High-performance liquid chromatography-tandem mass spectrometry as a reference for analysis of tacrolimus to assess two immunoassays in patients with liver and renal transplants

Which Kidney Transplant Recipients Can Benefit from the Initial Tacrolimus Dose Reduction?

Background

Observational data suggest that the fixed initial recommended tacrolimus (Tc) dosing (0.2 mg/kg/day) results in supratherapeutic drug levels in some patients during the early posttransplant period. The aim of the study was to analyze a wide panel of patient-related factors and their interactions which increase the risk for first Tc blood level > 15 ng/ml.

Materials and Methods

We performed a retrospective analysis of 488 consecutive adult kidney transplant recipients who were initially treated with triple immunosuppressive regimen containing tacrolimus twice daily. The analysis included the first assessment of Tc trough blood levels and several demographic, anthropometric, laboratory, and comedication data.

Results

The multiple logistic regression analysis showed that age > 55 years, BMI > 24.6 kg/m², blood hemoglobin concentration > 9.5 g/dl, and the presence of anti-HCV antibodies independently increased the risk for first Tc level > 15 ng/ml. The relative risk (RR) for first tacrolimus level > 15 ng/ml was 1.88 (95% CI 1.35–2.64, p < 0.001) for patients with one risk factor and 2.81 (2.02–3.89, p < 0.001) for patients with two risk factors.

Conclusions

Initial tacrolimus dose reduction should be considered in older, overweight, or obese kidney transplant recipients and in subjects with anti-HCV antibodies. Moreover, dose reduction of tacrolimus is especially important in patients with coexisting multiple risk factors.

Surface-activated chemical ionization and high-flow gradient chromatography to reduce matrix effect

The new atmospheric pressure chemical ionization source, named surface-activated chemical ionization (SACI), has been used in conjunction with high-flow gradient chromatography to reduce the matrix effect. This high-flow gradient chromatography approach avoids the co-elution of analyte and biological matrix compounds that leads to a reduction in quantitation errors due to matrix effect. However, this approach cannot be employed with the classical electrospray ionization (ESI) source that usually works at low eluent flow (< 300 microL/min). SACI can work at high eluent flow (100-2000 microL/min) and can be employed in conjunction with high-flow gradient chromatography. The reduction in matrix effect in tacrolimus analysis in protein-precipitated blood samples, an important immunosuppressive agent for renal transplantation, is presented and discussed.

Low Hematocrit and Serum Albumin Concentrations Underlie the Overestimation of Tacrolimus Concentrations by Microparticle Enzyme Immunoassay versus Liquid Chromatography–Tandem Mass Spectrometry

Background: Rapid liquid chromatography–tandem mass spectrometry (LC-MS/MS) methods are used increasingly for tacrolimus (TRL) monitoring but show a negative difference with respect to a microparticle immunoassay (MEIA). This report examines possible reasons for this difference between methods.

Methods: We collected 1156 blood samples from 277 adult and 121 pediatric recipients of liver, renal, and bone marrow grafts or hepatocyte or pancreatic islet cell implants. TRL was measured in whole blood by MEIA and LC-MS/MS, and hematologic and biochemical data were collected when available.

Results: LC-MS/MS was significantly more precise (P &lt;0.02) than the MEIA with increased sensitivity. The MEIA had a median difference of 16.2% vs LC-MS/MS overall, and this was significantly affected by patient cohort (P &lt;0.001). The difference was greater in adult or pediatric liver graft recipients while they were inpatients rather than outpatients (31.8% and 14.0% vs 7.5% and 6.5%, respectively). The difference was also greater in bone marrow than kidney graft recipients (32.8% vs 15.8%, respectively). Multiple linear regression analysis showed significant inverse relationships of this difference with hematocrit (packed cell volume) and plasma albumin (P &lt;0.001) in the total cohort and a positive relationship with plasma bilirubin in a subgroup of pediatric liver graft recipients.

Conclusions: Patients with a low packed cell volume and plasma albumin are likely to show artificially high concentrations of TRL when measured by MEIA. The increased risk of underimmunosuppression must be considered should doses be reduced to lower these seemingly high TRL concentrations.

Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation

The aim of this review is to analyse critically the recent literature on the clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplant recipients. Dosage and target concentration recommendations for tacrolimus vary from centre to centre, and large pharmacokinetic variability makes it difficult to predict what concentration will be achieved with a particular dose or dosage change. Therapeutic ranges have not been based on statistical approaches. The majority of pharmacokinetic studies have involved intense blood sampling in small homogeneous groups in the immediate post-transplant period. Most have used nonspecific immunoassays and provide little information on pharmacokinetic variability. Demographic investigations seeking correlations between pharmacokinetic parameters and patient factors have generally looked at one covariate at a time and have involved small patient numbers. Factors reported to influence the pharmacokinetics of tacrolimus include the patient group studied, hepatic dysfunction, hepatitis C status, time after transplantation, patient age, donor liver characteristics, recipient race, haematocrit and albumin concentrations, diurnal rhythm, food administration, corticosteroid dosage, diarrhoea and cytochrome P450 (CYP) isoenzyme and P-glycoprotein expression. Population analyses are adding to our understanding of the pharmacokinetics of tacrolimus, but such investigations are still in their infancy. A significant proportion of model variability remains unexplained. Population modelling and Bayesian forecasting may be improved if CYP isoenzymes and/or P-glycoprotein expression could be considered as covariates. Reports have been conflicting as to whether low tacrolimus trough concentrations are related to rejection. Several studies have demonstrated a correlation between high trough concentrations and toxicity, particularly nephrotoxicity. The best predictor of pharmacological effect may be drug concentrations in the transplanted organ itself. Researchers have started to question current reliance on trough measurement during therapeutic drug monitoring, with instances of toxicity and rejection occurring when trough concentrations are within 'acceptable' ranges. The correlation between blood concentration and drug exposure can be improved by use of non-trough timepoints. However, controversy exists as to whether this will provide any great benefit, given the added complexity in monitoring. Investigators are now attempting to quantify the pharmacological effects of tacrolimus on immune cells through assays that measure in vivo calcineurin inhibition and markers of immunosuppression such as cytokine concentration. To date, no studies have correlated pharmacodynamic marker assay results with immunosuppressive efficacy, as determined by allograft outcome, or investigated the relationship between calcineurin inhibition and drug adverse effects. Little is known about the magnitude of the pharmacodynamic variability of tacrolimus.

Liquid chromatography–negative ion electrospray tandem mass spectrometry method for the quantification of tacrolimus in human plasma and its bioanalytical applications

A simple, rapid, novel and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of tacrolimus (I) in human plasma, a narrow therapeutic index, potent macrolide immunosuppressive drug. The analyte and internal standard (tamsulosin (II)) were extracted by liquid-liquid extraction with t-butylmethylether using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on reverse phase Xterra ODS column with a mobile phase of 99% methanol and 1% 10mM ammonium acetate buffer. The deprotonate of analyte was quantitated in negative ionization by multiple reaction monitoring (MRM) with a mass spectrometer. The mass transitions m/z 802.5-->560.3 and m/z 407.2-->151.9 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.05-25ng/ml for tacrolimus in human plasma. The lower limit of quantitation was 50pg/ml with a relative standard deviation of less than 20%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. Run time of 2min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in comparative bioavailability studies. The tacrolimus plasma concentration profile could be obtained for pharmacokinetic study. The observed maximum plasma concentration (C(max)) of tacrolimus (5mg oral dose) is 440pg/ml, time to observed maximum plasma concentration (T(max)) is 2.5h and elimination half-life (T(1/2)) is 21h.

Pharmacokinetics of tacrolimus after multidose oral administration and efficacy in the prevention of allograft rejection in cats with renal transplants

OBJECTIVE

To describe pharmacokinetics of multi-dose oral administration of tacrolimus in healthy cats and evaluate the efficacy of tacrolimus in the prevention of allograft rejection in cats with renal transplants.

ANIMALS

6 healthy research cats.

PROCEDURE

Cats received tacrolimus (0.375 mg/kg, PO, q 12 h) for 14 days. Blood tacrolimus concentrations were measured by a high performance liquid chromatography-mass spectrometry assay. Each cat received an immunogenically mismatched renal allograft and native kidney nephrectomy. Tacrolimus dosage was modified to maintain a target blood concentration of 5 to 10 ng/mL. Cats were euthanatized if plasma creatinine concentration exceeded 7 mg/dL, body weight loss exceeded 20%, or on day 50 after surgery. Kaplan-Meier survival curves were plotted for 6 cats treated with tacrolimus and for 8 cats with renal transplants that did not receive immunosuppressive treatment.

RESULTS

Mean (+/- SD) values of elimination half-life, time to maximum concentration, maximum blood concentration, and area under the concentration versus time curve from the last dose of tacrolimus to 12 hours later were 20.5 +/- 9.8 hours, 0.77 +/- 0.37 hours, 27.5 +/- 31.8 ng/mL, and 161 +/- 168 hours x ng/mL, respectively. Tacrolimus treated cats survived longer (median, 44 days; range, 24 to 52 days) than untreated cats (median, 23 days; range, 8 to 34 days). On histologic evaluation, 3 cats had evidence of acute-active rejection, 1 cat had necrotizing vasculitis, and 2 cats euthanatized at study termination had normal appearing allografts.

CONCLUSIONS AND CLINICAL RELEVANCE

Tacrolimus may be an effective immunosuppressive agent for renal transplantation in cats.

Comparison of an ELISA and an LC/MS/MS method for measuring tacrolimus concentrations and making dosage decisions in transplant recipients

This study compared an enzyme-linked immunosorbent assay (ELISA) to a liquid chromatography-tandem mass spectrometry (LC/MS/MS) technique for measurement of tacrolimus concentrations in adult kidney and liver transplant recipients, and investigated how assay choice influenced pharmacokinetic parameter estimates and drug dosage decisions. Tacrolimus concentrations measured by both ELISA and LC/MS/MS from 29 kidney (n = 98 samples) and 27 liver (n = 97 samples) transplant recipients were used to evaluate the performance of these methods in the clinical setting. Tacrolimus concentrations measured by the two techniques were compared via regression analysis. Population pharmacokinetic models were developed independently using ELISA and LC/MS/MS data from 76 kidney recipients. Derived kinetic parameters were used to formulate "typical dosing" regimens for concentration targeting. Dosage recommendations for the two assays were compared. The relation between LC/MS/MS and ELISA measurements was best described by the regression equation ELISA = 1.02. (LC/MS/MS) + 0.14 in kidney recipients, and ELISA = 1.12. (LC/MS/MS) - 0.87 in liver recipients. ELISA displayed less accuracy than LC/MS/MS at lower tacrolimus concentrations. Population pharmacokinetic models based on ELISA and LC/MS/MS data were similar with residual random errors of 4.1 ng/mL and 3.7 ng/mL, respectively. Assay choice gave rise to dosage prediction differences ranging from 0% to 30%. ELISA measurements of tacrolimus are not automatically interchangeable with LC/MS/MS values. Assay differences were greatest in adult liver recipients, probably reflecting periods of liver dysfunction and impaired biliary secretion of metabolites. While the majority of data collected in this study suggested assay differences in adult kidney recipients were minimal, findings of ELISA dosage underpredictions of up to 25% in the long term must be investigated further.

Simultaneous quantification of sirolimus, everolimus, tacrolimus and cyclosporine by liquid chromatography-mass spectrometry (LC-MS)

We developed a universal liquid chromatography-mass spectrometry (LC-MS) assay with automated online extraction to quantify simultaneously the immunosuppressants sirolimus, everolimus, tacrolimus, and cyclosporine. Whole blood (300 microl) plus 6 microl 32-desmethoxyrapamycin (1 ng/microl) as internal standard was treated with 600 microl methanol/0.2 M ZnSO4 (80/20 v/v). After vortexing (30 s) and centrifugation (20000 g, 5 min) 50 microl of the supernatant were loaded on an extraction column, were washed by 0.35 ml/min water for 3 min and, after activation of a column-switching valve, were back-flushed by 0.25 ml/min methanol/ water (90/10 v/v) onto a C18 analytical column. After 22 min the extraction column was washed for 2 min with methanol and for 3 min with water before starting the next run. Column temperatures were kept at 33 degrees C. Sodium adduct ions [M+Na]+ ions were detected in the selected ion mode. For sirolimus, everolimus and tacrolimus the assay was linear from 0.3 to 200 microg/l and for cyclosporine from 5 to 1000 microg/l (all r2>0.999). Recovery of all immunosuppressants and the internal standard was >90% and in general, inter-day and intraday precision was <10%. The simultaneous quantification of blood levels by LC-MS seems to be the method of choice in transplanted patients receiving multiple immunosuppressants.

Simultaneous simple and fast quantification of three major immunosuppressants by liquid chromatography--tandem mass-spectrometry

OBJECTIVES

The aim of the current study was to develop a simple, fast and universal method for quantification of any combination of the three major immunosuppressants sirolimus, tacrolimus and cyclosporin in whole blood, using a LC-tandem mass spectrometer (API-2000, SCIEX, Toronto, Canada).

METHODS

250 microL whole blood was spiked with internal standard (ritonavir), and protein precipitated with 350 microL acetonitrile. The sample was centrifuged and 30 microL aliquot was injected onto the HPLC column, where it underwent an online extraction with ammonium acetate. After that the automatic switching valve was activated, changing the mobile phase to methanol and thereby eluting the analytes into the tandem mass spectrometer. The high selectivity of a tandem mass analyzer allows determination of any combination of the three drugs within a 5 min run.

RESULTS

Between-day precision was between 2.4% and 9.7% for all analytes at the concentrations tested. Accuracy ranged between 98.8% and 103.2% (n = 20). The method was linear over the measuring ranges of all analytes. Within-run precision was below %CV = 6% for all analytes. Good correlation with other analytical methods was observed.

CONCLUSIONS

The simplicity, universality and high throughput of the method make it suitable for application in a clinical laboratory. The method has been implemented in our laboratory for a routine use.

Recommendations for the outpatient surveillance of renal transplant recipients. American Society of Transplantation

Many complications after renal transplantation can be prevented if they are detected early. Guidelines have been developed for the prevention of diseases in the general population, but there are no comprehensive guidelines for the prevention of diseases and complications after renal transplantation. Therefore, the Clinical Practice Guidelines Committee of the American Society of Transplantation developed these guidelines to help physicians and other health care workers provide optimal care for renal transplant recipients. The guidelines are also intended to indirectly help patients receive the access to care that they need to ensure long-term allograft survival, by attempting to systematically define what that care encompasses. The guidelines are applicable to all adult and pediatric renal transplant recipients, and they cover the outpatient screening for and prevention of diseases and complications that commonly occur after renal transplantation. They do not cover the diagnosis and treatment of diseases and complications after they become manifest, and they do not cover the pretransplant evaluation of renal transplant candidates. The guidelines are comprehensive, but they do not pretend to cover every aspect of care. As much as possible, the guidelines are evidence-based, and each recommendation has been given a subjective grade to indicate the strength of evidence that supports the recommendation. It is hoped that these guidelines will provide a framework for additional discussion and research that will improve the care of renal transplant recipients.

Simultaneous quantification of tacrolimus and sirolimus, in human blood, by high-performance liquid chromatography-tandem mass spectrometry

In this paper the authors present a validated method for the simultaneous analysis of tacrolimus and sirolimus in human blood by high-performance liquid chromatography-electrospray tandem mass spectrometry. Blood samples (500 microL) were prepared by C18 solid-phase extraction. Mass spectrometric detection was by selected reaction monitoring. The assay was linear for both compounds over the range 0.25-100 microg/L (r2 > 0.996, n = 7). At the limit of quantification (0.25 microg/L), for both sirolimus and tacrolimus, the interday imprecision was < 3% and the analytical recovery was between 97.0% and 102%, respectively. The interbatch and intrabatch coefficients of variation of the method for both analytes, at the three quality control concentrations (0.5, 20, and 80 microg/L), were < 16% and < 10%, respectively. The analytical recovery, at the three control concentrations, ranged from 99.2% to 104% of the nominal concentration. The mean absolute recovery (+/- standard deviation) of tacrolimus, sirolimus, and internal standard was 82 +/- 7%, 89 +/- 12%, and 77 +/- 8%, respectively (n = 12). In conclusion, the method presented can be used for simultaneous determination of tacrolimus and sirolimus and will aid in pharmacokinetic studies and therapeutic drug monitoring of these drugs. Furthermore, this method has economic benefits in the clinical setting where these drugs are coadministered.

Analysis of whole blood tacrolimus concentrations in liver transplant patients exhibiting impaired liver function

In transplant patients with impaired liver function, HPLC methodologies have been suggested for monitoring whole blood tacrolimus concentrations because of the reported inaccuracy of immunoassay for whole blood tacrolimus concentrations. One hundred fifty whole blood samples from 50 subjects enrolled in a multicenter liver transplant trial were chosen for HPLC/MS/MS analysis without consideration of the clinical status of the patient at the time of sampling. These samples were chosen to represent the sampling intervals during the 12-week posttransplantation period. Retrospectively, the authors identified a subset of 39 samples from 27 subjects exhibiting impaired liver function as demonstrated by bilirubin concentrations > 3.0 mg/dL (mean +/-SD = 7.5 +/- 5.6 mg/dL). The authors compared the agreement of concentrations obtained from the PRO-Trac II ELISA and HPLC/MS/MS by least squares linear regression analysis and Bland/Altman analysis, in this subset against the agreement of concentrations for 76 samples with normal bilirubin. In the samples obtained from patients with impaired liver function the resulting regression equation was: ELISA = 1.19(HPLC) + 0.7; r = 0.9. The mean difference (HPLC/MS/MS - ELISA) was -2.5 ng/mL +/- 2.9 ng/mL (mean +/- SD). While 71% of samples agreed within 3 ng/mL, 3% (n = 1) exhibited a difference >10 ng/ml. The corresponding evaluation of the samples with normal bilirubin concentrations resulted in the regression equation ELISA = 0.96(HPLC) + 0.9; r = 0.9, and a mean difference of -0.6 ng/mL +/- 2.3 ng/mL. The authors conclude that while a small subset of patients with cholestasis may require closer evaluation with a more specific methodology, the majority of the patients may be satisfactorily monitored with the PRO-Trac II ELISA.

Quantitative analysis of sirolimus (Rapamycin) in blood by high-performance liquid chromatography-electrospray tandem mass spectrometry

We report here a quantitative method for the analysis of sirolimus in blood using solid-phase sample preparation and HPLC-electrospray-tandem mass spectrometry detection. Blood samples (500 microl) were prepared by pre-treatment with acetonitrile: 15 mM zinc sulphate (70:30, v/v), containing 32-demethoxysirolimus (internal standard) and C18 solid-phase extraction. The electrospray conditions were chosen to enhance the [M+NH4]+ species at the expense of other species. Detection was by multiple reactant monitoring with the mass transitions m/z 931.8-->864.6 and m/z 901.8-->834.4 employed for sirolimus and the internal standard, respectively. The method was linear over the range 0.2 to 100.0 microg l(-1). The accuracy and inter-day precision, over this concentration range, was 94.4% to 104.4% and 1.4% to 5.0%, respectively. The accuracy and total precision at the limit of quantitation (0.2 microg l(-1)) was 103.0% and 10.8%, respectively. The mean absolute recovery of sirolimus and the internal standard were 80.5% and 81.3%, respectively. The sensitivity and analytical concentration range of the method make it suitable for therapeutic drug monitoring and pharmacokinetic studies. Further, the ability of the method to measure parent drug specifically will facilitate the evaluation of immunoassays for sirolimus.

Evaluation of the tacrolimus II microparticle enzyme immunoassay (MEIA II) in liver and renal transplant recipients

We evaluated the MEIA II with blood samples with added tacrolimus (3.0, 5.0, 11.0, and 22.0 μg/L). The assay had acceptable recoveries (99–103%) and intraday imprecision (&lt;16.0%) across the range of concentrations studied, except for the recoveries at 3.0 μg/L (86.3%) and 5.0 μg/L (80.7%). Comparison of liver (n = 116) and renal (n = 113) patient samples measured by MEIA II against HPLC-tandem mass spectrometry (HPLC-MS/MS) found a mean overestimation of 15.6%. From these comparison data it can be calculated that at values of 5 and 20 μg/L in liver or renal transplant patient samples, measured by HPLC-MS/MS, MEIA II will have the corresponding range estimates of 3.6–7.9 μg/L and 20.9–25.4 μg/L, respectively. No clinically significant difference in results, in terms of overestimation or correlation, was observed between the two transplant groups studied. The MEIA II is an improvement on the previous MEIA I and is suitable for the therapeutic drug monitoring of tacrolimus where HPLC-MS/MS is unavailable.