Therapeutic drug monitoring of cyclosporin. Practical applications and limitations

Evaluation of drug interaction between cyclosporine and lercanidipine: a descriptive study

OBJECTIVES

Cyclosporine is an immunosuppressive drug with a high potential for drug interactions that is frequently used in renal transplant patients. The purpose of this study was to assess the change in cyclosporine concentration in patients taking cyclosporine and lercanidipine concurrently.

METHODS

The potential drug interactions in renal transplant patients who received lercanidipine and cyclosporine concurrently in a university hospital between January 2008 and January 2018 were evaluated retrospectively. Patients had renal transplantation from deceased donors or living related donors. The Drug Interaction Probability Scale (DIPS) criteria were used to assess the causality of cyclosporine and lercanidipine drug interaction.

RESULTS

The study included six renal transplant patients. The median cyclosporine concentration before lercanidipine use was 325 ng/mL (min-max 101-356) and 592.5 ng/mL (min-max 198-799) thereafter (p=0.028). Serum creatinine and proteinuria levels did not change significantly during lercanidipine treatment (p=0.686 and p=0.116, respectively). According to the DIPS evaluation, cyclosporine and lercanidipine interaction was classified as "possible (score 3)".

CONCLUSIONS

Concomitant use of cyclosporine and lercanidipine increases the concentration of cyclosporine, which may result in side effects during effective treatment in renal transplant patients. Therefore, cyclosporine concentrations should definitely be monitored while patients are taking lercanidipine.

Cyclosporine A trough concentrations are associated with acute GvHD after non-myeloablative allogeneic hematopoietic cell transplantation

Low plasma CsA concentrations (<300–350 ng/mL) early following allogeneic hematopoietic stem cell transplantation (HSCT) is associated with an increased risk of developing acute graft-versus-host disease (aGvHD). Nevertheless, the current optimal target trough concentration for CsA following HSCT is considered to be 200–400 ng/mL. Here, we performed a retrospective analysis of a homogeneous group of 129 patients who received HSCT after non-myeloablative conditioning, and we analyzed the impact of CsA trough concentration measured during the first four weeks (CsA W1-4) on the incidence aGvHD, relapse-free survival (RFS), non-relapse mortality (NRM), overall survival (OS), and toxicity. The 180-day incidence of grade II-IV aGvHD was 25% (32/129 patients). In multivariate analysis the incidence of grade II-IV aGvHD was significantly lower among patients with a CsA W1-4 concentration ≥350 ng/mL compared to patients with a concentration <350 ng/mL (18% versus 38%, respectively; P = 0.007), with a hazard ration (HR) of 0.38 (95% CI: 0.19–0.77). In contrast, we found no correlation between CsA trough concentration and RFS, NRM, or OS. Moreover, we found an increased incidence of hypomagnesemia at higher CsA concentrations, but no difference in the incidence of acute renal toxicity, hepatic toxicity, or electrolyte imbalance. Interestingly, 30% of patients experienced hyponatremia with no apparent cause other than the use of CsA, with urinalysis suggesting SIADH as the underlying cause. Our findings suggest that a CsA trough concentration of 350–500 ng/mL might be more appropriate in the first month following non-myeloablative HSCT.

Therapeutic reference range for plasma concentrations of paroxetine in patients with major depressive disorders

BACKGROUND

We investigated the relationship between plasma concentrations of paroxetine and the therapeutic effect of the drug, and we evaluated the therapeutic reference range for plasma concentration of paroxetine in patients with major depressive disorders (MDD).

METHODS

In this study, 120 patients with MDD were treated with 10-40 mg/d of paroxetine for 6 weeks, and 89 patients completed the protocol. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate the patients at 0, 1, 2, 4, and 6 weeks. At the 6-week treatment time point, the patients were divided into 7 groups according to their paroxetine plasma concentrations in increments of 20 ng/mL. We used an analysis of variance and a χ test to define the therapeutic reference range for plasma paroxetine concentrations.

RESULTS

We used 50% as the cutoff values for the percentage of MADRS improvement to determine the responder rates, and we defined remitters as patients with MADRS scores <10 at the 6-week treatment time point. We analyzed the responder and remitter rates of the patients according to their plasma paroxetine concentrations: 20 ng/mL, 40 ng/mL, and 60 ng/mL using the χ test. According to the results of the χ test in the responder rates, the 20-60 ng/mL plasma paroxetine group showed the highest effect size.

CONCLUSIONS

The results of this study suggested that a range of 20-60 ng/mL is the therapeutic reference range for concentrations of paroxetine in plasma in patients with MDD.

The influence of 5-HTTLPR genotype on the association between the plasma concentration and therapeutic effect of paroxetine in patients with major depressive disorder

INTRODUCTION

The efficacy of treatment with selective serotonin reuptake inhibitors in patients with major depressive disorder (MDD) can differ depending on the patient's serotonin transporter-linked polymorphic region (5-HTTLPR) genotype, and the effects of varying plasma concentrations of drugs can also vary. We investigated the association between the paroxetine plasma concentration and clinical response in patients with different 5-HTTLPR genotypes.

METHODS

Fifty-one patients were enrolled in this study. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate patients at 0, 1, 2, 4, and 6 weeks. The patients' paroxetine plasma concentrations at week 6 were measured using high-performance liquid chromatography. Additionally, their 5-HTTLPR polymorphisms (alleles S and L) were analyzed using a polymerase chain reaction with specific primers. We divided the participants into two groups based on their L haplotype: the SS group and the SL and LL group. We performed single and multiple regression analyses to investigate the associations between MADRS improvement and paroxetine plasma concentrations or other covariates for each group.

RESULTS

There were no significant differences between the two groups with regard to demographic or clinical data. In the SS group, the paroxetine plasma concentration was significantly negatively correlated with improvement in MADRS at week 6. In the SL and LL group, the paroxetine plasma concentration was significantly positively correlated with improvement in MADRS at week 6 according to the results of the single regression analysis; however, it was not significantly correlated with improvement in MADRS at week 6 according to the results of the multiple regression analysis.

CONCLUSION

Among patients with MDD who do not respond to paroxetine, a lower plasma concentration or a lower oral dose of paroxetine might be more effective in those with the SS genotype, and a higher plasma concentration might be more effective in those with the SL or LL genotype.

Bile and blood ratios of cyclosporin and its metabolites in patients on continuous infusion during the first three weeks after liver transplantation

Ten patients with orthotopic liver transplants were investigated during routine therapeutic monitoring to study the relationship between the concentrations of cyclosporin and its metabolites in blood, bile and urine, and whether this information can provide early signs of severe hepatic disorders post-transplantation. Cyclosporin (Sandimmun®) was administered by continuous infusion at a constant rate of 5 mg/kg/day, modified to keep the blood cyclosporin concentration within the target range (400 to 500 μg/L). The concentrations of cyclosporin and combined cyclosporin-metabolites in blood, bile and urine were assayed daily during the 3 post-transplantation weeks that the patients spent in intensive care.All patients developed cholestatis and cytolysis during the first week. The severity of these liver transplant disorders increased in 5 patients and decreased in the other 5 in the second week. The pharmacokinetics of cyclosporin differed in the 2 groups: in patients without severe hepatic disorders, the blood metabolites/cyclosporin ratio (M/C) stabilised at 1.2 ± 0.4 in week 2 and at 0.8 ± 0.2 in week 3, bile cyclosporin/blood cyclosporin (bile C/blood C) fluctuated around 13.5 (13.5 ± 9.5 in week 2 and 13.5 ± 9.0 in week 3) and the bile metabolite/blood metabolite (bile M/blood M) ratio was very high and variable (131 ± 86 in week 2 and 159 ± 116 in week 3). Metabolites significantly accumulated in the blood of patients with severe hepatic disorders (M/C = 2.8 ± 0.6 in week 2 and 3.5 ± 1.0 in week 3); bile C/blood C (2.6 ± 2.1 in week 2 and 3.4 ± 1.1 in week 3) and bile M/blood M (11.9 ± 7.8 in week 2 and 12.5 ± 7.9 in week 3) significantly decreased and showed less interindividual variability.Blood cyclosporin is usually monitored to help optimise the dosage. However, if this was extended to include the monitoring of metabolites in the blood, and cyclosporin and metabolites in the bile, it could provide an early indication of severe hepatic disorders in patients with transplanted livers.

Inverse correlation between clinical response to paroxetine and plasma drug concentration in patients with major depressive disorders

OBJECTIVE

There are few data concerning a clear relationship between the clinical effect of paroxetine and plasma drug concentrations, although therapeutic ranges have been established for some tricyclic antidepressants.

METHODS

In this study, 120 patients with major depressive disorders were treated with 10-40 mg/day of paroxetine for 6 weeks, and a total of 89 patients completed the protocol. A clinical evaluation using the Montgomery-Asberg Depression Rating Scale (MADRS) was performed at 0, 1, 2, 4 and 6 weeks.

RESULTS

Significant correlations were found between the plasma concentrations of paroxetine and the percentage improvement in the total MADRS scores (r = -0.282, p < 0.01) and the final MADRS scores at 6 weeks (r = 0.268, p < 0.05). The conventional receiver-operating-characteristic curve showed the fraction of true positive results and false negative results for various cut-off levels of paroxetine concentration for response and remission. The thresholds for both response and remission that gave the maximal sensitivity and specificity for paroxetine concentrations were 64.2 ng/ml.

CONCLUSIONS

These results suggest that plasma paroxetine concentrations are negatively associated with improvement and that response occurs at the upper threshold of 64.2 ng/ml of paroxetine. These findings should be replicated with a larger patient sample.

Evaluation of the MassTrak Immunosuppressant XE Kit for the determination of everolimus and cyclosporin A in human whole blood employing isotopically labeled internal standards

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is widely used for therapeutic drug monitoring of immunosuppressants given to transplant recipients. This study evaluated the performance of the newly introduced MassTrak Immunosuppressant XE Kit (Waters Corporation; “the Kit”) in the determination of everolimus and cyclosporin A (CsA) using LC-MS/MS.

The linearity, precision, detection limit, carryover and matrix effect of the Kit and comparison of the in-house method and Kit procedure were evaluated according to Clinical and Laboratory Standards Institute guidelines.

The Kit afforded good linearity in the measurement of everolimus from 2 to 26 ng/mL (R

The Kit employing isotopically labeled internal standards provides reliable measurements of immunosuppressant levels over a broad range of concentrations.

Immunosuppressive therapy for paediatric transplant patients: pharmacokinetic considerations

Immunosuppressive therapy in paediatric transplant recipients is changing as a consequence of the increasing number of available immunosuppressive agents. Generic and other new formulations are now emerging onto the market, clinical experience is growing, and it is expected that clinicians should tailor immunosuppressive protocols to individual patients by optimising dosages and drugs according to the maturation and clinical status of the child. Most information about the clinical pharmacokinetics of immunosuppressive drugs in paediatrics is centred on cyclosporin, tacrolimus and mycophenolate mofetil in renal and liver transplant recipients; data regarding other immunosuppressants and transplant types are limited. Although the clinical pharmacokinetics of these drugs in paediatric transplant recipients are still under investigation, it is evident that the pharmacokinetic parameters observed in adults may not be applicable to children, especially in younger age groups. In general, patients younger than 5 years old show higher clearance rates irrespective of the organ transplanted or drug used. Another important factor that frequently affects clearance in this patient population is the post-transplant time. In accordance with these findings, and in contrast with the usual under-dosage in children, the need for higher dosages in younger recipients and during the early post-transplant period seems evident. To achieve the best compromise between prevention of rejection and toxicity, dosage individualisation is required and this can be achieved through therapeutic drug monitoring (TDM). This approach is particularly useful to ensure the cost-effective management of paediatric transplant recipients in whom the pharmacokinetic behaviour, target concentrations for clinical use and optimal dosage strategies of a particular drug may not yet be well defined. Although TDM may be a tool for improving immunosuppressive therapy, there is little information concerning its positive contribution to clinical events, including outcomes, for paediatric patients. Substantial information to support the use of TDM exists for cyclosporin and, to a lesser extent, for tacrolimus, but a diversity of options affects their implementation in the clinical setting. The role of TDM in therapy with mycophenolate mofetil and sirolimus has yet to be defined regarding both methods and clinical indications. Pharmacodynamic monitoring appears more suited to other immunosuppressants such as azathioprine, corticosteroids and monoclonal or polyclonal antibodies. If coupled with pharmacokinetic measurements, such monitoring would allow earlier and more precise optimisation of therapy. Very few population pharmacokinetic studies have been carried out in paediatric transplant patients. This type of study is needed so that techniques such as Bayesian forecasting can be applied to optimise immunosuppressive therapy in paediatric transplant patients.

[The amount of the loss of cyclosporine A dose correlated with the amount of leaching di (2-ethylhexyl) phthalate from polyvinyl chloride infusion tube]

An interaction between cyclosporine A (CyA) injection and infusion tubes were examined. We used polyvinyl chloride (PVC) and polybutadiene (PB) tubes. CyA injection (Sandimmun) was diluted (0.495 mg CyA/ml) with saline and dripped through infusion tubes. The amounts of unsolved substances, loss of CyA dose and leached di (2-ethylhexyl) phthalate (DEHP) during the drip study were compared. CyA was not lost into the PB tube and no DEHP was leached. Therefore, using PVC tube, 11.9 mg of CyA were lost with in 24 h after the beginning of the administration, and the concentration of leached DEHP amounted to 93.6 micrograms/ml at 12 h. We also investigated the effects of the component of the einfusion solution on the loss of CyA into PVC tube using saline, electrolyte maintenance solution, 5% glucose and 10% maltose. Sugar-containing solutions were found to have less effects than other solutions on the loss of CyA dose and DEHP leaching. The leaching of DEHP may be a major factor for the generation of unsolved substances and the loss of CyA dose. In the clinical use of CyA injection, PB tube is the best selection and the sugar-containing solution is a second selection when PB infusion tubes are hard to obtain.

Parenteral nutrition and cyclosporine: do lipids make a difference? A prospective randomized crossover trial

AIMS

This prospective, controlled, randomized crossover trial was conducted to assess the effects of parenteral nutrition, with or without lipids, in cyclosporine (CyA) pharmacokinetics.

METHODS

10 adult patients were randomized on the day of allogeneic bone marrow transplantation to receive isocaloric and isonitrogenous parenteral nutrition admixtures without (regimen A) or with lipids (regimen B). Admixtures were started on average by day + 7.4; 5 patients received regimen A followed by B, 5 in reverse order. Blood samples were collected at day 4 after transplantation, under oral diet, and 4 days after the initiation of each regimen as the sole nutrition support. At each time point, 8 whole blood samples were analysed for CyA to evaluate: area under the curve (AUC), trough concentration and systemic clearance. Clinical/laboratory events were recorded until 31 months of follow-up.

RESULTS

There was no evidence of a period or treatment-by period interaction, thus results were combined for further analysis. There were no statistically significant differences between regimens in any CyA pharmacokinetic parameters; there were no significant differences from baseline values, except for a higher systemic clearance of CyA with regimen A (0.40+/-0.09 vs 0.29+/-0.06 L/Kg/h, p=0.03).

CONCLUSIONS

The provision of 0.8 g/Kg/d of a 50:50 mixture of medium and long chain triglycerides did not affect CyA parameters, which were closer to baseline. In the short or long term there were no attributable side effects.

Decrease in oral bioavailability of cyclosporin A by coadministration of probucol in rats

To assess the pharmacokinetic interaction of cyclosporin A with probucol, we administered cyclosporin A (10 mg/kg body weight) to rats orally or intravenously with or without pretreatment of probucol (10 mg/animal, daily for 8 days). The whole blood cyclosporin A concentration-time curves after oral administration showed a 34% reduction in peak concentration and a 30% decrease in area under the blood concentration-time curve (AUC) by administration of probucol. No apparent change in elimination half-life or volume of the central compartment was observed with the treatment of probucol. After intravenous administration of cyclosporin A, the blood levels could be described by a two-compartment open model. No differences were observed in the AUC, elimination half-life or total clearance of cyclosporin A by the pretreatment of probucol. Calculated bioavailability following oral administration of cyclosporin A decreased by 33% with the treatment of probucol. These results suggest that probucol may not profoundly influence the disposition of cyclosporin A. Coadministration of probucol could decrease the fraction of absorbed cyclosporin A after oral administration.

Blood concentrations and clinical effect of cyclosporin in psoriasis

After approval by the Local Ethical Committee, 60 psoriatic patients, who participated in a previous pharmacokinetic study on cyclosporin A (CsA), gave their informed consent to continue to be studied during the maintenance treatment and at withdrawal. Peak concentration (Cmax), area under the concentration-time curve (AUC), bioavailability, elimination half-life, distribution volume, and body clearance were determined at monthly check-ups, along with blood pressure, psoriasis area, severity index (PASI), and creatinine serum levels. No modifications over time of treatment were observed on kinetic parameters. At the dose of 5 mg/kg in two daily administrations, a complete remission of the disease was observed after 1 month's treatment. At withdrawal, a worsening of PASI appeared when CsA daily dose reached 2 mg/kg b.w., the mean trough levels or AUC values being, respectively, 100 and 2,200 ng/ml.hr. There was a trend for patients with hypertension and nephrotoxicity at the end of the maintenance treatment to have higher trough, Cmax, and AUC values. Furthermore, blood pressure and serum creatinine tended to correlate better with AUC and Cmax, than with trough levels.

Comparison of the steady state pharmacokinetics of two formulations of cyclosporin in patients with atopic dermatitis

A comparison was made of the efficacy, tolerability, safety and steady state pharmacokinetics of Sandimmun and Neoral in 11 stable atopic dermatitis patients already on Sandimmun. The study was of an open, crossover design. At entry into the trial, patients were switched to Neoral for 28 days. Treatment was switched back to Sandimmun for Days 28 to 42. The morning dose was given fasting, the evening dose after a standard meal. All measures of eczema severity improved during the Neoral treatment period. Neoral was markedly better tolerated with fewer side-effects. Switching from Sandimmun to Neoral at the same dose resulted in less variable pharmacokinetic profiles in both fasted and fed states. There was an increase in bioavailability with better, less variable and faster absorption, with a slightly reduced tmax, a higher mean Cmax (+43%) and a higher mean AUC (+30%) in fasted, but not fed patients. Higher trough levels (Cmin) occurred throughout for Neoral. These differences between the two formulations were not associated with any changes in safety parameters. Overall, Neoral was equivalent or superior to Sandimmun in tolerability and efficacy when given on a 1:1 dose basis.

The pharmacokinetics of a microemulsion formulation of cyclosporine in primary renal allograft recipients. The Neoral Study Group

This study was a randomized, double-blind, 12-week comparison of the pharmacokinetics, safety, and tolerability of two cyclosporine (CsA) formulations, cyclosporine emulsion capsules and oral solution for microemulsion and cyclosporine, in the postoperative management of renal transplant patients. Of the 101 patients, aged 18 to 65, who entered the study, 89 were evaluable for pharmacokinetics. Initial dosage was 10 mg/kg per day, administered twice daily in two equal doses. Dosages were adjusted to achieve target CsA concentrations. The pharmacokinetic (PK) parameters (dose-normalized) of greatest interest were maximum blood concentration (C(max)/dose), time to reach maximum concentration (t(max), area under the blood concentration-vs.-time curve (AUC/dose), and trough blood concentrations (Co h/dose). The relative CsA bioavailabilty was found to be significantly enhanced with cyclosporine emulsion compared with cyclosporine with a 16% to 31% increase in AUC and a 32% to 42% increase in C(max). Intrapatient variability of PK parameters was significantly lower with cyclosporine emulsion than with cyclosporine for AUC, C(oh), t(max), and C(max) in many instances. This indicates a more consistent, rapid, and more complete total absorption of CsA. Despite higher CsA C(max) levels and AUCs with cyclosporine emulsion, safety and tolerability (detailed in a parallel report) were comparable to those of cyclosporine. The PK advantages of cyclosporine emulsion over cyclosporine are either independent of food conditions or possibly reflective of more consistent absorption of CsA with cyclosporine emulsion. The findings suggest that de novo use of cyclosporine emulsion may simplify and improve management of organ transplant recipients and that the PK advantages of cyclosporine emulsion may translate into clinical benefits.

Cyclosporine monitoring in allogeneic bone marrow transplantation

Objective. To review the benefits and limitations of cyclosporine concentration monitoring to maximize efficacy of graft-versus-host disease prophylaxis and minimize risk of cyclosporine toxicity.

Data Sources. A CANCERLIT search of articles published from 1980 to 1995, using the MESH head ings "cyclosporine," and "bone marrow transplant." References listed in the identified publications were reviewed for additional pertinent literature.

Study Selection. Human clinical trials and re view articles evaluating cyclosporine pharmacokinet ics and pharmacodynamics in patients status follow ing bone marrow transplantation.

Data synthesis. Cyclosporine concentration monitoring has been proposed due to the critical need for drug efficacy, substanial drug-induced toxic ity, and high pharmacokinetic variability. Selection of biological fluid (blood, serum, or plasma) for moni toring as well as the selectivity of the assay employed for cyclosporine versus its metabolites, is a critical factor in evaluating this literature. Both the relation ship between cyclosporine trough concentration and clinical outcome has been evaluated in this patient population.

Conclusions. Cyclosporine trough concentra tion monitoring, especially in the blood using an assay specific for the parent compound, has a role in the care of the allogeneic bone marrow transplantation patient. Cyclosporine levels have been correlated with risk for nephrotoxicity and to a lesser extent hepatotoxicity. Low cyclosporine levels are one fac tor contributing to the risk for acute graft-versus-host disease in these patients. Proper evaluation of cyclo sporine levels with due consideration to patient spe cific factors can assist the clinician in maximizing the chances for graft-versus-host disease prevention while reducing the risk of cyclosporine side effects.

Clinically significant drug interactions with cyclosporin. An update

Since its approval in 1983 for immunosuppressive therapy in patients undergoing organ and bone marrow transplants, cyclosporin has had a major impact on organ transplantation. It has significantly improved 1-year and 2-year graft survival rates, and decreased morbidity in kidney, liver, heart, heart-lung and pancreas transplantation. Several studies have supported the efficacy of cyclosporin in preventing graft-versus-host disease in bone marrow transplantation. Cyclosporin is also possibly effective in treating diseases of autoimmune origin and as an antineoplastic agent. The introduction of therapeutic drug monitoring of cyclosporin was extremely useful because of the wide inter- and intraindividual variability in the pharmacokinetics of cyclosporin after oral or intravenous administration. Optimal long term use of cyclosporin requires careful monitoring of the blood (or plasma) concentrations. Sustained and clinically significant drug-drug interactions can occur during long term therapy with cyclosporin. The coadministration of multiple drugs with cyclosporin could result in graft rejection, renal dysfunction or other undesirable effects. Any interaction that leads to modified cyclosporin concentrations is of potential clinical importance. Cyclosporin itself may have significant effects on the pharmacokinetics and/or pharmacodynamics of coadministered drugs, such as digoxin, HMG-CoA reductase inhibitors and antineoplastic drugs affected by multidrug resistance. Many drugs have been shown to affect the pharmacokinetics and/or pharmacodynamics of cyclosporin. Interactions between cyclosporin and danazol, diltiazem, erythromycin, fluconazole, itraconazole, ketoconazole, metoclopramide, nicardipine, verapamil, carbamazepine, phenobarbital (phenobarbitone), phenytoin, rifampicin (rifampin) and cotrimoxazole (trimethoprim/sulfamethoxazole) are well documented in a large number of patients. Other interactions (such as those with aciclovir, estradiol and imipenem) are documented only in isolated case studies.

The use of therapeutic drug monitoring to optimise immunosuppressive therapy

Most experience of the therapeutic drug monitoring of immunosuppressive agents has been acquired in the field of solid organ transplantation; however, agents such as cyclosporin (cyclosporin A) are being increasingly utilised for the management of autoimmune diseases. Cyclosporin is the most widely studied immunosuppressant, but in spite of this many controversies still exist as to the optimum strategy for monitoring this drug. Owing to its widely variable pharmacokinetics and metabolism, and the absence of a simple method to measure therapeutic effectiveness, many factors should be considered. In most circumstances, measuring whole blood through concentrations of cyclosporin with a specific assay methodology is warranted. In addition, knowledge of other factors that may alter the pharmacokinetics (such as liver function, concomitant food or medications, gastrointestinal status, and time since transplantation) should be taken into account so that therapy can be appropriately adjusted. Other methods of monitoring have been investigated, such as AUC (area under the concentration-time curve) monitoring and immunological monitoring. However, further refinement of these techniques and greater experience with their efficacy must be accumulated before their role in the monitoring of cyclosporin can be defined. Tacrolimus, like cyclosporin, shares many of the difficulties in monitoring for efficacy and toxicity due largely to the variable pharmacokinetics; similarly to cyclosporin, whole blood through concentration monitoring should be utilised in combination with knowledge of the factors that may affect the pharmacokinetics. Muromonab CD3 (OKT3) is a monoclonal antibody used for the treatment and prophylaxis of acute allograft rejection. Several immunological monitoring techniques have been investigated for this agent. Monitoring CD3+ levels can assist clinicians in determining therapeutic efficacy, while measuring antimuromonab CD3 antibody titres can help determine if xenosensitisation has occurred, causing therapeutic ineffectiveness. The clinical monitoring of azathioprine, one of the first immunosuppressive agents used in transplantation, has historically been limited to monitoring complete blood counts for bone marrow suppression. However, newer techniques measuring intracellular DNA nucleotides appear to be promising. The new immunosuppressants on the horizon include mycophenolate mofetil and rapamycin. The clinical experience with therapeutic drug monitoring of these 2 compounds is scant in the literature; however, both agents have demonstrated efficacy in preventing or treating allograft rejection while maintaining a relatively well tolerated toxicity profile in recent clinical trials. Routine monitoring does not appear to be warranted for immunosuppressive therapy in autoimmune diseases.

Decreased cyclosporin A absorption after treatment with GoLytely lavage solution in rats

Recently we observed a case in which the cyclosporin A absorption decreased after treatment with GoLytely lavage solution in a kidney transplant patient. In this study, we confirmed the decrease of the blood concentration of cyclosporin A after oral administration by GoLytely (Macrogol 3350) based on experiments with rats. The peak blood cyclosporin A concentration, and the area under the blood drug concentration-time curve from 0 to 24 h in the GoLytely-administered group were significantly lower than the control group. In the case of gastrointestinal dysfunction such as diarrhoea, or in treatment with laxatives such as GoLytely lavage solution, whole blood cyclosporin levels must be carefully monitored, and intravenous cyclosporin A may be more suitable for providing adequate immunosuppression.

Pharmacokinetics of orally and intravenously administered cyclosporine in pre-kidney transplant patients

The pharmacokinetics of cyclosporine (CSA) and four metabolites were evaluated in eight hemodialysis subjects awaiting renal transplantation to compare metabolic patterns with those observed in post-transplant patients and normal volunteers. Each subject received a single 4-mg/kg intravenous and a single 10-mg/kg oral dose separated by a 1-week washout period. Blood samples were collected before and at .5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 14, and 24 hours after CSA dosing. Cyclosporine blood, plasma, and metabolite (M17, M1, M18, M21) levels were determined by high-pressure liquid chromatography. Mean (+/- standard deviation) CSA blood clearance was .47 +/- .15 L/hour/kg, steady-state volume of distribution (Vss) was 1.9 +/- .5 L/kg, and mean residence time (MRT) was 4.4 +/- 1.8 hours after intravenous dosing. With plasma, mean clearance was .70 +/- .31 L/hour/kg, Vss was 2.4 +/- 1.2 L/kg, and MRT was 3.7 +/- 2.2 hours. Cyclosporine bioavailability (F) averaged 24 +/- 11 and 24 +/- 15%, using blood and plasma, respectively. Values for clearance and Vss were approximately 30 to 100% greater than comparable estimates in healthy volunteers, but F and MRT were not altered to this extent. These changes might be explained on the basis of decreased protein binding in uremic patients. The area under the curve ratio for M17 and M1 to CSA increased an average of 1.7- and 3.9-fold, respectively, after oral dosing compared with intravenous administration, indicating increased conversion during first-pass metabolism.

Distribution characteristics of immunosuppressants FK506 and cyclosporin A in the blood compartment

Using two representative immunosuppressants, FK506 (FK) and cyclosporin A (CyA), of which the mechanism of pharmacological action is the same although there is a great difference in the pharmacological intensity, the distribution characteristics were studied in both in vivo and in vitro experiments using rat, dog, and human blood. Blood samples were fractionated by means of sedimentation in Ficoll-Paque, and the drug contents in the diluted plasma fraction, erythrocyte fraction, and lymphocyte fraction were measured by an HPLC method. FK distributes to the lymphocyte fraction to a level about three times greater than that of CyA, while CyA distributes to the erythrocyte fraction to a level ten times that of FK. The distribution pattern of these fractions was independent of the drug concentration and species after correcting the drug concentration in each fraction with the blood drug concentration. The uptakes of FK and CyA in the isolated lymphocytes obtained from the rat spleen and human peripheral blood were also studied. The amount of FK taken up by the spleen lymphocytes is five times greater than that of CyA. In the case of the uptake study using human peripheral blood lymphocytes, the concentration of FK in the lymphocyte is 100-fold higher than that of CyA. This difference in the lymphocyte level between the two immunosuppressants is thought to be one of the reasons why FK is more potent than CyA, a difference of about 100-fold in the in vitro pharmacological study and about tenfold in the in vivo organ transplantation experiments.

Pharmacodynamic monitoring of cyclosporin

The efficacy of cyclosporin as an immunosuppressive agent is largely based on clinical indicators such as graft survival, rejection or nephrotoxicity. Therapeutic monitoring is necessary to evaluate the efficacy of cyclosporin therapy. The most widely used method for monitoring cyclosporin therapy is the measurement of predose through blood concentrations of the drug. The relationship of a single or multiple blood cyclosporin concentration to slowly evolving outcomes is difficult to establish. Some investigators have found a good correlation between cyclosporin trough concentrations on the one hand and cyclosporin toxicity and rejection on the other, but others have not. Therapeutic monitoring of cyclosporin may be enhanced using some biological assays for immunosuppression (pharmacodynamic monitoring) in addition to cyclosporin trough concentrations (pharmacokinetic monitoring). However, direct monitoring of the immune response to cyclosporin therapy using a clinically applicable biological assay is difficult. Some pharmacodynamic parameters have been suggested as biological markers in the clinical monitoring of cyclosporin.

A review of assay methods for cyclosporin. Clinical implications

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

Pharmacokinetic drug interactions with rifampicin

Rifampicin, an antituberculosis drug, is usually administered for 4 to 12 months with other antituberculosis drugs or medications from other classes. A potential for drug interactions often exists because rifampicin is a potent inducer of hepatic drug metabolism, as evidenced by a proliferation of smooth endoplasmic reticulum and an increase in the cytochrome P450 content in the liver. The induction is a highly selective process and not every drug metabolised via oxidation is affected. Case reports and studies have demonstrated enhanced metabolism of several drugs; most of these interactions are clinically important. At the start of rifampicin treatment, and again at the end, clinicians must check the dosages of any accompanying medications with which rifampicin may potentially interact. Monitoring of clinical response and blood drug concentrations is essential to adjust the drug dosage during rifampicin therapy. Rifampicin also interacts with cholephils such as bilirubin and bromosulphthalein. Its pharmacokinetics are reported to be altered by ethambutol, p-aminosalicylic acid (through its excipient component), ketoconazole, cyclosporin, clofazimine, probenecid and phenobarbital through one or other of the following mechanisms--impaired absorption of rifampicin, competition between the drug and rifampicin for hepatic uptake and altered hepatic metabolism of rifampicin. Most interactions affecting rifampicin have been relatively minor or are not expected to alter its therapeutic efficacy.

Therapeutic monitoring of cyclosporin--an update

The success of organ transplantation is closely related to clinical use of the immunosuppressive drug cyclosporin (CsA). The dosage of CsA is complicated by the large intra- and interindividual variability in its pharmacokinetics, as well as by the narrow concentration range between insufficient immunosuppression and toxicity. Potential sources of error in the sampling procedure and the advantages and disadvantages of the available analytical methods are discussed. Traditionally, 12 or 24 hour trough concentrations of CsA are monitored. Recently, peak concentrations or estimation of AUCs by a limited sampling strategy have been tried to improve the relatively weak concentration-effect and concentration-toxicity relationships found with trough CsA concentration monitoring. Studies of the CsA concentration-effect relationships for various treatment indications are reviewed.

Cyclosporine monitoring in autoimmune and other diseases

Cyclosporine (CsA) is being increasingly used for the treatment of disorders other than transplantation. In contrast to transplant recipients, most of these patients can have CsA therapy discontinued without life-threatening consequences, and the dose of CsA can therefore be restricted in order to limit the incidence and severity of toxicity, including nephrotoxicity. The utility of either CsA blood levels or pharmacokinetic profiling to ensure adequacy of therapy or to prevent incipient as well as overt toxicity has not been confirmed in this group of patients, and prevention of nephrotoxicity usually depends on limiting the dose of CsA and careful assessment of renal function. Frequent measurement of CsA levels beyond the initiation period in patients with autoimmune and other nontransplant diseases cannot be currently justified, and should be reserved for those situations where drug interactions, unexpected toxicity or the possibility of inadequate therapy is likely.

Pharmacokinetic drug interactions with cyclosporin (Part II)

Part I of this article, which appeared in the previous issue of the Journal, considered the potential mechanisms of drug interactions with cyclosporin, and divided the interacting drugs into 2 categories. Drugs that decrease cyclosporin concentrations (e.g. anti-convulsants, rifampicin, etc.) were dealt with first; the authors then moved on to consider the second category, those that increase cyclosporin concentration (macrolide antibiotics, azole antifungal drugs). Part II continues the survey of this category.

Effect of ponsinomycin on cyclosporin pharmacokinetics

The influence of treatment with ponsinomycin, a new macrolide antibiotic, on the pharmacokinetics of cyclosporin A has been studied in 10 renal transplant patients. The pharmacokinetics of cyclosporin A was investigated at steady state, before and during treatment with ponsinomycin. On average, the blood levels of cyclosporin A were doubled by the macrolide, possibly due to a decrease in elimination or/and to an increase in absorption. Ponsinomycin should be use very carefully in patients treated with cyclosporin A.

Intensive care management of children following heart and heart-lung transplantation

We report the intensive care management of 23 children (age 3-15 years) following orthotopic heart (HT) and combined heart and lung transplantation (HLT) performed at our 2 institutes between February 1985 and August 1989. Cyclosporin A, azathioprine and steroids were given as routine immunosuppression, whilst anti-thymocyte globulin (ATG) was used for the first 3 post-operative days. Mean ventilation time was 24.6 h (range 4-74 h). Cardiovascular support comprised isoprenaline infusions in all patients (mean period 65.7 h) whilst dopamine and other inotropic agents were used less frequently. Sequential atrioventricular pacing was required more often in the HT patients (n = 9) than in the HLT patients (n = 4). Fluid input was restricted to maintain a plasma osmolality of 290-300 mosm/kg. There were 2 perioperative deaths both due to acute right heart failure. Other post-operative complications included: bleeding (n = 3); acute graft rejection (n = 4); infection (n = 3); systemic hypertension (n = 6); neurological abnormalities (n = 2); renal dysfunction (n = 6) and hyperglycaemia (n = 6).

Is cyclosporin A an inhibitor of drug metabolism?

1. The potential for a drug interaction between cyclosporin A and midazolam was investigated since both compounds appear to be metabolized by the same cytochrome P-450 isoenzyme. 2. In vitro evaluation of the binding of cyclosporin A to rat microsomal cytochrome P-450 indicated a Ks-value of 0.4 microM. In further studies with rat liver microsomes IC50-values of 6, 8 and 70 microM cyclosporin A were determined for the inhibition of the metabolism of midazolam to its alpha-OH-,4-OH- and di-OH-metabolites, respectively. 3. Comparative studies with human liver microsomes indicated IC50-values of approximately 300 microM for the formation of alpha-OH-midazolam and of 65 microM for the formation of 4-OH-midazolam. 4. The pharmacokinetics of a single intravenous dose of midazolam (0.075 mg kg-1) was studied in nine patients receiving cyclosporin A to prevent rejection of their transplanted kidneys. The average steady state blood concentrations of cyclosporin A, measured by r.i.a. using a specific monoclonal antibody, varied during a dosing interval between 175 and 600 ng ml-1. 5. In these patients the hepatic elimination of midazolam was characterized by a mean t1/2 (+/- s.d.) of 2.3 +/- 1.2 h and a plasma clearance (CL) of 414 +/- 95 ml min-1. These values were not different from those of normal human subjects (t1/2 = 1.5 to 4 h, CL = 350 to 700 ml min-1). 6. From the results of the in vitro experiments it is concluded that cyclosporin A may potentially inhibit drug metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)