Analytical Performance of QMS Everolimus Assay on Ortho Vitros 5,1 FS Fusion Analyzer: Measuring Everolimus Trough Levels for Solid Organ Transplant Recipients

Analytical Performance of the New Siemens Affinity Chrome-Mediated Immunoassay Everolimus Assay and Its Interchangeability With the Thermo Quantitative Microsphere System for Routine Therapeutic Drug Monitoring of Patients After Solid Organ Transplantation

BACKGROUND

A new homogeneous affinity chrome-mediated immunoassay (ACMIA) "EVRO" from Siemens Healthcare was evaluated for therapeutic drug monitoring of everolimus (EVL) with automated sample pretreatment and compared with quantitative microsphere system (QMS) "EVER" from Thermo Fisher Scientific.

METHODS

Imprecision, inaccuracy, and limit of quantitation (LoQ) of ACMIA/EVRO were verified using both hemolysate quality control (QC) samples and pooled whole blood specimens. The interchangeability of methods and the agreement of results were analyzed using 72 specimens (from 38, 30, and 4 kidney, liver, and lung transplant recipients, respectively).

RESULTS

Within-run imprecision ranged within %CV = 2.81-2.53 with pooled whole blood specimens and within %CV = 2.88-2.53 with QCs; total imprecision with QCs was within %CV = 2.14-1.51. Inaccuracy with value assigned QC was %△ = 5.36 at the 5.6 ng/mL level and %△ = 5.56 at the 11.7 ng/mL level. LoQ was 0.93 ng/mL (%CV = 10). Passing-Bablok regression showed a constant bias of 0.679 ng/mL (95% CI: 0.216-1.026) and a proportional bias of 1.326 (95% CI: 1.240-1.425). Bland-Altman analysis showed 5/72 (6.9%) paired differences exceeding the limits of agreement and 1/72 (1.4%) paired differences exceeding 1.96 SD to a combined bias of 39.9% after detrending.

CONCLUSIONS

ACMIA/EVRO shows satisfactory analytical performances that comply with recommendations, but it does not fulfill requirements for interchangeability with QMS/EVER. Particularly, this new assay using sirolimus-specific antibody shows a sizable proportional bias versus the more specific comparator, which may be because of EVL metabolites. This is supported by the lack of agreement for individual differences in most samples collected at the peak concentration (C2). Therefore, further evidence is needed to support the transition of EVL level monitoring from QMS/EVER to ACMIA/EVRO without making extensive changes to both reference interval and patient's baseline.

Multicenter Evaluation of a New Electrochemiluminescence Immunoassay for Everolimus Concentrations in Whole Blood

BACKGROUND

The precise monitoring of everolimus, an immunosuppressant drug, is vital for transplant recipients due to its narrow therapeutic range. This study evaluated the analytical performance of a new electrochemiluminescence immunoassay (ECLIA) for everolimus concentrations in whole blood.

METHODS

Accuracy, imprecision, and sensitivity studies for the Roche Elecsys everolimus ECLIA were performed at 5 European laboratories. The ECLIA was compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods, as well as the Quantitative Microsphere System everolimus assay.

RESULTS

Everolimus ECLIA accuracies were within the range 100% ± 9%. Coefficients of variation (CVs) across the target range were ≤4.8% for repeatability and ≤8.4% for intermediate imprecision, whereas multisite reproducibility at lower (2.71 mcg/L) and higher everolimus concentrations (3.0-30.0 mcg/L) resulted in CVs of ≤13.7% and ≤12.4%, respectively. The CV at the assay's lower limit of quantification without considering bias was excellent, estimated as ≤9.3% at 0.5 mcg/L. The weighted Deming regression analysis, used for comparison of the results obtained by everolimus ECLIA and by LC-MS/MS methods, yielded a slope of 1.21 [95% confidence interval (CI): 1.15-1.26], intercept of 0.478 mcg/L (95% CI: 0.241-0.716), and a Pearson correlation coefficient (r) of 0.91. A single-site comparison between the ECLIA and the Quantitative Microsphere System assay revealed a slope of 1.05 (95% CI: 0.917-1.17), intercept of 1.03 mcg/L (95% CI: 0.351-1.70), and r of 0.91.

CONCLUSIONS

Based on these results, the Roche Elecsys everolimus ECLIA can be considered suitable for routine therapeutic drug monitoring. A positive bias was observed with respect to LC-MS/MS methods, suggesting that it may be necessary to rebaseline individual patients when switching from LC-MS/MS to the ECLIA; however, this must also be considered for any change of method for everolimus measurement.

Therapeutic Drug Monitoring of Everolimus: Comparability of Concentrations Determined by 2 Immunoassays and a Liquid Chromatography Tandem Mass Spectrometry Method

BACKGROUND

Therapeutic drug monitoring is recommended to guide therapy with the immunosuppressant everolimus (EVL) in solid organ transplantation to prevent rejections and to limit toxicity. For therapeutic drug monitoring, predose EVL concentrations are measured in whole blood mainly by liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, 2 immunoassays [Quantitative Microsphere System (QMS) EVL and Elecsys EVL] are commercially available. The aim of this study was to evaluate the comparability of EVL results determined with the 2 immunoassays and a validated LC-MS/MS test using samples from kidney, liver, and heart transplant (KT, LT, and HT, respectively) recipients.

METHODS

Analysis of predose samples from KT (n = 56), LT (n = 60), and HT (n = 59) recipients, obtained at variable time points after transplantation, was performed by LC-MS/MS and with the 2 immunoassays. The QMS EVL assay was applied on Dimension Xpand Plus and the Elecsys EVL assay on cobas e 411 analyzer. Results were compared by the Spearman's rank correlation coefficient, unbiased Passing and Bablok linear regression test, and Bland-Altman plot.

RESULTS

Results generated with both immunoassays correlated well with those of LC-MS/MS. An overestimation of EVL concentrations by the Elecsys EVL compared with LC-MS/MS was observed (mean bias: 34.2%). Using the QMS EVL, a small but significant negative deviation (mean bias: -8.0%) was found. Looking at KT, HT, and LT samples separately, the bias to LC-MS/MS seen with the Elecsys EVL was similar. With the QMS EVL, the best agreement was observed with the KT samples followed by LT and HT.

CONCLUSIONS

Results generated by the 3 methods are not consistent regarding their diagnostic value. Both laboratories and manufacturers should take care to inform their costumers about the between-method differences to avoid misinterpretation of the results in clinical practice.

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.

Long-term cross-validation of everolimus therapeutic drug monitoring assays: the Zortracker study

BACKGROUND

This ongoing academic collaboration was initiated for providing support to set up, validate, and maintain everolimus therapeutic drug monitoring assays and to study long-term interlaboratory performance.

METHODS

This study was based on EDTA whole blood samples collected from transplant patients treated with everolimus in a prospective clinical trial. Samples were handled under controlled conditions during collection, storage and were shipped on dry ice to minimize freeze-thaw cycles. For more than 1.5 years, participating laboratories received a set of 3 blinded samples on a monthly basis. Among others, these samples included individual patient samples, patient sample pools to assess long-term performance, and patient samples pools enriched with isolated everolimus metabolites.

RESULTS

The results between liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and the everolimus Quantitative Microsphere System (QMS, Thermo Fisher) assay were comparable. The monthly interlaboratory variability (coefficient of variation %) for cross-validation samples ranged from 6.5% to 23.2% (average of 14.8%) for LC-MS/MS and 4.2% to 26.4% (average of 11.1%) for laboratories using the QMS assay. A blinded long-term pool sample was sent to the laboratories for 13 months. The result was 5.31 ± 0.86 ng/mL (range, 2.9-7.8 ng/mL) for the LC-MS/MS and 5.20 ± 0.54 ng/mL (range, 4.0-6.8 ng/mL) for QMS laboratories. Enrichment of patient sample pools with 5-25 ng/mL of purified everolimus metabolites (46-hydroxy everolimus and 39-O-desmethyl everolimus) did not affect the results of either LC-MS/MS or QMS assays.

CONCLUSIONS

Both LC-MS/MS and QMS assays gave similar results and showed similar performance, albeit with a trend toward higher interlaboratory variability among laboratories using LC-MS/MS than the QMS assay.

Therapeutic drug monitoring of immunosuppressants by liquid chromatography-mass spectrometry

Immunosuppressant medications allow the transplantation of tens of thousands of allografts per year and consequently have great potential to decrease patient morbidity and mortality. However, some medications have great risk associated with over- and under-dosing leading to adverse effects or allograft rejection, respectively. This necessitates immunosuppressant therapeutic drug monitoring accomplished by immunoassay or liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The former's accuracy can be hindered by metabolites of immunosuppressant medications, antibodies against these medications and heterophilic antibodies. Although LC-MS/MS has superior specificity which allows it to be less susceptible to interference, this methodology lacks standardization and the necessary throughput. Recent developments in LC-MS/MS quantitation, however, include patient-friendly sample submission as dried blood spots, higher sample throughput and commercialization. Here we critically review recent LC-MS/MS publications (January 2010 to July 2015) on the quantitation of cyclosporine A, tacrolimus, sirolimus and everolimus.