Cyclosporin monitoring in Australasia: survey of laboratory practices in 2000

Cyclosporine use in hematopoietic stem cell transplantation: pharmacokinetic approach

Cyclosporine is one of the most vital agents in the process of successful allogeneic hematopoietic stem cell transplantation. Despite a long history and worldwide extent of cyclosporine use for prevention of graft versus host disease, currently there are lots of uncertainties about its optimal method of application to reach the best clinical outcome. A major portion of this problem stems from complicated cyclosporine pharmacokinetics. Study of cyclosporine pharmacokinetic behavior can significantly help recognition of its effectiveness and consequently, optimization of dosing, administration, monitoring and management of adverse effects. In this review, highly accredited but sparse scientific data are gathered in order to provide a better insight for preparation of practice guidelines and directing future studies for allogeneic hematopoietic cell recipients.

A survey of therapeutic drug monitoring services in Malaysia

In Malaysia, therapeutic drug monitoring (TDM) service was started in the 1980s. Since then, the number of hospitals that offer the service has increased. In this paper, we report the findings of a nationwide survey describing the practice of TDM in these hospitals. Questionnaires were mailed to 128 government hospitals. Data were collected for general characteristics of the hospitals, administrative, and laboratory activities related to TDM service. One hundred and twenty-one hospitals responded to the survey. Thirty-four hospitals (28.1%) provided the service with their own TDM laboratories, 44 hospitals (36.4%) provided the service using other hospitals' laboratories and 43 hospitals (35.5%) did not provide the service at all. TDM services were more likely to be offered in larger hospitals with various medical specialties. Since it is managed entirely by hospital pharmacists, these pharmacists assume an important role in ensuring optimum use of the TDM service.

Current status of therapeutic drug monitoring in Australia and New Zealand: a need for improved assay evaluation, best practice guidelines, and professional development

The measurement of drug concentrations, for clinical purposes, occurs in many diagnostic laboratories throughout Australia and New Zealand. However, the provision of a comprehensive therapeutic drug monitoring (TDM) service requires the additional elements of pre- and postanalytical advice to ensure that concentrations reported are meaningful, interpretable, and clinically applicable to the individual patient. The aim of this project was to assess the status of TDM services in Australia and New Zealand. A range of professions involved in key aspects of TDM was surveyed by questionnaire in late 2007. Information gathered included: the list of drugs assayed; analytical methods used; interpretation services offered; interpretative methods used; and further monitoring advice provided. Fifty-seven responses were received, of which 42% were from hospitals (public and/or private); 11% a hospital (public and/or private) and pathology provider; and 47% a pathology provider only (public and/or private). Results showed that TDM is applied to a large number of different drugs. Poorly performing assay methods were used in some cases, even when published guidelines recommended alternative practices. Although there was a wide array of assays available, the evidence suggested a need for better selection of assay methods. In addition, only limited advice and/or interpretation of results was offered. Of concern, less than 50% of those providing advice on aminoglycoside dosing in adults used pharmacokinetic tools with six of 37 (16.2%) respondents using Bayesian pharmacokinetic tools, the method recommended in the Australian Therapeutic Guidelines: Antibiotic. In conclusion, the survey highlighted deficiencies in the provision of TDM services, in particular assay method selection and both quality and quantity of postanalytical advice. A range of recommendations, some of which may have international implications, are discussed. There is a need to include measures of impact on clinical decision-making when assessing assay methodologies. Best practice guidelines and professional standards of practice in TDM are needed, supported by an active program of professional development to ensure the benefits of TDM are realized. This will require significant partnerships between the various professions involved.

Therapeutic drug monitoring

PURPOSE OF REVIEW

Traditionally, therapeutic drug monitoring has been used for the management of epilepsy, cardiac arrhythmias, asthma and depression. This review provides an update, particularly for the newer clinical applications, and how therapeutic drug monitoring (including use of analytical and interpretation tools) can improve clinical outcomes.

RECENT FINDINGS

Improved drug assay methodologies and a greater understanding of pharmacokinetic and pharmacodynamic mechanisms has allowed the use of therapeutic drug monitoring for immunosuppressant drugs in organ transplant recipients, antiretroviral agents for HIV/AIDS and antimetabolite drugs for leukaemia. In addition, new computer software to analyse drug concentrations in complex populations is being developed and introduced into routine clinical applications to allow increasingly patient-specific assay interpretation.

SUMMARY

Therapeutic drug monitoring assists in improving clinical success rates and minimizing toxicity. The use of therapeutic drug monitoring is therefore likely to become more widespread as new modalities are adopted.

Immunosuppressive drug monitoring - what to use in clinical practice today to improve renal graft outcome

Therapeutic drug monitoring (TDM) of immunosuppressive therapy is becoming an increasingly complex matter as the number of compounds and their respective combinations are continuously expanding. Unfortunately, in clinical practice, monitoring predose trough blood concentrations is often not sufficient for guiding optimal long-term dosing of these drugs. The excellent short-term results obtained nowadays in renal transplantation confer a misleading feeling of safety despite the fact that long-term results have not substantially improved, definitely not to a point where longer graft survival could counteract the increasing need for transplant organs and less toxicity and side-effects could ameliorate patient survival. It is therefore a challenging task to try to tailor immunosuppressive drug therapy to the individual patient profile and this in a time-dependent manner. For the majority of currently used immunosuppressive drugs, measurement of total drug exposure by determination of the dose-interval area under the concentration curve (AUC) seems to provide more useful information for clinicians in terms of concentration-exposure and exposure-response as well as reproducibility. To simplify this laborious way of measuring drug exposure, several validated abbreviated AUC profiles, accurately predicting the dose-interval AUC, have been put forward. Together with an increasing knowledge of the time-related pharmacokinetic behaviour of immunosuppressive drug and their metabolites, studies are focusing on how to apply abbreviated AUC sampling methods in clinical transplantation, taking into account the numerous factors affecting drug pharmacokinetics. Eventually, TDM using abbreviated AUC profiles has to be prospectively tested against classic methods of drug monitoring in terms of cost-effectiveness, feasibility and clinical relevance with the ultimate goal of improving patient and graft survival.

Immunosuppressant Drug Monitoring: Is the Laboratory Meeting Clinical Expectations?

OBJECTIVE:

To review the literature relating to immunosuppressant drug measurement as performed in therapeutic drug monitoring laboratories associated with transplantation centers and consider whether the assay methods widely used for patient dosage management achieve acceptable quality criteria in the context of other sources of variability with these drugs.

DATA SOURCES:

Articles used were accessed primarily through MEDLINE, as well as references cited in related publications. Searches were restricted to organ transplantation in humans.

STUDY SELECTION AND DATA EXTRACTION:

Emphasis was placed on the literature relating to the quality of immunosuppressant drug assays, their limitations, and evidence of clinical benefit in dosage individualization.

DATA SYNTHESIS:

There is a dilemma evident between the quality of the analytical services offered by some diagnostic immunoassay manufacturers and the ability of a significant number of clinical laboratories globally to select only appropriate assay methods.

CONCLUSIONS:

In many cases, clinical laboratories fail to meet the reasonable clinical expectations required for interpretation of immunosuppressant drug assay results as an adjunct to optimal dosage individualization and patient care.

Time-related clinical determinants of long-term tacrolimus pharmacokinetics in combination therapy with mycophenolic acid and corticosteroids: a prospective study in one hundred de novo renal transplant recipients

BACKGROUND

Tacrolimus is an efficient primary immunosuppressive drug in renal transplantation but its long-term use is associated with calcineurin-inhibitor-related toxicity. The specific characteristics of the inter-relationship between dose, concentration and clinical (side-)effects for tacrolimus have not yet been identified and extensive long-term pharmacokinetic studies are presently lacking.

OBJECTIVE

To establish the characteristics of the long-term pharmacokinetics of tacrolimus, to determine the time-dependent factors that influence the pharmacokinetics within the first critical post-transplant year and to identify a more appropriate way of monitoring drug exposure in clinical practice.

STUDY DESIGN

A prospective pharmacokinetic study of tacrolimus was conducted in 100 de novo renal allograft recipients during the first year post-transplantation.

METHODS

Area under the concentration-time curve (AUC) blood samplings for tacrolimus were performed on days 7, 42, 90, 180 and 360 for all patients. Model-independent pharmacokinetic parameters for tacrolimus were calculated and dose-corrected when appropriate: AUC12, peak plasma concentration (Cmax), pre-dose trough concentration (C0), time to Cmax, average steady-state blood concentration, steady-state total body clearance, terminal half-life, volume of distribution and an estimate for tacrolimus bioavailability was derived from additional steady-state intravenous clearance data. The association between tacrolimus pharmacokinetic parameters and different clinical variables was evaluated on days 7, 42, 90, 180 and 360. The clinical variables were either donor-related (e.g. donor age), transplantation-related (e.g. delayed graft function), recipient-related (e.g. bodyweight), biochemical (e.g. serum albumin), therapeutic variables (e.g. corticosteroid dose) or disease variables (e.g. liver dysfunction).

RESULTS

Long-term tacrolimus dose-corrected exposure (AUC12, C0) is characterised by a late significant increase towards the end of the first year post-transplantation as the result of a significant increase in tacrolimus bioavailability (p < 0.05) and a slow decrease in tacrolimus steady-state clearance. Consequently, tacrolimus dose-requirements corrected for bodyweight decrease significantly in the first postoperative year (p < 0.05), in part because of the simultaneous tapering of the corticosteroid dose which significantly affects tacrolimus bioavailability (p < 0.05). Other clinical variables that significantly influenced tacrolimus administration, exposure and bioavailability in a time-related fashion were identified in this study (renal allograft function [p < 0.05], liver dysfunction [p < 0.05], diarrhoea [p < 0.05]), while the clinical relevance of other variables was considerably moderated by our findings (serum albumin, haematocrit). Time-unrelated variables proved to be of significant continuing clinical importance for tacrolimus dose-exposure pharmacokinetics throughout the first post-transplant year (recipient age [p < 0.05], gender [p < 0.01] and donor-receptor gender mismatch [p < 0.05]), while donor hypotension (p < 0.05) and cold ischaemia time (p < 0.05) also proved significant although at present the reasons for this are unknown. Finally, using multiple stepwise regression analysis we demonstrated that classical assessment of tacrolimus exposure by monitoring pre-dose trough blood concentration (or any other single concentration sampling timepoint) is not the most reliable method and that abbreviated AUC measurements may constitute a more accurate clinical tool for (therapeutic) monitoring of drug exposure.

CONCLUSION

Tacrolimus pharmacokinetics in the first year after renal transplantation are characterised by a specific time-dependent evolution. The identification of clinical variables that determine tacrolimus pharmacokinetics is an important aid in the development of reliable drug monitoring strategies using abbreviated AUC measurements.

Analytic Aspects of Cyclosporine Monitoring, on Behalf of the IFCC/IATDMCT Joint Working Group

The use of therapeutic drug monitoring strategies for cyclosporin (CsA) has evolved markedly in recent years since previous consensus guidelines were presented. Apart from the introduction of some new methods, the major change has been the shift away from the traditional predose/trough (C0) sample. The most popular alternative has been shown to be a 2-hour postdose (C2) sample. This has presented a challenge to clinical laboratories where typical C2 sample concentrations exceed the upper limit of the calibration range for their chosen CsA method, hence requiring an accurate dilution to be performed. Data from the Australian/New Zealand survey, as well as that in the International CsA Proficiency Testing Program, have demonstrated both a plethora of dilution protocols and resultant widespread failure of many laboratories to obtain accurate results. This paper compares data from several independent sources, pointing to international problems for reliable CsA measurement in clinical laboratories. This includes the CsA method selection criteria adopted by a large percentage of laboratories in various surveys, indicating that the least specific mFPIA methods have been widely adopted.

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.

New concepts in cyclosporine monitoring

PURPOSE OF REVIEW

Inadequate cyclosporine exposure is a key risk factor for acute rejection, and may contribute to the development of chronic rejection and graft failure. Pre-dose monitoring does not accurately measure drug exposure because of extensive inter- and intra-patient variability in cyclosporine absorption and metabolism. Limited sampling, using individual timed specimens, offers a new, simple and accurate alternative for clinical monitoring of cyclosporine.

RECENT FINDINGS

The area under the first 4 h of the concentration-time curve (AUC ) and the single-point concentration at 2 h post-dose (C2) are key measures of cyclosporine exposure. De novo studies show that achieving an AUC value of more than 4400 microg.h/l or a C2 level of 1500-2000 microg/l during the first 5 days post-transplant minimizes the risk of rejection and improves graft function. Maintenance studies suggest that reducing the C2 level to approximately 800 microg/l after 3-6 months may improve the serum creatinine level, blood pressure, general well-being and reduce adverse effects.

SUMMARY

Single-point C2 monitoring can be implemented quickly and simply with appropriate site and patient training. The timing of phlebotomy is more critical, but immunoassay bias is lower with 2 h post-dose than with trough level measures. Single-point C2 monitoring may be effective in liver and heart replacement, but initial target levels for liver transplantation are lower because cyclosporine is transported directly to the liver via the portal system. C2 monitoring is now being widely adopted as an accurate and practical measure of drug exposure, and can be combined with pharmacodynamic methods to optimize immunosuppression.