Consensus guidelines for therapeutic drug monitoring of rapamycin: report of the consensus panel

Status and Quality of Guidelines for Therapeutic Drug Monitoring Based on AGREE II Instrument

BACKGROUND

With the progress of therapeutic drug monitoring (TDM) technology and the development of evidence-based medicine, many guidelines were developed and implemented in recent decades.

OBJECTIVE

The aim was to evaluate the current status of TDM guidelines and provide suggestions for their development and updates based on Appraisal of Guidelines for Research and Evaluation (AGREE) II.

METHODS

The TDM guidelines were systematically searched for among databases including PubMed, Embase, China National Knowledge Infrastructure, Wanfang Data, and the Chinese biomedical literature service system and the official websites of TDM-related associations. The search period was from inception to 6 April 2023. Four researchers independently screened the literature and extracted data. Any disagreement was discussed and reconciled by another researcher. The quality of guidelines was assessed using the AGREE II instrument.

RESULTS

A total of 92 guidelines were included, including 57 technical guidelines, three management guidelines, and 32 comprehensive guidelines. The number of TDM guidelines has gradually increased since 1979. The United States published the most guidelines (20 guidelines), followed by China (15 guidelines) and the United Kingdom (ten guidelines), and 23 guidelines were developed by international organizations. Most guidelines are aimed at adult patients only, while 28 guidelines include special populations. With respect to formulation methods, there are 23 evidence-based guidelines. As for quality evaluation results based on AGREE II, comprehensive guidelines scored higher (58.16%) than technical guidelines (51.36%) and administrative guidelines (50.00%).

CONCLUSION

The number of TDM guidelines, especially technical and comprehensive ones, has significantly increased in recent years. Most guidelines are confronted with the problems of unclear methodology and low quality of evidence according to AGREE II. More evidence-based research on TDM and high-quality guideline development is recommended to promote individualized therapy.

Interlaboratory comparison study of immunosuppressant analysis using a fully automated LC-MS/MS system

OBJECTIVES

All guidelines recommend LC-MS/MS as the analytical method of choice for the quantification of immunosuppressants in whole blood. Until now, the lack of harmonization of methods and the complexity of the analytical technique have prevented its widespread use in clinical laboratories. This can be seen in international proficiency schemes, where more than half of the participants used immunoassays. With the Cascadion SM Clinical analyzer (Thermo Fisher Scientific, Oy, Vantaa, FI) a fully automated LC-MS/MS system has been introduced, which enables the use of LC-MS/MS without being an expert in mass spectrometry.

METHODS

To verify the interlaboratory comparison of the immunosuppressant assay on this type of instrument, three centers across Europe compared 1097 routine whole blood samples, each site sharing its own samples with the other two. In other experiments, the effects of freezing and thawing of whole blood samples was studied, and the use of secondary cups instead of primary tubes was assessed.

RESULTS

In the Bland-Altman plot, the comparison of the results of tacrolimus in fresh and frozen samples had an average bias of only 0.36%. The respective data for the comparison between the primary and secondary tubes had an average bias of 1.14%. The correlation coefficients for patient samples with cyclosporine A (n=411), everolimus (n=139), sirolimus (n=114) and tacrolimus (n=433) were 0.993, 0.993, 0.993 and 0.990, respectively.

CONCLUSIONS

The outcome of this study demonstrates a new level of result harmonization for LC-MS/MS based immunosuppressant analysis with a commercially available fully automated platform for routine clinical application.

Using ISO/TS 20914:2019 to calculate the measurement uncertainty of immunosuppressive drugs in a clinical laboratory

According to the standard ISO 15189 clinical routine laboratories shall estimate measurement uncertainty (MU) of patient results of their provided measurands. Up to now there was no accepted description on how to perform. Recently, the ISO technical standard ISO/TS 20914 was published giving a practical guide for uncertainty estimation. The immunosuppressive drugs Everolimus, Ciclosporin, Sirolimus and Tacrolimus have narrow therapeutic windows. Hence, their MU should be considered for deducing clinical decisions. Here, a pathway is presented in detail on how to estimate MU measuring immunosuppressants using a widespread CE certified assay via LC-MS/MS technology. Namely, the expanded measurement uncertainties are from 13% to 27% depending on analyte and concentration. The calculation based on n > 2000 measurements each of four control levels within one year. Lower uncertainties were observed if the material was native pooled blood (13% to 17%, n > 300 measurements, one year).

Quality of therapeutic drug monitoring guidelines is suboptimal: an evaluation using the Appraisal of Guidelines for Research and Evaluation II instrument

OBJECTIVES

Although therapeutic drug monitoring (TDM) guidelines are available, systematic evaluations of their methodological quality are scarce. This study aimed to assess the quality of current TDM guidelines using the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument.

STUDY DESIGN AND SETTING

We performed a systematic search to identify the relevant TDM guidelines in PubMed, EMBASE, CNKI, Wan Fang Database, CBM, VIP, four main guideline databases (NICE, NGC, GIN, and WHO guideline databases), and official websites of the governments and societies associated with TDM from the inception date to May 2018. Four independent appraisers rated the quality of each TDM guideline using the AGREE II instrument, and the mean score of each AGREE II item was calculated. The overall agreement among the appraisers was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

Twenty-eight TDM guidelines satisfied the eligibility criteria from among 12,235 references. The overall agreement among the appraisers was substantial (0.700-0.880). The mean scores for the six AGREE II domains were scope and purpose, 67.7% (95% CI, 64.0-71.4%); stakeholder involvement, 39.8% (95% CI, 33.3-46.3%); rigor of development, 36.0% (95% CI, 28.1-43.9%); clarity and presentation, 61.6% (95% CI, 55.7-67.4%); applicability, 30.6% (95% CI, 26.4-34.8%); and editorial independence, 49.2% (95% CI, 40.0-58.6%). The reviewers recommended only four guidelines, and most of the TDM guidelines were rated as "recommended with modifications."

CONCLUSION

Overall, the quality of TDM guidelines is suboptimal according to the evaluation using the AGREE II instrument. The domains of applicability, rigor of development, stakeholder involvement, and editorial independence of the guidelines need to be reported. In addition, guideline developers closely adhering to the AGREE II instrument and the Grading of Recommendations Assessment Development and Evaluation system are required to draft high-quality and reliable TDM guidelines.

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.

Comparing the effect of isotopically labeled or structural analog internal standards on the performance of a LC-MS/MS method to determine ciclosporin A, everolimus, sirolimus and tacrolimus in whole blood

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is routinely used for analysis of immunosuppressive drugs. This study investigated whether replacing analog internal standards (ANISs) with isotopically labeled internal standards (ILISs) has an impact on the performance of a LC-MS/MS method for the quantification of tacrolimus (TAC), sirolimus (SIR), ciclosporin A (CsA) and everolimus (EVE) in whole blood.

Following hemolysis, protein precipitation, and extraction with either ANISs (ascomycin, desmethoxy-rapamycin, CsD), or ILISs (TAC-

Within-day imprecision was <10%, between-day <8%, and trueness 91%–110% for all the analytes with both ISs. No carryover or matrix effects were observed. The median accuracy was −2.1% for CsA, 9.1% for EVE, 12.2% for SIR, and −1.2% for TAC with the ILISs; and −2% for CsA, 9.8% for EVE, 11.4% for SIR, and 0.2% for TAC with the ANISs. Results of patient and proficiency testing samples were not statistically different.

: Although ILISs are generally considered superior to ANISs, they may not be always essential. When optimizing a LC-MS/MS method other factors must be also considered.

Liquid chromatography-tandem mass spectrometry method for determination of Sirolimus coated drug eluting nano porous carbon stents

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has proved to powerful research tool due to its sensitivity, high selectivity, and high throughput efficiency..Sirolimus was extracted from plasma by two-step extraction procedure using chloroform as extracting solvent. Signal intensity was high using ESI(+) source provided for the quantitation of samples. Chromatographic separation was performed on phenomenax C-18 column (250 x 4.60 mm 5microns).Mobile phase contains acetonitrile, water (80; 20 v/v) + 0.1% acetic acid, flow rate 1 mL/min.The retention time of Sirolimus 8.4 min, the total run time10 min. Linearity correlation coefficients (r(2)) curve was 0.997183.calibraction range 10-1000 ng/mL. The UV detection of Sirolimus was at 278(277.78) nm. Sirolimus coated drug eluting stents, MRM (Multiple reaction monitoring) transition of Sirolimus m/z 936.83-208.84 was selected to obtain maximum sensitivity. LC/MS/MS results exhibited consistency in drug content on the stent surface. In-vitro release kinetic indicated the release of Sirolimus in 41 days from the date of implanted. Drug release was found at the first day, burst release was observed at 7(th) day of implantation. This study involved pharmacological coating of stents, based on the notion that sustained systemic local delivery of anti-proliferative agents. LC-MS/MS method has been successfully used in the pharmacokinetic analysis of Sirolimus coated drug eluting stents.

Impact of plasma and whole-blood anticoagulant counter ion choice on drug stability and matrix effects during bioanalysis

Background: Anticoagulants are used to prevent coagulation in blood samples. The plasma pH may change with a different counter ion and anticoagulant; thus, it is essential to determine effects on drug stability and the matrix effect during the bioanalytical method development. Results: Cross-validation of multiple compounds between different counter ions was performed and no impact from the counter ion nature was demonstrated. Moreover, plasma stabilities and matrix effects for both fluconazole and granisetron were investigated thoroughly in numerous counter ions/anticoagulants (K3ethylenediaminetetraacetic acid [K3EDTA], K2EDTA, NaEDTA, NaHeparin and LiHeparin). Sirolimus, a large cyclic molecule, was also tested in different whole-blood EDTA counter ions. Results showed percentage deviation less than 8.5% and percentage cross-validation less than 8.4%. Conclusion: None of the compounds tested had an impact on the matrix stabilities and matrix effect.

Quantification of sirolimus and everolimus by immunoassay techniques: test specificity and cross-reactivity evaluation

The possible cross-reactivity of immunoassays with structurally-related drugs was investigated. Innofluor Certican (FPIA) calibrators were measured by using IMx Sirolimus assay (MEIA) and MEIA Sirolimus calibrators were analysed by using FPIA Certican assay. Drug concentrations were measured in 95 and 100 samples from renal transplanted patients (RTP) on sirolimus or everolimus treatment by using immunoassays and LC/ESI-MSMS. A high cross-reactivity was found both for MEIA and FPIA. High correlation degrees, confirmed by the Bland-Altman and the Eksborg tests, were found between drug concentrations measured in real samples by both immunoassays (r = 0.909 and r = 0.970, respectively). LC/ESI-MSMS analysis of samples containing sirolimus showed no positivity for everolimus. Similarly, samples from patients on treatment with everolimus resulted negative as far as regards sirolimus. MEIA and FPIA could be considered mutually reliable and accurate alternatives for the specific-drug immunoassay. It should be noticed that in patients switching from one drug to the other unreal overestimation of the blood levels of the current administered immunosuppressant can occur.

Stability of sirolimus and everolimus measured by immunoassay techniques in whole blood samples from kidney transplant patients

The measurement of blood concentration of immunosuppressive drugs is strongly recommended because of the narrow therapeutic range. An important aspect in the therapeutic monitoring of a drug is its possible degradation. This paper is aimed at investigating the stability of two widely-used immunosuppressants, sirolimus and everolimus. Short (storage at 30 degrees C for 3 or 7 days) and long term (storage at -20 degrees C for 0-90 days with a single freeze-thaw cycle) stability of sirolimus and everolimus in whole blood samples from kidney transplant patients were examined by using MEIA and FPIA. Sirolimus and everolimus samples stored at 30 degrees C in light for up to a week showed a decrement in concentration of 5.2 percent and 6.1 percent, respectively. Our findings on long term stability for both sirolimus and everolimus highlight the possibility of storing samples at -20 degrees C for up to 90 days, without the need to use lower storage temperatures. The results have important implications for patients living far from laboratories where drug concentration is measured or when the storing of blood samples is needed for pharmacokinetic studies.

Immunoassay determination of rapamycin: reliability of the method with respect to liquid chromatography mass spectrometric quantification

Immunochemical assays represent a promising tool for quantification of immunosuppressants in organ transplanted patients, because they require small sample volumes and minimum sample pre-treatment; nevertheless considerations about method specificity, sensitivity and reproducibility cannot be overlooked. The present paper investigates the reliability of using the immunoparticle enzyme immunoassay (MEIA) for the quantification of blood rapamycin (RAPA) levels in therapeutic drug monitoring of renal transplanted patients with respect to a validated liquid chromatography tandem mass spectrometric (LC/ESI-MSMS) method, used as reference. Linearity of MEIA was tested over the range 0.0-30.0 ng/mL, with accuracy and precision within acceptable limits. Fifty-two blood samples were collected from 42 renal transplanted patients and analyzed simultaneously by both methods. The Pearson's regression analysis gave the following parameters: correlation equation [RAPA](MEIA) = 1.330 + 0.776 [RAPA](LC/ESI-MSMS), r = 0.8526, SD = 1.778, p < 0.0001. The obtained average rapamycin concentration was 8.8 +/- 3.4 ng/mL using MEIA and 9.6 +/- 3.7 ng/mL for LC/ESI-MSMS, with an overall underestimation of about 6% of the immunoenzymatic test. Accuracy of MEIA ranged from -33% to 36% with respect to the reference mass spectrometric method. Although immunoenzymatic test represents a fast and sufficiently accurate method for its use in clinical practice, specificity of the assay is still not sufficiently investigated and reference methods and/or Proficiency Testing Scheme should be used as external control.

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

OBJECTIVES

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

A Bayesian approach for population pharmacokinetic modelling of sirolimus

AIMS

To explore a Bayesian approach for the pharmacokinetic analysis of sirolimus concentration data arising from therapeutic drug monitoring (poorly informative concentration-time point design), and to explore possible covariate relationships for sirolimus pharmacokinetics.

METHODS

Sirolimus concentration-time data were available as part of routine clinical care from 25 kidney transplant recipients. Most samples were taken at or near the trough time point at steady state. The data were analyzed using a fully conditional Bayesian approach with PKBUGS (v 1.1)/WinBUGS (v 1.3). Features of the data included noncompliance and missing concentration measurements below the limit of sensitivity of the assay. Informative priors were used.

RESULTS

A two-compartment model with proportional residual error provided the best fit to the data (consisting of 315 sirolimus concentration-time points). The typical value for the apparent clearance (CL/F ) was 12.5 l h(-1) at the median age of 44 years. Apparent CL was found to be inversely related to age with a posterior probability of a clinically significant effect of 0.734.

CONCLUSIONS

A population pharmacokinetic model was developed for sirolimus using a novel approach. Bayesian modelling with informative priors allowed interpretation of a significant covariate relationship, even using poorly informative data.

Sirolimus--challenging current perspectives

Sirolimus is a potent immunosuppressant drug with a novel mechanism of action. It inhibits the mammalian target of rapamycin (mTOR) and blocks the cell cycle of various cell types, including T- and B-lymphocytes. Sirolimus is widely used as a maintenance immunosuppressive agent in organ transplantation. Also, a potentially benefit of this valuable drug in some immunologic and malignant diseases is currently under scrutiny.Classical side effects: hematological (anaemia, leucopenia, thrombocytopenia), hypercholesterolemia, arthralgias, extremity oedema and impaired wound healing have been frequently associated with the use of sirolimus. Additionally with its increased use, transplant professionals are encountering a variety of previously unreported and potentially more severe side effects.Here, we review the most recent data on sirolimus unexpected side effects (with an emphasis on pulmonary and renal toxicity), its use in renal transplantation and its new potential therapeutic indications (chronic glomerulopathies, polycystic kidney disease, different types of cancer). A brief description of the current knowledge of sirolimus therapeutic drug monitoring, methods of analysis, pharmacokinetics and drug interactions with calcineurin inhibitors is also included.

[Comparison of high-resolution liquid chromatography versus microparticle enzyme immunoassay for the measurement of sirolimus levels in renal transplantation]

OBJECTIVE

To compare sirolimus levels measured in whole blood using two analytical techniques: high-resolution liquid chromatography and microparticle enzyme immunoassay, and to evaluate whether hemoglobin, hematocrit, and time from kidney transplantation influence results obtained using the immune-enzymatic technique.

METHOD

A retrospective, observational study in which all transplanted patients with at least one measurement of sirolimus levels using high-resolution liquid chromatography or microparticle enzyme immunoassay from October 2004 to May 2005 were consecutively included. For statistical comparisons simple linear regression, ANCOVA, intra-class correlation coefficient, and the method of agreement limits were all used.

RESULTS

Ninety-one patients were assessed for a total of 307 measurements (median: 2, inter-quartile range: 1-4, range: 1-15) of sirolimus levels. The straight-line equation using the linear regression analysis was as follows: MEIA = 0.70 (95% CI: 0.39-1.01) + 1.14 (95% CI: 1.10-1.17) x HPLC/UV. The intra-class correlation coefficient between both measurements was 0.955 (95% CI 0.944-0.964). Mean overestimation using enzyme immunoassay was 24.8% +/- 19.4%. Difference in means between both measurements was 1.9 +/- 1.3 ng/mL. Agreement limits were established between -0.8 ng/mL (95% CI: -1.05; -0.55) and +4.6 ng/mL (95% CI: 4.35; 4.85). Factors such as post-transplant time, hemoglobin, and hematocrit did not influence overestimates obtained using enzyme immunoassays. These results were not influenced by non-independence in measurements.

CONCLUSIONS

Despite enzyme immunoassay overestimates in establishing sirolimus levels in whole blood, its correlation with chromatography is acceptable. Added to its benefits versus chromatographic techniques, this renders enzyme immunoassay a good alternative for the measurement of sirolimus levels in whole blood.

Sirolimus: the evidence for clinical pharmacokinetic monitoring

This review seeks to apply a decision-making algorithm to establish whether clinical pharmacokinetic monitoring (CPM) of sirolimus (rapamycin) in solid organ transplantation is indicated in specific patient populations. The need for CPM of sirolimus, although a regulatory requirement in Europe, has not yet been firmly established in North America and other parts of the world. Sirolimus has demonstrated immunosuppressive efficacy in renal, pancreatic islet cell, liver and heart transplant recipients. The pharmacological response of immunosuppressive therapy with sirolimus cannot be readily evaluated; however, a relationship between trough blood sirolimus concentrations, area under the plasma concentration-time curve (AUC) and the incidence of rejection has been proposed. Furthermore, sirolimus can be measured in whole blood by several assays--high-performance liquid chromatography with detection by tandem mass spectrometry, or with ultraviolet detection, radioreceptor assay or microparticle enzyme immunoassay. Both experimental animal and clinical data suggest that adverse events and their associated severity are correlated with blood concentrations. To prevent rejection and minimise toxicity, a therapeutic range of 4-12 microg/L (measured via chromatographic assays) is recommended when sirolimus is used in conjunction with ciclosporin. If ciclosporin therapy is discontinued, a target trough range of 12-20 microg/L is recommended. Sirolimus pharmacokinetics display large inter- and intrapatient variability, which may change in specific patient populations due to disease states or concurrent immunosuppressants or other interacting drugs. Due to the long half-life of sirolimus, dosage adjustments would ideally be based on trough levels obtained more than 5-7 days after initiation of therapy or dosage change. Once the initial dose titration is complete, monitoring sirolimus trough concentrations weekly for the first month and every 2 weeks for the second month appears to be appropriate. After the first 2 months of dose titration, routine CPM of sirolimus is not necessary in all patients, but may be warranted to achieve target concentrations in certain populations of patients, but the frequency of further monitoring remains to be determined and should be individualised.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.

Determination of rapamycin: quantification of the sodiated species by an ion trap mass spectrometer as an alternative to the ammoniated complex analysis by triple quadrupole

Rapamycin is a potent immunosuppressive drug capable of significantly reducing acute graft rejection in kidney, liver and heart transplant patients. Its immunosuppressive activity and adverse effects have been related to rapamycin concentration, and therapeutic drug monitoring of the drug is deemed appropriate. This work was aimed at developing a new quantification method based on the isolation of the [M+Na]+ ion as precursor and its further fragmentation through an ion trap mass spectrometer equipped with an electrospray ionization source. A limit of detection (LOD) of 0.7 ng/mL was obtained, while the lower limit of quantification (LLOQ) was 2.4 ng/mL. The accuracy and reproducibility of the responses were evaluated and compared with results obtained when the [M+NH4]+ ion was chosen as the precursor in a triple quadrupole mass spectrometer. In this case the LOD was 0.5 ng/mL and the LLOQ 1.7 ng/mL. Data showed that it would be possible to use the quantification of the sodiated species for the routine determination of rapamycin, as an alternative to the commonly adopted method based on the ammoniated complex.

Therapeutic drug monitoring of sirolimus: effect of concomitant immunosuppressive therapy and optimization of drug dosing

Sirolimus (SRL) is a new immunosuppressant which shares a common metabolic pathway with several other immunosuppressive agents. This leads to potential pharmacokinetic interactions that might affect SRL blood levels with relevant clinical consequences. As a validated laboratory, 2658 SRL trough samples (corresponding to 495 kidney transplant recipients treated with different immunosuppressive regimens) from more than 40 Italian Transplant Units were analyzed. We found that dose-normalized SRL trough levels were significantly higher in patients treated with cyclosporine (CsA) and SRL (4.15 +/- 2.23 ng/mL/mg SRL), compared with patients treated with mycophenolate mofetil (MMF) and SRL (3.26 +/- 1.86 ng/mL/mg SRL; p < 0.01) or with MMF, steroids and SRL (2.52 +/- 1.73 ng/mL/mg SRL; p < 0.01). Mean intra- and interpatient variabilities were 19% and 47%, respectively. Both parameters are significantly affected by the time postsurgery, with the first week post transplantation being associated with the greatest variability. As additional analysis, a simple dose-adjustment formula has been proposed as a useful tool to guide SRL dose changes. The proposed equation has been able to predict SRL concentration after a dose change in 73% of the tested samples. These findings suggest that different immunosuppressants significantly interfere with SRL bioavailability. Strategies aimed at reducing variability in SRL exposure may have a positive clinical impact.

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 sirolimus in heart transplant recipients with chronic renal impairment

BACKGROUND

A common clinical problem following organ transplantation is the development of renal failure due to calcineurin inhibitors. Sirolimus offers the potential of providing appropriate immunosuppression without nephrotoxicity. This study evaluates the impact of sirolimus monotherapy on renal function in patients late following heart transplantation and correlates trough sirolimus levels with area-under-the-concentration time curve measurements.

METHODS

Six male patients with renal impairment late following heart transplantation (mean 8 years) were offered sirolimus therapy. Calcineurin inhibition was discontinued in all patients on commencing sirolimus. Patients started on sirolimus 2 to 5 mg/d orally. Venous blood samples for pharmacokinetic studies and repeat creatinine clearance were performed before and 6 weeks after commencement of sirolimus in all subjects.

RESULTS

Sirolimus trough levels accurately reflected sirolimus area-under-the-concentration time curve measurements. There was no change in renal function. Mean creatinine clearance prior to commencing sirolimus was 26.7 (12.2) mL/min and the post-sirolimus creatinine clearance performed 6 weeks later was 23.4 (11.7) mL/min (P = .64).

CONCLUSIONS

Trough levels of sirolimus correlate with drug exposure and may be used to monitor sirolimus therapy. No improvement in renal function following calcineurin inhibitor withdrawal occurred in this cohort.

Therapeutic drug monitoring for sirolimus in whole blood of organ transplants by high-performance liquid chromatography with ultraviolet detection

We developed and validated an accurate, sensitive, precise and rapid HPLC method with UV detection for the determination of sirolimus in blood samples from renal, cardiac and hepatic transplants. This method overcomes most of the problems related to previously published assays using a narrow-bore column with base deactivated C18 reversed phase. Whole blood samples were purified by a combination of a precipitating blood matrix with zinc sulphate and a single step liquid-liquid extraction with acetone and 1-chlorobutane. Calibration curves (range 2.5-150 ng/ml), were linear with coefficients of correlation better than 0.996. The relative standard deviation was determined to be less than 8%. The present method has also been validated by a reference laboratory (St. George's Hospital Medical School, London, UK). More of 300 clinical samples have been analysed with this method.

Assessment of sirolimus concentrations in whole blood by high-performance liquid chromatography with ultraviolet detection

A novel, reversed-phase high-performance liquid chromatographic (HPLC) method is described for the analysis of sirolimus (SRL) in whole blood. The samples were purified by precipitating blood matrix with zinc sulfate, SRL was then extracted with acetone followed by solid-phase extraction. The method was linear over a range of 1-100 ng/ml and the lower limit of quantification was 2.5 ng/ml. The coefficient of variation (within day) was below 8.0% for the lowest SRL concentration. The day-to-day coefficient of variation was below 6.6%. The assay did not show interference peaks with immunosuppressive drugs commonly given to transplant patients. With the simplified extraction procedure described, 60 samples (including controls and calibration curve) can be quantified in a day. The sensitivity and rapidity of this analytical procedure makes it useful for routine therapeutic monitoring of SRL.

International Federation of Clinical Chemistry/International Association of Therapeutic Drug Monitoring and Clinical Toxicology working group on immunosuppressive drug monitoring

Issues surrounding the measurement and interpretation of immunosuppressive drug concentrations have been summarized in a number of consensus documents. The Scientific Division of the International Federation of Clinical Chemistry has formed a working group in collaboration with the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. This paper sets out the goals of the working group in light of the developments that have occurred in the field of immunosuppressive drug monitoring since the publication of the last consensus documents.

Current immunosuppressant regimens: considerations for critical care

While current immunosuppressive drug regimens have significantly increased the rate of successful transplantation outcomes, they convey potentially serious and overlapping adverse effects. Cyclosporine and tacrolimus are the cornerstones of current immunosuppression, achieving excellent one-year renal graft survival rates. Other promising new drugs include sirolimus, which has been demonstrated to reduce efficacy failure rates among renal transplant recipients, and everolimus, which is currently undergoing clinical trials. Agents targeting novel sites in the immune response or disrupting the ischemia-reperfusion cascades are currently under development. Among them, only FTY720 is undergoing large-scale human clinical trials. With its unique mechanism of action and synergistic interactions with cyclosporine and sirolimus, it may provide the foundation for a new era in immunosuppression.

High-throughput semi-automated 96-well liquid/liquid extraction and liquid chromatography/mass spectrometric analysis of everolimus (RAD 001) and cyclosporin a (CsA) in whole blood

A semi-automated high-throughput liquid/liquid extraction (LLE) assay was developed for RAD001 and cyclosporin A (CsA) in human blood. After addition of internal standard and ammonium hydroxide, samples were extracted twice with methyl tert-butyl ether (MTBE). The organic extract was evaporated to dryness and reconstituted in mobile phase. Where possible, sample transfer and LLE steps were automated using a Tomtec Quadra 96 workstation. Samples were analyzed using ESI-LC/MS/MS employing the transitions of ([M + NH(4)](+) --> [M + H](+)) for CsA and ([M + NH(4)](+) --> [M + H-(CH(3)OH + H(2)O)](+)) for RAD001, under isocratic chromatographic conditions (75:25, (v/v), acetonitrile/20 mM ammonium acetate) with a run time of 3.6 min. A lower limit of quantitation (LLOQ) of 0.368 ng/mL and 5.23 ng/mL was achieved for RAD001 and CsA, respectively, using a sample volume of 0.3 mL for the analysis. The method was validated over a 3-day period and the resulting calibration curves had a correlation coefficient >0.99 over the concentration range 0.368 to 409 ng/mL and 5.24 to 1748 ng/mL for RAD001 and CsA, respectively. The inter-day coefficient of variation (CV) was less than 15% at the LLOQ for both compounds. The method was applied to the analysis of clinical samples. Under normal working conditions four 96-well plates could be extracted and LC/MS analysis completed in less than 28 h. A marked improvement in sample throughput efficiency was realized with this LLE method when compared to existing solid phase extraction (SPE) methods which deal with both RAD001 and CsA.

Automated, fast and sensitive quantification of drugs in blood by liquid chromatography-mass spectrometry with on-line extraction: immunosuppressants

We developed a universal LC-mass spectrometry assay with automated online extraction (LC/LC-MS) to quantify the immunosuppressants cyclosporine, tacrolimus, sirolimus and SDZ-RAD alone or in combination in whole blood. After protein precipitation, samples were loaded on a C18 extraction column, were washed and, after activation of the column-switching valve, were backflushed onto the C8 analytical column. [M+Na]+ ions were detected in the selected ion mode. For tacrolimus, sirolimus and SDZ-RAD, the assay was linear from 0.25 to 100 microg/l and for cyclosporine from 7.5 to 1250 microg/l (all r2>0.99). Analytical recovery was >85% and, in general, inter-day, intra-day variability for precision and accuracy were <10%.

Measurement of sirolimus in whole blood using high-performance liquid chromatography with ultraviolet detection

BACKGROUND

Sirolimus, a potent immunosuppressive drug, exhibits intrapatient and interpatient variability of absorption and metabolism. Thus, therapeutic drug monitoring is important.

OBJECTIVE

This paper describes a reverse-phase high-performance liquid chromatography (HPLC) method, using ultraviolet (UV) absorption for detection, for measuring sirolimus levels in human whole-blood samples.

METHODS

The stability of sirolimus in whole blood was assessed under conditions likely to be encountered during transport of study samples to a central laboratory. The performance of the HPLC-UV assay in measuring sirolimus was compared with that of 3 established, validated HPLC assays with tandem mass-spectrometric (MS/MS) detection. Results of the HPLC-UV assay also were compared with results produced by a prototype microparticle enzyme immunoassay (MEIA).

RESULTS

Inaccuracy for 3 in-house control samples was < or =4%, whereas within-assay repeatability (coefficient of variation [CV]) was < or =5% and between-assay reproducibility was < or =6.6%. Mean recovery of sirolimus from blood was 81.5%+/-4.3%. The lower limit of quantification was set at 6.5 ng/mL, and the repeatability CV at this concentration was 4.2% (n = 6). Sirolimus-containing whole-blood samples were stable for 3 freeze/thaw cycles when stored at -20 degrees C and for > or =2 days when stored at ambient temperature. The sample extract was shown to be stable for up to 54 hours at ambient temperature (approximately 22 degrees C) after extraction. Results of the HPLC-UV assay were consistent with those of the HPLC/ MS/MS assays but lower than those produced by MEIA.

CONCLUSION

This HPLC-UV method is considered suitable for therapeutic drug monitoring of sirolimus.

Therapeutic monitoring of sirolimus in human whole-blood samples by high-performance liquid chromatography

BACKGROUND

Sirolimus is a macrolide antibiotic isolated from Streptomyces hygroscopicus that has demonstrated immunosuppressive activity. Human and animal studies have shown a good correlation of trough sirolimus concentrations with immunosuppressive efficacy.

OBJECTIVE

This report describes a reverse-phase high-performance liquid chromatography (HPLC) method used for therapeutic drug monitoring of sirolimus.

METHODS

A reverse-phase C18 column method was developed using an automated HPLC system and ultraviolet (UV) detection. Whole-blood samples collected in ethylenediamine-tetraacetic acid (EDTA) are first hemolyzed, and an internal standard (desmethoxysirolimus) is added to 1.0 mL of sample, which is then extracted with 1-chlorobutane and, after the organic layer is removed, evaporated to dryness. The residue is reconstituted in a 70% methanol/water mixture. Reconstituted extracts are analyzed by HPLC at a column temperature of 60 degrees C and a flow rate of 1.0 mL/min. Typically, chromatography requires 35 minutes between each sample injection. The UV detector is set at 278 nm with a response sensitivity of 0.010 AUFS (absorbance units full scale). Standards and controls prepared in hemolyzed EDTA-anticoagulated whole blood are extracted and run in parallel. Identification of peaks of interest is by retention time; quantification of sirolimus in controls and clinical samples uses a peak-height ratio (sirolimus/internal standard).

RESULTS

The assay's precision (coefficients of variation, 5.7%-14.4%) and sensitivity (2.5 ng/mL) were found to be appropriate for therapeutic monitoring purposes. Analytical recovery of 88.0% to 106.3% was observed throughout the assay's linear range (2.5-150.0 ng/mL). Stability studies at 20 degrees C to 25 degrees C and 2 degrees C to 8 degrees C showed an estimated recovery of sirolimus ranging from 85% to 110% of target concentrations (10-90 ng/mL). In a study comparing the results of 194 samples from kidney transplant recipients assayed by the HPLC-UV assay and by a microparticle enzyme immunoassay, the HPLC-UV method provided approximately 10% lower values.

CONCLUSION

The HPLC-UV assay is analytically capable of providing useful data for the clinical assessment of patients receiving sirolimus.

The quantification of sirolimus by high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in renal transplant recipients

BACKGROUND

Sirolimus, an immunosuppressive agent, is undergoing clinical trials in the prophylaxis of organ rejection.

OBJECTIVES

The aim of this study was to compare the performance of the semi-automated prototype (mode IA) microparticle enzyme immunoassay (MEIA) against a validated high-performance liquid chromatography-mass spectrometry (HPLC-MS) method for measuring sirolimus concentrations. A secondary objective was to identify potential factors that may influence sirolimus measurement.

METHODS

The comparison was based on predose samples (n = 841) from 74 renal transplant patients receiving sirolimus therapy. Samples were collected up to 12 months after transplantation.

RESULTS

The mean (+/- SD) overestimation by MEIA was 42.5%+/-16.9%. Several variables were investigated to determine potential contributors to the observed overestimation. Stratification of the data based on the mean sirolimus concentrations determined by both assays yielded no statistically significant differences in bias between concentration subgroups within the clinically relevant range. Multiple linear regression analysis identified HPLC-MS sirolimus concentration (P = 0.03), hemoglobin concentration (P < 0.001), and time after transplantation (P < 0.001) as significant variables in the prediction of overestimation by MEIA. Analysis of the effect of time after transplantation on overestimation yielded a statistically significant difference up to 6 months after transplantation (35.6% to 46.4%) compared with 9 (23.9%) and 12 months (24.4%). A relationship between hemoglobin concentration and time after transplantation may explain the reduction in bias observed after 6 months.

CONCLUSION

The MEIA overestimates sirolimus concentrations in renal transplant patients compared with HPLC-MS. The clinical importance of this observed overestimation requires further investigation.

An immunophilin-binding assay for sirolimus

OBJECTIVE

This review examines the performance of 4 assays for sirolimus in terms of their ability to meet 6 guidelines determined by a panel of experts.

BACKGROUND

Four methods have been described to date for the analysis of sirolimus concentrations in whole blood: high-performance liquid chromatography-mass spectrometry (HPLC-MS); microparticle enzyme immunoassay (MEIA); p70 S6 kinase inhibition; and an immunophilin-binding assay (IBA).

METHODS

A MEDLINE search of the literature was performed to identify relevant studies.

RESULTS

The HPLC methods suffer from precision problems because of the substantial specimen preparation required, and HPLC-MS methods are not practical for clinical use. Initial studies of the MEIA have found overestimation of sirolimus concentrations that may be caused by antibody cross-reactivity with sirolimus metabolites. Monitoring of sirolimus effects by p70 S6 kinase inhibition is as yet possible only theoretically, and the assay itself is not yet optimal. With the IBA, use of a T-cell protein that binds to sirolimus and that may be the intracellular target of the drug as the assay binding protein allows the assay to measure sirolimus selectively, even in the presence of structurally similar metabolites.

CONCLUSION

More than 200 clinical samples have been analyzed by the IBA, and correlation with HPLC values has been good, with a regression line slope near 1.0. In addition, the assay is easier to perform and more precise than HPLC, and has the potential to be automated. Thus, the IBA appears to have certain clear advantages over the other assays.

Proficiency-testing issues relating to sirolimus

BACKGROUND

A need exists to document laboratory proficiency to (1) compare results produced by different analytical techniques and (2) ensure consistency of results from multiple testing sites.

OBJECTIVES

To enable concentration-controlled studies of sirolimus to proceed with confidence, proficiency-testing schemes were put in place at laboratories selected to act as reference laboratories. The feasibility of establishing an ongoing proficiency-testing scheme was addressed with respect to sample stability. The scheme was then used to test proficiency for the measurement of sirolimus in 3 blinded samples each month.

METHODS

The method chosen for measurement of sirolimus was a prototype microparticle enzyme immunoassay. Initially, 15 laboratories were asked to analyze a series of 85 blinded samples that tested their inaccuracy, repeatability, and reproducibility for the measurement and their ability to dilute over-range samples competently. Both blood samples spiked with sirolimus and pooled blood samples from patients receiving the drug were circulated to a maximum of 50 laboratories.

RESULTS

Overall, both inaccuracy and imprecision were acceptable by predefined criteria. Inaccuracy for the immunoassay (percentage difference of the measured value against the nominal value) averaged -5% (95% CI, -9% to -1%). The mean percentage difference between the immunoassay and a high-performance liquid chromatographic assay with mass-spectrometric detection for the measurement of sirolimus in pooled samples (n = 5) from patients receiving the drug was 29% (95% CI, 24% to 34%).

CONCLUSION

The techniques documented here as part of the International Sirolimus Proficiency Testing Scheme could be applied to other clinical studies requiring protocol-driven dosing adjustments based on sirolimus measurements, irrespective of analytical technique used.

An immunoassay for the measurement of sirolimus

OBJECTIVE

This study assessed the performance characteristics of a new microparticle enzyme immunoassay (MEIA) for the determination of sirolimus in whole blood.

BACKGROUND

In clinical investigatory studies, dose adjustments of the immunosuppressive drug sirolimus have been carried out using either high-performance liquid chromatography (HPLC) or, more recently, this investigational immunoassay kit based on the MEIA technique.

METHODS

Calibration was made over the linear range 0 to 30 ng/mL. Inaccuracy and imprecision were assessed by means of 3 control samples supplied with the kit (5, 11, and 22 ng/mL) and dilution of an above-quantitation-limit sample (154 ng/mL). Specificity was determined by the addition of 2 sirolimus metabolites to sirolimus-free human whole blood or to I of the control samples supplied with the kit. In addition, whole-blood samples from patients receiving either cyclosporine or tacrolimus (N = 24) were analyzed for sirolimus. A comparison of the MEIA and a validated HPLC/MS/MS assay analyzed both pooled samples from patients receiving sirolimus and spiked samples (sirolimus 2-60 ng/mL). In a more extensive comparison of patient samples measured by the MEIA assay, a validated HPLC assay with UV detection (HPLC-UV) was used (HPLC-UV sirolimus 7-64 ng/mL).

RESULTS

Inaccuracy (between-run) was < or =16.2% at all 4 concentrations (N = 5). Within-assay imprecision (repeatability) was <6% (N = 5), and between-assay imprecision (reproducibility) for the same samples was < 11% (N = 5). Recovery, assessed by means of 3 in-house control samples prepared in both fresh and previously frozen sirolimus-free human whole blood, ranged from 93.9% to 109.5%. The limit of detection, determined by dilution of the lowest nonzero calibrator (3 ng/mL), was set at 1 ng/mL, at which repeatability was 20.5% (N = 5). Five ng/mL of hydroxysirolimus cross-reacted with the assay by a mean of between 44% and 50% (N = 4); 5 ng/mL of 41-O-demethylsirolimus cross-reacted with the assay by a mean of between 86% and 127% (N = 4). Assay specificity was further challenged by ethylenediamine-tetraacetic acid (EDTA)-whole-blood samples from transplant patients not receiving sirolimus. These samples had tacrolimus and cyclosporine concentrations of 7.8 to 15.9 ng/mL and 38 to 485 microg/L, respectively. The median result was 0 ng/mL (third quartile, 0.7 ng/mL; maximum, 1.4 ng/mL); no value was above the lowest nonzero calibrator. The results of the comparison between the MEIA and the HPLC/MS/MS assay showed mean positive biases of 21% and 8% for the MEIA in measuring sirolimus in pooled patient samples and spiked samples, respectively. The results of the comparison of the MEIA and HPLC-UV median sirolimus concentrations were 18.2 and 20.1. Whole-blood samples anticoagulated with EDTA and containing sirolimus were stable for analysis by MEIA for 3 freeze-thaw cycles when stored at -20 degrees C and for 10 days when stored at 4 degrees C or at ambient temperature. A decline in sirolimus concentration occurred when samples were stored at 37 degrees C.

CONCLUSION

The MEIA showed suitable precision across a clinically relevant concentration range. In terms of patient management, the practical significance of cross-reactivity with sirolimus metabolites remains to be assessed.

Stability of sirolimus (rapamycin) in whole blood

The effects of storage time (0-8 days), temperature (4 degrees C and 30 degrees C in dark and light), and freeze-thaw cycles on the stability of sirolimus in blood were examined. Sirolimus quantification was undertaken using HPLC-electrospray-tandem mass spectrometry. Whole blood samples supplemented with sirolimus (5.0, 15.0, and 30.0 microg/L) and pooled renal and heart transplant samples were found to be stable during the 8 days under all conditions (<10% decrease in concentration). No significant difference was observed in sirolimus concentration between freshly collected patient samples and sirolimus-supplemented samples (5.0, 15.0, and 30.0 microg/L) after three freeze-thaw cycles (p > 0.198). In conclusion, blood samples can be transported with or without cooling for up to 8 days without sirolimus results being compromised. The reanalysis of sirolimus samples, which may entail freeze-thaw cycles, can be undertaken if the number of cycles is three or less.

Biochemical characterization of the minor immunophilins

OBJECTIVE

We present biochemical characterization of the previously described 14 kDa, 37 kDa, and 52 kDa immunophilins and a newly identified 5-8 kDa immunophilin.

DESIGN AND METHODS

Proteins were tested for the following enzymatic activities-rotamase, G3PDH, protein kinase C, cAMP dependent protein kinase-and for the ability to inhibit calcineurin phosphatase when complexed with tacrolimus (FK506).

RESULTS

The 5-8 kDa protein, like the other minor immunophilins, lacks rotamase activity. Since the 37 kDa possesses G3PDH activity, the 5-8 kDa protein, 14 kDa protein, and 52 kDa protein were all tested and found to lack G3PDH activity. Additional work shows that none of the minor immunophilins possess protein kinase C or cyclic AMP-dependent protein kinase activity and that the 37 kDa and 5-8 kDa and probably the 52 kDa proteins are capable of inhibiting calcineurin phosphatase when bound to tacrolimus.

Prevention of acute allograft rejection in nonhuman primate lung transplant recipients: induction with chimeric anti-interleukin-2 receptor monoclonal antibody improves the tolerability and potentiates the immunosuppressive activity of a regimen using low doses of both microemulsion cyclosporine and 40-O-(2-hydroxyethyl)-rapamycin

BACKGROUND

In previous studies of cynomolgus monkey lung allograft recipients, we demonstrated significant immunosuppressive efficacy but reduced tolerability after combined treatment with high doses of microemulsion cyclosporine (CsA) and SDZ RAD (40-O-(2-hydroxyethyl)-rapamycin). The current study was designed to compare efficacy and tolerability of a combination of low-dose CsA and high-dose SDZ RAD (CTL group) to triple therapy using the chimeric anti-interleukin-2 (IL-2) receptor (CD25) monoclonal antibody (mAb) basiliximab (anti-IL-2 receptor mAb) for induction therapy (basiliximab: 5 mg intravenously on days 0 and 4) plus low-dose CsA and low-dose SDZ RAD for maintenance immunosuppression (CD25 group). CsA and anti-IL-2 receptor mAb are drugs that reduce cytokine synthesis and block IL-2-mediated lymphocyte stimulation, respectively. SDZ RAD blocks lymphocyte stimulation by other cytokines (e.g., IL-15) that are not inhibited by anti-IL-2 receptor mAb.

METHODS

Twelve unilateral lung transplants were performed. Recipients were observed for 49 days by daily weight assessment, hemograms, blood chemistries, radiographs, and lung biopsies. Monkeys were euthanized before day 49 in the event of excessive weight loss (>25%) or organ failure. Target CsA trough levels were 100-200 ng/ml. Target SDZ RAD trough levels in the CTL group (no mAb) were 20-40 ng/ml, and 10-20 ng/ml in the CD25 group.

RESULTS

None of the monkeys in the CD25 group needed to be euthanized early due to signs of drug toxicity. In contrast, four monkeys in the CTL group were sacrificed on days 28-35 as a result of excessive weight loss (n=3) and renal functional impairment (n=1). Three recipients in the CD25 group were euthanized on days 36, 38, and 46 as a result of persistent high fever associated with severe rejection. The median animal survival in the CTL group was 32 vs. 46 days in the CD25 group (P<0.04). The only two long-term survivors in the CTL group showed moderate rejection at day 49. The median rejection scores at day 14 (A0) and day 28 (A2) were identical in the two groups, despite the fact that the mean SDZ RAD trough level was significantly lower in the CD25 group (CTL: 38+/-3 ng/ml, CD25: 18+/-2 ng/ml, P<0.0001). After basiliximab levels fell below the minimum therapeutic level (1 mg/ml) on day 28, the median rejection score at day 49 increased to A4 in the CD25 group.

CONCLUSION

This is the first study to combine an anti-IL-2 receptor mAb with a drug from the rapamycin class plus CsA. Our study shows that induction therapy with basiliximab enabled SDZ RAD blood levels to be significantly reduced, which led to improved tolerability without the penalty of increased rejection.

Comparison of steady-state trough sirolimus samples by HPLC and a radioreceptor assay

OBJECTIVES

We have previously identified a minor immunophilin of 52 kDa molecular weight capable of binding tacrolimus and sirolimus. Because immunophilins are capable of binding both parent drug and metabolites and HPLC assays are typically used to assess parent drug in clinical situations, we used this immunophilin in a radioreceptor assay (RRA) to determine if any metabolites not included in the HPLC measurement would bind to the immunophilin and be associated with thrombocytopenia in patients receiving sirolimus.

DESIGN AND METHODS

We tested 51 steady-state trough whole blood samples from non-thrombocytopenic patients and 51 steady-state trough samples from thrombocytopenic patients and compared them to HPLC measurements of parent drug in the same samples. We also tested whole blood samples spiked with authentic sirolimus metabolites using RRA to ascertain the effect these metabolites have on the technique.

RESULTS

We found minimal cross-reactivity in this assay for sirolimus metabolites (binding ranged from <10% to 26%), and good correlation of the radioreceptor assay with HPLC (linear regression slope 0.92, y-intercept 0.79). There was no statistically significant difference between the RRA and HPLC results in two patient groups-thrombocytopenic and non-thrombocytopenic-using the paired t-test (p<0.005) and Bland-Altman analysis.

CONCLUSIONS

These findings indicate that although the RRA could be substituted for HPLC in therapeutic drug monitoring, the 52 kDa immunophilin does not offer an advantage in terms of detecting metabolites associated with thrombocytopenia. However, the RRA offers the advantages of shorter turnaround time, smaller sample volume and potential for automation.