Therapeutic Drug Monitoring of Immunosuppressant Drugs in Marmara University Hospital

Therapeutic drug monitoring of immunosuppressant drugs

Atholl Johnston & David W. Holt1

Clinical Pharmacology, St Bartholomew’s and The Royal London School of Medicine & Dentistry, Charterhouse Square, London EC1M 6BQ and1The Analytical Unit, Cardiological Sciences, St George’s Hospital Medical School, London SW17 ORE, UK

Introduction Azathioprine, steroids, anti-lymphocyte globulin, andOKT3

Individualizing a patient’s drug therapy to obtain theoptimum balance between therapeutic efficacy and the

The combination of azathioprine and prednisolone wasoccurrence of adverse events is the physician’s goal.

responsible for making clinical transplantation viable [4].However, achieving this goal is not always straight

With the addition of anti-lymphocyte globulin [5] (ALGforward, being complicated by within and between

or ATG if human thymocytes instead of human lympho-patient variability in both pharmacokinetics and pharmaco- cytes are used to immunise the animal host) they formeddynamics. In the early 1960s new analytical techniques

the basis of immunosuppression in the early years ofbecame available allowing the measurement of the low

transplantation and these drugs are still in widespread usedrug concentrations seen in biological fluids during drug

today. Monitoring the blood or plasma concentration oftreatment. This offered the opportunity to reduce the

these drugs is not considered worthwhile as they all havepharmacokinetic component of variability by controlling relatively wide therapeutic indices. The three agents aredrug therapy using concentrations in the body rather

generally given in fixed doses and are not subjected tothan by dose alone. This process became known as

therapeutic drug monitoring.therapeutic drug monitoring (TDM) [1].

However, a case can be made for the measurement ofFor a drug to be a suitable candidate for therapeutic

the activity of the enzyme thiopurine methyltransferasedrug monitoring it must satisfy the following criteria:- (TPMT) as an adjunct to azathioprine therapy [6].m There should be a clear relationship between drug

Azathioprine is not directly immunosuppressive, since itconcentration and effect.

must be metabolised first to 6-mercapto-purine, then bym The drug should have a narrow therapeutic index;

TPMT to 6-methyl-mercapto-purine and then on to thethat is, the difference in the concentrations exerting

pharmacologically active 6-thioguanine nucleotides. Thetherapeutic benefit and those causing adverse events expression of the enzyme TPMT is inherited in anshould be small.

autosomal co-dominant fashion and consequently variesm There should be considerable between-subject

widely within the population [7] with 11% of thepharmacokinetic variability and, therefore, a poor relation-

Caucasian population heterozygous and 0.3% homo-ship between dose and drug concentration/response.

zygous with respect to TPMT deficiency [8]. Potentiallym The pharmacological response of the drug should be fatal complications could be avoided if TPMT activity

difficult to assess or to distinguish from adverse events.was monitored in erythrocytes [9]. The therapeutic drug

The immunosuppressive drug cyclosporin satisfies allmonitoring of azathioprine in cancer chemotherapy is

four of these criteria and, despite over 16 years of clinicaloutside the scope of this article but has been reviewed

use with therapeutic drug monitoring, there is still norecently in this journal by Lennard [10].

firm consensus on the best way to use the drug. In OKT3 (muromonab-CD3) is a mouse-monoclonaladdition, the number of available agents for use as

antibody directed against the CD3 complex on T cellsimmunosuppressants has more than doubled in recent

[11]. When complexed with its antigen, the antibodyyears and the range of diseases in which these drugs are

prevents the initiation of signal transduction and blocksused has also widened [2]. The purpose of this review is

all T cell function [12]. In a pilot study using OKT3to examine the current strategies in use for the therapeutic serum concentrations as a guide to therapy in kidneydrug monitoring of immunosuppressant drugs [3] and to

transplant patients excellent results were reported for thediscuss some of the factors that impinge on the monitoring

prevention of early graft rejection [13]. Although thereof these drugs.

is a correlation between OKT3 concentration and T cellkilling the relationship is complicated by the patients’antibody response to murine-derived protein [14]. In

Correspondence: Atholl Johnston, Clinical Pharmacology, St Bartholomew’s & another study using flow cytometry measurements toThe Royal London School of Medicine & Dentistry, Charterhouse Square,

monitor OKT3 therapy the authors not only measuredLondon EC1M 6BQ, UK.Received 16 October 1998, accepted 16 November 1998. OKT3 concentration but also anti-OKT3 antibody

© 1999 Blackwell Science Ltd Br J Clin Pharmacol, 47, 339–350 339

A. Johnston & D. W. Holt

concentration and the number of CD3+ cells (the concentration remains an imperfect measure of the totalexposure to cyclosporin during a dose interval [3].therapeutic target of OKT3) [15]. Although the authors’

conclusions were positive about the use of flow cytometry In the SandimmunA era substantial efforts were madeby Kahan and co-workers to characterize the relationshipfor monitoring, their over all conclusions were that ‘this

treatment cannot protect against acute cellular rejection due to between area under the concentration-time curve forcyclosporin (AUC) and clinical events including patientthe presence of a dimly positive CD3+ population’. In those

centres using muromonab-CD3, TDM for OKT3 is not outcome [41]. Although many acknowledge the advan-tages of AUC monitoring, it has failed to gain widespreadin widespread use.acceptance because of the practical difficulties, both forthe patient and clinician, in implementing AUC measure-ments [42]. The advent of the microemulsion formulation

Cyclosporinof cyclosporin, NeoralA, with its improved pharmaco-kinetic characteristics [43], provides an opportunity toIn the early days of kidney transplantation, Calne gave

the 2 year graft survival rate for cadaveric renal simplify the measurement of AUC [42]. Previous studieswith SandimmunA have shown that the concentrationstransplantation in the USA as less than 18% [16]. Five

years later, in 1974, the same author reported that graft of three blood samples, drawn at specific times, can beused to derive an accurate estimate of cyclosporin AUCsurvival at 2 years, had risen to over 50% [17]. The

change was due to better surgical technique and improved [44]. For NeoralA a similar degree of accuracy in theprediction can be achieved by two optimally timed bloodpatient management since the main drug therapies,

azathioprine and prednisolone, had not changed. Twenty- samples [45]. Prospective studies are now underway tocompare pre-dose concentration monitoring with sparse,one years later, in those patients receiving that drug

combination, the 2 year graft survival was still only or limited sampling AUC monitoring.However, pre-dose, trough concentration and AUC#60% [18]. However, with the discovery [19, 20] and

use of cyclosporin for immunosuppression the 2 year monitoring are not the only options for the therapeuticmonitoring of cyclosporin. For some time, Cantarovichgraft survival for the majority of patients is now better

than 80% [18]. Long term graft survival has also improved; and co-workers have been advocating the use of a singletimed sample 6 h after dosing [46]. In a prospective studyafter the first year from transplant, the estimated graft

half-life in patients on cyclosporin alone is 30 years of heart transplant patients comparing pre-dose and 6 hcyclosporin concentration with control cyclosporin ther-compared with 10.5 years in those patients maintained

on azathioprine and steriods [18]. apy, the use of the 6 h value resulted in a 30% lower doseof the drug with the same effectiveness in preventingWhile the introduction of cyclosporin resulted in a

marked improvement in graft survival, its use was not rejection, and similar cardiac and renal function as seen inthose dosed using the pre-dose concentration [47]. Thesewithout problems. From the initial discovery of cyclospo-

rin [21] to the present day [22], the absorption of the authors have also reported a good relationship between6 h cyclosporin concentrations and efficacy in non-drug has been problematical [23]. Variable absorption and

a narrow therapeutic index (the drug causes irreversible infectious uveitis [48] and other auto-immune diseases [49].Another option that is being promoted for monitoringkidney damage when given in too high a dose [24]) has

resulted in the measurement of cyclosporin blood is the use of the cyclosporin blood concentration at 2 hpost-dose (C2). The rationale for this comes from theconcentrations so that the dose of the drug can be tailored

to the patient to maximise therapeutic efficacy while observation made during the clinical development ofNeoralA that in liver transplant patients there is an inverseminimising toxicity [25]. In the past, the utility of

cyclosporin therapeutic drug monitoring has been reduced relationship between the incidence of rejection and themaximum blood cyclosporin concentration (Cmax)by, choice of sample matrix for monitoring [26, 27], lack

of assay specificity [28], inconsistent assay performance [50–52]. As yet, the use of C2 monitoring has only beentested in a small open-labeled trial but the initial results[29], the variable absorption of the drug from the original

formulation (SandimmunA) [30] and the poor correlation look promising [53]. The opportunities presented by newtherapeutic drug monitoring strategies to optimise cyclo-between trough concentration and clinical effects [31].

Over time, the majority of these problems have been sporin therapy have been the subject of a recent consensusmeeting [54].addressed [32]; blood, and not plasma or serum, is the

chosen matrix for measurement [33, 34], assays are nowmore selective for the parent compound [35, 36], most

Tacrolimuslaboratories participate in proficiency testing [37] and thedrug has been re-formulated (NeoralA) to improve Tacrolimus ( previously known as FK506), like cyclospo-

rin, has been shown to be an effective immunosuppressiveabsorption [38–40]. However, trough whole blood

© 1999 Blackwell Science Ltd Br J Clin Pharmacol, 47, 339–350340


for the prevention of organ rejection after transplantation published data in peer reviewed journals, relating concen-tration to effect, is limited. Large scale multi-centre,and, like cyclosporin, too much drug is associated with

toxicity and too little with rejection. Again, like double-blind, randomised, controlled studies in renaltransplant patients have shown the effectiveness of MMFcyclosporin, whole blood concentration measurements

are used for the monitoring of tacrolimus therapy [55]. in the suppression of acute, biopsy proven, rejectionwhen used in combination with cyclosporin and steroidsInitial clinical trials did not include concentration

monitoring and patients often experienced neuro- and [69]. Logistic regression has been used to relate the AUCand Cmax of plasma MPA to the incidence of rejectionnephrotoxicity [56].

The pharmacokinetics of tacrolimus are highly variable in renal transplant patients and has demonstrated a highlystatistically significant relationship [63]. The results of the[57]. Since tacrolimus shares many of the pharmacokinetic

and pharmacodynamic problems associated with cyclospo- logistic regression and data from other trials [70] suggestthat low plasma MPA AUC is a significant risk factor inrin the rationale for therapeutic drug monitoring is

similar. An early observational study correlating concen- developing rejection [71]. These data have been con-firmed by the results of a randomised concentration-tration and effect failed to show a significant difference

between the blood concentration in those kidney controlled study of MMF in renal patients [72]. The linkbetween high MPA concentrations and adverse effectstransplant patients who did not experience rejection and

those who did [58]. However other, more statistically has not been characterised.The role of TDM in MMF therapy has yet to berigorous, studies have shown, in kidney and liver

transplant patients, significant associations of low tacrol- established. Some authors believe that the inter-individualpharmacokinetic variability is low and therefore the utilityimus concentrations with rejection and of high concen-

trations with nephrotoxicity [59]. Although the feasibility of TDM in the majority of patients would be limited[70]. Whereas others, using the same data, believe thatof a limited sampling scheme to predict AUC has been

demonstrated [60], as yet, trough, or pre-dose, whole the inter-individual pharmacokinetic variability is highand that TDM may have a worthwhile function in theblood concentration monitoring is still the method of

choice. Unlike cyclosporin, there is no move towards the control of MMF therapy [73]. Support for the latter viewcomes from a study of 30 de novo heart transplant patientsuse of other timed samples or AUC monitoring. This

may, in part, be due to the high correlation between receiving tacrolimus and MMF in which the dose ofMMF was adjusted to maintain the MPA trough plasmatrough concentration and Cmax or AUC [61].concentration between 2.5 and 4 mg l−1 [74]. Thesepatients were rejection free at 6 months post-transplantMycophenolate mofetil (MMF)and their MMF dose ranged between 0.5 and 6 g day−1

to achieve trough concentrations within a target range.This is the morpholinethylester of mycophenolic acid(MPA) and acts as a pro-drug for that compound [62]. Recent consensus guidelines are circumspect about

recommending TDM for the control of MMF therapyWhen given orally to man, MMF undergoes rapid andcomplete absorption and is hydrolyzed, pre-systemically, [75]. The guidelines suggest that TDM should be used

to establish that adequate MPA concentrations areto MPA, with no MMF measurable in plasma [63]. Thedrug reduces both B and T cell proliferation by inhibition achieved soon after surgery and that it could be useful in

cases of adverse reaction to MMF. These guidelines wereof de novo guanine nucleotide production [64]. Since,unlike cyclosporin and tacrolimus, both B and T cells are written from the view point of MMF as secondary

immunosuppression to cyclosporin or tacrolimus.inhibited it has been suggested that MMF may beeffective against both acute and chronic rejection [65]. In However, in a recent study it has been shown that MMF

can be used successfully as a primary immunosuppressantman, MPA is metabolised in the liver to MPAb-glucuronide (MPAG), an inactive metabolite which is [76] and if MMF is to be used as mono-therapy the role

of MPA TDM may assume more importance.present in plasma at approximately 40-fold higherconcentrations than MPA. The MPA glucuronide wasthought to be the only metabolite of MPA but, recently,

Sirolimusthis view has been challenged by comparative results ofanalyses using high performance liquid chromatography This is a macrolide antibiotic produced by Streptomyces

hygroscopicus, a fungus isolated originally from a soil sampleand enzyme immunoassay [66]. These showed a discrep-ancy between the assays and this was traced to previously from Easter Island (Rapa Nui). Sirolimus (previously

known as rapamycin), although similar in structure tounknown, possibly active, metabolites of MPA. Thesignificance of these findings is being assessed [67]. tacrolimus, exerts its immunosuppressant effect via a

different mechanism [77] and at another point in the cellAlthough the action of the active moiety, MPA, hasbeen known for over 25 years [68], the amount of cycle [78]. The initial clinical trials were with the drug



in combination with cyclosporin and were concentration Early attempts to set target ranges to achieve efficacy,while avoiding toxicity, were based on simple clinicalcontrolled [79]. These trials confirmed the clinical efficacy

of the drug [80, 81]. A recent review of the pharmaco- observations in patients who had undergone kidneytransplantation [31]. More systematic approaches havekinetics of sirolimus suggested a therapeutic range, based

on animal allo-transplant data, of 5 to 10 mg l−1 in whole been made by the retrospective statistical analysis of largevolumes of patient data gathered over a period of yearsblood [82]. However, the only consensus guidelines

published on the therapeutic monitoring of sirolimus [96]. However, the ranges arrived at are biased bysubjective judgments; a more objective approach has beenconcluded that there was not enough information

available about the clinical use of the drug to make taken by Perna et al. [97]. These authors used logisticregression to determine the most probable concentrationsrecommendations [83].for the occurrence of rejection and toxicity in renaltransplant patients. This approach has also been used by

Daclizumab and basiliximab Nicholls [71] to determine the therapeutic range formycophenolic acid and is applicable to the other

The binding of interleukin 2 (IL-2) to its receptor onimmunosuppressant agents and their combinations.

antigen activated T cells stimulates clonal proliferation ofMorris [98] has called the whole concept of the

the T cells that mediate organ allograft rejection [84].therapeutic range into question. This author suggests that

The receptor complex is made up of at least three sub-the concept should be abandoned as it puts too much

units (a, b and c) and, of these, only the a sub-unit isemphasis on achieving the desired numbers rather than

thought to be specific to IL-2 [85]. This presents atreating the patient. He favours a single concentration

potential therapeutic target for specific immunosuppres-approach in which clinicians aim, initially, to dose a

sive therapy and it has been exploited by a series ofpatient to achieve a set target concentration. The target

monoclonal antibodies raised against the IL-2 receptor’sis then individualised for that patient based on the number

a sub-unit (IL-2Ra). Two such antibodies are currentlyof rejection episodes, occurrence of toxicity, concomitant

available. One is a molecularly engineered human IgG1medication, etc. This has the advantage that pharmaco-

incorporating the antigen-binding regions of a murinekinetic variability is controlled by the target concentration

monoclonal antibody (daclizumab [86]) against IL-2Ra.and pharmacodynamic variability is dealt with by tailoring

The other is a murine-human chimeric antibody (basilixi-the target to the patient.

mab [87]) to IL-2Ra. Both have been used successfullySome of the problems alluded to by Morris could be

for the prevention of acute rejection following renaladdressed if the boundaries of the therapeutic ranges were

transplantation [88, 89]. The therapeutic index of thesenot seen as yes-no cut-off points. To do this the

antibodies is wide, neither antibody being associated withperformance characteristics of the concentrations need to

major adverse effects and, since the half life of bothbe seen in terms of a diagnostic test for determining the

antibodies is long, daclizumab (t1/2#6 days [90]) is givenprobability of drug-effectiveness or toxicity [99]. This,

as five, and basiliximab (t1/2>20 days [91]) as two,again, requires better information to be available to the

weight related intra-venous doses in the first 8 weeksclinician so that the blood or plasma concentrations can

following transplantation. Thus, there appears little to bebe interpreted within a Bayesian statistical framework and

gained from therapeutic drug monitoring for these agentsinformed decisions can be made [100].

[92, 93].

Assay methodologyThe ‘therapeutic’ range

Cyclosporin The correct measurement of cyclosporin hasbeen the subject of many publications [26, 27, 101] andIn a survey of the therapeutic ranges used by 21 transplant

centres to guide cyclosporin maintenance therapy in reviews [37, 95]. Currently four commercial companiesare producing eight different immunoassay assay systemskidney transplant patients there was a six fold range in

the concentrations considered effective and a three fold for the measurement of cyclosporin in whole blood(Table 1). In addition, a number of laboratories are usingrange in those considered toxic [94]. There was also

considerable variation in the width of the therapeutic high performance liquid chromatography (h.p.l.c.) tomeasure the drug. Using h.p.l.c., it is possible to separate‘window’. Although some of this variation must come

from the different combinations of immunosuppressant the parent compound from metabolites and for this reasonthis technique has long been considered the ‘golddrugs used and differences in assay methodology [35]

and, perhaps, specificity [95], much of the variation is standard’ in cyclosporin measurement, particularly whencoupled with mass-spectrometry. However, althoughdue to the empirical way that these ranges have

been derived. h.p.l.c. is specific for cyclosporin, the technique can



Table 1 Available assays for the measurement of cyclosporin and Metabolite assay uses a polyclonal antibody and producesabbreviations and manufacturers. results that are approximately 3 to 5 times those of

h.p.l.c. whereas the DiaSorin CYCLO-Trac-NS radio-Abbreviation Assay

immunoassay uses a monoclonal non-specific antibodyand gives results about 5 to 7 times higher than h.p.l.c.High performance liquid chromatography.H.p.l.c.The ratio of the non-specific assays to h.p.l.c. changesTDxsp Fluorescence polarisation immunoassay withwith the metabolite5parent compound ratio in the bloodmonoclonal specific antibody for the Abbott

TDxA analyser. and, therefore, will vary with transplant type and timeTDxns Fluorescence polarisation immunoassay drug and after transplant. The results of the non-specific assays

metabolite with polyclonal non-specific antibody have a poor correlation with clinical events [103].for the Abbott TDxA analyser. The other six immunoassays are regarded as ‘specific’

AxSYM Fluorescence polarisation immunoassay withfor the parent drug but do, to a limited extent, cross-monoclonal specific antibody for the Abbottreact with some of the metabolites of the drug and,AxSYMA analyser.therefore, do not necessarily give the same result for ar.i.a.sp Radioimmunoassay with monoclonal specific

antibody, DiaSorin Cyclo-Trac-SP. given sample (Figure 2). Although the differences betweenr.i.a.ns Radioimmunoassay with monoclonal non-specific the results of the ‘specific’ assays are due, in part, to the

antibody, DiaSorin Cyclo-Trac-NS. different cross-reactivities of the anti-bodies used, someEMIT Homogeneous enzyme immunoassay, methanol of the differences result from incorrect calibration [104].

extraction, EMIT Dade Behring.This can be seen clearly with the measurement of spikedEMITgl As EMIT but with patented ‘green liquid’samples (Figure 3). (It is interesting to note that for oneextraction system, EMIT Dade Behring.of the manufacturers the results of their three differentCEDIA Homogeneous enzyme immunoassay, CEDIA

Roche Diagnostics (no results shown, See Schutz assays do not agree). These differences in measurementet al.[106]). accuracy do not seem to affect the clinical usefulness of

the assays [103] but do add to variability of reportedconcentrations in the literature [105] and have an impact

suffer from poor precision and can give spurious results on the local target ranges [94]. However, in clinicaldue to interference from other sources [102]. conditions where the cyclosporin metabolite load in

Of the eight immunoassay variants, two are non- blood is high, for example, in liver transplant patientsspecific and cross-react, markedly, with the metabolites immediately post-transplant, h.p.l.c. is the only methodof cyclosporin, (Figure 1). The Abbott TDxA Drug and that can accurately measure the parent compound [106].

Cyclosporin (µgl–1)0 200 400 800

Met

hod

TDxns

R.i.a.

H.p.l.c.

600 1000 1200 1400 1600

Figure 1 Measurement of cyclosporin in an aliquot of pooled% Difference from h.p.l.c. mean

–20 –10 0 20

Met

hod

TDxsp

EMIT

AxSYM

10 30 40 60 80

EMITgl

R.i.a.

H.p.l.c.

50 70

Figure 2 Measurement of cyclosporin in an aliquot of pooledblood samples from heart transplant patients receiving the drug.The results are shown as Box and Whisker. The line is drawn blood samples from heart transplant patients receiving the drug.

The results are shown as Box and Whisker. The line is drawnacross the box at the median. The left of the box is at the firstquartile (Q1), and the right is at the third quartile (Q3) value. across the box at the median. The left of the box is at the first

quartile (Q1), and the right is at the third quartile (Q3) value.The whiskers are the lines that extend from the left and right ofthe box to the adjacent values within ±1.5×(Q3−Q1), values The whiskers are the lines that extend from the left and right of

the box to the adjacent values within ±1.5×(Q3−Q1), valuesoutside the whiskers are plotted as circles. The mean result isshown as a solid circle. plots for h.p.l.c. (11 centres), TDx non- outside the whiskers are plotted as circles. The mean result is

shown as a solid circle. plots for percentage difference from thespecific (19 Centres) and r.i.a. non-specific. The dotted line is atthe median value, 190 mg l−1, for h.p.l.c. (data from the median result for h.p.l.c. (11 centres), AxSYM, r.i.a.sp, EMIT,

EMITgl and TDxsp.Cyclosporin International Proficiency Testing Scheme [114]).



Mycophenolic acid Compared with the other immuno-suppressant drugs in current use, the plasma concentrationof MPA is much higher and this makes h.p.l.c.measurement of the drug straightforward. However, themajor glucuronide metabolite of MPA complicates theassay as it elutes much later than the parent drug and thisleads to extended run times. A commercial homogeneousenzyme immunoassay (Dade Behring) is available whichis capable of accurate and precise measurement of thedrug in the concentration range 0.5 to 15 mg l−1. Thisassay does not cross react with the major glucuronide ofMPA but does give results marginally higher than h.p.l.c.Cyclosporin (µgl–1)

100 110 120 140

Met

hod

TDxns

EMIT

AxSYM

130 150 160 180 200

EMITgl

R.i.a.

H.p.l.c.

170 190

TDxsp

because of cross reactivity to minor MPA metabolites [66].Figure 3 Measurement of cyclosporin in an aliquot of drug freeblood to which 150 mg l−1 of cyclosporin had been added. Theresults are shown as Box and Whisker. The line is drawn across Proficiency testingthe box at the median. The left of the box is at the first quartile

The difficulties in measuring blood cyclosporin concen-(Q1), and the right is at the third quartile (Q3) value. Thewhiskers are the lines that extend from the left and right of the tration led to the development of a proficiency-testingbox to the adjacent values within ±1.5×(Q3−Q1), values scheme for laboratories providing monitoring services foroutside the whiskers are plotted as circles. The mean result is the drug [29]. The Scheme has been in existence forshown as a solid circle. plots for h.p.l.c. (11 centres), AxSYM, over 14 years and has over 400 participating centresr.i.a.sp, EMIT, EMITgl, TDxsp and TDxns.

world-wide. The Scheme circulates three blood samplesper month to each participating centre and the measure-ments made on these samples enable laboratories to

Tacrolimus The concentrations of tacrolimus seen in the benchmark their analytical performance against currentlyblood of stable renal transplant patients is low, available best practice [111]. The manufacturer of<30 mg l−1, and this makes the measurement of the cyclosporin, Sandoz AG (now Novartis AG), initiallydrug difficult. In-house ELISA, commercial ELISA funded the Scheme to promote measurement accuracy of(DiaSorin), microparticulate enzyme immunoassays, and the drug. However, the individual centres, the drugh.p.l.c.-MS [107] methods have been available. The manufacturer and TDM reagent suppliers, now fund it.majority of laboratories monitoring tacrolimus use the In a similar fashion Fujisawa GmbH, the makers ofcommercial microparticulate enzyme immunoassay tacrolimus [112], have funded a scheme for that drug and(MEIA, Abbott Laboratories) which measures the drug Dade Behring, manufacturer of a kit for the measurementwithin the range 3 to 30 mg l−1 and cross-reacts to a of MPA, have funded a mycophenolate proficiencysmall degree with the metabolites of tacrolimus [108]. scheme [113]. These schemes have 200 and 38 members,

respectively. A sirolimus proficiency testing scheme wasSirolimus Therapeutic drug monitoring of sirolimus is introduced in January 1999 [114]. The role and rationalestill under investigation. The assays that are in current for proficiency testing schemes in immunosuppressiveuse are based on h.p.l.c. using either ultra-violet or mass drug monitoring has recently been reviewed [115].spectroscopy to detect the drug. However, a commercialMEIA (Abbott Laboratories) is being tested for wide-

Pharmacodynamic monitoringspread, routine, measurement of the drug [109].

Blood or plasma drug concentration measurements areonly a surrogate for effect. Their use would be unnecessaryReceptor assays Cyclosporin, tacrolimus and sirolimus bind

to a group of widely occurring proteins, the immunophil- were it possible to measure the immunosuppressive actionof these drugs directly. However, defining the pharmaco-ins. The two major immunophilins are cyclophilin, which

binds cyclosporin, and FK-binding protein 12, which dynamic target for monitoring is not an easy task. Forexample, in a recent study investigating immunologicalbinds tacrolimus and sirolimus. Receptor assays have

theoretical advantages over current immunoassays in that monitoring of azathioprine the authors examined multiplesubsets of peripheral blood lymphocytes, natural killerbinding is associated with pharmacological activity so

that only active drug or active metabolite concentration activity, the serum concentrations of IgG, IgM, interferonb (IFN b), tumour necrosis factor a (TNF a), interleukinis measured [110]. However, this contention still remains

to be proved and, as yet, these assays are not in routine 2 (IL-2), soluble interleukin 2 receptors (sIL-2R),interleukin 6 (IL-6) and the soluble adhesion moleculeclinical use.



sICAM-1 [116]. There is a danger that one surrogate was not compromised. Although not a formal pharmaco-economic study, the author also noted that there was awill be replaced by another.

Cyclosporin and tacrolimus inhibit T-cell proliferation, net saving of £1600 ($2500) per patient.which is thought to result from their inhibition ofcalcineurin [117]. This is a serine-threonine phosphatase Benefits of monitoringthat plays an essential role in intra-cellular, calcium-dependent, signal transduction [118]. Inhibition of cal- Evidence-based medicine is sadly lacking in the area of

drug monitoring [127]. Although the perception ofcineurin in activated T cells reduces the translocation ofthe cytoplasmic sub-unit of the nuclear factor to the therapeutic drug monitoring is that it is beneficial, and

aids patient management, there is little hard evidence tonuclear sub-unit and, hence, impairs the transcription ofgenes for many of the cytokines essential for the rejection support that view. Outside the field of immunosuppressive

drugs there are numerous articles, detailing predominantlyresponse [119]. For this reason calcineurin has been theprimary focus of pharmacodynamic monitoring for retrospective studies, which suggest that TDM has a

useful and cost effective role in monitoring therapy [128,cyclosporin. In a study of 62 renal transplant patients themeasured calcineurin activity in leukocytes was half that 129]. However, as the authors of a recent review of

clinical pharmacokinetics point out, there is little evidenceof controls [120]. The trough cyclosporin concentrationwas inversely related to the calcineurin activity. Since to support the effect of TDM on true patient outcomes

[128].tacrolimus acts on the same target, calcineurin would alsobe applicable for monitoring that drug. However, the For the immunosuppressive drugs some positive evi-

dence for TDM is given by the results of prospectivemeasurement of calcineurin activity is technically chal-lenging and a much simpler procedure would be required concentration-controlled clinical trials [130]. A concen-

tration-controlled trial is one in which patients are dosedbefore it could be used in the routine setting. In anycase, further studies are needed to confirm that calcineurin to achieve pre-assigned target concentrations and, there-

fore, the results can be assessed in terms of drugactivity correlates better with patient response than simpleblood concentrations. concentration and response rather than dose and response.

This type of trial has several benefits over the randomizedMycophenolic acid exerts its immunosuppressive actionby inhibition of inosine monophosphate dehydrogenase dose-controlled trials [131] and can provide the basis for

future TDM decisions.(IMPDH) and, thereby, blocking de novo purine biosynth-esis in lymphocytes [121]. An assay has been developed In a study of tacrolimus, patients were randomly

allocated to be targeted at low, medium or high drugfor the measurement of IMPDH activity in whole bloodto measure drug effect rather than concentration [122]. blood concentrations [132]. Although there was no

difference in the incidence of rejection or toxicity in theAs yet there are few published data to support the use ofthis assay, but initial studies suggest a correlation between three groups in the first 42 days post transplant, logistic

regression demonstrated a clear relationship betweenIMPDH activity and clinical events [123].Sirolimus is thought to exert its immunosuppressive concentration and effect (Table 2). In a study of similar

design using mycophenolate mofetil, patients were ran-activity by blocking the phosphorylation and activationof the P70 S6 kinase that is involved in cell signalling, domly allocated to a high, medium or low mycophenolic

acid AUC [72]. Again there was a clear concentrationand this prevents, or reduces, lymphocyte proliferation[124]. The measurement of P70 S6 activity is, therefore, related effect of the drug with rejection in the low,

medium and high groups of 26, 9 and 6%, respectively.a prime target for pharmacodynamic measurements. Anassay has been developed for its measurement in wholeblood and studies are ongoing to determine its utility in

Conclusionclinical practice [125].

Antithymocyte globulin (ATG) has been monitored in At present the majority of drug regimes in use fortransplantation are based on cyclosporin and excellentrenal transplant patients using the effect of ATG on

subsets of T lymphocytes [126]. In this study, the authoridentified the CD3+ lymphocytes as a pharmacodynamic Table 2 Incidence of toxicity and rejection by whole bloodmarker of ATG response. The dose of ATG administered tacrolimus concentration [132].to patients was titrated to maintain the patients’ absolute

Tacrolimus (mg l−1)CD3+ lymphocyte count at #50 cells ml−1 of blood.<5 5–15 >15Forty-four patients who were treated in this way for

steroid resistant rejection had significantly less seriousRejection (%) 34 17 5

viral infections than 10 patients who were treated on a Toxicity (%) 0 34 54fixed dose ATG regimen, but their 1 year graft survival



12 Smith SL. Ten years of Orthoclone OKT3 (muromonab-results can be obtained in solid organ transplantationCD3): a review. J Transplant Coordination 1996; 6:using this drug. This is also true in the treatment of109–119.autoimmune diseases [2]. However, cyclosporin’s domi-

13 Abramowicz D, Goldman M, Mat O, et al. OKT3 serumnance is being challenged as the number of immuno-levels as a guide for prophylactic therapy: a pilot study in

suppressive agents increases and clinical experience is kidney transplant recipients. Transpl Int 1994; 7: 258–263.gained with other drugs. We are entering an era in which 14 Schena FP. New insights into therapy with monoclonalcombination therapy will be the norm and clinicians will antibodies in allograft transplantation. Nephrol Dial

Transplant 1997; 12(Supplement 1): 55–58.tailor the immunosuppression to the characteristics of the15 Cinti P, Cocciolo P, Evangelista B, et al. OKT3individual patient changing dose and drugs as time

prophylaxis in kidney transplant recipients: drug monitoringprogresses and conditions change [133]. In addition,by flow cytometry. Transplant Proc 1996; 28: 3214–3216.generic [134] and other new formulations of cyclosporin

16 Calne RY. Organ transplantation. The present position and[135] will be available in the near future and these future prospects of organ transplantation. Trans Med Soctogether with the new drugs under clinical development, Lond 1969; 85: 56–67.such as FTY720 [136] and SDZ-RAD [137], and the 17 Calne RY. Immunosuppression and clinical organpossibilities of xenotransplantation [138] present future transplantation. Transplant Proc 1974; 6(4:Suppl 1):

Suppl-51. pp?.challenges which will add to the complexity of TDM.18 Opelz G. Influence of treatment with cyclosporine,

azathioprine and steroids on chronic allograft failure. TheCollaborative Transplant Study. Kidney International—

References Supplement 1995; 52: S89–S92.19 Borel JF, Feurer C, Gubler HU, Stahelin H. Biological1 Spector R, Park GD, Johnson GF, Vesell ES. Therapeutic

effects of cyclosporin A: a new antilymphocytic agent.drug monitoring. Clin Pharmacol Ther 1988; 43: 345–353.Agents Actions 1976; 6: 468–475.2 Holt DW, Johnston A. Cyclosporin monitoring: its role in

20 Borel JF, Kis ZL. The discovery and development ofautoimmune indications. J Autoimmunity 1992; 5: Suppl-82.cyclosporine (Sandimmune). Transplant Proc 1991; 23:pp. ?.1867–1874.3 Holt DW, Johnston A. Monitoring new

21 Borel JF, Kis ZL, Beveridge T. Meluzzi VJ, Adams J,immunosuppressive agents. Are the methods adequate?editors. The search for anti-inlammatory drugs. Boston,Drug Metabolism & Drug Interactions 1997; 14: 5–15.USA: Birkhauser; 1995; 2, The history of the discovery and4 Calne RY. The present position and future prospects ofdevelopment of cyclosporine. pp. 27–63.organ transplantation. Ann R Coll Surg Engl 1968; 42:

22 Dunn SP, Cooney GF, Kulinsky A, Falkenstein K, Pierson283–306.A, Meligeni J. Reduced cyclosporine absorption preceded5 Starzl TE, Marchioro TL, Porter KA, Iwasaki Y, Cerilliacute allograft rejection in a child with a liver transplant.GJ. The use of heterologous antilymphoid agents in canineLiver Transplantation & Surgery 1997; 3: 538–540.renal and liver homotransplantation and in human renal

23 Stahelin HF. The history of cyclosporin A (Sandimmune)homotransplantation. Surg Gynecol Obstet 1967; 124:revisited: another point of view. Experientia 1996; 52:301–308.5–13.6 Schutz E, Gummert J, Mohr FW, Armstrong VW,

24 Shaw LM, Kaplan B, Kaufman D. Toxic effects ofOellerich M. Should 6-thioguanine nucleotides beimmunosuppressive drugs: mechanisms and strategies formonitored in heart transplant recipients given azathioprine?controlling them. Clin Chem 1996; 42: 1316–1321.Ther Drug Monit 1996; 18: 228–233.

25 Holt DW, Johnston A. Thomson A, Starzl T, editors.7 Weinshilboum RM, Sladek SL. MercaptopurineImmunosuppressive Drugs: Developments in anti-rejectionpharmacogenetics: monogenic inheritance of erythrocytetherapy. London: Edward Arnold; 1994; 3, Pharmacokineticsthiopurine methyltransferase activity. Am J Hum Genetand monitoring of cyclosporin A. pp. 37–45.1980; 32: 651–662.

26 Johnston A, Marsden JT, Holt DW. The influence of8 Loennechen T, Yates CR, Fessing MY, Relling MV,haematocrit on blood cyclosporin measurements in vivo. BrKrynetski EY, Evans WE. Isolation of a human thipurineJ Clin Pharmacol 1988; 25: 509–513.S-methyltransferase (TPMT) complementary DNA with a

27 Johnston A, Marsden JT, Holt DW. Sample pretreatmentsingle nucleotide transition A719G (TPMT*3C) and itsto minimize interference from whole blood in theassociation with loss of TPMT protein and catalytic activityradioimmunoassay for cyclosporine. Transplantation 1987;in humans. Clin Pharmacol Ther 1998; 64: 46–51.44: 332.9 Gummert JF, Schutz E, Oellerich M, Mohr FW, Dalichau

28 Holt DW, Marsden JT, Johnston A. Measurement ofH. Monitoring of TPMT in heart transplant recipientscyclosporine: methodological problems. Transplant Procunder immunosuppressive therapy with azathioprine. Artif1986; 18(Suppl 5): 101–110.Organs 1995; 19: 918–920.

29 Johnston A, Marsden JT, Holt DW. The United Kingdom10 Lennard L. Therapeutic drug monitoring of antimetabolicCyclosporin Quality Assessment Scheme. Ther Drug Monitcytotoxic drugs. Br J Clin Pharmacol 1998; 47: 131–143.1986; 8: 200–204.11 Wilde MI, Goa KL. Muromonab CD3: a reappraisal of its

30 Tsang VT, Johnston A, Heritier F, Leaver N, Hodson ME,pharmacology and use as prophylaxis of solid organtransplant rejection. Drugs 1996; 51: 865–894. Yacoub M. Cyclosporin pharmacokinetics in heart-lung



transplant recipients with cystic fibrosis. Effects of with levels 6 h after the morning dose in heart transplantpatients. Clin Transplantation 1997; 11: t-405.pancreatic enzymes and ranitidine. Eur J Clin Pharmacol

48 Rocha G, Deschenes J, Cantarovich M. Cyclosporine1994; 46: 261–265.monitoring with levels 6 hours after the morning dose in31 Holt DW, Marsden JT, Johnston A, Bewick M, Taubepatients with noninfectious uveitis. Ophthalmology 1997;DH. Blood cyclosporin concentrations and renal allograft104: 245–251.dysfunction. Br Med J 1986; 293: 1057–1059.

49 Cantarovich M, Deschenes J. Cyclosporine dose adjustment32 Kahan BD, Shaw LM, Holt D, Grevel J, Johnston A.using levels obtained six hours after the morning dose:Consensus document: Hawk’s Cay meeting on therapeuticeffect on side effects in patients with autoimmune diseases.drug monitoring of cyclosporine. Clin Chem 1990; 36:Am J Nephrology 1997; 17: 450–457.1510–1516.

50 Grant D, Rochon J, Levy G. Comparison of the long-term33 Shaw LM, Yatscoff RW, Bowers LD, et al. Canadiantolerability, pharmacodynamics, and safety of SandimmuneConsensus Meeting on cyclosporine monitoring: report ofand Neoral in liver transplant recipients. Ontario Liverthe consensus panel. Clin Chem 1990; 36: 1841–1846.Transplant Study Group. Transplant Proc 1996; 28:34 Sketris I, Yatscoff R, Keown P, et al. Optimizing the use of2232–2233.cyclosporine in renal transplantation. Clin Biochem 1995; 28:

51 Levy GA, Grant D. Neoral in liver transplantation.195–211.Transplant Proc 1996; 28: 1019–1021.35 Holt DW, Johnston A. Cyclosporin assay techniques.

52 Freeman D, Grant D, Levy G, et al. Pharmacokinetics of aAccuracy and reproducibility variables impacting onnew oral formulation of cyclosporine in liver transplantmeasurements. Int J Rad Appl Instrum B 1990; 17: 733–736.recipients. Ther Drug Monit 1995; 17: 213–216.36 Holt DW, Johnston A. den Boer NC, van der Heiden C,

53 Levy G. New strategies for therapeutic drug monitoring ofLeijnse B, Souverijn JHM, editors.Clinical Chemistry.Neoral. Oxford: Blackwell Science; 1998; Two-hourPlenum Publishing Corporation; 1989; Practical applicationscyclosporin concentration (C2) as a monitoring tool for Neoral.of therapeutic drug monitoring: The impact of technologicalpp. 19–22.developments. pp. 93–102.

54 Keown P, Kahan BD, Johnston A, et al. Optimization of37 Holt DW, Johnston A, Roberts NB, Tredger JM, Trullcyclosporin therapy with new therapeutic drug monitoringAK. Methodological and clinical aspects of cyclosporinstrategies: Report from the international Neoral TDM

monitoring: report of the Association of Clinicaladvisory consensus meeting (Vancouver, November 1997).

Biochemists task force. Ann Clin Biochem 1994; 31:Transplant Proc 1998; 30: 1645–1649.

420–446.55 Jusko WJ, Thomson AW, Fung J, et al. Consensus

38 Dalrymple-Hay M, Meara M, Reynolds L, et al. Changingdocument: therapeutic monitoring of tacrolimus (FK-506).

stable heart transplant recipients from Sandimmune to Ther Drug Monit 1995; 17: 606–614.Neoral. Transplant Proc 1996; 28: 2285–2286. 56 McMaster P, Mirza DF, Ismail T, Vennarecci G, Patapis P,

39 Holt DW, Mueller EA, Kovarik JM, van Bree JB, Richard Mayer AD. Therapeutic drug monitoring of tacrolimus inF, Kutz K. Sandimmun neoral pharmacokinetics: impact of clinical transplantation. Ther Drug Monit 1995; 17:the new oral formulation. Transplant Proc 1995; 27: 602–605.1434–1437. 57 Venkataramanan R, Swaminathan A, Prasad T, et al.

40 Holt DW, Mueller EA, Kovarik JM, van Bree JB, Kutz K. Clinical pharmacokinetics of tacrolimus. Clin PharmacokinThe pharmacokinetics of Sandimmun Neoral: a new oral 1995; 29: 404–430.formulation of cyclosporine. Transplant Proc 1994; 26: 58 Anonymous. Japanese study of FK 506 on kidney2935–2939. transplantation: the benefit of monitoring the whole blood

41 Lindholm A, Kahan BD. Influence of cyclosporine FK 506 concentration. Japanese FK 506 Study Group.pharmacokinetics, trough concentrations, and AUC Transplant Proc 1991; 23: 3085–3088.monitoring on outcome after kidney transplantation. 59 Hedayat S, Kershner RP, Su G. Relationship of whole-Clinical Pharmacol Ther 1993; 54: 205–218. blood FK506 concentrations to rejection and toxicity in

42 Holt DW, Johnston A. Cyclosporin monitoring: trough or liver and kidney transplants. J Biopharm Stat 1996; 6:AUC? Perspectives 1996: 49–52. 411–424.

43 Holt DW, Johnston A. Cyclosporin microemulsion. A 60 Ku Y-M, Min DI. An abbreviated area-under-the-curveguide to usage and monitoring. BioDrugs 1997; 7: 175–197. monitoring for tacrolimus patients with liver transplants.

44 Johnston A, Sketris I, Marsden JT, et al. A limited sampling Ther Drug Monit 1998; 20: 219–223.strategy for the measurement of cyclosporine AUC. 61 Ihara H, Shinkuma D, Ichikawa Y, Nojima M, Nagano S,Transplant Proc 1990; 22: 1345–1346. Ikoma F. Intra- and interindividual variation in the

45 Johnston A, Kovarik JM, Mueller EA, Holt DW. pharmacokinetics of tacrolimus (FK506) in kidneyPredicting patients’ exposure to cyclosporin. Transplant transplant recipients—importance of trough level as aInternational 1996; 9: Suppl-7. pp. 5305–5307. practical indicator. Int J Urol 1995; 2: 151–155.

46 Cantarovich F, Bizollon C, Cantarovich D, Lefrancois N, 62 Lipsky JJ. Mycophenolate mofetil. Lancet 1996; 348:Dubernard JM, Traeger J. Cyclosporine plasma levels six 1357–1359.hours after oral administration. A useful tool for monitoring 63 Bullingham RE, Nicholls A, Hale M. Pharmacokinetics oftherapy. Transplantation 1988; 45: 389–394. mycophenolate mofetil (RS61443): a short review.

47 Cantarovich M, Besner JG, Fitchett DH, Latter DA. Transplant Proc 1996; 28: 925–929.64 Allison AC, Eugui EM. Immunosuppressive and otherEfficacy and side-effects of cyclosporine dose monitoring



effects of mycophenolic acid and an ester prodrug, 80 Kahan BD. Sirolimus: a new agent for clinical renaltransplantation. Transplant Proc 1997; 29: 48–50.mycophenolate mofetil. Immunol Rev 1993; 136: 5–28.

81 Stepkowski SM, Tian L, Wang ME, Qu X, Napoli K,65 Gray DW. Mycophenolate mofetil for transplantation: newKahan BD. Sirolimus in transplantation. Arch Immunol Therdrug, old problems? Lancet 1995; 346: 390.Exp (Warsz) 1997; 45: 383–390.66 Schutz E, Shipkova M, Armstrong VW, et al. Therapeutic

82 Trepanier DJ, Gallant H, LeGatt DF, Yatscoff RW.drug monitoring of mycophenolic acid: comparison ofRapamycin: Distribution, pharmacokinetics and therapeuticHPLC and immunoassay reveals new MPA metabolites.range investigations: An update. Clin Biochem 1998; 31:Transplant Proc 1998; 30: 1185–1187.345–351.67 Schutz E, Shipkova M, Armstrong VW, Niedmann PD,

83 Yatscoff RW, Boeckx R, Holt DW, et al. ConsensusOellerich M. Metabolism of MPA: Impact of metaboliteguidelines for therapeutic drug monitoring of rapamycin:patterns in MPA Monitoring. Berichte derreport of the consensus panel. Ther Drug Monit 1995; 17:OsterreichischenGesellschaft fur Klinische Chemie 1999; (in676–680.press).

84 Minami Y, Kono T, Miyazaki T, Taniguchi T. The IL-268 Brewin TB, Cole MP, Jones CT, Platt DS, Todd ID.receptor complex: its structure, function, and target genes.Mycophenolic acid (NSC-129185): preliminary clinicalAnn Rev Immunol 1993; 11: 245–268.trials. Cancer Chemother Rep 1972; 56: 83–87.

85 Taniguchi T, Minami Y. The IL-2/IL-2 receptor system: a69 Anonymous. Placebo-controlled study of mycophenolatecurrent overview. Cell 1993; 73: 5–8.mofetil combined with cyclosporin and corticosteroids for

86 Vincenti F, Lantz M, Birnbaum J, et al. A phase I trial ofprevention of acute rejection. European Mycophenolatehumanized anti-interleukin 2 receptor antibody in renalMofetil Cooperative Study Group. Lancet 1995; 345:transplantation. Transplantation 1997; 63: 33–38.1321–1325.

87 Amlot PL, Rawlings E, Fernando ON, et al. Prolonged70 Bullingham RES, Nicholls AJ, Kamm BR. Clinicalaction of a chimeric interleukin-2 receptor (CD25)pharmacokinetics of mycophenolate mofetil. Clinmonoclonal antibody used in cadaveric renalPharmacokinet 1998; 34: 429–455.transplantation. Transplantation 1995; 60: 748–756.71 Nicholls AJ. Opportunities for therapeutic drug monitoring

88 Kovarik JM, Rawlings E, Sweny P, et al. Prolongedof mycophenolate mofetil dose in renal transplantationimmunosuppressive effect and minimal immunogenicity

suggested by the pharmacokinetic/pharmacodynamicfrom chimeric (CD25) monoclonal antibody SDZ CHI 621

relationship for mycophenolic acid and suppression ofin renal transplantation. Transplant Proc 1996; 28: 913–914.

rejection. Clin Biochem 1998; 31: 329–333.89 Vincenti F, Kirkman R, Light S, et al. Interleukin-

72 Hale MD, Nicholls AJ, Bullingham RE, et al. The2-receptor blockade with daclizumab to prevent acute

pharmacokinetic–pharmacodynamic relationship for rejection in renal transplantation. Daclizumab Triplemycophenolate mofetil in renal transplantation. Clin Therapy Study Group. N Engl J Med 1998; 338: 161–165.Pharmacol Ther 1998; 64: 672–683. 90 Hakimi J, Mould D, Waldeman TA, et al. Antibody

73 Shaw LM, Korecka M, van Breeman R, Nowak I, therapeutics. CRC Press; 1997; 12, Development ofBrayman KL. Analysis, pharmacokinetics and therapeutic Zenapax: A humanized anti-tac antibody. pp. 277–300.drug monitoring of mycophenolic acid. Clin Biochem 1998; 91 Kovarik JM, Rawlings E, Sweny P, et al. Pharmacokinetics31: 323–328. and immunodynamics of chimeric IL-2 receptor

74 Meiser BM, Pfeiffer M, Jagiello-Kraatz M, et al. monoclonal antibody SDZ CHI 621 in renal allograftMycophenolate mofetil dose adjustment based on trough recipients. Transplant Int 1996; 9 Suppl 1: S32–S33.levels improves outcome after heart transplantion. J Heart 92 Kovarik J, Wolf P, Cisterne JM, et al. Disposition ofLung Transplant 1998; 17: 85. basiliximab, an interleukin-2 receptor monoclonal antibody,

75 Shaw LM, Nicholls A, Hale M, et al. Therapeutic in recipients of mismatched cadaver renal allografts.monitoring of mycophenolic acid: A consensus panel Transplantation 1997; 64: 1701–1705.report. Clin Biochem 1998; 31: 317–322. 93 Kovarik J, Breidenbach T, Gerbeau C, Korn A, Schmidt

76 Zanker B, Schneeberger H, Rothenpieler U, et al. A-G, Nashan B. Disposition and immunodynamics ofMycophenolate mofetil-based, cyclosporin-free induction basiliximab in liver allograft recipients. Clin Pharmacol Therand maintenance immunosuppression. Transplantation 1998; 1998; 64: 66–72.66: 44–49. 94 Oellerich M, Armstrong VW, Kahan B, et al. Lake Louise

77 Sehgal SN. RapamuneA (RAPA, rapamycin, sirolimus): Consensus Conference on cyclosporin monitoring in organMechanism of action immunosuppressive effect results from transplantation: report of the consensus panel. Ther Drugblockade of signal transduction and inhibition of cell cycle Monit 1995; 17: 642–654.progression. Clin Biochem 1998; 31: 335–340. 95 Holt DW, Johnston A. Cyclosporin A: analytical

78 Helderman JH. New immunologically non-specific methodology and factors affecting therapeutic drugimmunosuppressive agents dictate changes in standard monitoring. Ther Drug Monit 1995; 17: 625–630.protocols for renal transplant management. Nephrol Dial 96 LeGatt DF, Chooi M, Simpson AI, Yatscoff RW. EMITTransplant 1997; 12(Suppl 1): 51–54. cyclosporine assay: development of an application protocol

79 Brattstrom C, Holt DW, Backman L, et al. Concentration- for Technicon AXON System. Clin Biochem 1994; 27:controlled dosing of RapamuneA in renal allograft 387–394.recipients to optomise therapy. Montreal, Canada: 97 Perna A, Gotti E, de BE, Perico N, Remuzzi G. A

logistic-regression model provides novel guidelines toThe Transplant Society; 1998; 17th World Congress.



maximize the anti-acute rejection properties of cyclosporine monitoring of azathioprine treatment in multiple sclerosispatients. J Neurol 1997; 244: 167–174.with a minimum of toxicity. J Am Soc Nephrol 1996; 7:

117 Morris R. Modes of action of FK506, cyclosporin A and786–791.rapamycin. Transplant Proc 1994; 26: 3272–3275.98 Morris RG. Target concentration strategy for cyclosporin

118 Schreiber SL, Crabtree GR. The mechanism of action ofmonitoring. Clin Pharmacokin 1997; 32: 175–179.cyclosporin A and FK506. Immunol Today 1992; 13:99 Schumacher GE, Barr JT. Total testing process applied to136–142.therapeutic drug monitoring: impact on patients’ outcomes

119 Clipstone NA, Crabtree GR. Identification of calcineurinand economics. Clin Chem 1998; 44: 370–374.as a key signalling enzyme in T-lymphocyte activation.100 Schumacher GE, Barr JT. Bayesian and thresholdNature 1992; 357: 695–697.probabilities in therapeutic drug monitoring: when can

120 Batiuk TD, Pazderka F, Halloran PF. Calcineurin activity isserum drug concentrations alter clinical decisions? Amonly partially inhibited in leukocytes of cyclosporine-treatedJ Hosp Pharm 1994; 51: 321–327.patients. Transplantation 1995; 59: 1400–1404.101 Holt DW, White DJ. How to measure cyclosporin. Lancet

121 Eugui EM, Almquist SJ, Muller CD, Allison AC.1984; ii: 228.Lymphocyte-selective cytostatic and immunosuppressive102 Johnston A, Cullen G, Holt DW. Quality assurance foreffects of mycophenolic acid in vitro: role ofcyclosporin assays in body fluids. Ann Acad Med Singaporedeoxyguanosine nucleotide depletion. Scand J Immunol1991; 20: 3–8.1991; 33: 161–173.103 Lindholm A, Dahlqvist R, Groth GG, Sjoqvist F. A

122 Langman LJ, LeGatt DF, Halloran PF, Yatscoff RW.prospective study of cyclosporine concentration in relationPharmacodynamic assessment of mycophenolic acid-to its therapeutic effect and toxicity after renalinduced immunosuppression in renal transplant recipients.transplantation. Br J Clin Pharmacol 1990; 30: 443–452.Transplantation 1996; 62: 666–672.104 Johnston A, Holt DW. Calibration of the CYCLO-Trac

123 Yatscoff RW, Aspeslet LJ, Gallant HL. PharmacodynamicSP cyclosporine radioimmunoassay. Clin Chem 1993; 39:monitoring of immunosuppressive drugs. Clin Chem 1998;2532–2533.44: 428–432.105 McLachlan AJ, Tett SE. Effect of metabolic inhibitors on

124 Chung J, Kuo CJ, Crabtree GR, Blenis J. Rapamycin-cyclosporine pharmacokinetics using a population approach.FKBP specifically blocks growth-dependent activation of

Ther Drug Monit 1998; 20: 390–395.and signaling by the 70 kd S6 protein kinases. Cell 1992;

106 Schutz E, Svinarov D, Shipkova M, et al. Cyclosporin69: 1227–1236.

whole blood immunoassays (AxSYM, CEDIA, and Emit):125 Gallant HL, Yatscoff RW. P70 S6 kinase assay: a

A critical overview of performance characteristics andpharmacodynamic monitoring strategy for rapamycin; assay

comparison with HPLC. Clin Chem 1998; 44: 2158–2164. development. Transplant Proc 1996; 28: 3058–3061.107 Taylor PJ, Hogan NS, Lynch SV, Johnson AG, Pond SM. 126 Clark K. Monitoring antithymocyte globulin in renal

Improved therapeutic drug monitoring of tacrolimus transplantation. Ann Roy Coll Surg Engl 1996; 78: 536–540.(FK506) by tandem mass spectrometry. Clin Chem 1997; 127 Bogaert M. [Drug policy 1996]. [Dutch]. Verh K Acad43: 2189–2190. Geneeskd Belg 1997; 59: 227–236.

108 Schambeck CM, Bedel A, Keller F. Limit of quantitation 128 Ensom MH, Davis GA, Cropp CD, Ensom RJ. Clinical(Functional Sensitivity) of the new IMx Tacrolimus II pharmacokinetics in the 21st century. Does the evidencemicroparticulate immunoassay. Clin Chem 1998; 44: support definitive outcomes? Clin Pharmacokinet 1998; 34:2217–?. 265–279.

109 Holt DW, Jones K, Johnston A, et al. An immunoassay for 129 Destache CJ. Use of therapeutic drug monitoring inthe measurement of sirolimus. Clin Chem 1998; 44: 6 pharmacoeconomics. Ther Drug Monit 1993; 15: 608–610.(suppl), A94–?. 130 Shaw LM, Kaplan B, Brayman KL. Prospective

110 Soldin SJ. Role of immunophilins in therapeutic drug investigations of concentration-clinical response formonitoring of immunosuppressive drugs. Clin Biochem immunosuppressive drugs provide the scientific basis for1998; 31: 381–384. therapeutic drug monitoring. Clin Chem 1998; 44:

111 Johnston A, Holt DW. External quality assessment scheme 381–387.for cyclosporin in body fluids. Scand J Clin Lab Invest Suppl 131 Johnston A, Holt DW. Concentration-controlled trials.1993; 212: 48–53. What does the future hold? Clin Pharmacokinet 1995; 28:

112 Holt DW, Johnston A. Tacrolimus quality assessment. Ther 93–99.Drug Monit 1997; 19: 243. 132 Laskow DA, Vincenti F, Neylan JF, Mendez R, Matas

113 Holt DW, Jones K, Lee T, Stadler P, Johnston A. Quality AJ. An open-label, concentration-ranging trial of FK506 inassessment issues of new immunosuppressive drugs and primary kidney transplantation: a report of the Unitedexperimental experience. Ther Drug Monit 1996; 18: States Multicenter FK506 Kidney Transplant Group.362–367. Transplantation 1996; 62: 900–905.

114 Cyclosporin International Proficiency Testing Scheme 133 Ponticelli C, Tarantino A. Immunosuppressive protocols forURL: www.asil.demon.co.uk. renal transplantation. Nephrol Dial Transplant 1997;

115 Holt DW, Johnston A. Monitoring immunosuppressive 12(Supplement 1): 45–50.drugs: The rational for proficiency testing. Ligand Assay 134 Johnston A, Holt DW. Generic substitution for1998; 3: 2–6. cyclosporine: What should we be looking for in a new

formulation. Transplant Proc 1998; 30: 1652–1653.116 Salmaggi A, Corsini E, La ML, et al. Immunological



135 Al Meshal MA, Khidr SH, Bayomi MA, Al Angary AA. 137 Schuler W, Sedrani R, Cottens S, et al. SDZ RAD, a newOral administration of liposomes containing cyclosporine: A rapamycin derivative: pharmacological properties in vitropharmacokinetic study. Int J Pharmaceutics 1998; 168: and in vivo. Transplantation 1997; 64: 36–42.163–168. 138 Bach FH. Xenotransplantation: problems and prospects.

136 Troncoso P, Kahan BD. Preclinical evaluation of a new Ann Rev Med 1998; 49: 301–310.immunosuppressive agent, FTY720. Clin Biochem 1998; 31:369–373.


Documents

Therapeutic Drug Monitoring of Immunosuppressant Drugs in Marmara University Hospital