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.

Performance and Specificity of Monoclonal Immunoassays for Cyclosporine Monitoring: How Specific Is Specific?

Background: Immunoassays designed for the selective measurement of cyclosporin A (CsA) inadvertently show cross-reactivity for CsA metabolites. The extent and clinical significance of the resulting overestimation is controversial. A comprehensive assessment of old and new methods in clinical specimens is needed.

Methods: In a comprehensive evaluation, CsA was analyzed in 145 samples with the new CEDIA® assay and compared with the Emit® assay with the old and new pretreatments, the TDx® monoclonal and polyclonal assays, the AxSYM®, and HPLC. All samples were from patients with liver and/or kidney transplants.

Results: The CEDIA offered the easiest handling, followed by the AxSYM, which showed the longest calibration stability. The TDx monoclonal assay provided the lowest detection limit and the lowest CVs. The mean differences compared with HPLC were as follows: Emit, 9–12%; CEDIA, 18%; AxSYM, 29%; and TDx monoclonal, 57%. The CycloTrac® RIA paralleled the Emit results. In contrast to the mean differences, substantial (>200%) and variable overestimations of the CsA concentration were observed in individual patient samples. Metabolic ratios, estimates of the overall concentrations of several cross-reacting metabolites (nonspecific TDx polyclonal/specific reference method), correlated with the apparent biases of the various monoclonal assays. Metabolic ratios varied up to 10-fold, which translated into biases for individual samples between −7% and +174%. The higher the cross-reactivity of an assay was, the higher was the range of biases observed. The interindividual differences markedly exceeded other factors of influence (organ transplanted, hepatic function).

Conclusion: Because assay bias cannot be predicted in individual samples, substantially erratic CsA dosing can result. The specificity of CsA assays for parent CsA remains a major concern.

Renal function and biopsy findings after 5 years' treatment with low-dose cyclosporin for psoriasis

Renal biopsies were performed in eight patients with chronic plaque psoriasis who had been treated with low-dose cyclosporin (CyA) (range 1-6 mg/kg/day; average dose 3.3 mg/kg/day) for an average period of 5 years. In six of the eight patients biopsies showed features consistent with CyA nephrotoxicity. Tubular atrophy and arteriolar hyalinosis were present in all six, four had an increase in interstitium, and two showed an increased incidence of glomerular obsolescence. Two of the patients showed all of these features, two patients had three features, and the remaining patients had two features. Renal function was assessed by glomerular filtration rate (GFR) and serum creatinine. Both a fall in the GFR and a rise in the serum creatinine correlated with the severity of the features of CyA nephrotoxicity seen on biopsy. However, the best predictor of the biopsy findings was a failure of renal function to show significant improvement when CyA was discontinued for a month. CyA has been discontinued in two of the eight patients who had the most severe features of CyA nephrotoxicity on renal biopsy. In both patients there has been improvement of renal function after 1 year of follow-up.

NMR spectroscopy as a novel approach to the monitoring of renal transplant function

High field 1H NMR spectroscopy was used for the rapid multicomponent analysis of low molecular wt compounds in urine in order to investigate the patterns of metabolic changes associated with early renal allograft dysfunction. Urine samples were collected daily for 14 days from 33 patients who underwent primary renal allograft transplantation, and analyzed by 500 and/or 600 MHz 1H NMR spectroscopy. All patients received 20 mg prednisolone and 5 mg/kg b.d. oral cyclosporin A (CsA) solution. In this study no patient showed clinical or histopathological evidence of CsA nephrotoxicity. For each patient the NMR-generated metabolite data were correlated with the clinical observations, graft biopsy pathology, and data from conventional laboratory techniques for assessing renal function. The NMR spectra of urine from patients with immediate functioning grafts were similar with respect to their patterns of amino acids, organic acids and organic amines, whereas the patients with delayed or non-functioning grafts showed significantly different metabolite excretion patterns. In longitudinal studies on individual patients there were increased urinary levels of trimethylamine-N-oxide (TMAO), dimethylamine (DMA), lactate, acetate, succinate, glycine and alanine during episodes of graft dysfunction. However, only the urinary concentration of TMAO was statistically significantly higher (P < 0.025) in the urine collected from patients during episodes of graft dysfunction (410 +/- 102 microM TMAO/mM creatinine) than in patients with good graft function (91 +/- 18 microM TMAO/mM creatinine) or healthy control subjects (100 +/- 50 microM TMAO/mM creatinine). These findings suggest that graft dysfunction is associated with damage to the renal medulla which causes the release of TMAO into the urine from the damaged renal medullary cells. This provides a possible novel urinary marker for post-transplant graft dysfunction. This study shows that NMR spectroscopy of biofluids, when used in combination with conventional laboratory techniques, is a valuable aid to renal transplant monitoring.

The clinical significance of cyclosporine metabolites

Cyclosporine (CsA) is extensively metabolized, with over 14 metabolites having been characterized to date. The confirmation of structure and purity is a prerequisite for studies involving CsA metabolites. Analytical techniques such as fast atom bombardment/mass spectroscopy (FAB/MS), tandem mass spectrometry (MS), 1H- and 13C-nuclear magnetic resonance (NMR) can be used for such purposes. In vitro experiments indicate that metabolites are considerably less immunosuppressive and toxic than CsA. In vivo studies have been hampered by sufficient quantities of metabolites and a suitable animal model. Preliminary results in the rat suggest that CsA metabolites are less immunosuppressive and toxic than CsA, although these results must be confirmed using a more suitable animal model. Present data indicate that the routine monitoring of metabolites is not warranted in transplant patients, although additional information is required to confirm these findings.

Monoclonal antibody technology for cyclosporine monitoring

Monitoring blood levels of Cyclosporine (CsA) has been the basis for adjusting individual dosage regimens in the clinic. Radioimmunoassays using polyclonal antisera reacted with CsA and some CsA metabolites, leading to overestimation when compared with high-performance liquid chromatographic measurements of CsA. Monoclonal antibodies (mAbs) have the potential to discriminate between closely related molecules. MAbs with high affinity for CsA have been prepared and their fine-specificity characterized by cross-reactivity studies using a large series of CsA-derivatives. According to the known sites of metabolism on the CsA molecule and to its three-dimensional structure, it was possible to predict which mAb would be suitable for recognizing native Cs specifically.

Paradoxical effects of cyclosporine on concanavalin A-induced blastogenesis

The effects of increasing in vitro cyclosporine concentrations (0, 50 100 or 200 ng./ml.) on lymphocyte blastogenesis, measured by incorporation of tritiated thymidine and induced by varying levels of concanavalin A (0, 0.25, 1.0 or 5.0 ng./ml.), were studied in regard to mean serum level of cyclosporine in 26 renal allograft recipients. Results were compared to similar data obtained in healthy controls. Patients were divided into group 1 (13 patients, mean serum cyclosporine trough level less than 150 ng./ml.) and group 2 (13 patients, cyclosporine level greater than 150 ng./ml.). With no cyclosporine added to the assay proliferation of lymphocytes obtained from all patients inversely correlated to the mean serum trough cyclosporine level at all stimulatory levels of concanavalin A (0.25 ng./ml., p less than 0.01; 1.0 ng./ml., p less than 0.001 and 5.0 ng./ml., p less than 0.001) and was significantly lower than in controls (p less than 0.0002). Whereas increasing in vitro cyclosporine concentrations has produced the expected increase in suppression of blastogenesis in controls and group 1, a paradoxical effect became evident in group 2. Under stronger stimulatory conditions (concanavalin A 1.0 or 5.0 ng./ml.) increasing in vitro cyclosporine concentrations were associated with significantly decreased suppression of blastogenesis (p less than 0.01) compared to group 1. These results confirm previous reports and suggest that the duality of effect of cyclosporine in this in vitro model may be related to its functional relationship to the calcium ion (Ca++)/calmodulin complex and to its cellular concentration/solubility curve. These considerations may be of importance in adjusting cyclosporine dosage based on serum trough levels of cyclosporine.

The management of heart transplant recipients treated with cyclosporine in Ireland: monitoring of cyclosporine concentrations in blood

Thirty seven cardiac transplants have taken place at the National Cardiac Centre in Ireland since 1985. Data is presented on three still-surviving male patients aged 19 to 42 who received cardiac transplants in 1985 and 1986. Circulating levels of blood cyclosporine were measured by high pressure liquid chromatography and radioimmunoassay; plasma creatinine and bilirubin were also measured. In one of these patients the distribution of cyclosporine in blood was measured by high pressure liquid chromatography in a long term study. For all three patients cyclosporine levels in blood were compared with the daily dose of cyclosporine and biochemical and histopathological parameters.

Assessment of variables contributing to cyclosporine distribution in blood

Factors which can account for the poor correlation between whole blood and plasma Cyclosporine (CsA) levels in patients on CsA prophylaxis are evaluated. The study took account of the influence of plasma separation procedures, and the sample haematocrit on CsA distribution in the blood of renal transplant patients (n = 35). CsA was measured using both specific and non-specific CsA radioimmunoassays. Significant negative correlations occurred between CsA distribution and the haematocrit, independently of the plasma separation procedure or the specificity of the assay. All results were lower when using the specific assay but a significantly higher percentage of CsA was measured in the plasma by specific assay compared to nonspecific assay when plasma was separated at both 22 degrees C (t-test, p less than 0.02) and at 37 degrees C, p less than 0.01). This may relate to the selective binding of CsA and its analogues by blood cells. This study is a prelude to the development of more consistent plasma separation procedures in the monitoring of this drug.

Predictive value of cyclosporin A level for efficacy or renal dysfunction in psoriasis

Cyclosporin A (CyA) trough (pre-dose) levels were measured in whole blood with a radioimmunoassay (RIA) using specific monoclonal antibody in 193 patients receiving CyA for the treatment of psoriasis. These patients received either CyA 2.5 mg/kg/day (n = 134) or 5 mg/kg/day (n = 59). In addition, a subgroup of 94 patients also had CyA trough levels measured using a non-specific polyclonal RIA. Within each CyA dose group, no difference was detected between mean CyA trough levels in relation to success or failure nor to the presence or absence of renal dysfunction with the use of either the specific or non-specific RIA. Based on the experience in transplantation, CyA thresholds of 100 and 200 ng/ml (specific) were selected for the assessment of efficacy and renal dysfunction. The success rate was higher by 10-15% when the CyA level was above, rather than below, 100 ng/ml in both the CyA 2.5 mg and 5 mg/kg/day groups. A slightly increased incidence of renal dysfunction was only found in the 5 mg/kg/day group when the CyA level was above 200 ng/ml. Because of its low predictive value, measurement of the level of CyA was not particularly useful for monitoring patients with psoriasis treated with low-dose CyA.

Novel strategies for clinical drug analysis with new column technology in liquid chromatography

Clinical drug analysis has been the focus of much attention and controversy because of the increase in substance abuse testing of addicts, patients, employees and others, in addition to the rapidly growing fields of therapeutic drug monitoring and clinical toxicology. This review focuses on the latest methodological and technological advances in liquid chromatography (LC) as it is applied to clinical drug analysis. Based on the author's experience, key chromatographic parameters such as carbon load, functionalities and temperature are proposed for the separation of structurally similar metabolites and for resolving chromatographic interferences by other drugs and metabolites. Novel sample preparation for cyclosporine and gradient elution of its metabolites are reviewed, followed by an update on monitoring of 3'-azido-3'-deoxythymidine with emphasis on automated sample preparation. Various approaches of direct sample analysis are advocated for increased efficiency as a result of minimal sample preparation and potential advantages such as decreased exposure of personnel to infectious samples. An update of microbore LC indicates that 2-mm columns may be readily used for clinical paediatric and neonatal analysis without dedicated chromatographs. Potential applications of multidimensional-multimodal chromatography include analyses of a cocaine impurity, anticonvulsants, antidepressants, and five ingredients of a common cold medication.

Assay methods for cyclosporine monitoring following liver transplantation

This article reviews therapeutic drug monitoring for cyclosporine in liver transplantation. Brief descriptions of various immunoassay methods include sample matrix selection, assay reagents, and metabolite cross-reactivity information. Multiple comparisons of the various methods are outlined. Examples of the method-dependent relationship between clinical events and changes in cyclosporine concentration are presented. Other potential predictors of liver allograft function are listed.

An explanation of the noncorrespondence between assessment methods of cyclosporin

Various methods of determining cyclosporin (CyA) levels in patients after kidney transplantation were compared. These included polyclonal antibody (pcAb-), specific and nonspecific monoclonal antibody (S- and NmcAb-) radioimmunoassays (RIA), and high performance liquid chromatography (HPLC). The results obtained by the various methods when compared showed some correlation but did not correspond. A probable explanation for part of this noncorrespondence is the presence of monoclonally crossreactive metabolites (CyA-M). Another reason was that the concentration of CyA in the standards supplied with the RIA kits was found to be higher than stated.

Evaluation of the Incstar Cyclo-Trac sp kit for the determination of cyclosporine in blood

We measured cyclosporine in whole blood samples from renal and heart transplant patients by high performance liquid chromatography and by two radioimmunoassays with use of specified monoclonal antibodies. In particular, we evaluated the analytical performance of a new specific radioimmunoassay with an iodinated tracer. The reproducibility of the method is satisfactory (within-run CV 7.1 to 9.5% and between-run CV 7.2 to 10.3%). The limit of detection is 10.3 micrograms/L and the analytical recovery between 99 and 114%. The results obtained with samples from both renal heart transplant patients agree well with those obtained by HPLC and by a specific RIA that uses a tritiated tracer.