Evaluation of the Architect® tacrolimus assay in kidney, liver, and heart transplant recipients

A joint population pharmacokinetic model to assess the high variability of whole-blood and intracellular tacrolimus in early adult renal transplant recipients

Tacrolimus (TAC) has high pharmacokinetic (PK) variability during the early transplantation period. The relationships between whole-blood and intracellular TAC concentrations and clinical outcomes remain controversial. This study identifies the factors affecting the PK variability of TAC and characterizes the relationships between whole-blood and intracellular TAC concentrations. Data regarding whole-blood TAC concentrations of 1,787 samples from 215 renal transplant recipients (<90 days postoperative) across two centers and intracellular TAC concentrations (648 samples) digitized from previous studies were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were screened, and the distribution of whole-blood to intracellular TAC concentration ratios (RWB:IC) was estimated. The final model was evaluated using bootstrap, goodness of fit, and prediction-corrected visual predictive checks. The optimal dosing regimens and target ranges for each type of immune cell subsets were determined using Monte Carlo simulations. A two-compartment model adequately described the data, and the estimated mean TAC CL/F was 23.6 L·h-1 (relative standard error: 11.5 %). The hematocrit level, CYP3A5*3 carrier status, co-administration with Wuzhi capsules, and tapering prednisolone dose may contribute to the high variability of TAC PK variability during the early post-transplant period. The estimated RWB:IC of all TAC concentrations in peripheral blood mononuclear cells (PBMCs) was 4940, and inter-center variability of PBMCs was observed. The simulated TAC target range in PBMCs was 20.2-85.9 pg·million cells-1. Inter-center variability in intracellular concentrations should be taken into account in further analyses. TAC dosage adjustments can be guided based on PK/PD variability and simulated intracellular concentrations.

Tacrolimus Monitoring in Liver Transplant Recipients, Posttransplant Cholestasis: A Comparative Between 2 Commercial Immunoassays and a Liquid Chromatography-Tandem Mass Spectrometry Method

BACKGROUND

Cholestasis commonly occurs after orthotopic liver transplantation. It can be extrahepatic because of mechanical obstruction or intrahepatic because of various causes. During cholestasis episodes, blood concentrations of tacrolimus (TAC) metabolites may increase, potentially affecting TAC concentrations measured by immunoassays. This study aimed to simultaneously evaluate the analytical performance of 2 TAC immunoassays, a quantitative microsphere system (QMS) immunoassay, and chemiluminescence microparticle immunoassay, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a reference method in liver transplant recipients.

METHODS

This single-center study included 265 patients who underwent orthotopic liver transplantation. In total, 942 blood samples were collected. TAC trough concentrations were measured using LC-MS/MS and 2 immunoassays in parallel. The plasma concentrations of conjugated bilirubin were measured in all samples. The results were analyzed using Bland-Altman plots and Passing-Bablok regressions.

RESULTS

The Bland-Altman plot analysis showed that the TAC QMS immunoassay has a significant bias (+37%) compared with LC-MS/MS, and this bias was higher in patients with cholestasis with hyperbilirubinemia (≤+70% in patients with conjugated bilirubin >150 µmol/L). In comparison, the chemiluminescence microparticle immunoassay showed acceptable analytical performance in patients with hyperbilirubinemia (bias <10%).

CONCLUSIONS

In agreement with previous findings, the TAC QMS immunoassay showed a positive bias compared with LC-MS/MS. This bias is remarkably high in patients with cholestasis and hyperbilirubinemia, suggesting the cross-reactivity of TAC metabolites with the monoclonal antibody used in the QMS immunoassay.

Automated LC-MS/MS: Ready for the clinical routine Laboratory?

Background

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a sensitive method with high specificity. However, its routine use in the clinical laboratory is hampered by its high complexity and lack of automation. Studies demonstrate excellent analytical performance using the first fully automated LC-MS/MS for 25-hydroxy vitamin D and immunosuppressant drugs (ISD) in hospital routine laboratories.

Objectives

Our objectives were (1) to verify the suitability of an automated LC-MS/MS in a commercial laboratory, which differs from the needs of hospital laboratories, and (2) examine its usability among operators with various professional backgrounds.

Methods

We assessed the analytical assay performance for vitamin D and the ISDs cyclosporine A and tacrolimus over five months. The assays were compared to an identical analyzer in a hospital laboratory, to in-house LC-MS/MS methods, and to chemiluminescent microparticle immunoassays (CMIA). Nine operators evaluated the usability of the fully automated LC-MS/MS system by means of a structured questionnaire.

Results

The automated system exhibited a high precision (CV < 8%), accuracy (bias < 7%) and good agreement with concentrations of external quality assessment (EQA) samples. Comparable results were obtained with an identical analyzer in a hospital routine laboratory. Acceptable median deviations of results versus an in-house LC-MS/MS were observed for 25-OH vitamin D3 (-10.6%), cyclosporine A (-4.3%) and tacrolimus (-6.6%). The median bias between the automated system and immunoassays was only acceptable for 25-OH vitamin D3 (6.6%). All users stated that they had had a good experience with the fully automated LC-MS/MS system.

Conclusions

A fully automated LC-MS/MS can be easily integrated for routine diagnostics in a commercial laboratory.

Determination of tacrolimus in human whole blood in kidney transplant recipients using a rapid and specific LC-MS/MS method

OBJECTIVE

To develop and validate an LC-M/SMS method for the determination of tacrolimus in human whole blood.

METHOD

The LC-MS/MS method for the determination of tacrolimus in whole blood was developed and validated according to the guidelines. Concentrations of TAC in 100 kidney transplant patients measured by LC-MS/MS were compared with CMIA using correlation analysis and Bland-Altman plots.

RESULTS

The method had a total chromatographic run time of 5 min. The calibration curves were linear over the range of 0.5-100.0 ng/mL with a lower limit of quantification of 1 ng/mL. The intra- and interday accuracy was within the range of 93.3%-109.2% and 96.0%-108.4%, respectively, with precision ranging from 0.8 to 9.4%. The mean extraction recoveries of TAC ranged from 102.6 to 107.8%. The mean concentrations of TAC in whole blood of kidney transplant patients measured by the two assays were different at 1, 3 months and all time points (p < 0.001), but no significant difference was observed at 6 months (p = 0.094). The correlation of data was good with the correlation coefficients (r2 ) of 0.7581, 0.8811, 0.8777, and 0.8077, respectively. Passing-Bablok regression analysis demonstrated good correlations with r2 values higher than 0.88 between TAC levels measured by LC-MS/MS and CMIA. Using Bland-Altman plots yielded average biases of 1.29, 0.79, 0.11, and 0.65 ng/mL at 1, 3, and 6 months and all time points.

CONCLUSION

The LC-MS/MS method was validated for the accurate determination of TAC in human whole blood. The comparison of tacrolimus concentrations measured by the LC-MS/MS with CMIA showed a good correlation and agreement of two methods, suggesting LC-MS/MS should be used routinely to monitor TAC concentrations in kidney transplant patients.

Targeted Metabolomics Analysis Suggests That Tacrolimus Alters Protection against Oxidative Stress

Tacrolimus (FK506) is an immunosuppressant that is experiencing a continuous rise in usage worldwide. The related side effects are known to be globally dose-dependent. Despite numerous studies on FK506, the mechanisms underlying FK506 toxicity are still not well understood. It is therefore essential to explore the toxicity mediated by FK506. To accomplish this, we conducted a targeted metabolomic analysis using LC-MS on the plasma samples of patients undergoing FK506 treatment. The aim was to identify any associated altered metabolic pathway. Another anti-calcineurin immunosuppressive therapy, ciclosporin (CSA), was also studied. Increased plasma concentrations of pipecolic acid (PA) and sarcosine, along with a decrease in the glycine/sarcosine ratio and a tendency of increased plasma lysine was observed in patients under FK506 compared to control samples. Patients under CSA do not show an increase in plasma PA compared to the control samples, which does not support a metabolic link between the calcineurin and PA. The metabolomics changes observed in patients under FK506 highlight a possible link between FK506 and the action of an enzyme involved in both PA and sarcosine catabolism and oxidative pathway, the Peroxisomal sarcosine oxidase (PIPOX). Moreover, PA could be investigated as a potential biomarker of early nephrotoxicity in the follow-up of patients under FK506.

Population Pharmacokinetic Evaluation with External Validation of Tacrolimus in Chinese Primary Nephrotic Syndrome Patients

PURPOSE

The generalizability of numerous tacrolimus population pharmacokinetic (popPK) models constructed to promote optimal tacrolimus dosing in patients with primary nephrotic syndrome (PNS) is unclear. This study aimed to evaluate the predictive performance of published tacrolimus popPK models for PNS patients with an external data set.

METHODS

We prospectively collected 223 concentrations from 50 Chinese adult patients with PNS who were undergoing tacrolimus treatment. Data on published tacrolimus popPK models for adults and children with PNS were extracted from the literature. Model predictability was evaluated with prediction-based and simulation-based diagnostics and Bayesian forecasting.

RESULTS

In prediction-based evaluation, none of the 11 identified published popPK models of tacrolimus had met a predefined criteria of a mean prediction error ≤  ± 20%, and the prediction error within ± 30% of the identified models didn't exceed 50%. Simulation-based diagnostics also indicated unsatisfactory predictability. Bayesian forecasting demonstrated amelioration in the model predictability with the inclusion of 2-3 prior observations. Moreover, the predictive performance of nonlinear models was not better than that of one-compartment models.

CONCLUSIONS

The prediction of tacrolimus concentrations for patients with PNS remains challenging; published models are not applicable for extrapolation to other hospitals. Bayesian forecasting significantly improved model predictability and thereby helped to individualize tacrolimus dosing.

Evaluation of a batched-extraction method for measurement of sirolimus, tacrolimus, and cyclosporine on the Architect i2000SR

BACKGROUND

Manual extraction of immunosuppressants is required before measurement on the Architect immunoassay analyzer. The individual extraction of samples places clinical laboratory staff at risk for ergonomic injury. We evaluated the analytical performance of a batched extraction method for measuring sirolimus, tacrolimus, and cyclosporine using the Architect i2000SR.

METHODS

Residual whole blood samples from patients receiving immunosuppressant therapy were used for evaluation. The analytical evaluation included imprecision, linearity, and method comparison. Technologist-to-technologist variation was also assessed.

RESULTS

Total imprecision ranged from 2.58-3.13% for sirolimus, 2.70-3.77% for tacrolimus, and 7.82-12.41% for cyclosporine. Linearity was verified from 0.44 - 19.49 μg/l for sirolimus, 0.05-26.15 μg/l for tacrolimus, and 0.15-991.55 μg/l for cyclosporine. Deming regression analysis showed slope and intercept were not significant for either technologist-to-technologist comparison or for batched vs. individual processing comparison. Bland-Altman analysis of individual vs. batched processing revealed a mean bias of 1.29% (LLOA: -14.63%, ULOA: 17.21%) for sirolimus, 2.07% (LLOA: -10.87%, ULOA: 15%) for tacrolimus, and -1.56% (LLOA: -20.05%, ULOA: 16.94%) for cyclosporine. The values were not significantly different from the bias and LLOAs observed for technologist-to-technologist comparison.

CONCLUSIONS

The imprecision and linearity of batched methods met analytical goals. The batched method also correlated well with the individual extraction methods. The ULOA and LLOA for all drugs tested exceeded a TAE or ± 15%. However, similar range of differences was observed between technologists, suggesting that batch processing did not increase or reduce variability due to manual preparation steps.

Wuzhi Capsule Dosage Affects Tacrolimus Elimination in Adult Kidney Transplant Recipients, as Determined by a Population Pharmacokinetics Analysis

Purpose

In this study, we aimed to establish a tacrolimus population pharmacokinetic model and better understand the drug-drug interaction between Wuzhi capsule and tacrolimus in Chinese renal transplant recipients.

Patients and Methods

We performed a population pharmacokinetic analysis using a non-linear mixed-effects model to determine the suitable Wuzhi capsule dose in combination with tacrolimus. Data on 1378 tacrolimus steady-state concentrations were obtained from 142 patients who received kidney transplant in Changhai Hospital and Huashan Hospital. Demographic characteristics, laboratory tests, genetic polymorphisms, and co-medications were evaluated.

Results

The one-compartment model best described data. Our final model identified creatinine clearance rate, hematocrit, Wuzhi capsule dose, CYP3A5*3 genetic polymorphisms, and tacrolimus daily dose as significant covariates for tacrolimus clearance, with the value of 14.4 L h^-1, and the between-subject variability (BSV) was 25.4%. The Wuzhi capsule showed a dose-dependent effect on tacrolimus pharmacokinetics, demonstrating a stronger inhibitory effect than inductive effect.

Conclusion

Our model can accurately describe population pharmacokinetics of tacrolimus when combined with different doses of Wuzhi capsule. Additionally, this model can be used for individualizing tacrolimus dose following kidney transplantation.

Rapid determination of tacrolimus and sirolimus in whole human blood by direct coupling of solid-phase microextraction to mass spectrometry via microfluidic open interface

Immunosuppressive drugs are administered to decrease immune system activity (e.g. of patients undergoing solid organ transplant). Concentrations of immunosuppressive drugs (ISDs) in circulating blood must be closely monitored during the period of immunosuppression therapy due to adverse effects that take place when concentration levels fall outside of the very narrow therapeutic concentration range of these drugs. This study presents the rapid determination of four relevant immunosuppressive drugs (tacrolimus, sirolimus, everolimus, and cyclosporine A) in whole human blood by directly coupling solid-phase microextraction to mass spectrometry via the microfluidic open interface (Bio-SPME-MOI-MS/MS). The BioSPME-MOI-MS/MS method offers ≤ 10% imprecision of in-house prepared quality controls over a 10-day period, ≤ 10% imprecision of ClinCal® Recipe calibrators over a three-day period, and single total turnaround time of ∼ 60 min (4.5 min for high throughput). The limits of quantification were determined to be 0.8 ng mL^-1 for tacrolimus, 0.7 ng mL^-1 sirolimus, 1.0 ng mL^-1 for everolimus, and 0.8 ng mL^-1 for cyclosporine. The limits of detection were determined to be 0.3 ng mL^-1 for tacrolimus, 0.2 ng mL^-1 for sirolimus, 0.3 ng mL^-1 for everolimus, and 0.3 ng mL^-1 for cyclosporine A. The R² values for all analytes were above 0.9992 with linear dynamic range from 1.0 mL^-1 to 50.0 ng mL^-1 for tacrolimus, sirolimus, and everolimus while from 2.5 ng mL^-1 to 500.0 ng mL^-1 for cyclosporine A. To further evaluate the performance of the present method, 95 residual whole blood samples of tacrolimus and sirolimus from patients undergoing immunosuppression therapy were used to compare the Bio-SPME-MOI-MS/MS method against a clinically validated reference method based on chemiluminescent microparticle immunoassay, showing acceptable results. Our results demonstrated that Bio-SPME-MOI-MS/MS can be considered as a suitable alternative to existing methods for the determination of immunosuppressive drugs in whole blood providing faster analysis, better selectivity and sensitivity, and a wider dynamic range than current existing approaches.

False Immunosuppressant Measurement by LC-MS/MS Method Due to Radiopaque Agents

BACKGROUND

Although liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) is preferred as a reliable method, some molecules in the blood matrix may lead to false positive or false negative results. False positive or negative results show the direction of the deviation rate from the target value.

AIM

The aim of this study was to investigate the effect of seven different radiopaque agents on four immunosuppressant drugs.

METHODS

Every agent coded with RM1 to RM7 was added to control materials containing tacrolimus, everolimus, sirolimus, and cyclosporine A drugs. Measurements were performed using an LC-MS/MS instrument. Bias values were calculated to detect the deviation rates.

RESULTS

All RMs led to false negative results in the tacrolimus and cyclosporine A levels at a rate of -19.77% (95% CI, -27.16 to 12.52) to -44.45% (95% CI, -49.20 to -39.69). The smallest deviations were seen in the everolimus levels with the administration of RM6 (gadodiamide) and in the sirolimus levels with RM1 (gadobutrol) at the rates of 4.04% (95% CI, -11.36 to -3.17) and 2.11% (95% CI, -7.18 to 7.11), respectively. The most affected drug by RM4 (gadopentetate dimeglumine salt) was sirolimus at the rate of 114.01% (95% CI, 97.31 - 130.76). RM5 (gadodiamide) interfered cyclosporine A at the most. The highest deviations were observed with the administration of RM3 (iohexol) in the everolimus and sirolimus levels at the rates of 153.72% (95% CI, 142.44 to 164.78) and 171.41% (95% CI, 157.91 to 184.97), respectively.

CONCLUSION

Radiopaque agents interfered the measurement of immunosuppressant drugs. Especially, everolimus and sirolimus levels were affected due to using iohexol. The choice of gadodiamide or ioversol is important to reduce the risk of interference for everolimus measurement. The blood samples should be obtained for measurement of drug levels before contrast-enhanced imaging.

Accuracy evaluation of Roche and Siemens tacrolimus and cyclosporine assays in comparison with liquid chromatography-tandem mass spectrometry

Therapeutic drug monitoring of tacrolimus and cyclosporine is crucial to the success of organ transplantation. We evaluated the analytical performances and accuracy of two commercially available tacrolimus and cyclosporine assays (Roche ISD and Siemens) in comparison with liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 342 leftover whole blood samples requested for tacrolimus or cyclosporine assays were stored at -20 °C until analysis. Repeatability and between-run imprecision were evaluated using quality control materials provided by the manufacturer. Ring trial samples were used for the assessment of recovery. The results of the Roche ISD assay were compared with those of Siemens tacrolimus and cyclosporine assays and LC-MS/MS. Repeatability and between-run imprecision were 2.1-5.3% and 2.6-7.5%, respectively. Recovery of Roche ISD was 85.7 - 90.6% for cyclosporine and 96.2-98.5% for tacrolimus. The two immunoassays showed slight positive biases relative to LC-MS/MS for cyclosporine. For tacrolimus, Roche ISD produced virtually identical results to those of LC-MS/MS, whereas Siemens showed proportional differences, especially in patients receiving kidney transplantation. The analytical performances of Roche ISD were generally acceptable, especially regarding accuracy. Clinical laboratory staff should be aware of the strengths and weaknesses of commercial immunoassays in order to ensure accurate results.

Immunologic Monitoring to Personalize Immunosuppression After Liver Transplant

Although immunosuppressive drugs have enhanced patient outcomes in transplantation, the liver transplant community has made significant research efforts into the discovery of more accurate and precise methods of posttransplant monitoring and diagnosing. Current research in biomarkers reveals many promising approaches.

False Elevation of the Blood Tacrolimus Concentration, as Assessed by an Affinity Column-mediated Immunoassay (ACMIA), Led to Acute T Cell-mediated Rejection after Kidney Transplantation

Tacrolimus is the most commonly used immunosuppressant. Because of its narrow therapeutic range, it is necessary to frequently monitor its concentration. We report the case of a 25-year-old man who underwent kidney transplantation whose tacrolimus concentrations, as measured by an affinity column-mediated immunoassay, were falsely elevated. As we reduced the dose of tacrolimus, the recipient developed T cell-mediated rejection. Using the same blood samples, an enzyme-multiplied immunoassay technique showed that the patient's levels of tacrolimus were extremely low. A further examination indicated that the false increase in the tacrolimus concentration was likely due to an unknown interfering substance. We administered methylprednisolone and antithymocyte-globulin. The patient's serum creatinine level decreased and remained stable after these treatments.

Tacrolimus: A Review of Laboratory Detection Methods and Indications for Use

Tacrolimus (Tac) is an immunosuppressive drug that is used in preventing organ and tissue rejection in patients after transplantation. Tac administration requires frequent and diligent monitoring by physicians to ensure proper dosage and to limit the potential for harmful adverse effects, which can include renal damage, neurotoxicity, and other serious adverse events. Tac is a calcineurin inhibitor, which suppresses the function of T-cells. Its success as an immunosuppressive agent has been well documented in preventing graft-vs-host disease in several types of organ transplants. This literature review will discuss Tac metabolism and its role in preventing tissue and organ transplant rejection. A variety of detection techniques used in the clinical laboratory, including dried-blood-spot analysis, liquid chromatography-tandem mass spectrometry, and immunoassay also will be discussed.

Evaluation of electrochemiluminescence immunoassays for immunosuppressive drugs on the Roche cobas e411 analyzer

Background:  Therapeutic drug monitoring of immunosuppressant drugs are used to monitor drug efficacy and toxicity and to prevent organ transplant rejection. This study evaluates the analytical performance of semi-automated electrochemiluminescence immunoassays (ECLIA) for cyclosporine (CSA), tacrolimus (TAC) and sirolimus (SRL) on the Roche cobas e 411 analyzer at a major transplant hospital to assess method suitability and limitations.

Methods: Residual whole blood samples from patients undergoing immunosuppressant therapy were used for evaluation. Imprecision, linearity, functional sensitivity, method comparisons and lot-to-lot comparisons were assessed.

Results: Total imprecision ranged from 3.3 to 7.1% for CSA, 3.9 to 9.4% for TAC, and 4.6 to 8.2% for SRL. Linearity was verified from 30.0 to 960.9 μg/L for CSA, from 1.1 to 27.1 μg/L for TAC, and from 0.5 to 32.3 µg/L for SRL. The functional sensitivity met the manufacturer’s claims and was determined to be <6.5 μg/L for CSA, 1.1 μg/L for TAC, and <0.1 µg/L for SRL (CV≤20%). Deming regression analysis of method comparisons with the ARCHITECT immunoassay yielded slopes of 0.917 (95%CI: 0.885-0.949) and r of 0.985 for CSA, 0.938 (95%CI: 0.895-0.981) and r of 0.974 for TAC, and 0.842 (0.810-1.110) and r of 0.982 for SRL. Deming regression analysis of comparisons with the LC–MS/MS method yielded slopes of 1.331 (95%CI: 1.167-1.496) and r of 0.969 for CSA, 0.924 (95%CI: 0.843-1.005) and r of 0.984 for TAC, and 0.971 (95%CI: 0.913-1.030) and r of 0.993 for SRL.

Conclusions: The cobas e 411 ECLIA for CSA, TAC, and SRL have acceptable precision, linearity, and functional sensitivity. The method comparisons correlated well with the ARCHITECT immunoassay and LC–MS/MS and is fit for therapeutic drug monitoring

External evaluation of published population pharmacokinetic models of tacrolimus in adult renal transplant recipients

AIM

Several tacrolimus population pharmacokinetic models in adult renal transplant recipients have been established to facilitate dose individualization. However, their applicability when extrapolated to other clinical centres is not clear. This study aimed to (1) evaluate model external predictability and (2) analyze potential influencing factors.

METHODS

Published models were screened from the literature and were evaluated using an external dataset with 52 patients (609 trough samples) collected by postoperative day 90 via methods that included (1) prediction-based prediction error (PE%), (2) simulation-based prediction- and variability-corrected visual predictive check (pvcVPC) and normalized prediction distribution error (NPDE) tests and (3) Bayesian forecasting to assess the influence of prior observations on model predictability. The factors influencing model predictability, particularly the impact of structural models, were evaluated.

RESULTS

Sixteen published models were evaluated. In prediction-based diagnostics, the PE% within ±30% was less than 50% in all models, indicating unsatisfactory predictability. In simulation-based diagnostics, both the pvcVPC and the NPDE indicated model misspecification. Bayesian forecasting improved model predictability significantly with prior 2-3 observations. The various factors influencing model extrapolation included bioassays, the covariates involved (CYP3A5*3 polymorphism, postoperative time and haematocrit) and whether non-linear kinetics were used.

CONCLUSIONS

The published models were unsatisfactory in prediction- and simulation-based diagnostics, thus inappropriate for direct extrapolation correspondingly. However Bayesian forecasting could improve the predictability considerably with priors. The incorporation of non-linear pharmacokinetics in modelling might be a promising approach to improving model predictability.

Limited sampling strategy for prolonged-release tacrolimus in renal transplant patients by use of the dried blood spot technique

Purpose

The aim of this study was to develop a clinically applicable limited sampling strategy for ambulatory Caucasian kidney transplant patients to estimate area under the curve in a 24-h period (AUC_0–24) of prolonged-release tacrolimus.

Methods

Twenty six kidney recipients, at least 6 months after transplantation, receiving prolonged-release tacrolimus, were enrolled. In each patient, seven blood samples were collected during a period of 24 h by use of the validated dried blood spot method. Best subset selection multiple linear regression was performed to derive limited sampling strategy (LSS). The equations were constrained to include a maximum of three samples collected within 4 h after the intake to maintain clinical applicability. To assess the predictive performance of LSS, residuals for each patient were calculated based on models fitted to a dataset where that patient was omitted.

Results

The prediction formula for the AUC_0–24 using the time points 0, 2, and 4 h after ingestion (C_0h-C_2h-C_4h) provided the highest correlation with the AUC_0–24 (r² = 0.95): AUC_0–24 = 44.9 + 8.9 × C_0h + 2.1 × C_2h + 7.6 × C_4h. Measures for bias and precision, i.e., median percentage prediction error (MPPE) and median absolute prediction error (MAPE), were 0.4 and 4.8 %, respectively. For the same patients, the correlation between C_24h and AUC_0–24 was worse (r² = 0.77) while MPPE and MAPE were 6.2 and 7.2 %, respectively.

Conclusion

In the outpatient department, a LSS using C_0h-C_2h-C_4h can be used for reliable estimation of the AUC_0–24 of prolonged-release tacrolimus_.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-015-1863-6) contains supplementary material, which is available to authorized users.

Comparison of pharmacokinetics and pathology for low-dose tacrolimus once-daily and twice-daily in living kidney transplantation: prospective trial in once-daily versus twice-daily tacrolimus

BACKGROUND

A prolonged-release formulation of tacrolimus (Tacrolimus QD) was developed to allow once-daily dosing and to have similar safety and efficacy profiles to twice-daily tacrolimus (Tacrolimus BID). This study compared the pharmacokinetics (PK) and renal pathology by protocol biopsy in de novo living kidney transplant recipients treated with either low-dose Tacrolimus QD or Tacrolimus BID.

METHODS

Between November 2009 and January 2011, 102 consecutive adult patients were randomized to receive either low-dose Tacrolimus QD or Tacrolimus BID. All patients underwent PK study and protocol biopsy on postoperative day 14. Additional protocol biopsies were performed between 6 and 12 months after renal transplantation.

RESULTS

During the 1-year follow up, the incidence of biopsy-proven acute rejection and toxic tubulopathy was low and similar in both groups. Twenty-four hours area under the curve (AUC0-24) was not different in both groups (285 ± 78.7 and 281 ± 62.4 ng hr/mL in Tacrolimus QD and Tacrolimus BID, respectively). C0 was well correlated with AUC0-24 in both groups and AUC0-24 between 260 and 280 in the Tacrolimus QD group was achieved by 6 to 8 ng/mL of C0. Acute nephrotoxicity was less than 10% in both groups without any clinical manifestation.

CONCLUSION

Clinical efficacy, safety, and PK profile of Tacrolimus QD is same as those of Tacrolimus BID.

Association between CYP3A5 genotypes in graft liver and increase in tacrolimus biotransformation from steroid treatment in living-donor liver transplant patients

  We retrospectively examined whether cytochrome P450 (CYP) 3A5 genotypes are associated with high-dose steroid pulse treatment-induced functional gain of tacrolimus biotransformation in living-donor liver transplant patients. Concentrations of tacrolimus and its 3 primary metabolites, 13-O-demethyl tacrolimus (M-I), 31-O-demethyl tacrolimus (M-II), and 15-O-demethyl tacrolimus (M-III), were measured in trough blood samples from 18 liver transplant patients, by liquid chromatography-tandem mass spectrometry/mass spectrometry (LC-MS/MS). In patients engrafted with a CYP3A5*1-carrying liver but not with a CYP3A5*3/*3-carrying liver, the concentration/dose ratio of tacrolimus significantly fell after therapy, while ratios of M-I/tacrolimus, M-II/tacrolimus, and M-III/tacrolimus were significantly higher after therapy than before (p = 0.032, p = 0.023, and p = 0.0078, respectively). After steroid pulse therapy, the concentration of tacrolimus measured by immunoassay was significantly higher than that measured by LC-MS/MS in patients engrafted with a CYP3A5*1-carrying liver, but not those engrafted with a CYP3A5*3/*3-carrying liver. This suggests that the increased ratio of tacrolimus metabolites/tacrolimus can be explained by induction of CYP3A5 via high-dose steroid pulse therapy. Further, the concentrations of tacrolimus measured by the immunoassays were overestimated, partly because of cross-reactivity of the monoclonal antibody they incorporated to detect tacrolimus, with the increased metabolites in patients with a CYP3A5*1-carrying graft liver.

Impact of interferences including metabolite crossreactivity on therapeutic drug monitoring results

Therapeutic drug monitoring is an integral part of services offered by toxicology laboratories because certain drugs require routine monitoring for dosage adjustment to achieve optimal therapeutic response and avoid adverse drug reactions. Immunoassays are widely used for therapeutic drug monitoring. However, immunoassays suffer from interferences from both exogenous and endogenous compounds including metabolites of the parent drug. Digoxin immunoassays are affected more commonly than any other immunoassays used for therapeutic drug monitoring. Digoxin immunoassays are affected by endogenous digoxin-like immunoreactive substances and exogenous compounds such as various drugs, certain herbal supplements, and Digibind. Carbamazepine is metabolized to carbamazepine 10, 11-epoxide, and the crossreactivity of this metabolite with carbamazepine immunoassay may vary from 0% to 94%. Immunoassays used for measuring concentrations of tricyclic antidepressants are affected by tricyclic antidepressant metabolites and by a number of other drugs. Immunoassays for immunosuppressants are also subjected to significant interferences from metabolites, and liquid chromatography combined with mass spectrometry or tandem mass spectrometry is recommended for therapeutic drug monitoring of immunosuppressants. However, liquid chromatography combined with mass spectrometry may also suffer from interferences, for example, due to ion suppression or from isobaric ions.

Impact of CYP3A5 genetic polymorphism on cross-reactivity in tacrolimus chemiluminescent immunoassay in kidney transplant recipients

BACKGROUND

Tacrolimus immunoassays possess cross-reactivity with metabolites in the blood. The aim of this study was to evaluate the cross-reactivity in tacrolimus chemiluminescent immunoassay (CLIA) in kidney transplant recipients and to characterize the cross-reactivity according to CYP3A5 genetic polymorphism.

METHODS

The subjects were 50 kidney transplant recipients receiving low-dose tacrolimus. Blood levels of tacrolimus at 12h (C(12)) measured by CLIA were compared with that by LC-MS/MS using Bland-Altman analysis. The influence of CYP3A5 genotypes on the cross-reactivity in tacrolimus CLIA was evaluated by interaction plots.

RESULTS

No significant difference was observed in tacrolimus C(12) between the CYP3A5*1/*3 and CYP3A5*3/*3 genotypes. The dose-normalized C(12) of tacrolimus was significantly higher in the CYP3A5*3/*3 genotype than in the CYP3A5*1/*3 genotype. The C(12) ratio of 13-O-demethylate to tacrolimus was significantly lower in the CYP3A5*3/*3 genotype than in the CYP3A5*1/*3 genotype. Tacrolimus C(12) measured by CLIA was 35% higher than that by LC-MS/MS. A higher cross-reactivity was observed in the patients with a tacrolimus C(12) of less than 3 μg/l and CYP3A5*1/*3 genotype.

CONCLUSION

This study confirmed the cross-reactivity in CLIA in kidney transplant recipients receiving low-dose tacrolimus. High metabolic capacity associated with the CYP3A5*1 genotype affected the cross-reactivity in patients with low tacrolimus levels.

Pharmacokinetic differences corroborate observed low tacrolimus dosage in Native American renal transplant patients

We have observed in clinical practice that Native Americans require lower dosages of tacrolimus to attain similar target blood trough levels compared to whites after renal transplant. Because there are no pharmacokinetic studies of tacrolimus in this ethnic group, we investigated whether this clinical observation could be corroborated by pharmacokinetic differences between Native Americans and other ethnic and racial groups. We recruited 24 adult Native American kidney transplant recipients on stable oral doses of tacrolimus for at least 1 month posttransplant. We conducted a 12-h steady-state pharmacokinetic profile for all of the patients and estimated pharmacokinetic parameters using NONMEM. The concentration-time data were fit to a linear two compartment model with first-order absorption and lag time using an empirical Bayesian approach. The mean estimate of oral clearance (CL/F) was 11.1 l/h. Compared with previously reported data in other ethnic and racial groups, the Native American cohort has approximately one third the clearance of other groups. Our pharmacokinetic study reveals the clinically observed low dose of tacrolimus in Native American renal transplant patients is associated with a decreased oral tacrolimus clearance. There is scant information available on the genetic or environmental characteristics unique to this ethnic group that affect pharmacokinetics compared to other, better-studied groups, and elucidation of these factors will provide information to further facilitate individualized drug treatment for tacrolimus and a wide range of other drugs with similar clearance processes.