Clinical laboratory diagnostics of immunosuppressants: One laboratory’s journey

Laboratory support for the organ transplant patient is the provision of the best testing technology for a specific and accurate determination of immunosuppressive drug level. This translates to better management with the therapeutic cocktail of immunosuppressive drugs used with a lesser incidence of organ rejection and side effects. Over the years, development of automated immunoassay/chemistry test platforms with standardization of test protocols has demonstrated great improvements. The present clinical laboratory services with tandem mass spectrometry in our hospital present more precise and specific therapeutic drug monitoring so necessary still for the patient. This article follows the evolving testing technologies over the years for immunosuppressive drug monitoring following the organ transplants programme (renal in general) in Singapore General Hospital.

The new CYP3A4 intron 6 C>T polymorphism (CYP3A4*22) is associated with an increased risk of delayed graft function and worse renal function in cyclosporine-treated kidney transplant patients

OBJECTIVE

Cyclosporine A (CsA) is a substrate of cytochrome P450 3A4 (CYP3A4). Recently, a newly discovered intron 6 single-nucleotide polymorphism in CYP3A4 (rs35599367 C>T), defining the CYP3A4*22 allele, has been linked to reduced hepatic expression and activity of CYP3A4. In the present study, the clinical impact of this single-nucleotide polymorphism was investigated in a cohort of patients receiving a CsA-based immunosuppressive regimen.

MATERIALS AND METHODS

A total of 172 de-novo kidney transplant recipients, receiving CsA/mycophenolate mofetil as immunosuppressive therapy and participating in the Fixed-Dose Concentration Controlled study, were genotyped for the new CYP3A4*22 allele. CsA C(0) and/or C(2) levels were measured on days 3 and 10 and in months 1, 3, 6, and 12 after transplantation. Plasma creatinine concentrations, delayed graft function (DGF), and biopsy-proven acute rejection were recorded.

RESULTS

The CYP3A4*22 allele was significantly associated with a higher risk of DGF compared with the CYP3A4*1/*1 patients after adjustment for known risk factors [odds ratio (OR)=6.34, confidence interval (CI(95%): 1.38-29.3), P=0.015]. Mixed-model analysis demonstrated that the overall creatinine clearance was 20% lower in CYP3A4*22 allele carriers compared with CYP3A4*1/*1 patients [CI(95%) (-33.1 to -7.2%), P=0.002]. For ABCB1 3435C>T, T-variant carriers had a decreased risk of developing DGF compared with CC patients [CT: OR=0.30, CI(95%) (0.11-0.77), P=0.011; TT: OR=0.18, CI(95%) (0.05-0.67), P=0.011].

CONCLUSION

CYP3A4*22 constitutes a risk factor for DGF and worse creatinine clearance in patients receiving CsA-based immunosuppressive therapy. Therefore, pretransplant genotyping for the CYP3A4*22 allele might help clinicians to identify patients at risk of DGF and poor renal function when treated with CsA.

Effect of a new functional CYP3A4 polymorphism on calcineurin inhibitors' dose requirements and trough blood levels in stable renal transplant patients

AIMS

CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the immunosuppressants tacrolimus (Tac) and cyclosporine (CsA). The objective of the study was to assess the potential influence of a new functional SNP in CYP3A4 on the pharmacokinetic parameters assessed by dose requirements and trough blood levels of both calcineurin inhibitors (CNI) in stable renal transplant patients.

PATIENTS & METHODS

A total of 99 stable renal transplant patients receiving either Tac (n = 49) or CsA (n = 50) were genotyped for the CYP3A4 intron 6 C>T (rs35599367) and CYP3A5*3 SNPs. Trough blood levels ([Tac](0) or [CsA](0) in ng/ml), dose-adjusted [Tac](0) or [CsA](0) (ng/ml per mg/kg bodyweight) as well as doses (mg/kg bodyweight) required to achieve target concentrations were compared among patients according to allelic status for CYP3A4 and CYP3A5.

RESULTS

Dose-adjusted concentrations were 2.0- and 1.6-fold higher in T-variant allele carriers for the CYP3A4 intron 6 C>T SNP compared with homozygous CC for Tac and CsA, respectively. When CYP3A4/CYP3A5 genotypes were combined, the difference was even more striking as the so-defined CYP3A poor metabolizer group presented dose-adjusted concentration 1.6- and 4.1-fold higher for Tac, and 1.5- and 2.2-fold higher for CsA than the intermediate metabolizer and extensive metabolizer groups, respectively. Multiple linear regression analysis revealed that, taken together, both CYP3A4 intron 6 and CYP3A5*3 SNPs explained more than 60 and 20% of the variability observed in dose-adjusted [Tac](0) and [CsA](0), respectively.

CONCLUSION

The CYP3A4 intron 6 C>T polymorphism is associated with altered Tac and CsA metabolism. CYP3A4 intron 6 C>T along with CYP3A5*3 (especially for Tac) pharmacogenetic testing performed just before transplantation may help identifying patients at risk of CNI overexposure and contribute to limit CNI-related nephrotoxicity by refining the starting dose according to their genotype. Original submitted 5 May 2011; Revision submitted 29 June 2011.

Multisite analytical evaluation of the Abbott ARCHITECT cyclosporine assay

The objective of this study was to evaluate the analytical performance of the Abbott ARCHITECT Cyclosporine (CsA) immunoassay in 7 clinical laboratories in comparison to liquid chromatography/tandem mass spectrometry (LC/MS/MS), Abbott TDx, Cobas Integra 800, and the Dade Dimension Xpand immunoassay. The ARCHITECT assay uses a whole blood specimen, a pretreatment step with organic reagents to precipitate proteins and extract the drug, followed by a 2-step automated immunoassay with magnetic microparticles coated with anti-CsA antibody and an acridinium-CsA tracer. Imprecision testing at the 7 evaluation sites gave a range of total % coefficient of variations of 7.5%-12.2% at 87.5 ng/mL, 6.6%-14.3% at 411 ng/mL, and 5.2%-10.7% at 916 ng/mL. The lower limit of quantification ranged from 12 to 20 ng/mL. Purified CsA metabolites AM1, AM1c, AM4N, AM9, and AM19 were tested in whole blood by the ARCHITECT assay and showed minimal cross-reactivity at all 7 sites. In particular, AM1 and AM9 cross-reactivity in the ARCHITECT assay, ranged from -2.5% to 0.2% and -0.8% to 2.2%, respectively, and was significantly lower than for the TDx assay, in which the values were 3.2% and 16.1%, respectively. Comparable testing of metabolites in the Dade Dimension Xpand assay at 2 evaluation sites showed cross-reactivity to AM4N (6.4% and 6.8%) and AM9 (2.6% and 3.6%) and testing on the Roche Integra 800 showed cross-reactivity to AM1c (2.4%), AM9 (10.7%), and AM19 (2.8%). Cyclosporine International Proficiency Testing Scheme samples, consisting of both pooled specimens from patients receiving CsA therapy as well as whole-blood specimens supplemented with CsA, were tested by the ARCHITECT assay at 6 sites and showed an average bias of -24 to -58 ng/mL versus LC/MSMS CsA and -2 to -37 ng/mL versus AxSYM CsA. Studies were performed with the ARCHITECT CsA assay on patient specimens with the following results: ARCHITECT CsA assay versus LC/MSMS, average bias of 31 ng/mL; ARCHITECT versus the Dade Dimension assay (4 sites), average biases of -7 to -228 ng/mL; ARCHITECT versus AxSYM and TDx, average biases of -4 and -53 ng/mL, respectively. Spearman correlation coefficients were >or=0.89. The ARCHITECT CsA assay has significantly reduced CsA metabolite interference relative to other immunoassays and is a convenient and sensitive semiautomated method to measure CsA in whole blood.

Population pharmacokinetics of sirolimus in de novo Chinese adult renal transplant patients

AIMS

This study was aimed at determining the population pharmacokinetics of sirolimus and identifying factors that explain pharmacokinetic variability in de novo Chinese adult renal transplant patients.

METHODS

Data were retrospectively extracted from a formal multicentre clinical trial, which was originally designed to evaluate the safety and efficacy of cyclosporin dose reduction and cyclosporin elimination in patients receiving sirolimus. All patients received 12-month treatment, i.e. induction therapy with cyclosporin, sirolimus and corticosteroids during the first 3 months followed by either cyclosporin dose reduction or cyclosporin discontinuation thereafter. Eight-hundred and four sirolimus trough blood concentrations (C(0)) from 112 patients were used to develop a population pharmacokinetic model using the NONMEM program. A one-compartment model with first-order absorption and elimination was selected as the base model. The influence of demographic characteristics, biochemical and haematological indices, cyclosporin daily dose, cyclosporin C(0) as well as other commonly used co-medications were explored.

RESULTS

The typical values with interindividual variability for apparent clearance (CL/F) and apparent volume of distribution (V/F) were 10.1 l h(-1) (23.8%) and 3670 l (56.7%), respectively. The residual variability was 29.9%. CL/F decreased significantly with silymarin or glycyrrhizin co-therapy in hepatically impaired patients, and with increasing total cholesterol levels or cyclosporin C(0). Moreover, CL/F increased nonlinearly with increasing sirolimus daily dose. The median parameter estimates from a nonparametric bootstrap procedure were comparable and within 5% of the estimates from NONMEM.

CONCLUSIONS

These results provide important information for clinicians to optimize sirolimus regimens in Chinese renal transplant patients.

Repeated intrathecal injections of recombinant human 4-sulphatase remove dural storage in mature mucopolysaccharidosis VI cats primed with a short-course tolerisation regimen

All MPS-VI cats treated thus far with weekly intravenous enzyme replacement therapy (IV ERT) with recombinant human N-acetylgalactosamine-4-sulphatase (rhASB) from 3 months of age onwards developed circulating anti-rhASB antibodies. In view of this, the possibility of inducing immune tolerance by using a short-course tolerisation regimen was tested. Starting at 4 months of age, MPS-VI (n=5) and unaffected cats (n=2) received cyclosporine and azathioprine over a 22-day period plus weekly IV ERT with 0.1mg/kg rhASB. After a 4-week resting period, these cats were administered weekly IV ERT with 1mg/kg rhASB until 11 or 17 months of age. Four unaffected cats (n=4) received weekly IV ERT only. Health, growth and seroconversion were regularly monitored. Four out of five MPS-VI cats tolerated rhASB well, as indicated by negligible or low antibody titres and absence of hypersensitivity reactions. One MPS-VI cat exhibited elevated antibody titres and hypersensitivity reactions during some IV treatments. The two unaffected cats that received the tolerisation regimen remained seronegative, however, only half of the unaffected cats not submitted to this regimen seroconverted. Only minor side-effects were attributed to the short-course of cyclosporine and azathioprine. Two MPS-VI cats also well-tolerated four weekly intrathecal injections of rhASB and consequently exhibited less oligosaccharide fragments in cerebrospinal fluid and less vacuolation within their dura mater. These data indicate that a relatively high rate of immunotolerance towards rhASB can be achieved in MPS-VI cats with a short-course tolerisation regimen ultimately permitting removal of lysosomal storage within the dura mater with the use of intrathecal therapy.

Influence of CYP3A5 genetic polymorphism on cyclosporine A metabolism and elimination in Chinese renal transplant recipients

AIM

To investigate whether the CYP3A5*3 polymorphism would affect cyclosporine A (CsA) metabolism in Chinese renal transplant patients.

METHODS

The CYP3A5*3 genotype was determined in Chinese renal transplant recipients using polymerase chain reaction and amplification of specific alleles (PCR-ASA). The concentrations of CsA and metabolites were separately measured by fluorescence polarization immunoassay and dose-adjusted trough concentrations and metabolic ratio (MR) values were calculated.

RESULTS

The trough concentrations adjusted with the dose was significantly higher in the wild allele carriers compared to both the homozygous (*3*3) and heterozygous variants (*1*3). However, no significant difference was found for the dose-adjusted metabolite concentrations. The MR values for the 3 genotype groups were as follows: 0.92+/-0.62 for CYP3A5*3/ *3 (n=14), 0.99+/-0.51 for CYP3A5*1/*3 (n=15), and 1.45+/-0.62 for CYP3A5*1/*1 (n=9), respectively. Post hoc comparisons showed that only the MR values between the CYP3A5*3/*3 group and the CYP3A5*1/*1 group were significantly different.

CONCLUSION

The CYP3A5*3 polymorphism exerted little effect on cyclosporine metabolism. The MR may be a more accurate indicator for therapeutic drug monitoring, considering its integrated information on body exposure of both parent drugs and metabolites.

Pharmacokinetics of cyclosporine in recipients of marginal versus standard liver transplants

In the field of transplants, the practice of using marginal donor livers has become widely accepted, yielding good clinical results. This study investigated and compared the pharmacokinetics of cyclosporine in marginal and standard liver transplant recipients. Twenty-four de novo liver transplant patients, 12 with marginal and 12 with standard (normal) grafts, were treated with a microemulsion formulation of cyclosporine (capsules 100 mg) as immunosuppressive therapy. Blood concentration profiles were measured, and pharmacokinetic calculations performed at days 3 and 10 after transplantation. Different sampling strategies to predict drug exposure (AUC(0-12 h)) were compared, and the best limited-sampling strategies to monitor the desired blood levels were determined. Marginal and standard patients showed a significant difference in blood concentration and pharmacokinetic profiles of cyclosporine at the day 10 post-transplantation. Blood concentration at 4h (C(4 h)) was the single best timepoint to estimate AUC(0-12 h) in marginal liver transplant (r(2)=0.700), while C(2h) was confirmed to be the optimal choice with standard graft (r2=0.720). Two blood samples at 2 and 6 h significantly improved the prediction model in both groups (r2=0.920). Our data suggest that patients receiving a marginal liver transplant present a different pharmacokinetic profile of cyclosporine from those receiving standard graft, which should be taken into account in dosing the patient to avoid subtherapeutic blood concentrations or toxic effects.

The effect of CYP3A5 and MDR1 (ABCB1) polymorphisms on cyclosporine and tacrolimus dose requirements and trough blood levels in stable renal transplant patients

Cyclosporine and tacrolimus are immunosuppressive drugs largely used in renal transplantation. They are characterized by a wide inter-individual variability in their pharmacokinetics with a potential impact on their therapeutic efficacy or induced toxicity. CYP3A5 and P-glycoprotein appear as important determinants of the metabolism of these drugs. The objective of this study was to investigate the effect of CYP3A5 and MDR1 (ABCB1) polymorphisms on cyclosporine and tacrolimus dose requirements and trough blood concentrations in stable transplant patients. Stable renal transplant recipients receiving cyclosporine (n = 50) or tacrolimus (n = 50) were genotyped for CYP3A5*3 and *6, and MDR1 C1236T, G2677T/A and C3435T. Dose-adjusted trough blood levels (ng/ml per mg/kg body weight) as well as doses (mg/kg body weight) required to achieve target blood concentrations were compared among patients according to allelic status for CYP3A5 and MDR1. Dose-adjusted trough concentrations were three-fold and 1.6-fold higher in CYP3A5*3/*3 patients than in CYP3A5*1/*3 patients for tacrolimus and cyclosporine, respectively. In the case of tacrolimus, the difference was even more striking when considering CYP3A5*1/*1 patients showing dose-adjusted trough concentrations 5.8-fold lower than CYP3A5*3/*3 patients. For both drugs, no association was found between trough blood concentrations or dose requirement and MDR1 genotype. Multiple regression analyses showed that CYP3A5*1/*3 polymorphism explained up to 45% of the variability in dose requirement in relation to tacrolimus use. Given the importance of rapidly achieving target blood concentrations after transplantation, further prospective studies should consider the immediate post-graft period and assess the influence of this specific polymorphism. Beside non-genetic factors (e.g. steroids dosing, drugs interactions), CYP3A5 pharmacogenetic testing performed just before transplantation could contribute to a better individualization of immunosuppressive therapy.

Sensitivity of Whole-Blood T Lymphocytes in Individual Patients to Tacrolimus (FK 506): Impact of Interleukin-2 mRNA Expression as Surrogate Measure of Immunosuppressive Effect

Background: To optimize immunosuppressive treatment in individual transplant patients, functional measurements of the effects of tacrolimus (FK 506) are of clinical importance. Previous investigations have demonstrated the occurrence of tacrolimus-resistant production of interleukin-2 (IL-2) in vitro, which may explain in part why rejection episodes are still a frequent problem despite attainment of therapeutic blood concentrations and HLA matching. However, an adequate surrogate marker to define the tacrolimus response in individual patients has not been established.

Methods: We investigated the immunosuppressive effects of tacrolimus on anti-CD3/anti-CD28 T-cell costimulation in a human whole-blood assay, analyzing T-cell proliferation, activation marker expression (CD25, CD69), IL-2 protein expression, and cytokine mRNA expression in vitro (n = 11 healthy individuals). We also quantified IL-2 mRNA expression in patients undergoing tacrolimus (n = 4) or cyclosporin A (CsA; n = 4) monotherapy before ex vivo living-donor kidney transplantation.

Results: T-cell proliferation; CD25, CD69, and IL-2 concentrations; and IL-4 mRNA were significantly decreased in vitro. In contrast, cytokine mRNA profiles revealed variable tacrolimus sensitivity. Whole-blood samples from 3 of 11 healthy individuals demonstrated marked suppression of IL-2 mRNA expression (>50%) when tacrolimus was administered in vitro. When CsA was added to whole-blood cultures, the influence on IL-2 mRNA expression was comparable to that of tacrolimus in 9 of 11 individuals. Two individuals responded conversely, indicating that differences in the in vitro response to tacrolimus and CsA among individuals may be attributable to potential heterogeneity in the involvement of the CD28 pathway. Kinetic profiles of IL-2 mRNA expression also revealed individually distinct degrees of calcineurin inhibitor sensitivity in patients undergoing tacrolimus or CsA monotherapy before living-donor kidney transplantation.

Conclusions: Our results suggest an individual degree of calcineurin inhibitor sensitivity of activated whole-blood lymphocytes based on IL-2 mRNA expression. Our approach is potentially valuable for identifying transplant patients in whom IL-2 mRNA expression is unaffected or even enhanced after initiation of immunosuppressive therapy. Such individuals may be less sensitive to the immunosuppressive agent and therefore at increased risk of transplant rejection. Prospective studies are necessary to determine the correlation of IL-2 mRNA expression with the clinical risk of transplant rejection.

Inhibitors of Calcineurin

Before the early 1980s, patient and allograft survival for solid organ transplant recipients was dismal. By 1983, the first calcineurin blocker, cyclosporine (Sandimmun), had been introduced, and outcomes were dramatically improved. However, cyclosporine macroemulsion had suboptimal pharmacokinetics, significant drug interactions, and several adverse effects, including nephrotoxicity, neurotoxicity, hyperlipidemia, and hypertension. Recent advances with cyclosporine include the introduction of modified dosage formulations: Neoral, a microemulsion, and several generic microemulsion products. The potent second-generation calcineurin blocker tacrolimus (Prograf) was introduced in 1994 and has become the drug of choice for several types of transplant recipients. Although tacrolimus has improved pharmacokinetics and therapeutic drugmonitoring parameters, it has adverse effects such as nephrotoxicity, neurotoxicity, and diabetes. Thus, current immunosuppressive regimens implementing calcineurin blockers often involve additional immunosuppressive agents to “spare” the use of these agents, minimizing their adverse effects. This article reviews the mechanisms of action, pharmacokinetics, clinical use, therapeutic drug monitoring, drug interactions, adverse effects, and dosing of cyclosporine and tacrolimus in solid organ transplant recipients.

A longitudinal replicate study of immunosuppressive drugs: a College of American Pathologists study

OBJECTIVE

To identify the sources of analytical variation for cyclosporine and tacrolimus in a 3-year longitudinal study.

DESIGN

Two pools of whole blood were spiked with cyclosporine and tacrolimus, respectively. One aliquot of cyclosporine and 2 of the tacrolimus pool were distributed in the first and last mailing for years 1999 to 2001. For both drugs, the total variance for each method was partitioned into within- and between-laboratory components.

SETTING

The A and C mailings of the 1999, 2000, and 2001 AACC/CAP [American Association for Clinical Chemistry/College of American Pathologists] Immunosuppressive Drugs (CS) Monitoring Survey.

MAIN OUTCOME MEASURES

For each drug, total variance was partitioned into specimen, mailing, year, and interlaboratory effects for each analytical method.

PARTICIPANTS

The 292 laboratories for cyclosporine and 177 laboratories for tacrolimus enrolled in the survey from 1999 to 2001.

RESULTS

For both cyclosporine and tacrolimus, the major source of imprecision came from within-laboratory factors, which accounted for nearly 85% (range, 77% to 90%) of the total variance. For cyclosporine, the major component of within-laboratory variance was between-mailing, within-year effect, whereas for tacrolimus it was the between-year, within-laboratory variation.

CONCLUSION

The major source of long-term survey imprecision for cyclosporine and tacrolimus is within-laboratory factors. The finding that 85% of the total variance was due to within-laboratory variation is similar to other therapeutic drugs.

Relationship between cyclosporine concentrations obtained using the Roche Cobas Integra and Abbott TDx monoclonal immunoassays in pre-dose and two hour post-dose blood samples from kidney transplant recipients

Current evidence suggests that cyclosporine (CsA) concentration in blood samples taken 2 hours after Neoral microemulsion (Novartis Pharmaceuticals; East Hanover, NJ) administration (C2) predicts clinical events in transplant patients better than the pre-dose (trough) concentration (C0). Similarly, previous findings have shown that the metabolites/CsA ratio is substantially lower in C2 than in C0 samples; however the between-monoclonal immunoassay differences for C2 samples have received little attention in the literature. In 56 C samples and 60 C samples from renal transplant patients, CsA levels were determined using the monoclonal fluorescence polarization immunoassay (mFPIA) from Abbott (Abbott Park, IL) and the homogeneous enzyme immunoassay technique (HEIT) from Roche Diagnostics (Basel, Switzerland). In both cases a high correlation coefficient between the results was obtained (r > or = 0.971), with a linear regression for C0 samples: mFPIA = 1.47 HEIT + 22.0 and for C2 samples: mFPIA = 1.11 HEIT + 71.96. The difference between the linear regression slopes was statistically significant (P < 0.001), and the mFPIA/HEIT ratio was significantly higher for C than for C samples (P < 0.001).

Cyclosporin monitoring in Australasia: 2002 update of consensus guidelines

Therapeutic drug monitoring of cyclosporin (CsA) has been established as part of the routine clinical treatment of patients following organ transplantation for more than 20 years, and based on contemporary knowledge, many consensus guidelines have been published to assist clinics and laboratories attain optimal strategies for patient care. This article addresses the newer directions in CsA monitoring, with particular reference to the Australasian situation that has evolved since the 1993 Australasian guideline. These changes have included the introduction of alternative assay methodologies, changed CsA formulation from Sandimmun to Neoral throughout Australasia, and alternatives to trough concentration (C0) monitoring, especially 2-hour concentration (C2) monitoring and associated validated dilution protocols to accurately quantitate the higher whole blood CsA concentrations. The revision was prepared following a recent survey of all Australasian CsA-monitoring laboratories where discordant practices were evident.

Comparison of trough, 2-hour, and limited AUC blood sampling for monitoring cyclosporin (Neoral) at day 7 post-renal transplantation and incidence of rejection in the first month

The use of alternative strategies to the traditional pre-dose/trough (C0) blood sampling for cyclosporine (CsA) therapeutic drug monitoring has the potential to revolutionize analytical practices which have, in many centers, been established for some 20 years. While the C0 sample has previously been recommended, current attitudes are increasingly proposing alternatives for assessing CsA exposure, including various limited sampling strategies of the AUC (lssAUC) in the early postdose period, or alternative single-point nontrough samples, such as a 2-hour postdose sample (C2). The present study has reviewed a series of consecutive renal transplant recipients over 18 months where CsA was the primary immunosuppressant. The lssAUC performed at around day 7 posttransplantation included drawing blood at 0, 2, and 4 hours postdose, giving AUC(0-4). The aim of this study was to review the occurrence of acute biopsy-proven rejection in the first month and consider which of (simultaneously measured) C0, C2 or AUC(0-4) was a better early indicator of this adverse outcome. The result was best described by comparing the data from rejectors (n = 13) and nonrejectors (n = 42) for these 3 indices of CsA exposure (i.e., C0, C2 or AUC(0-4)). There was no evidence that C0 predicted the likelihood of such adverse clinical outcomes. In contrast, rejectors tended to have lower mean C2 CsA concentrations, and the incidence of rejection was 0.0 when C2 exceeded 1200 microg/L (n = 10). While the data are limited in the higher C2 CsA concentration range, it is nevertheless consistent with more recent recommendations suggesting that the CsA at C2 should target 1700 microg/L in this first month posttransplantation. As 64% of the patients were also receiving a CsA-sparing agent (diltiazem [DTZ]), the relationships were also investigated to determine whether any affect of concomitant DTZ therapy could be demonstrated. However, in this small sample, no significant affect of DTZ was seen.

Provision of laboratory services for heart and lung transplantation in Australia

BACKGROUND

Laboratory services for the support of heart and lung transplantation in Australia have adapted to the special needs of the clinicians looking after the heart and lung transplantation patients.

METHODS

Pre-transplantation standardized tests encompassing a wide variety of different parameters are carried out both to establish the suitability of patients for a transplant and to maximize the chance of success following this procedure. Potential solid organ recipients routinely have blood samples sent to a number of centers Australia-wide so that human leukocyte antigen (HLA) presensitization can be checked for at the time a donor becomes available in any state in Australia. Although prospective HLA matching is not performed for thoracic organ transplant recipients, pre-existing antibodies to donor HLA antigens are a contra-indication to transplantation. Following transplantation, the predominant roles of the laboratory are in the monitoring of immunosuppressive drug levels, in the detection of allograft rejection, and in the detection of bacterial infection or viral reactivation. While a number of markers have been proposed in the detection of rejection, we currently rely on interpretation of the histological analysis of biopsies. The treatment with immune suppressive agents, in particular cyclosporin A, has made organ transplantation from non-HLA identical donors possible. As cyclosporin A and other immune suppressive drugs have significant side effects, their concentrations need to be carefully followed to guarantee sufficient immune suppression while avoiding renal failure and other complications including excessive immunosuppression and infectious disease risk. Recently, the role of viral reactivation with the human cytomegalovirus (HCMV) has attained more prominence. HCMV is a potential pathogen in up to 90% of thoracic organ transplant recipients and in the pre-gancyclovir era, it was a major cause of morbidity and mortality in at-risk lung transplant recipients. New PCR-based assays that measure the viral load levels of HCMV allow earlier intervention and more appropriate treatment strategies to prevent the HCMV disease syndromes and optimize the HCMV prophylaxis strategy.

CONCLUSIONS

Diagnostic pathology testing to support heart and lung transplantation is a combination of routine testing and specialized testing. Depending on the time-critical nature of the tests, this testing has to be done on site or in more centralized testing facilities. Further developments in the laboratory support of heart and lung transplantation will hopefully continue to improve both the short- and long-term outcomes of thoracic organ transplant recipients.

Comparison of five cyclosporin immunoassays with HPLC

High performance liquid chromatography (HPLC) is the reference method for cyclosporin (CyA) measurements but therapeutic monitoring of the drug is frequently made using the more practical immunoassays. Cross-reactivity with CyA metabolites may compromise the specificity of immunoassays, particularly in liver graft recipients where metabolites may accumulate. The aim of this study was to compare with HPLC the performance of two recently introduced CyA immunoassays (the AxSYM fluorescent polarisation immunoassay (FPIA) and non-extraction CEDIA assay). The comparison was extended to the well-established TDx monoclonal FPIA (TDx mono) and the enzyme multiplied (EMIT)-specific assays and to the polyclonal FPIA (TDx poly), in which metabolite cross-reactivity is extensive. Assays were performed on 106 blood samples (taken 6 days to 118 months post-liver transplant) and results were compared by non-parametric regression analysis and difference plots. AxSYM and CEDIA showed both constant and proportional bias against HPLC (unlike EMIT) but the mean difference from HPLC was least for AxSYM (2.7 microg/l vs. 11.7, 9.4 and 54 microg/l for CEDIA, EMIT and TDx mono, respectively. (TDx poly - HPLC) values were proportional to all immunoassay results, with slopes of 0.33, 0.38 and 0.45 for EMIT, AxSYM and CEDIA, respectively. Our data suggest close agreement between AxSYM, CEDIA and EMIT results.

Comparison of the fluorescent polarization (TDx) and the enzymatic competitive (EMIT 2000) immune assays for the measurement of cyclosporin A blood concentration

Evaluation of Cyclosporin A (CyA) blood concentration is imperative in solid organ transplantation in order to achieve maximal immunosuppression with the least side effects. We compared the results of whole blood concentrations of CyA in 50 blood samples simultaneously evaluated by the fluorescent polarization immune assay (TDx) and the enzymatic competitive immune assay (EMIT 2000). There was a strong correlation between both kits for any range of CyA blood concentration (R=0.99, p<0.001). The within-run and between-days coefficient of variation were less than 4% for both assays. The cost for each CyA measurement was 50% lower for the EMIT assay when compared to the TDx assay. We concluded that the EMIT is as accurate as the TDx in measuring CyA blood concentration and has the advantage of a lower cost, as well as the possibility of widespread access to the EMIT methodology in contrast to the TDx equipment, allowing the laboratory to perform several routines within a working day.

Evaluation of the AxSYM monoclonal cyclosporin assay and comparison with radioimmunoassay

Recently, a semiautomated fluorescence polarization immunoassay (FPIA) for determination of parent cyclosporin (CsA) has been developed for the Abbott AxSYM system. The new CsA assay measures the drug from an extracted whole blood specimen. The authors report here the evaluation of this new assay and the comparison with a previously validated radioimmunoassay (RIA) method (CYCLO-Trac SP). To assess the imprecision, the authors used tri-level controls supplied by both Abbott and Bio-Rad manufacturers. The within-run CV ranged from 4.4% to 7.3% and the between-day CV ranged from 4.4% to 7.6%. Mean recovery of the drug from clinical specimens spiked with kit calibrators was 108.4%. Fluorescence polarization immunoassay AxSYM (y) was correlated to RIA (x) by using 132 trough blood specimens (44 renal, 44 liver, and 44 heart) from transplant recipients and resulted in the following Passing-Bablok linear regression equation: y = 6.7 + 0.97x, r = 0.989, S(x/y) = 12.9. The percentage of overestimation (mean, range) by FPIA AxSYM versus RIA was (3.8%, range -17.7% to 39.1%). The results observed with this new method from follow-up studies in patients during the early course after transplant were not consistently higher than those obtained by RIA. These findings contrast with previously reported results that compared FPIA TDx assay with RIA. The authors conclude that FPIA AxSYM is a precise method for measuring CsA and offers results similar to those obtained by RIA with a marked reduction in assay time.

Comparison of predose vs 2-h postdose blood metabolites/cyclosporine ratios in kidney and liver transplant patients

OBJECTIVES

It has recently been suggested that when adjusting doses of cyclosporine (CsA), determining its concentration in blood samples taken 2 h postdose (C(2)) is more clinically beneficial than using the predose concentration (C(0)). We determined C(0) and C(2) concentrations of CsA and their metabolites in samples taken from nine kidney and seven liver transplant patients. Similarly, the so-called metabolic ratios (MR)-metabolites to CsA parent ratios-were calculated to characterise the most suitable moment of blood sampling for obtaining a greater analytical specificity with monoclonal immunoassays.

METHODS

The determination of CsA and CsA + metabolites was made using the enzyme multiplied immunotechnique and the polyclonal fluorescence polarization immunoassay Abbott TDx, respectively.

RESULTS

The poor correlation between C(0) and C(2) of CsA (n = 82, r = 0.387, p < 0.001) is greatly inferior to that obtained between C(0) and C(2) of metabolites (n = 82, r = 0.912, p < 0.001). A highly significant difference (p < 0.001) was found between MR(0) values (mean 2.87 +/- 0.12, median 2.48) and MR(2) values (mean 1.73 +/- 0.09, median 1.46), although there is a good correlation between them (r = 0.878, p < 0.001).

CONCLUSIONS

The extent of the positive bias (deviation) of CsA immunoassays compared with the high-performance liquid chromatography results is related to the MR values. As the MR(2) values are significantly lower than the corresponding MR(0), in practice a greater analytical specificity would be obtained with the different monoclonal immunoassays in the determination of the 2 h postdose CsA concentration than in that of trough concentration.

Cyclosporin assays, metabolite cross-reactivity, and pharmacokinetic monitoring

The range of cyclosporin (CsA) immunoassays has become the mainstay in many therapeutic drug monitoring laboratories for delivering CsA concentration data to support clinical care of patients after transplantation. However, these assays have been criticized because of the varying degree of CsA-metabolite interferences that introduce analytical errors. The introduction of another such CsA assay (on the AXSyM analyzer) has been considered, as the manufacturer has represented it as having a low CsA-metabolite cross-reactivity profile compared with chromatographic methods. A case is presented to question how this apparent result was obtained in view of the method using the same antibody as another CsA method from the same manufacturer (fluorescence polarizaton immunoassay on the TDx analyzer) which is well known to have poor performance in regard to CsA-metabolite cross-reactivity. The implications for this problem may be even more serious as more patients are monitored using the CsA AUC strategies, rather than the traditional trough concentration approach. Such issues reinforce the need for the clinical laboratory to be critical of methods offered commercially based on scientific/pharmacologic skills.