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

Quantitative prediction of CYP3A-mediated drug-drug interactions by correctly estimating fraction metabolized using human liver chimeric mice

BACKGROUND AND PURPOSE

Fraction metabolized (fm ) and fraction transported (ft ) are important for understanding drug-drug interactions (DDIs) in drug discovery and development. However, current in vitro systems cannot accurately estimate in vivo fm due to inability to reflect the ft by efflux transporters (ft,efflux ). This study demonstrates how CYP3A-mediated DDI for CYP3A/P-gp substrates can be predicted using Hu-PXB mice as human liver chimeric mice.

EXPERIMENTAL APPROACH

For estimating human in vitro fm by CYP3A enzyme (fm,CYP3A,in vitro ), six drugs, including CYP3A/P-gp substrates (alprazolam, cyclosporine, docetaxel, midazolam, prednisolone, and theophylline) and human hepatocytes were incubated with or without ketoconazole as a CYP3A inhibitor. We calculated fm,CYP3A,in vitro based on hepatic intrinsic clearance. To estimate human in vivo fm,CYP3A (fm,CYP3A,in vivo ), we collected information on clinical DDI caused by ketoconazole for these six drugs. We calculated fm,CYP3A,in vivo using the change of total clearance (CLtotal ). For evaluating the human DDI predictability, the six drugs were administered intravenously to Hu-PXB and SCID mice with or without ketoconazole. We calculated the change of CLtotal caused by ketoconazole. We compared the CLtotal change in humans with that in Hu-PXB and SCID mice.

KEY RESULTS

The fm,CYP3A,in vitro was overestimated compared to the fm,CYP3A,in vivo . Hu-PXB mice showed much better correlation in the change of CLtotal with humans (R2  = 0.95) compared to SCID mice (R2  = 0.0058).

CONCLUSIONS AND IMPLICATIONS

CYP3A-mediated DDI can be predicted by correctly estimating human fm,CYP3A,in vivo using Hu-PXB mice. These mice could be useful predicting hepatic fm and ft,efflux .

A Physiology-Based Model of Human Bile Acid Metabolism for Predicting Bile Acid Tissue Levels After Drug Administration in Healthy Subjects and BRIC Type 2 Patients

Drug-induced liver injury (DILI) is a matter of concern in the course of drug development and patient safety, often leading to discontinuation of drug-development programs or early withdrawal of drugs from market. Hepatocellular toxicity or impairment of bile acid (BA) metabolism, known as cholestasis, are the two clinical forms of DILI. Whole-body physiology-based modelling allows a mechanistic investigation of the physiological processes leading to cholestasis in man. Objectives of the present study were: (1) the development of a physiology-based model of the human BA metabolism, (2) population-based model validation and characterisation, and (3) the prediction and quantification of altered BA levels in special genotype subgroups and after drug administration. The developed physiology-based bile acid (PBBA) model describes the systemic BA circulation in humans and includes mechanistically relevant active and passive processes such as the hepatic synthesis, gallbladder emptying, transition through the gastrointestinal tract, reabsorption into the liver, distribution within the whole body, and excretion via urine and faeces. The kinetics of active processes were determined for the exemplary BA glycochenodeoxycholic acid (GCDCA) based on blood plasma concentration-time profiles. The robustness of our PBBA model was verified with population simulations of healthy individuals. In addition to plasma levels, the possibility to estimate BA concentrations in relevant tissues like the intracellular space of the liver enhance the mechanistic understanding of cholestasis. We analysed BA levels in various tissues of Benign Recurrent Intrahepatic Cholestasis type 2 (BRIC2) patients and our simulations suggest a higher susceptibility of BRIC2 patients toward cholestatic DILI due to BA accumulation in the liver. The effect of drugs on systemic BA levels were simulated for cyclosporine A (CsA). Our results confirmed the higher risk of DILI after CsA administration in healthy and BRIC2 patients. The presented PBBA model enhances our mechanistic understanding underlying cholestasis and drug-induced alterations of BA levels in blood and organs. The developed PBBA model might be applied in the future to anticipate potential risk of cholestasis in patients.

Population pharmacokinetics of cyclosporine in transplant recipients

A number of classical pharmacokinetic studies have been conducted in transplant patients. However, they suffer from some limitations, for example, (1) the study design was limited to intense blood sampling in small groups of patients during a certain posttransplant period, (2) patient factors were evaluated one at a time to identify their association with the pharmacokinetic parameters, and (3) mean pharmacokinetic parameters often cannot be precisely estimated due to large intraindividual variability. Population pharmacokinetics provides a potential means of addressing these limitations and is a powerful tool to evaluate the magnitude and consistency of drug exposure. Population pharmacokinetic studies of cyclosporine focused solely on developing limited sampling strategies and Bayesian estimators to estimate drug exposure, have been summarized before, and are, therefore, not a subject of this review. The major focus of this review is to describe factors (demographic factors, hepatic and gastrointestinal functions, drug-drug interactions, genetic polymorphisms of drug metabolizing enzymes and transporters) that have been identified to contribute to the large portion of observed variability in the pharmacokinetics of cyclosporine in transplant patients. This review summarizes and interprets the conclusions as well as the nonlinear mixed-effects modeling methodologies used in such studies. A highly diversified collection of structural models, variability models, and covariate submodels have been evaluated and validated using internal or external validation methods. This review also highlights areas where additional research is warranted to improve the models since a portion of model variability still remains unexplained.

Cyclosporine inhibition of hepatic and intestinal CYP3A4, uptake and efflux transporters: application of PBPK modeling in the assessment of drug-drug interaction potential

PURPOSE

To apply physiologically-based pharmacokinetic (PBPK) modeling to investigate the consequences of reduction in activity of hepatic and intestinal uptake and efflux transporters by cyclosporine and its metabolite AM1.

METHODS

Inhibitory potencies of cyclosporine and AM1 against OATP1B1, OATP1B3 and OATP2B1 were investigated in HEK293 cells +/- pre-incubation. Cyclosporine PBPK model implemented in Matlab was used to assess interaction potential (+/- metabolite) against different processes (uptake, efflux and metabolism) in liver and intestine and to predict quantitatively drug-drug interaction with repaglinide.

RESULTS

Cyclosporine and AM1 were potent inhibitors of OATP1B1 and OATP1B3, IC(50) ranging from 0.019-0.093 μM following pre-incubation. Cyclosporine PBPK model predicted the highest interaction potential against liver uptake transporters, with a maximal reduction of >70% in OATP1B1 activity; the effect on hepatic efflux and metabolism was minimal. In contrast, 80-97% of intestinal P-gp and CYP3A4 activity was reduced due to the 50-fold higher cyclosporine enterocytic concentrations relative to unbound hepatic inlet. The inclusion of AM1 resulted in a minor increase in the predicted maximal reduction of OATP1B1/1B3 activity. Good predictability of cyclosporine-repaglinide DDI and the impact of dose staggering are illustrated.

CONCLUSIONS

This study highlights the application of PBPK modeling for quantitative prediction of transporter-mediated DDIs with concomitant consideration of P450 inhibition.

Explaining variability in ciclosporin exposure in adult kidney transplant recipients

Purpose

Optimal ciclosporin A (CsA) exposure in kidney transplant recipients is difficult to attain because of variability in CsA pharmacokinetics. A better understanding of the variability in CsA exposure could be a good means of individualizing therapy. Specifically, genetic variability in genes involved in CsA metabolism could explain exposure differences. Therefore, this study is aimed at identifying a relationship between genetic polymorphisms and the variability in CsA exposure, while accounting for non-genetic sources of variability.

Methods

De novo kidney transplant patients (n = 33) were treated with CsA for 1 year and extensive blood sampling was performed on multiple occasions throughout the year. The effects of the non-genetic covariates hematocrit, serum albumin concentration, cholesterol, demographics (i.e., body weight), CsA dose interval, prednisolone dose and genetic polymorphisms in genes encoding ABCB1, CYP3A4, CYP3A5, and PXR on CsA pharmacokinetics were studied using non-linear mixed effect modeling.

Results

The pharmacokinetics of CsA were described by a two-compartment disposition model with delayed absorption. Body weight was identified as the most important covariate and explained 35% of the random inter-individual variability in CsA clearance. Moreover, concurrent prednisolone use at a dosage of 20 mg/day or higher was associated with a 22% higher clearance of CsA, hence lower CsA exposure. In contrast, no considerable genotype effects (i.e., greater than 30–50%) on CsA clearance were found for the selected genes.

Conclusions

It appears that the selected genetic markers explain variability in CsA exposure insufficiently to be of clinical relevance. Therefore, therapeutic drug monitoring is still required to optimize CsA exposure after administration of individualized doses based on body weight and, as this study suggests, co-administration of prednisolone.

A prospective cross-over study comparing the pharmacokinetics of cyclosporine A and its metabolites after oral versus short-time intravenous cyclosporine A administration in pre-heart transplant patients

Sometimes intravenous administration of cyclosporine (CsA) is essential before oral administration is possible. There are only a few reports available on the interindividual variability of CsA metabolism and different metabolite pattern depending on intravenous versus oral administration of CsA in heart transplant (HTx) patients. For effective inhibition of calcineurin we used a short infusion reaching peak concentrations after 2 hours. In a prospective cross-over study we compared the pharmacokinetics of CsA and its metabolites after oral (2.0 mg/kg body weight) versus intravenous (0.7 mg/kg body weight; 2-hour infusion) CsA administration (single test dose) in 7 pre-HTx patients. The pharmacokinetic parameters of CsA and its metabolites were analyzed using high-pressure liquid chromatography. The pharmacokinetic parameter area under the concentration time curve (AUC(0-infinity)) of CsA after intravenous administration was significantly lower (2903 ng*h*mL(-1)) than that after oral administration (4344 ng*h*mL(-1); P=.01). Peak concentrations, time to peak concentration, and terminal elimination half life were not significantly different. Short-time infusion of CsA resulted in a significant decrease in the AUC of the metabolites AM1 (3-fold), AM9 (10-fold), and AM1c (3-fold). A 2-hour infusion of CsA is just as effective as oral administration and the reduced amount of metabolites is advantageous for the patient.

Developmental pharmacokinetics of ciclosporin--a population pharmacokinetic study in paediatric renal transplant candidates

AIMS

To use population pharmacokinetic modelling to characterize the influence of developmental and demographic factors on the pharmacokinetic variability of ciclosporin.

METHODS

Pharmacokinetic modelling was performed in NONMEM using a dataset comprising 162 pretransplant children, aged 0.36-17.5 years. Ciclosporin was given intravenously (3 mg kg(-1)) and orally (10 mg kg(-1)) on separate occasions followed by blood sampling for 24 h.

RESULTS

A three-compartment model with first-order absorption without lag-time best described the pharmacokinetics of ciclosporin. The most important covariate affecting systemic clearance (CL) and distribution volume (V) was body weight (BW; scaled allometrically), responsible for a fourfold difference in uncorrected ciclosporin CL and a sixfold difference in ciclosporin V. The other significant covariates, haematocrit, plasma cholesterol and creatinine, were estimated to explain 20-30% of interindividual differences in CL and V of ciclosporin. No age-related changes in oral bioavailability or in BW-normalized V were seen. The BW-normalized CL (CL/BW) declined with age and prepubertal children (<8 years) had an approximately 25% higher CL/BW than did older children. Normalization of CL for allometric BW (BW(3/4)) removed its relationship to age.

CONCLUSION

The relationship between CL and allometric BW is consistent with a gradual reduction in relative liver size, until adult values, and a relatively constant CYP3A4 content in the liver from about 6-12 months of age to adulthood. Ciclosporin oral bioavailability, known previously to display large interindividual variability, is not influenced by age. These findings can enable better individualization of ciclosporin dosing in infants, children and adolescents.

Cyclosporin A disposition following acute traumatic brain injury

Although the precise mechanism of action remains to be defined, Cyclosporin A (CsA) has demonstrated potential for neuroprotection in animal models. Predictive dosing strategies for CsA in acute traumatic brain injured (TBI) patients must account for the influence of the acute phase response on drug disposition. To characterize CsA pharmacokinetic parameters early following acute TBI, serial blood samples from patients enrolled into a Phase II dose-escalation trial were analyzed. Within eight hours of injury, thirty patients admitted with acute severe TBI were prospectively randomized into three cohorts (n = 8 CsA; n = 2 placebo per cohort) in this dose-escalation trial. Patients received one of three doses (I = 0.625 mg/kg/dose; II = 1.25 mg/kg/dose; III = 2.5 mg/kg/dose) or placebo intravenously every 12 h for 72 h. Serial blood collection began prior to dose 1 and continued for 72 h following the completion of six doses. Whole blood concentrations were determined by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection. Pharmacokinetic parameters were determined for each patient by fitting the concentration-time profile to a two-compartmental model with first order elimination. Mean area under the curve and predicted maximal blood concentration increased with each dosing cohort (I = 9840 h*microg/L, 398 microg/L; II = 18300 h*microg/L, 645 microg/L; III = 32500 h*microg/L, 1300 microg/L). Whole blood clearance, steady state volume of distribution, and beta half-life were independent of dose and higher than published reports from other populations: 0.420 L/h/kg, 5.91 L/kg, and 17.3 h, respectively. These data show patients with acute severe TBI demonstrate a more rapid clearance and a larger distribution volume of CsA. Pharmacokinetic parameters derived from this study will guide dosing strategies for future prospective clinical trials evaluating CsA therapy following acute TBI.

Single-dose daily infusion of cyclosporine for prevention of Graft-versus-host disease after allogeneic bone marrow transplantation from HLA allele-matched, unrelated donors

Peak blood concentration of cyclosporine (CsA) in renal transplantation patients was recently reported to be associated with clinical efficacy. We therefore evaluated the toxicity and efficacy of a regimen of once-daily infusion of CsA plus a short course of methotrexate as prophylaxis of graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation from an HLA allele-matched, unrelated donor. Nineteen patients with hematologic malignancies received CsA, 3 mg/kg per day, as a 4-hour intravenous (IV) infusion from day -1. After engraftment, patients received CsA orally at twice the IV dose. The CsA dose was adjusted to maintain the blood trough level between 150 and 200 ng/mL. Methotrexate was administered IV at doses of 10 mg/m(2) on day 1 and 7 mg/m(2) on days 3, 6, and 11. Bone marrow engraftment occurred in all patients. Grade 1 and grade 2 GVHD occurred in 6 (31.6%) and 7 (36.8%) of the 19 patients, respectively. No patient had grade 3 or 4 GVHD. Acute nephrotoxicity developed in 1 (5.3%) of the 19 patients, and hypertension developed in 3 (15.8%) of the 19 patients. We evaluated the pharmacokinetics of 4-hour CsA infusion in 10 patients. The mean trough concentration, mean peak concentration, mean time to peak concentration, and area under the curve (24 hours) were 161 +/- 43 ng/mL, 1498 +/- 387 ng/mL, 3.2 +/- 1.0 hours, and 10,848 +/- 1,991 ng +/- h/mL, respectively. This regimen was well tolerated and did not enhance the risk of severe GVHD in patients undergoing allogeneic bone marrow transplantation from an HLA allele-matched, unrelated donor.

Diltiazem co-treatment in renal transplant patients receiving microemulsion cyclosporin

BACKGROUND

Usage of cyclosporin (the Hong Kong Hospital Authority's single largest item of drug expenditure) continues to increase, mainly due to increasing numbers of renal allograft patients taking it as long-term antirejection therapy. Diltiazem, an antihypertensive agent, interferes with the first pass extraction of oral cyclosporin, thus serving to conserve its dosage.

AIMS

In renal transplant patients, to assess whether diltiazem co-treatment could achieve worthwhile dosage conservation of Neoral (a relatively new microemulsified cyclosporin formulation), safely.

METHODS

A randomized, placebo-controlled, double-blind clinical trial was undertaken at three local hospitals. Renal transplant recipients receiving Neoral as prophylactic immunosuppression were randomized to two treatment arms. Active treatment consisted of diltiazem tablets 30 or 60 mg twice daily for patients weighing < 60 or >or= 60 kg, respectively. One hundred and ten eligible patients gave their informed consent, and were followed up for at least six months. The mean difference in the dollar cost in the sixth month was the primary outcome. Secondary/ancillary outcomes included changes in cyclosporin dosage and blood level, and untoward clinical events including rejection. Outcomes were evaluated by intention to treat analyses.

RESULTS

During weeks 23-26 (sixth month) post randomization, diltiazem co-treatment yielded an estimated average cost saving per patient on drugs of 15%[the 95% confidence interval (CI) of the difference being HK dollars 609 +/- 517 or pound 50 +/- 42], with no apparent excess of untoward or adverse events, complications, hospitalization, outpatient visits, or inferior quality of life.

CONCLUSIONS

This diltiazem co-treatment regime applied to the nearly 1800 surviving renal allograft patients followed up in Hospital Authority hospitals could have saved approximately HK dollars 14.3 million ( pound 1.17 million) annually, without adverse sequelae.

Comparison of cyclophilin binding assay and radioimmunoassay in monitoring of blood cyclosporine

Cyclosporine binds with cyclophilin, an abundant protein found in almost all tissues, and the resulting complex interacts with calcineurin diminishing T-cell activation. Cyclophilin can be regarded as a cellular "receptor" for cyclosporine. Measuring cyclosporine binding to cyclophilin may offer a link between pharmacokinetics and pharmacodynamics that could improve monitoring of cyclosporine therapy. The authors investigated the feasibility of the cyclophilin binding assay and compared the results with a standard specific monoclonal radioimmunoassay in 100 blood samples taken for therapeutic drug monitoring. The results obtained with these methods were related closely with each other (r = 0.96; p < 0.001) but the mean (+/-SEM) concentrations were approximately two-fold higher in cyclophilin binding assay than in radioimmunoassay (520.4 +/- 49.9 ng/ml versus 257.7 +/- 28.6 ng/ml, respectively, p < 0.001). The shapes of the cyclosporine concentration versus time curves in two patients after a liver and heart transplantation, respectively, were similar after both methods but cyclophilin binding assay gave higher values than radioimmunoassay. Before firm conclusions on the clinical value of cyclophilin binding assay can be made, comparative studies in patients linking cyclosporine concentrations measured with cyclophilin binding assay and standard methods to the therapeutic outcome are needed.

Immunopharmacodynamic studies of cyclosporine in patients awaiting renal transplantation

The immunopharmacodynamics of cyclosporine were investigated in eight hemodialysis patients awaiting renal transplantation. Cyclosporine was administered orally (10 mg/kg) and intravenously (4 mg/kg), with both administrations separated by at least one week. Plasma samples were processed at 37 degrees C and analyzed for specific cyclosporine and its four major metabolites (AM1, AM1c, AM9, and AM4N) using high-performance liquid chromatography. In addition, the in vitro immunosuppressive activity of these serial plasma samples was estimated as a relative percentage inhibition of third party mitogenic lymphocyte proliferation stimulated with phytohemagglutinin. The relationships between concentration and effect of cyclosporine versus time were noted. These results suggest that unchanged cyclosporine concentrations in plasma correlate with mitogen-induced lymphocyte suppression yielding significant immunosuppressant activity of cyclosporine. Control studies with plasma from healthy volunteers spiked with cyclosporine in the concentration range of 0-10,000 ng/mL were developed. A sigmoidal Emax model was fitted to the effect versus plasma concentration data. The ratio of effect versus predicted effect were calculated for intravenous cyclosporine dosing. There was a good correlation between the observed and predicted inhibitory effect.

Disposition of intravenous and oral cyclosporine after administration with grapefruit juice

OBJECTIVE

To examine the effect of grapefruit juice on the disposition of cyclosporine after administration of oral and intravenous doses to healthy male subjects.

METHODS

Subjects received two oral doses of cyclosporine (7.5 mg/kg) and two intravenous doses (2.5 mg/kg infused for 3 hours), with each dose separated by a 1-week washout period. Grapefruit juice (250 ml) was ingested immediately before one oral and one intravenous dose and again 2 hours later. Blood samples were collected for a 24-hour period, and whole blood concentrations of cyclosporine were measured with use of a specific monoclonal radioimmunoassay.

RESULTS

Grapefruit juice had no effect on any pharmacokinetic parameter when given with intravenous cyclosporine. After oral administration, grapefruit juice significantly increased peak concentration (936 versus 1340 ng/ml), as well as area under the curve (6722 versus 10,730 ng . hr/ml) but had no effect on elimination half-life. Absolute bioavailability of cyclosporine was increased from 0.22 to 0.36 (average increase, 62%) by grapefruit juice.

CONCLUSIONS

The lack of effect on systemic clearance after intravenous cyclosporine suggests that grapefruit juice improves oral bioavailability by increasing absorption or reducing gut wall metabolism. The latter is more likely in view of studies that suggest significant gut wall metabolism of cyclosporine by CYP3A enzymes known to be inhibited by components of grapefruit juice.