Multi-center evaluation of a commercial Kit for tacrolimus determination by LC/MS/MS

Cascadion™ SM Clinical Analyzer: Evaluation of the whole blood immunosuppressants quantification and routine usability

BACKGROUND

Liquid chromatography coupled with tandem mass spectrometry (LC- MS/MS) tends to overcome other methods for therapeutic drugs monitoring (TDM) due to its very good analytical performances. Nevertheless, the lack of automation still limits its use in laboratory medicine. The Cascadion SM Clinical Analyzer (Thermo Fisher Scientific) is the first fully automated LC-MS/MS instrument available. We evaluated its immunosuppressant drugs (ISD) assay and the incorporation of such instrument into a core-laboratory.

METHODS

An extended analytical verification of the Cascadion ISD panel including cyclosporin A, tacrolimus, everolimus and sirolimus was performed. It was compared to the MassTox ISD assay (Chromsystems). Different preanalytical and analytical conditions were tested. Finally, a turnaround-time evaluation and a satisfaction survey of users after 11 months of use in a core-laboratory were performed.

RESULTS

Precision and linearity results were within the analytical goals fixed. The comparison with the MassTox ISD assay showed results in agreement except for cyclosporin A where a bias of -11.6% was observed, probably due to a greater trueness of the Cascadion method. Additional experiments showed good performances. The random accessibility and the ease of use by non-specialized staff members allowed a wider working time range and a reduction of the turnaround-time of 55%.

CONCLUSION

The Cascadion ISD Panel held its promises in term of analytical performances, workflow aspects and ease of use by non-specialized staff.

Development and Validation of the New Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Unbound Tacrolimus in the Plasma Ultrafiltrate of Transplant Recipients

(1) Background: Only unbound tacrolimus particles are considered to be active and capable of crossing cellular membranes. Thus, the free-drug concentration might be better associated with clinical effects than the total drug concentration used for dosage adjustment. We propose a new, fully validated online liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for unbound tacrolimus concentration measurement. (2) Methods: The determination of the unbound tacrolimus concentration in plasma ultrafiltrate was performed with the Nexera LC system with LCMS-8050 triple quadrupole MS using ascomycin as an internal standard. Chromatographic separation was made using a HypurityC18 analytical column. MS/MS with electrospray ionization and positive-ion multiple-reaction monitoring was used. The unbound tacrolimus level was determined in 36 patients after solid organ transplantation (n = 140). (3) Results: A lower limit of quantification 0.1 pg/mL was achieved, and the assay was linear between 0.1 and 20 pg/mL (R2 = 0.991). No carry-over was detected. The within-run and between-run accuracies ranged between 97.8–109.7% and 98.3–107.1%, while the greatest imprecision was 10.6% and 10.7%, respectively. Free tacrolimus in patients’ plasma ultrafiltrate varied between 0.06 and 18.25 pg/mL (median: 0.98 pg/mL). (4) Conclusions: The proposed method can be easily implemented. The significance of the unbound tacrolimus concentration needs to be investigated. This may facilitate the individualization and optimization of immunosuppressive treatment.

A new paper-based biosensor for therapeutic drug monitoring

Tacrolimus is one of the most effective and prevalent drugs used to combat vascularized composite allotransplantation rejection. We have fabricated a rapid and easy-to-use six-layer paper based microfluidic device using the principles of competitive immunoassays and vertical flow microfluidics for colorimetric detection of tacrolimus in a small volume of blood.

Proteomic applications in pathology and laboratory medicine: Present state and future prospects

Clinical mass spectrometry applications have traditionally focused on small molecules, particularly in the areas of therapeutic drug monitoring, toxicology, and measurement of endogenous and exogenous steroids. More recently, the use of matrix assisted laser desorption/ionization time of flight mass spectrometry for the identification of microbial pathogens has been widely implemented. Following this evolution, there has been an expanding role for the measurement of peptides and proteins in pathology and laboratory medicine. This review explores the current state of protein measurement by clinical mass spectrometry and the analytical strategies employed, as well as emerging applications in clinical chemistry, clinical microbiology and anatomical pathology.

Simultaneous determination of cyclosporine and tacrolimus in human whole blood by ultra-high performance liquid chromatography tandem mass spectrometry and comparison with a chemiluminescence microparticle immunoassay

Overestimation of immunoassays for cyclosporine (CsA) and tacrolimus (TAC) analysis in human whole blood is a problem. The liquid chromatography tandem mass spectrometry is recommended as a golden method for CsA and TAC analysis. The aim of the study is to develop and validate an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous determination of CsA and TAC in human whole blood and evaluate its agreement with a chemiluminescence microparticle immunoassay (CMIA). The UHPLC-MS/MS method for simultaneous determination of CsA and TAC in human whole blood was developed and validated according to the guidelines. A total of 177 CsA and 220 TAC samples were determined by UHPLC-MS/MS and CMIA, and the agreement of the two methods was evaluated by Bland-Altman plot. The calibration range of UHPLC-MS/MS method was 5 to 2000 ng/mL for CsA and 0.2 to 80 ng/mL for TAC. The inaccuracy and imprecision were -13.33% to 11.80% and <11.74% for CsA and -8.94% to 6.53% and <10.84% for TAC, respectively. Evaluated by Bland-Altman plot, the mean overestimation of CMIA compared to UHPLC-MS/MS was 53.7% for CsA and 48.1% for TAC.

Evaluation of the Waters MassTrak LC-MS/MS Assay for Tacrolimus and a Comparison to the Abbott Architect Immunoassay

BACKGROUND

Tacrolimus (Prograf, Advagraf, and FK-506) is the most commonly prescribed calcineurin inhibitor after kidney and liver transplantation. The use of tacrolimus (in conjunction with other drugs) has successfully contributed to the maintenance of solid organ allografts; however, it also exhibits toxic side effects. Therapeutic drug monitoring of tacrolimus is used as an aid to achieve drug concentrations within a narrow therapeutic window.

METHODS

The Waters MassTrak Immunosuppressants assay (LC-MS/MS) for the quantification of tacrolimus in whole blood was evaluated for precision, linearity, lower limit of quantification, matrix effects, and accuracy. A method comparison with the Abbott Architect Tacrolimus immunoassay was also performed.

RESULTS

The mean concentration (nanograms per milliliter) and coefficient of variation for low, mid, and high patient pools were 0.6% ± 19.9%, 16.0% ± 5.4%, and 31.2% ± 5.8%, respectively. The MassTrak assay was linear from 0.5 to 30.0 ng/mL. Although the MassTrak and Architect assays correlated well (R = 0.97) for patient samples, the MassTrak assay displayed an average negative bias of 18.5% versus Architect (range of 0.0%-36.7%). Analysis of a certified tacrolimus reference material in human whole blood [European Reference Materials (ERM)-DA110a, LGC Standards] on both platforms failed to completely explain the observed difference for patient samples.

CONCLUSIONS

Two widely used assays for therapeutic drug monitoring of tacrolimus are not in agreement with one another. Care should be exercised when interpreting results generated on these 2 assay platforms.

Fexofenadine, a Putative In Vivo P-glycoprotein Probe, Fails to Predict Clearance of the Substrate Tacrolimus in Renal Recipients

Whether the combined use of probe drugs for CYP3A4 and P-glycoprotein can clarify the relative contribution of these proteins to pharmacokinetic variability of a dual substrate like tacrolimus has never been assessed. Seventy renal recipients underwent simultaneous 8-h pharmacokinetic profiles for tacrolimus, the CYP3A4 probe midazolam, and the putative P-glycoprotein probe fexofenadine. Patients were genotyped for polymorphisms in CYP3A5, CYP3A4, ABCB1, ABCC2 and SLCO2B1, -1B1, and 1B3. Carriers of the ABCB1 2677G>A polymorphism displayed lower fexofenadine C_max (-66%; P = 0.012) and a trend toward higher clearance (+157%; P = 0.078). Predictors of tacrolimus clearance were CYP3A5 genotype, midazolam clearance, hematocrit, weight, and age (R² = 0.61). Fexofenadine pharmacokinetic parameters were not predictive of tacrolimus clearance. In conclusion, fexofenadine pharmacokinetics varied considerably between renal recipients but most of this variability remained unexplained, with only minor effects of genetic polymorphisms. Fexofenadine cannot be used to assess in vivo CYP3A4-P-glycoprotein interplay in tacrolimus-treated renal recipients.

Advances in Clinical Mass Spectrometry

Although mass spectrometry has been used clinically for decades, the advent of immunoassay technology moved the clinical laboratory to more labor saving automated platforms requiring little if any sample preparation. It became clear, however, that immunoassays lacked sufficient sensitivity and specificity necessary for measurement of certain analytes or for measurement of analytes in specific patient populations. This limitation prompted clinical laboratories to revisit mass spectrometry which could additionally be used to develop assays for which there was no commercial source. In this chapter, the clinical applications of mass spectrometry in therapeutic drug monitoring, toxicology, and steroid hormone analysis will be reviewed. Technologic advances and new clinical applications will also be discussed.

Comparative performance of oral midazolam clearance and plasma 4β-hydroxycholesterol to explain interindividual variability in tacrolimus clearance

AIMS

We compared the CYP3A4 metrics weight-corrected midazolam apparent oral clearance (MDZ Cl/F/W) and plasma 4β-hydroxycholesterol/cholesterol (4β-OHC/C) as they relate to tacrolimus (TAC) Cl/F/W in renal transplant recipients.

METHODS

For a cohort of 147 patients, 8 h area under the curve (AUC) values for TAC and oral MDZ were calculated besides measurement of 4β-OHC/C. A subgroup of 70 patients additionally underwent intravenous erythromycin breath test (EBT) and were administered the intravenous MDZ probe. All patients were genotyped for common polymorphisms in CYP3A4, CYP3A5 and P450 oxidoreductase, among others.

RESULTS

MDZ Cl/F/W, 4β-OHC/C/W, EBT and TAC Cl/F/W were all moderately correlated (r = 0.262-0.505). Neither MDZ Cl/F/W nor 4β-OHC/C/W explained variability in TAC Cl/F/W in CYP3A5 expressors (n = 29). For CYP3A5 non-expressors (n = 118), factors explaining variability in TAC Cl/F/W in a MDZ-based model were MDZ Cl/F/W (R²  = 0.201), haematocrit (R²  = 0.139), TAC formulation (R²  = 0.107) and age (R²  = 0.032; total R²  = 0.479). In the 4β-OHC/C/W-based model, predictors were 4β-OHC/C/W (R²  = 0.196), haematocrit (R²  = 0.059) and age (R²  = 0.057; total R²  = 0.312). When genotype information was ignored, predictors of TAC Cl/F/W in the whole cohort were 4β-OHC/C/W (R²  = 0.167), MDZ Cl/F/W (R²  = 0.045); Tac QD formulation (R²  = 0.036), and haematocrit (R²  = 0.032; total R²  = 0.315). 4β-OHC/C/W, but not MDZ Cl/F/W, was higher in CYP3A5 expressors because it was higher in CYP3A4*1b carriers, which were almost all CYP3A5 expressors.

CONCLUSIONS

A MDZ-based model explained more variability in TAC clearance in CYP3A5 non-expressors. However, 4β-OHC/C/W was superior in a model in which no genotype information was available, likely because 4β-OHC/C/W was influenced by the CYP3A4*1b polymorphism.

Progressive decline in tacrolimus clearance after renal transplantation is partially explained by decreasing CYP3A4 activity and increasing haematocrit

AIMS

The long-term disposition of tacrolimus following kidney transplantation is characterized by a gradual decrease in dose requirements and increase in dose-corrected exposure. This phenomenon has been attributed to a progressive decline in cytochrome P450 3A4 (CYP3A4) activity, although this has never been demonstrated in vivo.

METHODS

Sixty-five tacrolimus- and 10 cyclosporine-treated renal transplant recipients underwent pharmacokinetic testing at day 7 and months 1, 3, 6 and 12 after transplantation, including 8-h area under the concentration-time curve (AUC) for tacrolimus or cyclosporine and assessment of CYP3A4 activity using oral and intravenous midazolam (MDZ) drug probes.

RESULTS

Tacrolimus clearance decreased gradually throughout the entire first year but only in CYP3A5*3/*3 homozygous recipients (25.6 ± 11.1 l h(-1) at day 7; 17 ± 9.1 l h(-1) at month 12; P < 0.001). In mixed model analysis, decreasing CYP3A4 activity, measured by apparent oral MDZ clearance (924 ± 443 ml min(-1) at day 7 vs. 730 ± 344 ml min(-1) at month 1; P < 0.001), explained 55.4% of the decline in tacrolimus clearance in the first month. CYP3A4 activity decreased by 18.9 ml min(-1) for every milligram of methylprednisolone dose tapering within the first month; beyond this point it remained stable. A gradual rise in haematocrit throughout the entire first year explained 31.7% of the decrease in tacrolimus clearance in the first month and 23.6% of the decrease between months 1 and 12. Cyclosporine clearance did not change over time.

CONCLUSIONS

The maturation of tacrolimus disposition in the first year after renal transplantation observed in CYP3A5*3/*3 homozygous patients can partly be explained by a (steroid tapering-related) decline in CYP3A4 activity and a progressive increase in haematocrit.

Transplant patient classification and tacrolimus assays: more evidence of the need for assay standardization

BACKGROUND

A global tacrolimus proficiency study recently showed clinically significant variability between laboratories, the inability of a common calibrator to harmonize methods, and differences in patient classification depending on the test method. The authors evaluated (1) the effect of a change in methodology on patient classification based on tacrolimus blood concentration and (2) the ability of 2 methods to position the concentration in a given specimen within the correct range.

METHODS

A total of 839 consecutive samples were analyzed at The Rogosin Institute and New York Presbyterian Hospital for routine tacrolimus monitoring over 30 days. Concordance analysis between the methods was performed covering dosage target ranges of 8-10, 6-8, 4-6 ng/mL currently used at our center. Six Sigma Metrics were applied to statistically evaluate the discordance rate.

RESULTS

Deming regression comparing liquid chromatography-tandem mass spectrometry and immunoassay yielded y = 0.927x - 0.24; 95% confidence interval, 0.903-0.951; R = 0.875; n = 839. There were 310 pairs (37%) discordant by 1, 21 (2.5%) discordant by 2, and 4 (0.5%) discordant by 3 therapeutic ranges. Surprisingly, 40% of patient samples were discordant when therapeutic ranges were 2 ng/mL wide. This discordant rate is equivalent to 1.7 Sigma and falls far below the minimum acceptable threshold of 3 Sigma.

CONCLUSIONS

Both methods are capable of measuring tacrolimus in the clinically relevant range between 1 and 10 ng/mL, yet 40% of the samples were discordant with an unacceptable Sigma level. Standardization of tacrolimus assays will mitigate this issue.

FK506 reduces neuroinflammation and dopaminergic neurodegeneration in an α-synuclein-based rat model for Parkinson's disease

Alpha-synuclein (α-synuclein) is considered a key player in Parkinson's disease (PD), but the exact relationship between α-synuclein aggregation and dopaminergic neurodegeneration remains unresolved. There is increasing evidence that neuroinflammatory processes are closely linked to dopaminergic cell death, but whether the inflammatory process is causally involved in PD or rather reflects secondary consequences of nigrostriatal pathway injury is still under debate. We evaluated the therapeutic effect of the immunophilin ligand FK506 in a rAAV2/7 α-synuclein overexpression rat model. Treatment with FK506 significantly increased the survival of dopaminergic neurons in a dose-dependent manner. No reduction in α-synuclein aggregation was apparent in this time window, but FK506 significantly lowered the infiltration of both T helper and cytotoxic T cells and the number and subtype of microglia and macrophages. These data suggest that the anti-inflammatory properties of FK506 decrease neurodegeneration in this α-synuclein-based PD model, pointing to a causal role of neuroinflammation in the pathogenesis of PD.

The CYP3A4*22 C>T single nucleotide polymorphism is associated with reduced midazolam and tacrolimus clearance in stable renal allograft recipients

Tacrolimus, a dual substrate of CYP3A4 and CYP3A5 has a narrow therapeutic index and is characterized by high between-subject variability in oral bioavailability. This study investigated the effects of the recently described CYP3A4*22 intron 6 C>T single nucleotide polymorphism on in vivo CYP3A4 activity as measured by midazolam (MDZ) clearance and tacrolimus pharmacokinetics in two cohorts of renal allograft recipients, taking into account the CYP3A5*1/*3 genotype and other determinants of drug disposition. In CYP3A5 non-expressers, the presence of one CYP3A4*22T-allele was associated with a 31.7-33.6% reduction in MDZ apparent oral clearance, reflecting reduced in vivo CYP3A4 activity. In addition, at ⩾12 months after transplantation, steady-state clearance of tacrolimus was 36.8% decreased compared with homozygous CYP3A4*22CC-wild type patients, leading to 50% lower dose requirements. Both concurrent observations in stable renal allograft recipients are consistent with a reduced in vivo CYP3A4 activity for the CYP3A4*22T-allele.

Impact of CYP3A5 genotype on tacrolimus versus midazolam clearance in renal transplant recipients: new insights in CYP3A5-mediated drug metabolism

BACKGROUND & AIM

In vitro studies have identified both midazolam and tacrolimus as dual CYP3A4 and CYP3A5 substrates. In vivo; however, the CYP3A5 genotype has a marked impact on tacrolimus pharmacokinetics, whereas it seems not to affect midazolam pharmacokinetics. The aim of the current study was to explore this paradigm in a relevant clinical setting.

PATIENTS & METHODS

A case-control study in 80 tacrolimus-treated renal transplant recipients comparing systemic and apparent oral midazolam clearance and tacrolimus pharmacokinetics in CYP3A5 expressers (CYP3A5*1 allele carriers) and CYP3A5 nonexpressers (CYP3A5*3/*3) was performed.

RESULTS

CYP3A5 expressers display an approximately 2.4-fold higher tacrolimus clearance as compared with CYP3A5 nonexpressers, whereas there are no differences in systemic and apparent oral midazolam clearance.

CONCLUSION

These data confirm that in vivo CYP3A5 plays an important role in tacrolimus metabolism, while its contribution to midazolam metabolism in a relevant study population is limited. Furthermore, these data suggest that midazolam is to be considered as a phenotypic probe for in vivo CYP3A4 activity rather than combined CYP3A4 and CYP3A5 activity.

Standardization of LC-MS for Therapeutic Drug Monitoring of Tacrolimus

BACKGROUND

LC-MS is increasingly used for therapeutic drug monitoring of tacrolimus. A recent summary from an international proficiency-testing scheme demonstrated that the mass spectrometry respondents were the largest method group. However, these methods lack standardization, which may explain the relatively poor interlaboratory agreement for such methods. This study aimed to provide one path toward the standardization of tacrolimus quantification by use of LC-MS.

METHODS

A 40-member whole blood tacrolimus proficiency panel was circulated to 7 laboratories, 4 in the US and 3 in Europe, offering routine LC-MS–based quantification of tacrolimus. All laboratories used a common LC-MS platform and followed the manufacturer's instructions that accompanied an LC-MS reagent kit intended for tacrolimus quantification in whole blood samples. Four patient pools were prepared that had sufficient volume to allow comparison with a tacrolimus reference measurement procedure.

RESULTS

For the 40-member panel, the standardized MassTrak LC-MS assay demonstrated excellent agreement with a validated LC-MS method used by Analytical Services International (y = 1.02x − 0.02; r = 0.99). The CVs for the pooled patient samples ranged from 2.0% to 5.4%. The mean difference from the reference measurement procedure ranged from 0.4% to 4.4%.

CONCLUSIONS

Tacrolimus assay standardization, which must include all facets of the analysis, is necessary to compare patient results between laboratories and to interpret consensus guidelines. LC-MS can provide accurate and precise measurement of tacrolimus between laboratories.

Challenges in implementing clinical liquid chromatography-tandem mass spectrometry methods--the light at the end of the tunnel

The use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the clinical setting is a relatively new application. One of the significant barriers hampering the transition of LC-MS/MS from the research lab into a clinical setting is the uncertainty of how to successfully develop and validate a method that meets guidelines for clinical applications. Here, we have taken this seemingly overwhelming process and broken it into five general stages for consideration: assessing the clinical validity of a new LC-MS/MS assay, determination of feasibility, assay development, assay validation and post-implementation monitoring. Although various publications are available and serve as resources for determining development processes and acceptability criteria for specific LC-MS/MS assays, many of them are general recommendations or are specific to research applications that may not translate either practically or clinically. In this perspective special feature article, a resource is compiled that describes key differences between LC-MS/MS methods for research use versus clinical use. In addition, the challenges facing the expanding role of this technique in the clinical setting are discussed, including instrumentation/automation challenges, potential regulation of laboratory developed tests by the US Food and Drug Administration and standardization and harmonization of MS methods through the use of traceable materials and availability of guidance documents.

In vivo CYP3A4 activity, CYP3A5 genotype, and hematocrit predict tacrolimus dose requirements and clearance in renal transplant patients

Tacrolimus is metabolized by CYP3A4 and CYP3A5 and is characterized by a narrow therapeutic index and highly variable pharmacokinetics. This cross-sectional study in 59 renal transplant patients investigated the relationship among in vivo CYP3A4 activity (assessed using midazolam as a drug probe), CYP3A5 genotype on the one hand, and tacrolimus pharmacokinetics on the other hand, taking into account other potential determinants of tacrolimus disposition. In vivo CYP3A4 activity and CYP3A5 genotype explain 56-59% of variability in tacrolimus dose requirements and clearance, contributing ~25 and 30%, respectively. Hematocrit explains an additional 4-14%. These data indicate that CYP3A4- and CYP3A5-mediated tacrolimus metabolisms are major determinants of tacrolimus disposition in vivo and explain a substantial part of the clinically observed high interindividual variability in tacrolimus pharmacokinetics. Furthermore, these data provide a potential basis for a comprehensive approach to predicting tacrolimus dose requirement in individual patients and hence provide a strategy to tailor immunosuppressive therapy in transplant recipients.

The role of liquid chromatography-tandem mass spectrometry in the clinical laboratory

Liquid chromatography coupled to mass spectrometry (LC-MS/MS) is increasingly used as a routine methodology in clinical laboratories for the analysis of low molecular weight molecules. The high specificity in combination with high sensitivity and multi-analyte potential makes it an attractive complementary method to traditional methodology used for routine applications. Its strength and weaknesses in this context will be discussed and examples of successful clinical applications will be given. For LC-MS/MS to truly fulfil its promise in clinical diagnosis, the prerequisite steps being sample pre-treatment, chromatographic separation and detection by selected reaction monitoring must become more integrated as they are in conventional clinical analysers. The availability of ready-to-use reagents kits, eliminating efforts needed for method development and extensive validation, are likely to contribute to a wider acceptance of LC-MS/MS in clinical laboratories. Growing applicability of LC-MS/MS in the clinical laboratory field is expected from quantitative protein analysis.

The Need for Standardization of Tacrolimus Assays

BACKGROUND

Owing to the lack of an internationally recognized tacrolimus reference material and reference method, current LC-MS and immunoassay test methods used to monitor tacrolimus concentrations in whole blood are not standardized. The aim of this study was to assess the need for tacrolimus assay standardization.

METHODS

We sent a blinded 40-member whole-blood tacrolimus proficiency panel (0–30 μg/L) to 22 clinical laboratories in 14 countries to be tested by the following assays: Abbott ARCHITECT (n = 17), LC-MS (n = 9), and Siemens Dade Dimension (n = 5). Selected LC-MS laboratories (n = 4) also received a common calibrator set. We compared test results to a validated LC-MS method. Four samples from the proficiency panel were assigned reference values by using exact-matching isotope-dilution mass spectrometr at LGC.

RESULTS

The range of CVs observed with the tacrolimus proficiency panel was as follows: LC-MS 11.4%–18.7%, ARCHITECT 3.9%–9.5%, and Siemens Dade 5.0%–48.1%. The range of historical within-site QC CVs obtained with the use of 3 control concentrations were as follows: LC-MS low 3.8%–10.7%, medium 2.0%–9.3%, high 2.3%–9.0%; ARCHITECT low 2.5%–9.5%, medium 2.5%–8.6%, high 2.9%–18.6%; and Siemens/Dade Dimension low 8.7%–23.0%, medium 7.6%–13.2%, high 4.4%–10.4%. Assay bias observed between the 4 LC-MS sites was not corrected by implementation of a common calibrator set.

CONCLUSIONS

Tacrolimus assay standardization will be necessary to compare patient results between clinical laboratories. Improved assay accuracy is required to provide optimized drug dosing and consistent care across transplant centers globally.

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.

Development and validation of a quantitative assay based on tandem mass spectrometry

Many routine hospital and clinical research assays have relied upon immunoassay procedures to achieve sensitive measurements of a range of important analytes. Some of the methods have been developed in-house but increasingly commercial kits and automated analysers have become commonplace. The accuracies of these methods are under question in health care. Mass spectrometry (MS) is potentially a more accurate technique with the ability to demonstrate specificity. An introduction of the basic analytical aspects of liquid chromatography (LC)–MS/MS leads on to the validation of the method before general use. LC coupled with MS and tandem mass spectrometry (MSn) is being adopted in a number of hospital laboratories for the quantitative analysis of a number of analytes from physiological matrices, but standards for development and validation of such assays are not easily available. Most assays can be regarded as in-house methods and herein may lay the failure so far for mass spectrometric methods to improve quality of results between laboratories for an analyte using the same technology. Manufacturers are taking on board the experience of clinical laboratories with kits containing all or most of the disposable items and reagents. A number of documents and guidelines have been consulted. These documents are expensive to purchase, are often very long and not easy to read. This review highlights the specific requirements for introduction of a tandem mass spectrometric test for small molecules into a routine hospital laboratory. A number of experiments need to be planned and executed in order to describe a new quantitative method in terms of selectivity, accuracy, imprecision, sensitivity and stability. The introduction of a quantitative method based on tandem MS requires careful validation. This review has distilled out important points from a number of key documents in order to provide a working validation guideline for clinical laboratories. In a supplementary file a working document for assembling the assay validation is proposed.

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.