Immunosuppression Monitoring-What Clinician Needs to Know?

The liver is well known for its immunotolerance, but rejection without immunosuppression is frequently encountered post liver transplantation, especially in humans.1 Indeed, the amount of immunosuppression required post liver transplant is less compared to other organ transplants like kidney, heart, and intestine.2 Reports of successful weaning of immunosuppression have been reported but are not practiced for fear of unwanted alloimmune response leading to rejection. Life-long immunosuppression is needed in most patients for graft survival but is associated with side effects like renal dysfunction, metabolic abnormalities, or risk of de novo malignancies. Also, the appropriate dose of immunosuppression to achieve adequate graft function and prevention of toxicities is very important. One shoe does not fit all. There are significant individual variations in response and side effect profile. Also, the level of immunosuppression varies with the underlying liver disease like autoimmune disease requires higher immunosuppression. Thus, monitoring the adequate immunosuppression with the minimization of drug toxicity is imperative post-transplant. Unfortunately, the current methods for immunosuppression monitoring rely on testing the immunosuppressive drug levels rather than the immune system activity. We have discussed the concept of alloreactivity, available methods of immunosuppression and drug monitoring and investigational methods in this review.

Therapeutic Drug Monitoring of Mycophenolic Acid

Mycophenolic acid (MPA) is an immunosuppressant requiring therapeutic drug monitoring. Although immunoassays are commercially available, there is significant positive bias using this approach when compared to high-performance liquid chromatography or LC combined with mass spectrometry (LC/MS) or tandem mass spectrometry (LC/MS/MS). Positive bias is due to variable cross-reactivity of MPA acyl glucuronide with antibodies traditionally used in immunoassay formats. As can be expected, the magnitude of bias varies considerably. MPA strongly binds albumin and, as a result, disproportionate increases in free MPA occur in patients with uremia, hypoalbuminemia, and hepatic dysfunction. As such, monitoring free MPA poses additional challenges. Because MPA inhibits inosine monophosphate dehydrogenase, monitoring this enzyme may provide an alternative approach.

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

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.

Immunosuppression and transplant vascular disease: benefits and adverse effects

Cardiac allograft vasculopathy (CAV) occurs within 5 years of transplantation surgery and represents the main cause of death in long-term heart transplant survivors. The detailed pathogenesis of CAV is unknown, but there are strong indications that immunologic mechanisms, which are regulated by nonimmunologic factors, are the major cause of this phenomenon. Cyclosporine A (CsA) is a frequently used immunosuppressive agent in transplant medicine to prevent rejection. The mechanism of action of CsA involves initial binding to cyclophilin to form a complex that then inhibits calcineurin (CN), leading to reduced interleukin (IL)-2 production as part of the signal transduction pathway for the activation of B-lymphocytes and T-lymphocytes. Based on this proposed mechanism, it was expected that CsA should be an effective strategy in attenuating the host immune response against transplanted allograft tissue; however, CsA has not changed the outcome of CAV. Several mechanisms have been suggested for the ineffectiveness of CsA in long-term prevention of CAV. For example, routine therapeutic doses of CsA may block CN incompletely (50%), whereas complete blockade requires doses that are not clinically tolerable. Another explanation is the possible activation of T-cell receptors directly (CN independent) by the immune response, which induces protein kinase C theta (PKCtheta) and leads to IL-2 production and immune rejection. Moreover, there may be a role for nonimmunologic mechanisms, such as complement, which cannot be controlled by CsA, or CsA may cause hypercholesterolemia or induce overexpression of transforming growth factor-beta (TGF-beta). This review also compares the effect of CsA with other immunosuppressants in allograft artery preservation and their clinical efficacy.

Development of a HPLC method for the determination of cyclosporin-A in rat blood and plasma using naproxen as an internal standard

An isocratic reversed phase high-performance liquid chromatographic (HPLC) method with ultraviolet detection at 205 nm has been developed for the determination of cyclosporin-A (CyA) in rat blood and plasma. Naproxen was successfully used as an internal standard. Blood or plasma samples were pretreated by liquid-liquid extraction with diethyl ether. The ether extract was evaporated and the residue was reconstituted in acetonitrile-0.04 M monobasic potassium phosphate buffer (pH 2.5) solvent mixture. After washing with n-hexane, 30 microl of the reconstituted solution was injected into HPLC system. Good chromatographic separation between CyA and internal standard peaks was achieved by using a stainless steel analytical column packed with 4 microm Nova-Pak Phenyl material. The system was operated at 75 degrees C using a mobile phase consisting of acetonitrile-0.04 M monobasic potassium phosphate (pH 2.5) (65:35 v/v) at a flow rate of 1 ml/min. The calibration curve for CyA in rat blood was linear over the tested concentration range of 0.0033-0.0166 M with a correlation coefficient of 0.989. For rat plasma, the range of the concentrations tested were between 0.002 and 0.0166 M and showed linearity with a correlation coefficient of 0.953. The intra- and inter-run precision and accuracy results were 1.24-21.87 and 3.1-12.23%, respectively. The low volume of blood or plasma needed (200 microl), simplicity of the extraction process, short run time (5 min) and low injection volume (30 microl) make this method suitable for quick and routine analysis.

Red blood cells: a neglected compartment in topotecan pharmacokinetic analysis

Previously, a gender dependency of topotecan was found in the pharmacokinetics in the plasma compartment. Here, we prospectively studied the red blood cell (RBC) partitioning of topotecan and evaluated its consequences for overall drug disposition. Blood samples were obtained from 12 patients receiving cisplatin followed by i.v. topotecan. Topotecan pharmacokinetic analysis was performed in whole blood, plasma and RBCs. Significantly slower clearance was noted in females (n=7) compared to males (n=5) for lactone and total topotecan in plasma (p<0.0001), and for total drug in RBCs (p=0.027), but not in whole blood. In addition, no gender-dependent differences were observed in the terminal half-lives of topotecan in any of the compartments. The area under the curve ratios for RBC total to plasma lactone were 2.53+/-0.0640 and 2.13+/-0.442 in males and females, respectively. Hence, topotecan displays preferential affinity for RBCs compared to plasma, although these cells do not act as a depot in which drug accumulates over time. RBCs thus play a principal role in the distribution kinetics of topotecan and have a major impact on its plasma pharmacokinetics. The data warrant a change from current practice in pharmacokinetic studies with this agent and provide further evidence that, in general, the choice of the appropriate assay matrix should be rationally based.

Distribution of cyclosporin in organ transplant recipients

Cyclosporin is an immunosuppressive agent with a narrow therapeutic index. The total concentration of cyclosporin in blood is usually monitored to guide dosage adjustment and to compensate for substantial interindividual and intraindividual variability in cyclosporin pharmacokinetics. Cyclosporin is a highly lipophilic molecule and widely distributes into blood, plasma and tissue components. It mainly accumulates in fat-rich organs, including adipose tissue and liver. In blood, it binds to erythrocytes in a saturable fashion that is dependent on haematocrit, temperature and the concentration of plasma proteins. In plasma, it binds primarily to lipoproteins, including high-density, low-density and very-low-density lipoprotein, and, to a lesser extent, albumin. The unbound fraction of cyclosporin in plasma (CsA(fu)) expressed as a percentage is approximately 2%. It has been shown that both the pharmacokinetic and pharmacodynamic properties of cyclosporin are related to its binding characteristics in plasma. Furthermore, there is some evidence to indicate that the unbound concentration of cyclosporin (CsA(U)) has a closer association with both kidney and heart allograft rejection than the total (bound + unbound) concentration. However, the measurement of CsA(fu) is inherently complex and cannot easily be performed in a clinical setting. Mathematical models that calculate CsA(fu), and hence CsA(U), from the concentration of plasma lipoproteins may be a more practical option, and should provide a more accurate correlate of effectiveness and toxicity of this drug in transplant recipients than do conventional monitoring procedures. In conclusion, the distribution characteristics of cyclosporin in blood, plasma and various tissues are clinically important. Further investigations are needed to verify whether determination of CsA(U) improves the clinical management of transplant recipients.

Evaluation of a No-Pretreatment Cyclosporin A Assay on the Dade Behring Dimension RxL Clinical Chemistry Analyzer

Background: Monitoring whole-blood concentrations of cyclosporin A (CsA) is common practice in the management of solid organ and bone marrow transplant recipients. In a multicenter study we evaluated a new, direct (no pretreatment) CsA assay on the Dade Behring Dimension RxLTM system and compared results with those from the Abbott TDx CsA immunoassay and a HPLC method.

Methods: Whole-blood samples from heart (n = 111; 35 patients), liver (n = 201; 44 patients), kidney (n = 279; 65 patients), and miscellaneous organ (n = 77; 12 lung, 12 bone marrow, 5 kidney/pancreas, and 1 pancreas patient) recipients were obtained from patient populations of the participating institutions. Routine clinical monitoring of CsA was performed using either the TDx method or HPLC.

Results: The minimum detectable concentration of CsA averaged 9.4 μg/L, and the lower limit of quantification was 30 μg/L. The method was linear from 30 to 500 μg/L. Cross-reactivity with seven different CsA metabolites ranged from 0.0% to 5.7% for the Dimension RxL assay compared with 0.4–15.9% for the TDx assay. Total imprecision (CV) averaged 6.2%, and within-run imprecision averaged 4.9%. Passing–Bablok linear regression analyses of all samples from two sites yielded the following: RxL = 0.81 × TDx − 16.8; and RxL = 1.12 × HPLC − 1.7.

Conclusions: The Dade Behring CsA assay for the random-access Dimension platform offers adequate performance characteristics for routine clinical use, does not require a manual pretreatment step, and demonstrates less cross-reactivity with CsA metabolites than another commonly used immunoassay.

In-vivo distribution and erythrocyte binding characteristics of cyclosporin in renal transplant patients

The pharmacokinetic parameters of cyclosporin, a potent immunosuppressive agent, show large intra- and inter-individual variability, possibly because of the different analytical methods used. A recently developed cyclosporin-specific radioimmunoassay has been used to study the in-vivo distribution and binding characteristics of cyclosporin in whole blood, plasma and erythrocytes of fifteen renal transplant patients. The profiles of cyclosporin concentration-time curves after an oral dose of cyclosporin had either one peak (ten patients, group A) or two (five patients, group B). Essentially no difference was observed between the two groups in the relationship between equilibrium cyclosporin concentrations in erythrocyte and plasma as a function of whole-blood concentration. The equilibrium in-vivo cyclosporin concentrations in erythrocyte and plasma were, however, markedly lower than those previously observed under in-vitro conditions. The ratio of cyclosporin concentration in erythrocytes (CE) to that in plasma (CP) changed with time, in inverse proportion to the change in cyclosporin concentration in blood, over the range 0.63-2.80 in individual patients with an average of 1.36 +/- 0.07 (mean +/- s.e.m.) for group A and 1.42 +/- 0.23 for group B. The apparent cyclosporin binding affinity (Kd) to erythrocytes under in-vivo conditions averaged 452.2 +/- 47.6 nM (543.5 +/- 57.2 ng mL-1) for group A and 419.4 +/- 41.2 nM (504.1 +/- 49.5 ng mL-1) for group B, whereas apparent cyclosporin binding capacity (Bmax) of the blood cell averaged 0.83 +/- 0.07 nmol mL-1 for group A and 0.78 +/- 0.07 nmol mL-1 for group B. Significantly reduced average Kd (262.7 +/- 40.2 nM or 315.8 +/- 48.9 ng mL-1, P < 0.01) and Bmax (0.56 +/- 0.08 nmol mL-1, P < 0.05) values were observed during the period after Tmax (4-12 h after the drug ingestion) in group A patients. Apparent Kd and Bmax, determined by a nonlinear regression technique, were 131.6 +/- 29.4 and 1088.0 +/- 114.7 nM (158.2 +/- 35.4 and 1307.8 +/- 137.9 ng mL-1) and 0.178 +/- 0.024 and 0.814 +/- 0.078 nmol mL-1, respectively, during the 4-12 h period in group A patients. These findings reveal distinct differences in in-vivo distribution of cyclosporin and the binding characteristics of the compound to erythrocytes from those previously observed under in-vitro conditions. The significantly lower Kd of cyclosporin binding to erythrocytes during the elimination phase suggests a potential effect of cyclosporin-containing erythrocytes or of cyclosporin contained in erythrocytes during cyclosporin treatment.

Gel chromatographic analysis of cyclosporin and its metabolites in human blood compartments

Gel chromatography combined with specific and non-specific cyclosporin radioimmunoassays was adopted for quantitative analysis of cyclosporin and metabolites in free and protein-bound forms in blood compartments of kidney transplant patients. The analytical method was proved to be useful for the purpose, although plasma protein-bound forms of neither cyclosporin nor metabolites could be quantitated in the system. The present study also provided, by gel chromatographic analysis, additional examples to prove that concentrations of cyclosporin metabolites in blood compartments may not be deduced or inferred simply from those of cyclosporin.

Distribution kinetics of FK-506, a novel immunosuppressant, after intravenous administration to rats in comparison with cyclosporin A

The distribution kinetics of a novel potent immunosuppressant, FK-506 (FK) has been studied in comparison with cyclosporin A (CyA) both in vivo and in vitro using blood specimens. The infusion studies on FK, 5.0 mg kg-1 through the portal and femoral veins showed that the mean hepatic extraction ratio of FK was 27.9 per cent. The effect of clamping both the hepatic artery and the portal vein on the plasma disappearance profiles of FK, 5.0 mg kg-1, and CyA, 3.5 mg kg-1 was studied. The plasma disposition kinetics of CyA was almost the same as in the normal rats. However, the plasma FK levels were about 10 times higher than those obtained in the control group rats. This difference is attributed to the restricted initial distribution of FK to the liver, because the volume of the initial distribution space, V1, of FK was about 10 times smaller than that obtained in normal rats. In in vitro experiments, drug distribution was studied in blood samples (2.0 ml) spiked with FK or CyA, 1.0 micrograms ml-1. The plasma drug levels measured at 2 min after drug administration were 0.842 +/- 0.012 micrograms ml-1 and 0.769 +/- 0.047 micrograms ml-1 for FK and CyA, respectively. The distribution volume in the blood compartment, VB, was determined by dividing the spiked amount of drugs with these plasma concentrations. The VB was 2.38 +/- 0.04 ml for FK and 2.62 +/- 0.16 ml for CyA. There was no significant difference in VB between FK and CyA. The plasma free fraction, fp of the drugs was measured by the equilibrium dialysis method. For FK, the mean fp values (+/- SE) were 1.31 +/- 0.18 per cent (2.0 micrograms ml-1) and 1.93 +/- 0.18 per cent (5.0 micrograms ml-1). For CyA, the fp values were 4.85 +/- 0.36 per cent (1.0 micrograms ml-1) and 5.75 +/- 0.82 per cent (5.0 micrograms ml-1). The hydrophobicity parameter, logP' determined through the HPLC method was 0.386 for FK and 0.545 for CyA. Although FK was less hydrophobic than CyA, its protein binding was higher than CyA.

Practical aspects in the use of cyclosporin in paediatric nephrology

Many factors must be considered for the effective and safe use of cyclosporin A (CsA) in paediatric nephrology. Detailed knowledge of the variable bioavailability, tissue distribution, and metabolism, as well as causes which lead to their alteration are necessary. Factors which affect the activity of the mixed function oxidase system cytochrome P-450 must be considered, i.e. liver dysfunction and many drugs. Precise knowledge of the CsA determination method and the spectrum of metabolites is essential. In children with renal transplants, a body surface area-related dose will better meet the dose requirements than a body weight related-dose. For drug level monitoring whole blood rather than plasma should be used, and the parent drug level should be the main determinant; elevated metabolite levels may be important in suspected nephrotoxicity or liver dysfunction. Pharmacokinetic profiles are necessary to discover absorption problems or increased CsA clearance rates which necessitate shorter dosing intervals. In children with steroid-dependent minimal change nephrotic syndrome, remission without steroids is maintained as long as CsA is given. The appropriate starting dosage is 150 mg/m2 per day; trough level monitoring is mandatory to prevent nephrotoxicity and to confirm adequate immunosuppressive drug levels which should be 80-160 ng/ml (parent drug level). Although the benefit of CsA has been reported in some cases of lupus erythematosus, its use should be restricted to severe cases only until its efficacy and safety has been confirmed in controlled trials.

Cyclosporin A and its metabolites, distribution in blood and tissues

Cyclosporin A (CsA), a non-myelotoxic immunosuppressant, and its metabolites are widely distributed in the body. Highest concentrations of CsA have been detected in the pancreas, adipose tissue and liver, lowest concentrations in brain, muscle, blood and other body fluids. Metabolites are distributed differently to CsA. In addition to lipid partition, intracellular binding to cyclophilin, a peptidyl-prolyl cis-trans isomerase, appears to play a role in its tissue distribution. The temperature dependence of such binding in erythrocytes poses difficulty in serum or plasma measurements. Tissue specific processes may also influence action and toxicity of CsA and its metabolites; thus, a better understanding of the complex distribution pattern of CsA and its metabolites would be important for establishing improved strategies and selection of appropriate specific methodologies for drug monitoring.

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.

The effects of haematocrit, plasma protein concentration and temperature of drug-containing blood in-vitro on the concentrations of the drug in the plasma

Factors which influence the plasma drug concentrations in whole blood have been investigated in-vitro using human blood containing radio-labelled phenytoin or chlorpromazine. Phenytoin (3.55 micrograms mL-1, 0.01 mM) or chlorpromazine (2.74 micrograms mL-1, 0.01 mM) was mixed with normal or modified blood and the plasma drug level was measured. Plasma phenytoin and chlorpromazine levels decreased with decrease in the protein concentration of plasma, but were not influenced by addition of gamma-globulin to the blood specimen. Plasma phenytoin levels increased with an increase in haematocrit from 20 to 45%, whereas the chlorpromazine level remained constant. The partition coefficients of phenytoin and chlorpromazine between blood cells and plasma were almost the same at various haematocrit values. By cooling the blood containing each drug to 4 degrees C, plasma phenytoin and chlorpromazine levels were higher compared with those at 37 degrees C. Similar temperature effects on the drug levels in plasma were obtained when the washed erythrocytes were resuspended in albumin medium, but not when resuspended in saline.

Influence of demographic factors on cyclosporine pharmacokinetics in adult uremic patients

The causes of variability in cyclosporine (CS) clearance (CL) are mostly unknown. The pharmacokinetics of CS were studied in 30 adult uremic patients after single intravenous and oral doses by analyzing serial concentrations in serum by radioimmunoassay (SR) and in whole blood by radioimmunoassay (WR) and high pressure liquid chromatography (WH). Bioavailability (F) and CL were calculated by noncompartmental models and were significantly different depending upon the assay method except for FSR = FWR: FSR = 43.2 +/- 21.7%; FWR = 43.5 +/- 18.5%; FWH = 36.4 +/- 17.3%; CLSR = 849 +/- 363 ml/min; CLWR = 380 +/- 156 ml/min; CLWH = 559 +/- 174 ml/min. The age of the patients and parameters describing body size such as weight, surface area and percent of ideal weight were not correlated with CL. The height of the patients correlated with CLWH but not CLSR or CLWR. Parameters responsible for CS binding in blood such as cholesterol, triglyceride, hemoglobin concentration or hematocrit did not explain variability in CL. Of the factors indicative of liver function alanine transaminase activity but not aspartate transaminase, lactate dehydrogenase, alkaline phosphatase activity nor total bilirubin concentration in serum was correlated with CL. F was not correlated with any of the demographic factors except for alanine transaminase. None of the significant correlations explained enough of the variability to afford a reliable prediction of CL or F.

A simple improved method for the measurement of cyclosporin by liquid-liquid extraction of whole blood and isocratic HPLC

The current HPLC methods of cyclosporin measurement have been reviewed and all aspects assessed. A simple isocratic C-18 reverse phase HPLC method with improved efficiency is described for the routine measurement of cyclosporin in whole blood. An alkaline ether extraction is followed by an acid wash, solvent evaporation and two hexane washes of the reconstituted extract. The turn-round time for a single sample is 1 h. Daily batches of up to 40 patient samples can be easily measured with this method. The results are compared with those from the Sandoz radioimmunoassay (RIA) method.

The influence of haematocrit on blood cyclosporin measurements in vivo

The influence of haematocrit on blood cyclosporin measurements has been studied in 276 paired blood and plasma samples from 21 renal transplant patients. A highly significant correlation was found between blood and plasma cyclosporin concentrations, r = 0.8744, but the correlation between blood or plasma cyclosporin and haematocrit was not significant. The ratio of blood/plasma cyclosporin did not significantly increase with increasing haematocrit. It was concluded that in vivo the influence of haematocrit on the measurement of blood cyclosporin concentrations was negligible.

Adverse reactions and interactions of cyclosporin

Cyclosporin is a potent, widely used specific immunosuppressive agent which affects T-helper cells, and has little myelotoxicity. Its pharmacokinetics are complex and many of its actions remain poorly understood. Numerous side effects have been reported, affecting most organs. Most troublesome have been renal injury, systemic hypertension and vascular changes. Oral use is more effective than intramuscular and safer than the intravenous route. Interactions with other drugs include those which affect hepatic metabolism and those which reduce clearance. Aminoglycosides, macrolide antibiotics, imidazole derivatives, calcium channel blockers, sulphonamides and steroids are included in such interactions. Other metabolic effects of cyclosporin are more subtle and include hyperchloraemic alkalosis, changes in serum potassium and magnesium and effects on testosterone and prolactin levels. Acute poisoning with cyclosporin has been reported, again without myelosuppression. Cyclosporin is an important agent with multisystem toxicity, which requires precise monitoring of drug concentrations, liver and renal function, haemoglobin levels and plasma electrolytes. Cyclosporin pharmacodynamics and interactions with other drugs need to be carefully considered if lower rates of toxicity are to be achieved.

Blood protein binding of cyclosporine in transplant patients

The objective of this study was to compare the binding of cyclosporine to blood proteins between four healthy subjects and five liver and eight renal transplant patients. Fresh heparinized blood was obtained, to which sufficient quantities of tritium-labelled cyclosporine and unlabelled cyclosporine were added to blood samples or red blood cell (RBC) suspensions. Concentrations of cyclosporine in whole blood, plasma, RBC suspension, and phosphate buffer were estimated by liquid scintigraphy. The blood:plasma ratio of cyclosporine in transplant patients was significantly lower (P less than .05) than that in healthy volunteers. The RBC:buffer ratio, a measure of affinity of RBCs for cyclosporine, was highest in those with liver transplants and lowest in those with kidney transplants. The unbound fraction of cyclosporine in plasma was less in transplant patients than in healthy volunteers. The results of this study indicate that there are differences in blood protein binding of cyclosporine between transplant patients that may contribute to the differences in the pharmacokinetics and pharmacodynamics of this drug.

Liquid chromatographic determination of cyclosporin A in serum with use of a solid-phase extraction. Comparison between high-performance liquid chromatography and radioimmunoassay levels in clinical investigations

A simple reliable liquid chromatographic method for assay of cyclosporin A in serum or urine is described. Samples were cleaned up on a solid-phase extraction system (cyanopropyl column). The system involved a reversed-phase C18 Ultrasphere column maintained at 72 degrees C and an acetonitrile linear gradient (65 to 95%) in 0.14% triethylammonium phosphate. Liquid chromatographic analysis of radioimmunoassay standards shows that some samples contain a contaminant peak. Comparison of cyclosporin A levels obtained by radioimmunoassay and high-performance liquid chromatography in clinical investigations show that the former values are generally, but not always, higher than the latter, and that cyclosporin A is very differently metabolized depending on the patient, disease and treatment.

Liquid chromatographic determination of cyclosporine in whole blood with the advanced automated sample processing unit

We describe a rapid, precise, cost-effective, and accurate isocratic liquid chromatographic (LC) procedure for determining cyclosporine in whole blood. The cyclosporine is extracted from 0.5 ml of whole blood together with 200 micrograms of cyclosporin D, added per liter as internal standard, by using an Advanced Automated Sample Processing (AASP) unit. The on-line solid-phase extraction is performed on an octasilane sorbent cartridge which is interfaced with a Perkin-Elmer 83 X 4.6 mm I.D. cartridge column, packed with 3-micron octadecyl packing. The column is eluted with a mobile phase containing acetonitrile-water (13:7) at a flow-rate of 1.0 ml/min at a column temperature of 70 degrees C. The column effluent is monitored at 210 nm. The absolute recovery of cyclosporine exceeded 87% and the linearity extended up to 2000 micrograms/l. Within-run and day-to-day coefficients of variation were less than 8%. The correlation between AASP-LC and manual Bond-Elut extraction-LC method was excellent (r = 0.97).

Cyclosporine: structure, pharmacokinetics, and therapeutic drug monitoring

Cyclosporine is an 11-amino acid cyclic peptide immunosuppressant that has revolutionized organ transplantation. Alone or in combination with prednisone and azathiaprine, it is preferred in hepatic, cardiac, and high-risk renal transplantation. Its unusual primary structure of hydrophobic, N-methylated amino acids results in a compact conformation in the crystal which changes to multiple conformations in hydrophilic solvents. The unusual structure produces unusual pharmacokinetic behavior which is still poorly understood. The metabolism occurs predominately in the liver and is affected by several drugs known to alter hepatic metabolism. At least ten metabolites have been identified but are inadequately characterized. The unique behavior of cyclosporine necessitates therapeutic drug monitoring (TDM) for individualization of therapy. Cyclosporine has been monitored in both whole blood and plasma by both RIA and HPLC with significantly different results for each combination. When cyclosporine is assayed by HPLC in a compulsive regimen of TDM, a correlation is observed between immunosuppression, toxicity, and concentration. To distinguish renal or hepatic toxicity from rejection, biopsies, clinical status, and blood concentrations of cyclosporine must be simultaneously analyzed. After extensive experimental and clinical study, cyclosporine remains an enigma with clear clinical benefit.