A comparison of cyclosporine assays using sequential samples from selected transplant patients

Monitoring cyclosporin in blood: between-assay differences at trough and 2 hours post-dose (C2)

With the introduction of a cyclosporin monitoring strategy based on the use of a sample collected 2 hours after dosing (C2) rather than the predose sample (C0), there was concern that the differences in blood cyclosporin results from the various assay systems would result in assay-specific target ranges for C2 monitoring. In addition, it was not known if the different proportion of cyclosporin metabolites in the blood 2 hours after dosing compared with that seen in predose samples would alter the relationship between the various assay methodologies. The aim of this study was to address these issues using blood samples from patients who had undergone kidney and liver transplantation. To do this, paired samples were collected predose and 2 hours after cyclosporin dosing at various periods following transplantation in kidney (88 paired samples) and liver (165 paired samples) transplant recipients. Cyclosporin was measured in these samples using five different immunoassays (radioimmunoassay, two fluorescent polarization immunoassays, and two homogeneous immunoassays) and high-performance liquid chromatography-mass spectrometry. The results of the study showed that when using these immunoassays to measure blood cyclosporin concentrations at C0, the cross-reactivity of the antibodies in the different immunoassay kits resulted in target therapeutic ranges that would need to vary between assays to maintain parity. However, when the same assays were used to measure the blood cyclosporin concentration at C2, the results were congruent, and assay-specific target therapeutic ranges should not be necessary. Thus, when adopting a C2 monitoring strategy, it is possible to use target therapeutic ranges that are independent of the assay system used.

Lack of specificity of cyclosporine immunoassays. Results of a College of American Pathologists Study

OBJECTIVE

To evaluate the cross-reactivity of the 6 most abundant cyclosporine A (CsA) metabolites in commonly used assays for CsA.

DESIGN

Whole blood samples containing either only 62 ng/mL CsA (A) or 62 ng/mL CsA and between 49 and 86 ng/mL of 1 of the 6 most abundant CsA metabolites (B) were lyophilized. One sample of A and 1 of B were mailed to each of the laboratories participating in the College of American Pathologists Proficiency Testing Program quarterly during a 3-year period (1999-2001). Method means and coefficients of variation were calculated for each mailing.

RESULTS

The study showed significant cross-reactivity of metabolites in all the immunoassay systems studied. Overall degree of interference decreased from Abbott TDx polyclonal > Abbott TDx monoclonal > DiaSorin > Syva EMIT. High-performance liquid chromatography methods gave results close to those found using mass spectrometric techniques.

CONCLUSIONS

Significant metabolite interference was found to occur with the immunoassay systems studied.

The potential replacement of HPLC by 125I-RIA for the characterization of cyclosporin A: a bioavailability study after oral administration in healthy human subjects

A significant overestimation of cyclosporin A (CsA) by a radioimmunoassay using 125I-labeled monoclonal antibody (125I-RIA), compared to the reference HPLC method, has been reported for a limited number of samples from transplant patients. However, the extent of the discrepancy, with respect to bioavailability parameters, has not been examined for the case of the oral administration of a single dose CsA to healthy subjects where a number of factors which might be involved in this overestimation (e.g. under steady state condition and a significant accumulation of CsA metabolites) would be absent. Therefore, the objective of this study was to assess the effect of potential difference manifested by the two analytical procedures, 125I-RIA and HPLC, on the bioavailability analysis of CsA. An oral CsA formulation was administered to 22 healthy male subjects and the blood samples were analysed by both 125I-RIA and HPLC. Significant discrepancies in the estimated CsA concentrations by the two methods (paired t-test, P < 0.001) were found. The difference (bias) increased with increasing concentrations of blood CsA (P < 0.001). However, despite the bias in CsA estimations, the AUC and Cmax, obtained by 125I-RIA and HPLC methods showed only small differences (i.e. 2% for AUC and 7% for Cmax). Thus, our results suggest that the bias of the 125I-RIA vis-a-vis the HPLC method in the estimation of CsA blood levels may not, in practice, affect the bioavailability analysis (e.g. bioequivalence study) of CsA in a situation where a single dose CsA is orally administered to healthy subjects.

The EMIT Cyclosporine Assay: development of application protocols for the Boehringer Mannheim Hitachi 911 and 917 analyzers

OBJECTIVE

The purpose of this work was to develop applications for the EMIT Cyclosporine (CsA) Assay on the Hitachi 911 and 917 analyzers.

METHODS AND RESULTS

Instrument settings were optimized to arrive at the following assay characteristics on the Hitachi 917. Limit of sensitivity was 50 micrograms/L. Intra-assay coefficients of variation (CV) were 8.1% (n = 20; mean = 62 micrograms/L) and 4.2% (n = 20; mean = 315 micrograms/L), while interassay CVs were 13.0% (n = mean = 73 micrograms/L) and 5.7% (n = 43; mean = 391 micrograms/L). Recoveries of 95-104% were obtained by spiking aliquots of 3 whole blood patient pools of known CsA concentrations with CsA. Serial dilutions of 3 patient specimens demonstrated linear relationships between expected and actual CsA concentrations (r = 0.99, 0.99, 0.98; regression lines: y = 1.19x -17.1; y = 0.75x + 18.0; y = 1.01x + 3.7). Specimen carryover was not evident. Calibration stability is at least 10 days. Comparable assay characteristics were found for the Hitachi 911. Sequentially-collected trough whole blood specimens from renal (n = 3), liver (n = 3) and heart (n = 4) transplant patients prescribed CsA were collected up to 78 days post-transplant and analyzed by EMIT on the Hitachi 917 and also by fluorescence polarization immunoassay (FPIA) and high performance liquid chromatography (HPLC). The following linear regression equations were produced for the renal [EMIT = 0.801 (TDx) + 4.98, r = 0.91, Sy/x = 32, n = 37; EMIT = 0.877 (HPLC) + 56, r = 0.87, Sy/x = 38, n = 37]; liver [EMIT = 0.808 (TDx) - 27, r = 0.94, Sy/x = 42, n = 37; EMIT = 0.953 (HPLC) + 44, r = 0.89, Sy/x = 57, n = 37] and heart [EMIT = 0.820 (TDx) - 24, r = 0.94, Sy/x = 31, n = 45, EMIT = 0.956 (HPLC) + 54, r = 0.91, Sy/x = 38, n = 45] patient samples. FPIA values average 32% more than EMIT-derived CsA concentrations on the Hitachi 917, which in turn averaged 15% more than HPLC values. In addition, these levels were compared intra-individually. CsA concentrations within all patients were significantly higher (p < 0.05, paired t-test) by FPIA compared to EMIT and by FPIA compared to HPLC. Although CsA concentrations within most patients were significantly higher (p < 0.05) by EMIT compared to HPLC, levels determined in 4 transplant patients (1 renal, 1 liver, 2 heart) were not different.

CONCLUSION

Development of applications for the EMIT CsA Assay on two highly automated, random access instruments, the Hitachi 911 and Hitachi 917, enhances the versatility of the immunoassay for routine therapeutic drug monitoring of this immunosuppressant in the clinical setting.

Effect of assay methodology on pharmacokinetic differences between cyclosporine Neoral® and Sandimmune® formulations

The new oral formulation of cyclosporine (CsA), Neoral® (CsA-N), results in increased area under the curve (AUC) and decreased intra- and interindividual variation in blood concentrations and other pharmacokinetic (PK) parameters when compared with the current Sandimmune® (CsA-S) formulation. The present study examines the effect of assay methodology on variability in blood concentrations and PK parameters for renal transplant patients receiving CsA-N and CsA-S and whether this variation is reduced with CsA-N. The results show that interindividual variations in PK parameters for patients receiving CsA-N were less than those for patients receiving CsA-S. Both blood concentrations and dose of CsA better correlated with abbreviated (4-h) AUC after administration of CsA-N. For both CsA-S and CsA-N, blood concentrations at 4 h postdose exhibited the best correlation with AUC. All samples were analyzed by three common procedures: HPLC, RIA, and fluorescence polarization immunoassay (FPIA). There were no significant differences observed in blood concentrations or PK parameters obtained from FPIA and RIA. HPLC results, however, were lower because of specificity of this method for the parent drug. The assay methodology did not have an effect on interindividual variability, indicating that the cross-reactivity of metabolites in commonly used immunoassays for CsA does not contribute to the PK variability observed in renal transplant patients.

The use of therapeutic drug monitoring to optimise immunosuppressive therapy

Most experience of the therapeutic drug monitoring of immunosuppressive agents has been acquired in the field of solid organ transplantation; however, agents such as cyclosporin (cyclosporin A) are being increasingly utilised for the management of autoimmune diseases. Cyclosporin is the most widely studied immunosuppressant, but in spite of this many controversies still exist as to the optimum strategy for monitoring this drug. Owing to its widely variable pharmacokinetics and metabolism, and the absence of a simple method to measure therapeutic effectiveness, many factors should be considered. In most circumstances, measuring whole blood through concentrations of cyclosporin with a specific assay methodology is warranted. In addition, knowledge of other factors that may alter the pharmacokinetics (such as liver function, concomitant food or medications, gastrointestinal status, and time since transplantation) should be taken into account so that therapy can be appropriately adjusted. Other methods of monitoring have been investigated, such as AUC (area under the concentration-time curve) monitoring and immunological monitoring. However, further refinement of these techniques and greater experience with their efficacy must be accumulated before their role in the monitoring of cyclosporin can be defined. Tacrolimus, like cyclosporin, shares many of the difficulties in monitoring for efficacy and toxicity due largely to the variable pharmacokinetics; similarly to cyclosporin, whole blood through concentration monitoring should be utilised in combination with knowledge of the factors that may affect the pharmacokinetics. Muromonab CD3 (OKT3) is a monoclonal antibody used for the treatment and prophylaxis of acute allograft rejection. Several immunological monitoring techniques have been investigated for this agent. Monitoring CD3+ levels can assist clinicians in determining therapeutic efficacy, while measuring antimuromonab CD3 antibody titres can help determine if xenosensitisation has occurred, causing therapeutic ineffectiveness. The clinical monitoring of azathioprine, one of the first immunosuppressive agents used in transplantation, has historically been limited to monitoring complete blood counts for bone marrow suppression. However, newer techniques measuring intracellular DNA nucleotides appear to be promising. The new immunosuppressants on the horizon include mycophenolate mofetil and rapamycin. The clinical experience with therapeutic drug monitoring of these 2 compounds is scant in the literature; however, both agents have demonstrated efficacy in preventing or treating allograft rejection while maintaining a relatively well tolerated toxicity profile in recent clinical trials. Routine monitoring does not appear to be warranted for immunosuppressive therapy in autoimmune diseases.

Optimizing the use of cyclosporine in renal transplantation

OBJECTIVE

To review the existing data on the use of cyclosporine (CsA) in kidney transplantation, particularly with respect to therapeutic drug monitoring.

DATA SOURCES

A literature search was conducted of applicable articles related to therapeutic drug monitoring of cyclosporine in renal transplantation. Previous consensus guidelines were examined. Discussions on issues related to this topic convened in Toronto, ON, on June 15-16, 1994.

DATA SYNTHESIS

The literature was analyzed to examine patient factors and drug interactions affecting CsA concentrations, the effect of CsA concentrations on patient outcome, current methods of analysis, pharmacodynamic monitoring, and new immunosuppressants.

CONCLUSIONS

CsA has improved the success of kidney transplantation, reducing the incidence and severity of acute rejection and improving short-term patient and graft survival. The rate of graft loss after the first year (primarily due to chronic rejection) has remained largely unchanged. Sandimmune Neoral offers promise due to its better bioavailability and limited dependence on bile flow for absorption. Long-term studies are underway to determine its effectiveness and safety. Indications for therapeutic drug monitoring for CsA are provided.