Monitoring of blood levels of cyclosporine in renal and cardiac transplant recipients--comparison of HPLC to Incstar CYCLO-Trac SP RIA

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.

Comparison of high performance liquid chromatography and immunoassay methods for measurement of cyclosporine A blood concentrations after feline kidney transplantation

OBJECTIVE

To compare two methods of whole blood cyclosporine A (CsA) measurement in cats.

STUDY DESIGN

Whole blood samples were analyzed for CsA concentrations with use of high performance liquid chromatography (HPLC) and monoclonal immunoassay methods.

ANIMALS

Blood (n = 36 samples) was obtained from six cats after renal transplantation.

METHODS

Results were compared by linear regression analysis using both pooled and individual patient data. Eight samples were off-scale on the immunoassay and were excluded.

RESULTS

There was significant correlation between CsA measured using HPLC and immunoassay methods (P < .001; r = .942; r2 = .887). However, individuals varied nonrandomly from the mean pooled patient data. Correlation between the assay methods was higher for individual patients using data only from that specific individual (mean r value = .976; r2 = .955). Clinical utility of the immunoassay (ie, results would prompt an appropriate CsA dosage adjustment) was good when based on individually derived conversion factors (27 of 28 [96.5%] of decision events).

CONCLUSION

HPLC is superior for measurement of blood CsA concentrations in cats after kidney transplantation. However, an immunoassay may provide reliable information for CsA management if a comparative database (HPLC v immunoassay) has been previously determined in a specific patient.

CLINICAL RELEVANCE

Locally available monitoring of CsA by immunoassay in cats may provide significant advantages when shipping of blood samples to distant locations is required to obtain analysis by HPLC. These advantages may include cost and timeliness of results in circumstances where daily blood CsA concentrations may be desired, such as when managing an acute rejection reaction.

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.

Simultaneous quantification of cyclosporin A and its major metabolites by time‐of‐flight secondary‐ion mass spectrometry and matrix‐assisted laser desorption/ionization mass spectrometry utilizing data analysis techniques: Comparison with high‐performance liquid chromatography

Simultaneous quantification of cyclosporin A (CsA) and its major metabolite (AM1) in blood has been achieved using time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI/TOF‐MS). Previous investigations indicated that spectral interferences exist in the analysis of CsA blood samples by the above methods. In TOF‐SIMS, interference is caused by overlap of the Ag‐cationized internal standard, cyclosporin D (CsD), with the Ag‐cationized metabolite, AM1. To resolve this interference and obtain quantitative information, cross‐correlation analysis was applied to the TOF‐SIMS data. Application of damped non‐linear least squares curve‐fitting was carried out to resolve an interference in the MALDI/TOF‐MS data due to multiple cationization products (i.e. Na and K). Measurement of standard samples indicates that the minimum accuracy (95% confidence level) of the TOF‐SIMS method was better than 9% for CsA and 13% for AM1 using only one standard curve'. Similarly, the minimum accuracy of the MALDI/TOF‐MS method was determined to be 14% for CsA and better than 25% for AM1. Blood samples obtained from transplant patients receiving CsA were analyzed by polyclonal fluorescence polarization immunoassay, high‐performance liquid chromatography (HPLC), and by both TOF‐MS methods. Both TOF‐MS results for CsA and mono‐hydroxylated CsA are in good agreement with the HPLC results.

A review of assay methods for cyclosporin. Clinical implications

Cyclosporin is a unique immunosuppressive agent with a narrow therapeutic range. The pharmacokinetics of the drug present substantial within- and between-patient variability and drug interactions can significantly alter blood cyclosporin concentrations. Monitoring of cyclosporin concentrations in blood is an invaluable and essential aid in adjusting dosage to ensure adequate immunosuppression while minimising toxicity. The principal rationale behind therapeutic monitoring of cyclosporin is the fact that the incidence of rejection is higher at low cyclosporin concentrations and toxicity occurs more often at high concentrations. In renal transplant recipients, cyclosporin concentrations help to discriminate between insufficient immunosuppression and cyclosporin-induced nephrotoxicity. There are several methods available, both specific and nonspecific, for the routine measurement of cyclosporin. Radioimmunoassay and fluorescence polarisation immunoassay are most widely employed, while high performance liquid chromatography remains the reference procedure. The allegedly specific immunoassays tend to slightly overestimate the actual blood cyclosporin concentrations. There is a need for assay systems capable of measuring the biological activity of cyclosporin. Cyclosporin concentrations should be determined by a specific method, using whole blood as the sample matrix. The routine monitoring of individual cyclosporin metabolites is not warranted, but characterising the metabolite pattern of cyclosporin by concomitant use of a nonspecific and a specific assay can be clinically useful in patients with cyclosporin-associated toxicity or impaired liver function. In organ transplantation, measurement of blood cyclosporin concentration should be continued periodically as long as the therapy continues, whereas monitoring is only indicated in special circumstances in patients with autoimmune and other nontransplant diseases. The assessment of a 'therapeutic window' for cyclosporin is complicated for several reasons and definite target ranges cannot be given. Cyclosporin concentrations should always be interpreted in conjunction with the recent blood concentration history and other relevant clinical and laboratory data.