Therapeutic Drug Monitoring of Immunosuppressant Drugs by High-Performance Liquid Chromatography–Mass Spectrometry

The Effect of Polymerization Techniques on the Creation of Molecularly Imprinted Polymer Sensors and Their Application on Pharmaceutical Compounds

Molecularly imprinted polymers (MIPs) have become more prevalent in fabricating sensor applications, particularly in medicine, pharmaceuticals, food quality monitoring, and the environment. The ease of their preparation, adaptability of templates, superior affinity and specificity, improved stability, and the possibility for downsizing are only a few benefits of these sensors. Moreover, from a medical perspective, monitoring therapeutic medications and determining pharmaceutical compounds in their pharmaceutical forms and biological systems is very important. Additionally, because medications are hazardous to the environment, effective, quick, and affordable determination in the surrounding environment is of major importance. Concerning a variety of performance criteria, including sensitivity, specificity, low detection limits, and affordability, MIP sensors outperform other published technologies for analyzing pharmaceutical drugs. MIP sensors have, therefore, been widely used as one of the most crucial techniques for analyzing pharmaceuticals. The first part of this review provides a detailed explanation of the many polymerization techniques that were employed to create high-performing MIP sensors. In the subsequent section of the review, the utilization of MIP-based sensors for quantifying the drugs in their pharmaceutical preparation, biological specimens, and environmental samples are covered in depth. Finally, a critical evaluation of the potential future research paths for MIP-based sensors clarifies the use of MIP in pharmaceutical fields.

Mass Spectrometry in Clinical Laboratory: Applications in Therapeutic Drug Monitoring and Toxicology

Mass spectrometry (MS) coupled with liquid chromatography (LC) or gas chromatography (GC) has been proven to be a powerful platform in research and specialized clinical laboratories for decades. In clinical laboratories, it is used for compound identification and quantification. Due to the ability to provide specific identification, high sensitivity, and simultaneous analysis of multiple analytes (>100) in recent years, application of MS in routine clinical laboratories has increased significantly. Although MS is used in many laboratory areas, therapeutic drug monitoring, drugs of abuse, and clinical toxicology remain the primary focuses of the field. Due to rapid increase in the number of prescription drugs and drugs of abuse (e.g., novel psychoactive substances), clinical laboratories are challenged with developing new MS assays to meet the clinical needs of the patients. We are here to present "off-the-shelf" and "ready-to-use" protocols of recent developments in new assays to help the clinical laboratory community adopt the technology and analysis for the betterment of patient care.

Whole-genome resequencing to unveil genetic characteristics and selection signatures of specific pathogen-free ducks

Specific pathogen-free ducks are important high-grade laboratory animals, with a key role in research related to poultry biosecurity, production, and breeding. However, the genetic characteristics of experimental duck varieties remain poorly explored. Herein we performed whole-genome resequencing to construct a single nucleotide polymorphism genetic map of the genomes of 3 experimental duck varieties [Jinding ducks (JD), Shaoxing ducks (SX), and Fujian Shanma ducks (SM)] to determine their genetic characteristics and identify selection signatures. Subsequent analyses of population structure and genetic diversity revealed that each duck variety formed a monophyletic group, with SM showing richer genetic diversity than JD and SX. Further, on exploring shared selection signatures, we found 2 overlapping genomic regions on chromosome Z of all experimental ducks, which comprised immune response-related genes (IL7R and IL6ST). Moreover, growth and skeletal development (IGF1R and GDF5), meat quality (FoxO1), and stress resistance (HSP90B1 and Gpx8-b) candidate gene loci were identified in strongly selected signatures specific to JD, SM, and SX, respectively. Our results identified the population genetic basis of experimental ducks at the whole-genome level, providing a framework for future molecular investigations of genetic variations and phenotypic changes. We believe that such studies will eventually contribute to the management of experimental animal resources.

Mass spectrometry quantitation of immunosuppressive drugs in clinical specimens using online solid-phase extraction and accurate-mass full scan-single ion monitoring

Introduction

Therapeutic drug monitoring (TDM) of immunosuppressants is essential for optimal care of transplant patients. Immunoassays and liquid chromatography-mass spectrometry (LC-MS) are the most commonly used methods for TDM. However, immunoassays can suffer from interference from heterophile antibodies and structurally similar drugs and metabolites. Additionally, nominal-mass LC-MS assays can be difficult to optimize and are limited in the number of detectable compounds.

Objectives

The aim of this study was to implement a mass spectrometry-based test for immunosuppressant TDM using online solid-phase extraction (SPE) and accurate-mass full scan-single ion monitoring (FS-SIM) data acquisition mode.

Methods

LC-MS analysis was performed on a TLX-2 multi-channel HPLC with a Q-Exactive Plus mass spectrometer. TurboFlow online SPE was used for sample clean up. The accurate-mass MS was set to positive electrospray ionization mode with FS-SIM for quantitation of tacrolimus, sirolimus, everolimus, and cyclosporine A. MS² fragmentation pattern was used for compound confirmation.

Results

The method was validated in terms of precision, analytical bias, limit of quantitation, linearity, carryover, sample stability, and interference. Quantitation of tacrolimus, sirolimus, everolimus, and cyclosporine A correlated well with results from an independent reference laboratory (r = 0.926-0.984).

Conclusions

Accurate-mass FS-SIM can be successfully utilized for immunosuppressant TDM with good correlation with results generated by standard methods. TurboFlow online SPE allows for a simple "protein crash and shoot" sample preparation protocol. Compared to traditional MRM, analyte quantitation by FS-SIM facilitates a streamlined assay optimization process.

Immunosuppressant Monitoring-Performance of the First Mass Spectrometry-Based Automated Clinical Analyzer Cascadion

BACKGROUND

Automatic analyzers simplify processes and may help improve standardization. The first automated analyzer based on mass spectrometry is available and offers a panel for monitoring cyclosporin A, tacrolimus, sirolimus, and everolimus. Method comparisons and evaluation tests are presented to verify the capability of the Cascadion system for use in a clinical laboratory.

METHODS

Sample preparation and measurements were performed using the Cascadion clinical analyzer. More than 1000 measurement values of patient samples were compared with an in vitro diagnostic-certified assay run on a liquid chromatography tandem mass spectrometry instrument. Precision and accuracy were determined using commercial quality control and external quality assessment (EQA) samples.

RESULTS

A good correlation between the 2 instruments was observed (Pearson correlation r = 0.956-0.996). Deming regression revealed 95% confidence intervals of slopes and intercepts covering the values 1 and 0, for sirolimus and everolimus, respectively, indicating equivalence of both measuring systems. However, for cyclosporin A, a bias was observed and confirmed using a Bland-Altman plot (-9.1%). Measurement repeatability and intermediate measurement precision were appropriate showing coefficients of variation of 0.9%-6.1% and 2.0%-5.3%, respectively. Accuracy according to internal quality controls was 85%-111% and 81%-100% in the EQA samples of Reference Institute of Bioanalytics and Laboratory of the Government Chemist, respectively. High robustness was found with regard to the linearity of the calibration lines (linear regression coefficient r2 > 0.99). Carryover was negligible (0.1%).

CONCLUSIONS

The Cascadion automatic analyzer produced convincing results in the measurement of patient, control, and EQA samples. The throughput was sufficient for routine use. Overall, it can be used as an alternative to open liquid chromatography tandem mass spectrometry instruments for immunosuppressant monitoring, simplifying processes without the need for specially trained personnel.

Dried blood microsampling-assisted therapeutic drug monitoring of immunosuppressants: An overview

In the field of solid organ transplantation, chemotherapy and autoimmune disorders, treatment with immunosuppressant drugs requires intensive follow-up of the blood concentrations via therapeutic drug monitoring (TDM) because of their narrow therapeutic window and high intra- and inter-subject variability. This requires frequent hospital visits and venepunctures to allow the determination of these analytes, putting a high burden on the patients. In the context of patient-centric thinking, it is becoming increasingly established that at least part of these conventional blood draws could be replaced by microsampling, allowing home-sampling and increasing the quality of life for these patients. In this review we discuss the published methods - mostly using liquid chromatography coupled to tandem mass spectrometry - that have utilized (volumetric) dried blood samples as an alternative for conventional liquid whole blood for the TDM of immunosuppressant drugs. Furthermore, some pre-analytical considerations using DBS or volumetric alternatives are considered, as well as the applicability on clinical samples. The implementation status in clinical practice is also discussed, including (1) the cost-effectiveness of this approach compared to venepuncture, (2) the availability of multiplexed methods, (3) the status of harmonization and (4) patient perception. A brief perspective on potential future developments for the dried blood-based TDM of immunosuppressant drugs is provided, by considering how obstacles for the implementation of these strategies into clinical practice might be overcome.

Comparison of LC-MS/MS and EMIT methods for the precise determination of blood sirolimus in children with vascular anomalies

Sirolimus (SRL) is a mammalian target of rapamycin (mTOR) inhibitor. The whole blood concentration of SRL is routinely monitored to tailor dosage and prevent toxicity. Currently, the enzyme multiplied immunoassay technique (EMIT) is often applied to perform therapeutic drug monitoring (TDM) of SRL, but the cross-reactivity with various metabolites is of great concern. A more specific method is required, such as liquid chromatography–tandem mass spectrometry (LC-MS/MS). However, no study on the method comparison of the EMIT and LC-MS/MS for the measurement of whole blood SRL concentration in children with vascular anomalies has been reported. This study developed a simple and sensitive LC-MS/MS assay for the determination of SRL. Meanwhile, consistency between LC-MS/MS and the EMIT was evaluated by linear regression and Bland–Altman analysis. Whole blood samples were deproteinized with methanol for erythrocyte lysis, and the resulting solution was injected into the LC-MS/MS system using the positive electrospray ionization mode. The multiple reaction monitoring transitions of m/z 931.7 → 864.6 and m/z 934.7 → 864.6 were used for SRL and SRL-d3 as the internal standards, respectively. The analytes were separated on a C18 column with a gradient mobile phase (0.1 mM formic acid and 0.05 mM ammonium acetate in methanol/ultrapure water). Blood samples collected from children with vascular anomalies undergoing SRL therapy were tested by EMIT and by LC-MS/MS. The linear range of LC-MS/MS was 0.500–50.0 ng/ml and that of the EMIT was 3.50–30.0 ng/ml. A significant positive correlation between the two assays was established with a regression equation described as [EMIT] = 1.281 × [LC−MS/MS] + 2.450 (r = 0.8361). Bland–Altman plots showed a mean concentration overestimation of 4.7 ng/ml [95% CI: (−3.1, 12.6)] and a positive bias of 63.1% [95% CI: (−36.1, 162.3)] generated by the EMIT more than that of by LC-MS/MS. In conclusion, the two methods were closely correlated, indicating that switching between the two methods is feasible. Considering the overestimation nature of the EMIT assay, switching from the EMIT to the LC-MS/MS method deserves close attention and necessary re-evaluation for the target therapeutic reference range, may be required when methods are switched within the same clinical laboratory or results are compared between different laboratories.

High Calcineurin Inhibitor Intrapatient Variability Is Associated With Renal Allograft Inflammation, Chronicity, and Graft Loss

Background

High calcineurin inhibitor (CNI) intrapatient variability (IPV) has been associated with poor kidney allograft outcomes. However, the relationship between early allograft histological changes, their progression, and CNI-IPV is less well studied. Hence, we evaluated effect of CNI-IPV defined by the degree of fluctuation of CNI levels in all kidney transplant patients over 2 to 12 months posttransplant on early allograft inflammation, subsequent chronicity, and later clinical outcomes.

Methods

Two hundred eighty-six patients transplanted from January 2013 to November 2014 were enrolled with protocol and indication biopsies. The mean CNI-IPV was 28.5% and a quarter of our cohort had IPV of 35% or greater (high CNI IPV). Baseline demographic differences were similar between high and low CNI IPV groups.

Results

High CNI-IPV was associated with a higher incidence of acute rejection (AR) within 1 year (52% vs 31% P < 0.001), more persistent/recurrent AR by 1 year (18.2% vs 6.2%, P = 0.002), higher-grade AR (≥Banff 1B, 27.5% vs 7.3%, P < 0.001), and worse interstitial fibrosis/tubular atrophy (P = 0.005). High CNI-IPV was associated with increased graft loss (GL) and impending graft loss (iGL, defined as eGFR<30 ml/min and >30% decline in eGFR from baseline), regardless of donor-specific antibody, delayed graft function, rejection, or race. In a multivariate Cox Proportional Hazards Model, high CNI-IPV was independently associated with GL + iGL (hazard ratio, 3.1; 95% confidence interval, 1.6-5.9, P < 0.001).

Conclusions

High CNI-IPV within 1 year posttransplant is associated with higher incidence of AR, severe AR, allograft chronicity, GL, and iGL. This represents a subset of patients who are at risk for poor kidney transplant outcomes and potentially a modifiable risk factor for late allograft loss.

Antineoplastic drugs and their analysis: a state of the art review

We provide an overview of the analytical methods available for the quantification of antineoplastic drugs in pharmaceutical formulations, biological and environmental samples.

Therapeutic Drug Monitoring of Everolimus: A Consensus Report

In 2014, the Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology called a meeting of international experts to provide recommendations to guide therapeutic drug monitoring (TDM) of everolimus (EVR) and its optimal use in clinical practice. EVR is a potent inhibitor of the mammalian target of rapamycin, approved for the prevention of organ transplant rejection and for the treatment of various types of cancer and tuberous sclerosis complex. EVR fulfills the prerequisites for TDM, having a narrow therapeutic range, high interindividual pharmacokinetic variability, and established drug exposure-response relationships. EVR trough concentrations (C0) demonstrate a good relationship with overall exposure, providing a simple and reliable index for TDM. Whole-blood samples should be used for measurement of EVR C0, and sampling times should be standardized to occur within 1 hour before the next dose, which should be taken at the same time everyday and preferably without food. In transplantation settings, EVR should be generally targeted to a C0 of 3-8 ng/mL when used in combination with other immunosuppressive drugs (calcineurin inhibitors and glucocorticoids); in calcineurin inhibitor-free regimens, the EVR target C0 range should be 6-10 ng/mL. Further studies are required to determine the clinical utility of TDM in nontransplantation settings. The choice of analytical method and differences between methods should be carefully considered when determining EVR concentrations, and when comparing and interpreting clinical trial outcomes. At present, a fully validated liquid chromatography tandem mass spectrometry assay is the preferred method for determination of EVR C0, with a lower limit of quantification close to 1 ng/mL. Use of certified commercially available whole-blood calibrators to avoid calibration bias and participation in external proficiency-testing programs to allow continuous cross-validation and proof of analytical quality are highly recommended. Development of alternative assays to facilitate on-site measurement of EVR C0 is encouraged.

Comparison between ultra-performance liquid chromatography with tandem mass spectrometry and a chemiluminescence immunoassay in the determination of cyclosporin A and tacrolimus levels in whole blood

Regular immunosuppressant drug monitoring is important for maintaining the drug concentrations of organ recipients within the therapeutic range. The standardized liquid chromatography-tandem mass spectrometry (LC-TMS) technique has been used for the accurate analysis of immunosuppressive drugs. In the present study, the performance of the recently developed high-throughput, rapid ultra-performance liquid chromatography combined with tandem mass spectrometry (UPLC-TMS) method was validated for the simultaneous measurement of cyclosporin A and tacrolimus in whole blood. The method of measuring cyclosporin A and tacrolimus using UPLC-TMS was established and the precision, limit of detection (LOD), limit of quantitation (LOQ) and matrix effect were validated. In addition, the performance of UPLC-TMS was compared with that of a chemiluminescence immunoassay (CLIA) in >3,400 clinical specimens. The UPLC-TMS revealed a within-run and between-run precision of <8% and showed a bias of <5%. The LOD and LOQ were 2.0 and 2.5 ng/ml for cyclosporin A, and 0.3 and 0.4 ng/ml for tacrolimus, respectively. Interference from the matrix was not observed. The CLIA measurements of cyclosporin A and tacrolimus showed correlations corresponding with the formulae: Concentration_(CLIA) = 1.18 × UPLC-TMS - 5.85; [95% CI: proportional, 1.16-1.19; constant, -6.86-(-4.81)] and Concentration_(CLIA) = 1.14 × UPLC-TMS - 0.38; [(95% CI: proportional, 1.13-1.14; constant, -0.35-(-0.43)], respectively. The majority of results were higher for the immunoassay than for the UPLC-TMS. The newly developed rapid UPLC-TMS method was suitable for use with a large therapeutic concentration range of the analyzed immunosuppressive drugs. Sample preparation was simple and it was possible to detect several immunosuppressants simultaneously, thus significantly lowering the cost of analysis. In conclusion, this method may contribute to improved accuracy and may be preferred to immunoassays for the routine clinical measurement of immunosuppressive drug concentrations in whole blood.

Drug interaction between tacrolimus and ertapenem in renal transplantation recipients

To show drug interactions between tacrolimus and ertapenem, we retrospectively evaluated 13 renal transplant recipients who had been treated with ertapenem for urinary tract infections during prescription of a constant dose. The mean dose of tacrolimus to achieve desired therapeutic concentrations decreased significantly after beginning ertapenem. The decrease from 0.079 mg/kg to 0.043 mg/kg occurred 2 days after initiation of ertapenem (P < .005). These results suggest that ertapenem, which is not metabolized through the cytochrome (CYP) P450 3A metabolic pathway, interacts with tacrolimus by an unknown mechanism. This report recommends tacrolimus concentration monitoring and dose reductions when the two drugs are administered in combination.

Simultaneous determination of cyclosporine, sirolimus, and tacrolimus in whole blood using liquid chromatography-tandem mass spectrometry

A multiple reaction monitoring, positive ionization electrospray, liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described for the simultaneous quantification of cyclosporine, sirolimus, and tacrolimus in human whole blood. Proteins in the samples are precipitated with a mixture of methanol and zinc sulfate. The supernatant is injected into the LC-MS/MS for analysis. Chromatography involves the use of a C18 column and ammonium acetate/water/methanol-containing mobile phases. The MS/MS is operated in positive ion electrospray mode. Quantification is achieved by comparing peak area ratios of MRMs of analytes and internal standards with that of calibrators. Calibration curves are constructed from peak area ratios of MRMs of calibrators and internal standards versus concentrations. MRMs used are ascomycin (m/z 809.5 → 756.5), cyclosporine A (m/z 1,219.9 → 1,203.1), cyclosporine D (m/z 1,234.0 → 1,217.0), sirolimus (m/z 931.6 → 864.5), and tacrolimus (m/z 821.5 → 768.4).

Therapeutic drug monitoring of tacrolimus by liquid chromatography-tandem mass spectrometry: is it truly a routine test?

Therapeutic drug monitoring of tacrolimus by high-performance liquid chromatography-tandem mass spectrometry has become standard practice. We report on the long-term (4.5 years) use of one such method. Whole blood samples (25 μL) were treated with zinc sulphate (100 μL) and acetonitrile containing ascomycin (internal standard, 250 μL). A high-performance liquid chromatography-tandem mass spectrometer operating in positive ion mode with an electrospray interface was used. Chromatography was performed on a TDM C(18) cartridge column (10 mm × 2.1 mm, 10 μm, Waters) using a switch gradient. A total of 4029 batches were analyzed for tacrolimus; this comprised of 81950 analyses of which 61027 were patient samples. Calibration curves (1.0-50 μg/L) were run on 1765 occasions (mean r(2)=0.999; range r(2)=0.988-0.999). Inter-batch accuracy and imprecision of the method (2.5, 12.5 and 30.0 μg/L), when in routine use, was 97.6-98.5% and <8.0%, respectively (n=4031). Evaluation of the method against other methods in an external quality control scheme revealed good agreement by linear regression analysis (y=0.924x+0.196, r(2)=0.985). The percentage difference between our results and that of all methods revealed a mean bias of -6.3% and a range of -33.3% to 11.1%. During the evaluation period, four batch failures occurred (0.1% failure rate) and greater than 1000 samples per analytical column was achieved. In conclusion, the described method is ideally suited as a routine test for tacrolimus in the clinical setting.

LC-MS/MS for immunosuppressant therapeutic drug monitoring

Due to their narrow therapeutic indices and highly variable pharmacokinetics, therapeutic drug monitoring is necessary to individualize immunosuppressant dosage following organ transplantation. Until recently, monitoring was performed primarily using immunoassays, however, there is an increasing shift to HPLC coupled with MS/MS, due to its greater sensitivity and specificity. Online sample clean-up with either a single analytical column or with 2D chromatography significantly reduces manual handling and is essential to minimize matrix effects and maximize specificity and, coupled with rapid chromatography, allows the simultaneous analysis of the major immunosuppressants, with rapid sample throughput. Thus, LC-MS/MS is an attractive and versatile technique that facilitates rapid development of analytical methods, including new immunosuppressants as they become approved for clinical use.

Evaluation of the MassTrak Immunosuppressant XE Kit for the determination of everolimus and cyclosporin A in human whole blood employing isotopically labeled internal standards

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is widely used for therapeutic drug monitoring of immunosuppressants given to transplant recipients. This study evaluated the performance of the newly introduced MassTrak Immunosuppressant XE Kit (Waters Corporation; “the Kit”) in the determination of everolimus and cyclosporin A (CsA) using LC-MS/MS.

The linearity, precision, detection limit, carryover and matrix effect of the Kit and comparison of the in-house method and Kit procedure were evaluated according to Clinical and Laboratory Standards Institute guidelines.

The Kit afforded good linearity in the measurement of everolimus from 2 to 26 ng/mL (R

The Kit employing isotopically labeled internal standards provides reliable measurements of immunosuppressant levels over a broad range of concentrations.

Liquid chromatography-tandem mass spectrometry method for simultaneous determination of cyclosporine A and its three metabolites AM1, AM9 and AM4N in whole blood and isolated lymphocytes in renal transplant patients

A LC-MS/MS method was developed and validated for the determination of cyclosporine A (CsA) and its three phase 1 metabolites AM1, AM9, and AM4N in whole blood and lymphocytes isolated on the Histopaque gradient. 200 microL of whole blood was precipitated with 10 mol/L zinc sulfate in acetonitrile/methanol (40:60, v/v) and lymphocytes isolated from 1.5 mL blood were extracted with acetonitrile/methanol (40:60, v/v). The analytes and internal standard cyclosporine D were separated on RP column BEH C18, 2.1 x 50 mm, 1.7 microm using gradient LC-MS/MS analysis in positive electrospray mode. Time of analysis was 5 min. Linearity in blood was 5-2000 microg/L for CsA, AM1, and AM9; 2-500 microg/L for AM4N; and 2-500 microg/L for all substances in lymphocytes. Coefficient of variations was 1.8-9.8% and recovery was 92.0-110.0%. The method was used in early and chronic renal transplant patients for therapeutic drug monitoring of CsA to compare either its share in lymphocytes as target organ or binding to one lymphocyte. The same parameters were calculated for all metabolites tested.

The current role of liquid chromatography-tandem mass spectrometry in therapeutic drug monitoring of immunosuppressant and antiretroviral drugs

Therapeutic drug monitoring of critical dose immunosuppressant drugs is established clinical practice and there are similar good reasons to monitor antiretrovirals. The aim of this article is to review the recent literature (last five years), with particular reference to the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). LC-MS/MS offers many potential advantages. The superior selectivity of LC-MS/MS over immunoassays for immunosuppressant drugs has been widely reported. Simultaneous measurement of a number of drugs can be performed. It is currently routine practice for the four major immunosuppressants (cyclosporin, tacrolimus, sirolimus and everolimus) to be simultaneously measured in whole blood. While up to 17 antiretroviral drugs have been simultaneously measured in plasma. The exquisite sensitivity of LC-MS/MS also provides the opportunity to measure these drugs in alternative matrices, such as dried blood spots, saliva, peripheral blood mononuclear cells and tissue. However, the clinical utility of measuring these classes of drugs in alternative matrices is still to be determined.

Steroid measurement with LC-MS/MS in pediatric endocrinology

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an increasingly common tool in the clinical laboratory. Established applications include routine assays for detecting inborn errors of metabolism and for monitoring therapeutic drugs and steroids. Steroid profiling is a very effective method for distinguishing almost all steroid related disorders. It allows accurate diagnosis and is very useful in many clinical situations. Most methods for the determination of steroid hormones are based on immunoassays, which are rapid and easy to perform. However, the reliability of steroid immunoassays has been shown to be doubtful because of the lack of specificity and of matrix effects. Immunological methods, especially direct assays, often overestimate true steroid values. This is of particular importance in the newborn period and in early infancy. Problems with steroid immunoassays have further been reported for female patients or when analysing different media, e.g. saliva. Patient follow-up over time or between laboratories, as well as longitudinal studies are extremely difficult. In contrast to immunoassays, which allow the measurement of only a single steroid at a time, LC-MS/MS has the advantage that a wide spectrum of steroid hormones can be measured simultaneously. The applicability for clinical samples and problems in pediatric endocrinology will be discussed.

Preliminary Evaluation of the New TACR Flex Method Versus MEIA Method in the Therapeutic Monitoring of Tacrolimus in Organ Transplantation

Tacrolimus (FK506) is an effective macrolide immunosuppressant widely used to prevent organ rejection following transplantation. Monitoring blood levels of tacrolimus is essential to assess organ rejection versus toxicity, because of the narrow therapeutic range and pharmacokinetic variability. The increased request for therapeutic drug monitoring is an interesting challenge for clinical laboratories. The automated immunoassay methods provide correct results and a turnaround time considerably reduced compared to HPLC and HPLC-MS which remain the gold standard for accuracy and economical advantages. A new immunoassay method, TACR Flex Dimension, is a commercially available, automated pretreatment test. The purpose of this study was to compare two analytical methods: the MEIA II tacrolimus immunoassay using the IMx analyzer and the new TACR Flex tacrolimus immunoassay on the Dimension system. Tacrolimus results obtained using the two methods were compared using European control and 93 whole blood samples from kidney and liver transplant patients. The tacrolimus concentrations measured by Flex Dimension for all samples were higher (0.7 to 16.1 ng/mL) than results obtained with MEIA (0.2 to 13.4 ng/mL), a mean difference expressed in percentage of 31.7%, and a correlation coefficient of 0.85. The data obtained by both methods using three European controls showed similar concentrations. The TACR Flex Dimension method provided a higher automation level and therefore a lower incidence of preanalytical errors and a lower turnaround time.

Comparison of the CEDIA® and MEIA® assays for the measurement of sirolimus in organ transplant recipients

OBJECTIVES

This study evaluated two immunoassays, the CEDIA assay and the MEIA assay, used for the measurement of whole blood levels of sirolimus in organ transplant recipients.

DESIGN AND METHODS

We report on the performance characteristics (total precision, limit of quantitation (functional sensitivity), limit of detection (analytical sensitivity), linearity, accuracy) for each assay. Patient correlation studies were performed, and the results were analyzed using Bland-Altman plots and Passing-Bablok analysis.

RESULTS

Total precision for the MEIA assay, corresponding to three mean concentrations of 5.0, 10.6 and 20.2 ng/mL, was 10.5, 8.5, and 6.7%, respectively. The limit of detection was determined to be 1.1 ng/mL and the limit of quantitation was 1.5 ng/mL. The mean recovery for CEDIA was 105.4%, and analysis of proficiency material demonstrated a large negative bias with respect to the mass spectrometry peer mean-later determined to be due to matrix interference. Results for the CEDIA assay showed a total precision, corresponding to a mean concentration of 5.4, 10.5 and 20.7 ng/mL, of 13.5, 5.6, and 4.1%, respectively. The limit of detection was found to be 4.8 ng/mL, with a limit of quantitation of 5.2 ng/mL. The mean recovery for MEIA was 110.1%, and analysis of proficiency material demonstrated good agreement with the mass spectrometry peer mean with a slight positive bias. Both assays were acceptably linear over the reportable range of the assay. Patient correlation studies demonstrated a positive average bias for both assays versus results from LC-MS measurement (0.9 ng/mL for MEIA, 2.1 ng/mL for CEDIA).

CONCLUSION

Based on this evaluation, the MEIA demonstrated acceptable performance for use in clinical monitoring of sirolimus. However, based on a higher limit of quantitation that falls within the therapeutic interval, the CEDIA is not recommended for clinical monitoring of sirolimus.

Current role of LC-MS in therapeutic drug monitoring

The role of liquid chromatography coupled with mass spectrometry (LC-MS) techniques in routine therapeutic drug monitoring activity is becoming increasingly important. This paper reviews LC-MS methods published in the last few years for certain classes of drugs subject to therapeutic drug monitoring: immunosuppressants, antifungal drugs, antiretroviral drugs, antidepressants and antipsychotics. For each class of compounds, we focussed on the most interesting methods and evaluated the current role of LC-MS in therapeutic drug monitoring.

Simultaneous LC–MS–MS determination of cyclosporine A, tacrolimus, and sirolimus in whole blood as well as mycophenolic acid in plasma using common pretreatment procedure

The purpose of the study was to develop rapid and simple procedure for simultaneous determination of cyclosporine A (CsA), tacrolimus (TCR), and sirolimus (SIR) in whole blood and mycophenolic acid (MPA) in plasma. Ascomycin (ASCO), cyclosporine D (CsD), and desmethoxysirolimus (DMSIR) were used as internal standards (IS) for TCR, CsA and MPA, and SIR, respectively. In the method development, six-level blood calibrators were used for CsA (range 47-1725 ng/ml), TCR (range 2.1-38.8 ng/ml), and SIR (range 2.4-39.6 ng/ml). Four-level calibrators were used for MPA (range 0.15-5.48 microg/ml). Four levels of quality control (QC) standards were used for blood samples, together with two levels of QC standards in plasma. All QC standards and calibrators were obtained from commercial sources. Sample preparation based on precipitation of 50 microl of sample in zinc sulfate-methanol-acetonitrile mixture containing IS, followed by centrifugation. HPLC was performed on ChromSpher pi column, 30 mm x 3 mm, in ballistic gradient of ammonium formate buffer-methanol at 0.8 ml flow rate. Following gradient elution profile was applied: 0-1.2 min at 30% methanol (divert valve to waste), 1.21-3.1 min 97% methanol (divert valve to detector), 3.11-3.7 min 30% methanol (divert valve to waste). ESI-MS-MS (MRM) was done on TSQ Quantum instrument with ESI source in positive ion mode. Ammoniated adducts of protonated molecules were used as precursor ions for all analytes but MPA. For this compound sodium adduct was used. Following transitions were monitored: for CsA m/z 1220-1203; for CsD 1234-1217; for SIR 931.6-864.5 and 882.6; for DMSIR 902-834.5; for TCR 821.5-768.5 and 785.5; for ASCO 809.5-756; for MPA 343-211.6; for MPA-glucuronide 514-306 and 211.6. The limits of quantitation were: 1 ng/ml for TCR and SIR, 20 ng/ml for CsA, and 0.1 microg/ml for MPA. Post-column infusion experiments showed that no positive or negative peaks appeared after injection of matrix in the elution range of target compounds. General signal suppression caused by matrix ranged from 20-40%, and was caused mainly by zinc sulfate present in deproteinizing solution. Extracted samples were stable for 2 days at 4 degrees C and for at least 20 days at -20 degrees C. MPA was fully separated from its glucuronide, which was eluted at around 0.7-0.8 min and directed to the waste. Some mutual cross-contribution of CsD and CsA was observed (below 1%), other IS did not contribute to target compounds and vice versa. Observations of chromatograms from patients taken single therapy demonstrated that possible metabolites of CsA, TCR, or SIR did not interfere with target compounds or IS.

Comparative bioavailability of the microemulsion formulation of cyclosporine (Neoral) with a generic dispersion formulation (Cicloral) in young healthy male volunteers

The aim of this study was to compare the bioavailability of cyclosporine (CyA) from the generic dispersion formulation Cicloral (CIC) with the microemulsion formulation Neoral (NEO) and the original Sandimmune (SIM) capsules after single doses of 100, 300, or 600 mg of drug, respectively. The study was performed according to an open 3-period cross-over design with 12 young healthy male volunteers for each dosage. The concentrations of CyA and its main metabolites were determined by high performance liquid chromatography in whole blood and urine up to 48 hours postdosing. Peak concentrations and area under the time-concentration curve were greater for the NEO and CIC formulations compared with SIM, and the mean bioavailability of CIC was significantly (P<0.05) lower compared with NEO. The bioavailability of SIM compared with NEO was 54% to 71%, in agreement with previous results. Bioequivalence was not demonstrated between CIC (test) and NEO (reference) as the 90% confidence intervals were outside the 80% to 125% guidelines based on log-transformed AUCs, and were 75.2% to 87.7% at 100 mg, 79.2% to 91.8% at 300 mg, and 76.6% to 94.5% at 600 mg doses. The respective values for Cmax were 78.9% to 94.6%, 80.7% to 95.0%, and 71.4% to 84.1%. A good correlation was demonstrated between the urinary recovery of CyA and the AUC4. Therefore, the urinary recovery of CyA may be helpful as a surrogate parameter for the systemic exposure of patients to CyA. Whereas the relative amount of hydroxylated metabolites (AM1, AM9, AM1c) was similar for all formulations and doses, the urinary recovery of the N-demethylated metabolite AM4N decreased with increasing dose indicating saturable metabolism. No relationship could be demonstrated between CYP3A activity using dextromethorphan as a probe for the metabolic clearance of CyA.

Application of the EMIT 2000 Tacrolimus assay on the Abbott Architect c8000 high volume clinical chemistry analyzer

OBJECTIVES

Evaluation of the performance of the EMIT 2000 Tacrolimus assay on the Abbott Architect c8000 analyzer.

DESIGN AND METHODS

Imprecision studies were performed and patient samples were assayed by EMIT assay and by LC-MS/MS.

RESULTS

Limit of quantification was established at 2.8 microg/L. A positive bias of 17.5% between results measured on EMIT and on LC-MS/MS was detected.

CONCLUSIONS

EMIT 2000 Tacrolimus assay is suitable for automated analyses of Tacrolimus on the Architect c8000.

Evaluation of a fluorescent polarization immunoassay for whole blood everolimus determination using samples from renal transplant recipients

OBJECTIVES

This study compared the performance of a fluorescent polarization immunoassay (FPIA) against HPLC-tandem mass spectrometry (HPLC-MS) for the measurement of everolimus in renal transplant recipients.

DESIGN AND METHODS

A total of 333 pre-dose samples from 45 renal transplant patients were analyzed by FPIA and HPLC-MS.

RESULTS

The inter-batch inaccuracy and precision of the FPIA for control samples were <or=6% and <or=13.0%, respectively (n = 17). The comparison of patient results yielded the Deming regression equation FPIA = 1.19 x HPLC-MS + 0.51. The mean bias was 24.4% (95% CI: -3.0 to 54.2%, range: -30.1% to 79.4%).

CONCLUSIONS

The FPIA had acceptable analytical performance during the study but compared to HPLC-MS overestimated everolimus in patient samples. This overestimation is probably due to calibration differences between the methods and cross-reactivity of the FPIA antibody with everolimus metabolites. The clinical importance of the observed overestimation by FPIA requires further investigation.

Simultaneous determination of everolimus and cyclosporine concentrations by HPLC with ultraviolet detection

In the clinical practice of organ transplantation everolimus (RAD) is used in combination with cyclosporine (CsA), the most common antirejection agent. Both drugs show a narrow therapeutic window, which requires strict monitoring of their blood concentration. Simple methods for simultaneous measurement of RAD and CsA concentration are needed. As we have recently developed an HPLC-UV assay for RAD determination, we decided to implement it to allow concomitant measurement of CsA. The within- and between-day coefficients of variation of the measurement were less than 12.1% for RAD and 9.8% for CsA. The within- and between-day inaccuracy of quality control samples were less than 9.7% for RAD and less than 4.9% for CsA. The method was found accurate and precise and useful for simultaneous therapeutic monitoring of the two drugs.

The nucleotide derivatives inosine and inosinic acid inhibit intestinal absorption of mizoribine in rats

Inosine is absorbed via a N1 transporter that is selective for purine nucleosides. It is conceivable that inosine and inosinic acid might affect the intestinal absorption of mizoribine, an imidazole nucleoside that inhibits the de novo production pathway of guanine ribonucleotide. An in situ loop experiment was performed using four intestinal loop segments prepared by ligation: segment 1, about 6 to 9 cm from the end of the pylorus; segment 2, about 10 to 13 cm; segment 3, about 14 to 17 cm; and segment 4, about 18 to 21 cm. Mizoribine (0.1 mg/ml) or mizoribine+inosine (1 or 10 mg/ml) were infused into each loop. The absorption rate in the most proximal segment of intestinal loop was the highest. In the presence of inosine, this rate decreased significantly. Urinary recovery rates of mizoribine were significantly decreased by pretreatment with inosine or inosinic acid. The Cmax in the group given mizoribine+inosinic acid was significantly lower than that in the group given mizoribine alone. These results strongly indicate that (I) the N1 transporter in the intestine might act to absorb mizoribine; and (II) inosine and inosinic acid might competitively inhibit the absorption of mizoribine via the N1 transporter.

Cyclosporin A, tacrolimus and sirolimus are potent inhibitors of the human breast cancer resistance protein (ABCG2) and reverse resistance to mitoxantrone and topotecan

PURPOSE

Several studies have demonstrated significant interactions between immunosuppressants (e.g., cyclosporin A) and chemotherapeutic drugs that are BCRP substrates (e.g., irinotecan), resulting in increased bioavailability and reduced clearance of these agents. One possible mechanism underlying this observation is that the immunosuppressants modulate the pharmacokinetics of these drugs by inhibiting BCRP. Therefore, the aim of this study was to determine whether the immunosuppressants cyclosporin A, tacrolimus and sirolimus are inhibitors and/or substrates of BCRP.

METHODS

First, the effect of the immunosuppressants on BCRP efflux activity in BCRP-expressing HEK cells was measured by flow cytometry.

RESULTS

Cyclosporin A, tacrolimus and sirolimus significantly inhibited BCRP-mediated efflux of pheophorbide A, mitoxantrone and BODIPY-prazosin. The EC(50) values of cyclosporin A, tacrolimus and sirolimus for inhibition of BCRP-mediated pheophorbide A efflux were 4.3 +/- 1.9 microM, 3.6 +/- 1.8 microM and 1.9 +/- 0.4 microM, respectively. Cyclosporin A, tacrolimus and sirolimus also effectively reversed resistance of HEK cells to topotecan and mitoxantrone conferred by BCRP. When direct efflux of cyclosporin A, tacrolimus and sirolimus was measured, these compounds were found not to be transported by BCRP. Consistent with this finding, BCRP did not confer resistance to the immunosuppressants in HEK cells.

CONCLUSION

These results indicate that cyclosporin A, tacrolimus and sirolimus are effective inhibitors but not substrates of BCRP. These findings could explain the altered pharmacokinetics of BCRP substrate drugs when co-administered with the immunosuppressants and suggest that pharmacokinetic modulation by the immunosuppressants may improve the therapeutic outcome of these drugs.

Applicability of bioanalysis of multiple analytes in drug discovery and development: review of select case studies including assay development considerations

The development of sound bioanalytical method(s) is of paramount importance during the process of drug discovery and development culminating in a marketing approval. Although the bioanalytical procedure(s) originally developed during the discovery stage may not necessarily be fit to support the drug development scenario, they may be suitably modified and validated, as deemed necessary. Several reviews have appeared over the years describing analytical approaches including various techniques, detection systems, automation tools that are available for an effective separation, enhanced selectivity and sensitivity for quantitation of many analytes. The intention of this review is to cover various key areas where analytical method development becomes necessary during different stages of drug discovery research and development process. The key areas covered in this article with relevant case studies include: (a) simultaneous assay for parent compound and metabolites that are purported to display pharmacological activity; (b) bioanalytical procedures for determination of multiple drugs in combating a disease; (c) analytical measurement of chirality aspects in the pharmacokinetics, metabolism and biotransformation investigations; (d) drug monitoring for therapeutic benefits and/or occupational hazard; (e) analysis of drugs from complex and/or less frequently used matrices; (f) analytical determination during in vitro experiments (metabolism and permeability related) and in situ intestinal perfusion experiments; (g) determination of a major metabolite as a surrogate for the parent molecule; (h) analytical approaches for universal determination of CYP450 probe substrates and metabolites; (i) analytical applicability to prodrug evaluations-simultaneous determination of prodrug, parent and metabolites; (j) quantitative determination of parent compound and/or phase II metabolite(s) via direct or indirect approaches; (k) applicability in analysis of multiple compounds in select disease areas and/or in clinically important drug-drug interaction studies. A tabular representation of select examples of analysis is provided covering areas of separation conditions, validation aspects and applicable conclusion. A limited discussion is provided on relevant aspects of the need for developing bioanalytical procedures for speedy drug discovery and development. Additionally, some key elements such as internal standard selection, likely issues of mass detection, matrix effect, chiral aspects etc. are provided for consideration during method development.

Simultaneous quantitative determination of cyclosporine A and its three main metabolites (AM1, AM4N and AM9) in human blood by liquid chromatography/mass spectrometry using a rapid sample processing method

We have developed a sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method for the simultaneous determination of cyclosporine A (CsA) and its three main metabolites (AM1, AM4N and AM9) in human blood. Following protein precipitation, supernatant was directly injected into the LC/MS system. Chromatographic separation was accomplished on a Symmetry C8 (4.6 x 75 mm, 3.5 microm) column with a linear gradient elution prior to detection by atmospheric pressure chemical ionization (APCI) MS using selected ion monitoring (SIM) in positive mode. This method can be applied to single mass equipment. The analytical range for each analyte was set at 1-2500 ng/mL using 100 microL of blood sample. The analytical method was fully validated according to FDA guidance. Intra-day mean accuracy and precision were 95.2-113.5% and 0.9-8.9%, respectively. Inter-day mean accuracy and precision were 95.8-107.0% and 1.5-10.7%, respectively. In blood all analytes were stable during three freeze/thaw cycles, for 24 h at room temperature and for 12 months at or below -15 degrees C. Stability was also confirmed in processed samples for 24 h at 10 degrees C and for 6 months at 4 degrees C in methanol. In addition, we confirmed the method could avoid matrix effects from transplant subjects' samples. This LC/MS technique provided an excellent method for simultaneous quantitative determination of CsA and its three metabolites for evaluation of their pharmacokinetic profiles.

Simultaneous determination of three isomeric metabolites of tacrolimus (FK506) in human whole blood and plasma using high performance liquid chromatography–tandem mass spectrometry

An ammonium-adduct based liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous determination of three isomeric metabolites of tacrolimus (FK506), 13-O-demethylated (M1), 31-O-demethylated (M2) and 15-O-demethylated (M3) tacrolimus in human whole blood and plasma. These metabolites and the internal standards were extracted from biological matrix by methylbutyl ether (MTBE). Separation was achieved on a Genesis C(18) column with a gradient mobile phase elution. Ammonium-adduct ions formed by a Turbo Ionspray in positive ion mode were used to detect each analyte and internal standard. The MS/MS detection was by monitoring the fragmentation of 807.5-->772.4 (m/z) for M1, 807.5-->754.5 (m/z) for both M2 and M3, 795.5-->760.5 (m/z) for IS1 (FR298701) and 961.5-->908.5 (m/z) for IS2 (FR290198) on a triple quadrupole mass spectrometer (Sciex API 3000). The retention times were approximately 4.1 min for M1, 6.8 min for M2, 6.0 min for M3, and 3.9 min for IS1 and 6.4 min for IS2, respectively. The validated dynamic range was 0.2-20 ng/ml for all three metabolites based on a sample volume of 0.25-ml. The linearity of calibration curves for M1, M2, and M3 in both matrices had a correlation coefficient of >/=0.9984. In whole blood, validation data showed intra-batch (n=6) CVs of </=5.9% and REs between -4.9 and 3.6% and inter-batch (N=18) CVs of </=4.9% and REs between -3.5 and 1.5% for all three metabolites. In human plasma, validation data showed intra-batch (n=6) CVs of </=7.3% and REs between -5.1 and 7.6% and inter-batch (N=18) CVs of </=6.6% and REs between -0.3 and 4.7% for all three metabolites. Extraction recoveries were 72% for M1, 87% for M2, 69% for M3, 79% for IS1, and 74% for IS2 from blood; and 94% for M1, 96% for M2, 98% for M3, 92% for IS1, and 93% for IS2 from plasma. All three metabolites in human blood and plasma were stable for three freeze-thaw cycles, or 24-h ambient storage, or 12 months storage at approximately -80 degrees C. Extracted samples were stable for at least 50h at room temperature (RT). This method has been successfully used to analyze whole blood and plasma samples from human pharmacokinetic studies. Several key factors affecting the performance of the assay methods have also been addressed briefly.