoteryx were employed to develop and validate the assay for the quantitation of voriconazole and voriconazole N-oxide. Mitra® devices utilize volumetric absorptive microsampling (VAMS™) technology that enables accurate and precise collection of a fixed volume (10 μL of blood), reducing or eliminating the volumetric blood hematocrit assay-bias associated with the dried blood spotting technique. We developed an ultra-performance liquid chromatographic method with tandem mass spectrometry detection for quantification of voriconazole and voriconazole N-oxide. Sample extraction of Mitra® devices, followed by reversed-phase chromatographic separation and selective detection using tandem mass spectrometry with a 4.00 minute runtime per sample was employed. Standard curves were linear between 10.0 to 10,000 ng/mL for both voriconazole and voriconazole N-oxide. Intra- and inter-day accuracy were within 87-102% and precision (CV) was <12% based on a 3-day validation study. Recoveries were ≥94 % for voriconazole and ≥87 % for voriconazole N-oxide. Voriconazole and voriconazole N-oxide were stable in human whole blood under assay conditions (19 h at room temperature and 24 h in autosampler). Voriconazole was stable for 1-month in dried microsamples under different conditions (4, -20 and -78 °C). This assay provides an efficient quantitation of voriconazole and voriconazole N-oxide and is ready to be implemented for the analysis of whole blood microsamples in a pediatric clinical trial investigating the impact of intestinal inhibition of CYP3A4 on voriconazole pharmacokinetics.

A sensitive and validated HPLC-UV method for the quantitative determination of the new antifungal drug isavuconazole in human plasma

Isavuconazole is a broad-spectrum triazole antifungal drug recently approved for the therapy of both invasive aspergillosis and mucormycosis. To support a widespread therapeutic drug monitoring of isavuconazole, a simple, sensitive, and precise high-performance liquid chromatography method with UV detection was developed and fully validated for the quantification of this drug in human plasma. The method involved a combined protein precipitation-solid-phase extraction and a chromatographic separation on a Waters XTerra RP₁₈ (150 × 4.6 mm, 3.5 μm) column using an isocratic mobile phase of ammonium acetate buffer (pH 8.0, 10 mm) and acetonitrile (45:55, v/v). The UV detection was performed at 285 nm. This method was linear (correlation coefficients ≥0.998), specific (no interference with plasma components or various potentially co-administrated drugs), sensitive (lower limit of quantification of 0.025 μg/mL), reproducible (coefficients of variation were ≤7.9%) and accurate (deviations ranged from -5.0 to 8.0%) over the range of 0.025-10 μg/mL. The method fulfilled all of the US Food and Drug Administration guidelines validation criteria and performed well in an international proficiency testing program. The assay was also successfully applied to routine therapeutic drug monitoring of patients and to drug stability investigations under various conditions.

Investigation of transition ion ratio variation for liquid chromatography-tandem mass spectrometry: A case study approach

BACKGROUND

A transition ion ratio (TIR) is the ratio of one fragment over another from the same precursor and is frequently monitored in liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for analyte identification. The Clinical and Laboratory Standards Institute (CLSI) C50-A guidelines give a static percent allowable TIR deviation based on the TIR level. Anecdotally, we observed failures of these rules for some of our LC-MS/MS assays. We determined what parameters may affect TIRs in a clinical setting and whether TIR variations may be analyte, matrix, instrument service, and/or concentration dependent.

METHODS

Data was collected from the validation and selected periods after implementation for urine benzodiazepines (7 analytes) and plasma azole antifungals (6 analytes). TIRs for the calibrators and quality control materials on a Thermo TSQ™ Quantum Ultra from July 2016 to February 2017 for benzodiazepines in urine and Thermo TSQ™ Vantage from May 2016 to Oct 2016 for azoles in serum were monitored.

RESULTS

The statistically significant day-to-day TIR shift ranged from 5.7 to 27.0% of the days studies for benzodiazepines and from 5.6 to 27.8% of the days studied for azoles excluding shifts caused by instrument services. Instrument service had significant impact on all benzodiazepines except oxazepam with p-values ranging from 1.79 × 10^-6 to 1.53 × 10^-39 and 4 of the 6 azoles (fluconazole, isavuconazole, voriconazole, and itraconazole) with (p from 7.89 × 10^-3 to 1.98 × 10^-12). Lorazepam, α-hydroxyalprazolam, and hydroxyitraconazole showed significant concentration dependent TIR variations.

CONCLUSIONS

TIR variations may be affected by instrument services, and can be concentration and analyte dependent. Instead of using a static percent deviation rule, establishment of TIR variation criteria for each analyte during test development and validation may provide a more useful tool for analyte identification.