Clinical pharmacokinetics of cyclosporin

Cyclosporine A Downregulates Selenoprotein P Expression via a Signal Transducer and Activator of Transcription 3-Forkhead Box Protein O1 Pathway in Hepatocytes In Vitro

Cyclosporine A (CsA) is an immunosuppressant applied worldwide for preventing graft rejection and autoimmune diseases. However, CsA elevates oxidative stress, which can lead to liver injuries. The present study aimed to clarify the mechanisms underlying the CsA-mediated oxidative stress. Among the redox proteins, CsA concentration-dependently downregulated Selenop-encoding selenoprotein P, a major circulating antioxidant protein reducing reactive oxygen species, in hepatocytes cell lines and primary hepatocytes. The luciferase assay identified the CsA-responsive element in the SELENOP promoter containing a putative binding site for forkhead box protein O (FoxO) 1. The CsA-mediated suppression on the SELENOP promoter was independent of the nuclear factor of activated T-cell, a classic target repressed by CsA. A chromatin immunoprecipitation assay showed that CsA suppressed the FoxO1 binding to the SELENOP promoter. Foxo1 knockdown significantly downregulated Selenop expression in H4IIEC3 cells. Furthermore, CsA downregulated FoxO1 by inactivating its upstream signal transducer and activator of transcription 3 (STAT3). Knockdown of Stat3 downregulated Foxo1 and Selenop expression in hepatocytes. These findings revealed a novel mechanism underlying CsA-induced oxidative stress by downregulating the STAT3-FoxO1-Selenop pathway in hepatocytes. SIGNIFICANCE STATEMENT: This study shows that Cyclosporine A (CsA) downregulates Selenop, an antioxidant protein, by suppressing the signal transducer and activator of transcription 3-forkhead box protein O1 pathway in hepatocytes, possibly one of the causations of CsA-induced oxidative stress in hepatocytes. The present study sheds light on the previously unrecognized CsA-redox axis.

Cyclosporine A downregulates selenoprotein P expression via a STAT3-FoxO1 pathway in hepatocytes in vitro

Cyclosporine A (CsA) is a worldwide applied immunosuppressant for preventing graft rejection and autoimmune diseases. However, CsA elevates oxidative stress leading to liver injuries. The present study aimed to clarify the mechanisms underlying the CsA-mediated oxidative stress. Among the redox proteins, CsA concentration-dependently downregulated Selenop encoding selenoprotein P (SeP), a major circulating antioxidant protein reducing reactive oxygen species (ROS), in hepatocytes cell lines and primary hepatocytes. The luciferase assay identified the CsA-responsive element in the SELENOP promoter containing a putative binding site for FoxO1. The CsA-mediated suppression on the SELENOP promoter was independent of NFAT, a classic target repressed by CsA. A ChIP assay showed that CsA suppressed the FoxO1 binding to the SELENOP promoter. Foxo1 knockdown significantly downregulated Selenop expression in H4IIEC3 cells. Furthermore, CsA downregulated FoxO1 by inactivating its upstream signal transducer and activator of transcription 3 (STAT3). Knockdown of Stat3 downregulated Foxo1 and Selenop expression in hepatocytes. These findings revealed a novel mechanism underlying CsA-induced oxidative stress via downregulating the STAT3-FoxO1-Selenop pathway in hepatocytes. Significance Statement Our study shows that CsA downregulates Selenop, an antioxidant protein, via suppressing the STAT3-FoxO1 pathway in hepatocytes, possibly one of the causations of CsA-induced oxidative stress in hepatocytes. The present study sheds light on the previously unrecognized CsA-redox axis.

Molecular Dynamics Simulations and Experimental Results Provide Insight into Clinical Performance Differences between Sandimmune® and Neoral® Lipid-Based Formulations

OBJECTIVE

Molecular dynamics (MD) simulations provide an in silico method to study the structure of lipid-based formulations (LBFs) and the incorporation of poorly water-soluble drugs within such formulations. In order to validate the ability of MD to effectively model the properties of LBFs, this work investigates the well-known cyclosporine A formulations, Sandimmune® and Neoral®. Sandimmune® exhibits poor dispersibility and its absorption from the gastrointestinal tract is enhanced when administered after food, whereas Neoral® disperses comparatively well and shows no food effect.

METHODS

MD simulations were performed of both LBFs to investigate the differences observed in fasted and fed conditions. These conditions were also tested using an in vitro experimental model of dispersion and digestion.

RESULTS

These MD simulations were able to show that the food effect observed for Sandimmune® can be explained by large changes in drug solubilization on addition of bile. In contrast, Neoral® is well dispersed in water or in simulated fasted conditions, and this dispersion is relatively unchanged on moving to fed conditions. These differences were confirmed using dispersion and digestion in vitro experimental model.

CONCLUSIONS

The current data suggests that MD simulations are a potential method to model the fate of LBFs in the gastrointestinal tract, predict their dispersion and digestion, investigate behaviour of APIs within the formulations, and provide insights into the clinical performance of LBFs.

Investigating the Impact of Crohn's Disease on the Bioaccessibility of a Lipid-Based Formulation with an In Vitro Dynamic Gastrointestinal Model

The aim of the study was to investigate the impact of Crohn's disease (CD) on the performance of a lipid-based formulation of ciprofloxacin in a complex gastrointestinal simulator (TIM-1, TNO) and to compare the luminal environment in terms of bile salt and lipid composition in CD and healthy conditions. CD conditions were simulated in the TIM-1 system with a reduced concentration of porcine pancreatin and porcine bile. The bioaccessibility of ciprofloxacin was similar in simulated CD and healthy conditions considering its extent as well as its time course in the jejunum and ileum filtrate. Differences were observed in terms of the luminal concentration of triglycerides, monoglycerides, and fatty acids in the different TIM-1 compartments, indicating a reduction and delay in the lipolysis of formulation excipients in CD. The quantitative analysis of bile salts revealed higher concentrations for healthy conditions (standard TIM-1 fasted-state protocol) in the duodenum and jejunum TIM-1 compartments compared to published data in human intestinal fluids of healthy subjects. The reduced concentrations of bile salts in simulated CD conditions correspond to the levels observed in human intestinal fluids of healthy subjects in the fasted state.A lipidomics approach with ultra performance liquid chromatography (UPLC)/mass spectrometry (MS) has proven to be a time-efficient method to semiquantitatively analyze differences in fatty acid and bile salt levels between healthy and CD conditions. The dynamic luminal environment in CD and healthy conditions after administration of a lipid-based formulation can be simulated using the TIM-1 system. For ciprofloxacin, an altered luminal lipid composition had no impact on its performance indicating a low risk of altered performance in CD patients.

Higher plasma bilirubin predicts veno-occlusive disease in early childhood undergoing hematopoietic stem cell transplantation with cyclosporine

AIM: To analyze the association between plasma bilirubin levels and veno-occlusive disease (VOD) in non-adult patients undergoing hematopoietic stem cell transplantation (HSCT) during cyclosporine therapy.

METHODS: A total of 123 patients taking cyclosporine were evaluated using an electronic medical system at the Seoul National University Children’s Hospital from the years 2004 through 2011. Patients were grouped by age and analyzed for incidence and type of adverse drug reactions (ADRs) including VOD.

RESULTS: The HSCT patients were divided into three age groups: G#1 ≥ 18; 9 ≤ G#2 ≤ 17; and G#3 ≤ 8 years of age). The majority of transplant donor types were cord blood transplantations. Most prevalent ADRs represented acute graft-vs-host disease (aGVHD) and VOD. Although the incidences of aGVHD did not vary among the groups, the higher frequency ratios of VOD in G#3 suggested that an age of 8 or younger is a risk factor for developing VOD in HSCT patients. After cyclosporine therapy, the trough plasma concentrations of cyclosporine were lower in G#3 than in G#1, indicative of its increased clearance. Moreover, in G#3 only, a maximal total bilirubin level (BILmax) of ≥ 1.4 mg/dL correlated with VOD incidence after cyclosporine therapy.

CONCLUSION: HSCT patients 8 years of age or younger are more at risk for developing VOD, diagnosed as hyperbilirubinemia, tender hepatomegaly, and ascites/weight gain after cyclosporine therapy, which may be represented by a criterion of plasma BILmax being ≥ 1.4 mg/dL, suggestive of more sensitive VOD indication in this age group.

Rhubarb decreased the systemic exposure of cyclosporine, a probe substrate of P-glycoprotein and CYP 3A

1. Rhubarb, rhizome of Rheum palmatum L. (RP), is an important herb in clinical Chinese medicine. 2. Cyclosporine (CSP) is an immunosuppressant with narrow therapeutic window. The oral bioavailability of CSP was associated with P-glycoprotein (P-gp) and CYP 3A4. CSP was used as a probe substrate to investigate the in vivo modulation effects of RP on P-gp and CYP 3A. 3. Rats were orally administered 2.5 mg/kg of CSP with and without 0.25 and 1.0 g/kg of RP. The blood CSP concentration was determined by a specific monoclonal fluorescence polarization immunoassay. 4. Both dosages of RP significantly decreased the Cmax and AUC0-t of CSP in rats. Mechanism studies indicated that RP activated the functions of P-gp and CYP 3A. 5. RP ingestion reduced the systemic exposure of CSP through activating P-gp and CYP 3A.

Influence of Absorption, Distribution, Metabolism, and Excretion Genomic Variants on Tacrolimus/Sirolimus Blood Levels and Graft-versus-Host Disease after Allogeneic Hematopoietic Cell Transplantation

Allelic variants of genes implicated in drug absorption, distribution, metabolism, and excretion (ADME) determine the pharmacokinetic variability of many medications and are increasingly recognized as important factors determining the success or failure of medical treatments. Both tacrolimus and sirolimus have narrow therapeutic ranges maintained by therapeutic drug monitoring (TDM). Using an ADME panel that covers >99% of the PharmaADME working group core list (188 single nucleotide polymorphism [SNP] and 12 copy number variant [CNV] assays in 36 pharmacogenetically relevant genes), we studied 177 patients who underwent allogeneic hematopoietic cell transplantation (HCT) using tacrolimus/sirolimus-based graft-versus-host disease (GVHD) prophylaxis. We tested for possible associations between ADME variants and tacrolimus/sirolimus drug levels, concentration/dose (C/D) ratio, and clinical endpoints, including acute GVHD. A total of 62 SNP and 6 CNV assays were evaluable after removing the variants, which were homozygous in (nearly) all samples. For sirolimus, rs2032582 (ABCB1) T-carriers versus non-T-carriers were associated with higher blood levels (P = .01), with similar results for C/D ratio. Generalized estimating equation analysis supported these findings. For tacrolimus, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were associated with higher blood levels than CYP3A5*1/*1 (P = .002). By multivariable analysis, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were independently associated with decreased acute GVHD compared with CYP3A5*1/*1, after adjustment for conditioning, donor type, race/ethnicity, and age. We demonstrated association of specific ADME genetic polymorphisms with blood levels of tacrolimus/sirolimus, and incidence of acute GVHD after HCT, in spite of TDM and dose adjustment. A larger ongoing study will determine whether these associations have clinical utility beyond TDM.

Comparison of the influence of cyclosporine and tacrolimus on the pharmacokinetics of prednisolone in adult male kidney transplant recipients

BACKGROUND AND OBJECTIVE

Cyclosporine has been observed to precipitate cushingoid features in kidney transplant recipients already on prednisolone. Some pharmacokinetic studies have demonstrated increased prednisolone exposure in patients on cyclosporine therapy compared with azathioprine, whereas other studies have found no difference. The objective of this study was to determine whether cyclosporine impacts on prednisolone exposure as compared with tacrolimus.

METHODS

Adult male kidney transplant recipients treated with prednisolone and either cyclosporine or tacrolimus were recruited for pharmacokinetic blood sampling at the outpatient clinic at the Princess Alexandra Hospital, Brisbane, Australia. Prednisolone plasma concentrations were determined using ultra-high-performance liquid chromatography. Dose-adjusted area under the plasma concentration-time curve (AUC) of free and total prednisolone was estimated using a previously developed limited sampling strategy and non-compartmental analysis.

RESULTS

A total of 55 patients were eligible for analysis; 38 % received cyclosporine and 62 % received tacrolimus co-therapy. No significant difference in mean dose-adjusted total prednisolone AUC from 0 to 6 h post-dose or mean dose-adjusted free prednisolone AUC from 0 to 12 h was observed between the cyclosporine and tacrolimus groups (449 versus 428 nmol·h/L/mg, p = 0.43, and 32 versus 30 nmol·h/L/mg, p = 0.51, respectively).

CONCLUSION

Cyclosporine does not change the dose-adjusted exposure of prednisolone compared with tacrolimus. Adult kidney transplant recipients can therefore continue on their usual prednisolone dose when changing therapy between cyclosporine and tacrolimus.

High intra-individual variability of cyclosporine pharmacokinetics in lung transplant recipients without cystic fibrosis

BACKGROUND

There has been little study on the variability of CsA pharmacokinetics in stable lung transplant (LT) recipients without cystic fibrosis. This study was conducted to determine the prevalence of high intra-individual variability of CsA in LT recipients and its implications in CsA monitoring.

METHODS

Twenty-nine pharmacokinetic curves were performed in 10 consecutive stable patients from a single center. The intra-individual coefficient of variation (CV) of the AUC₀₋₁₂ h was calculated in each case. Patients were grouped according to whether their CV was high (≥20%) or low (<20%). Correlations between cyclosporine CsA concentration at each time point, AUC₀₋₄ h , and AUC₀₋₁₂ h were also calculated.

RESULTS

Six (60%) patients presented low CVs and four (40%) high CVs. In patients with low CVs, the best correlation of AUC₀₋₁₂ h was with CsA concentration at two h post-dose (C₂) (r = 0.674, p = 0.002), whereas in those with high CV, the best correlation was with C5 (r = 0.800, p = 0.003). In the latter group, the correlation with C₂ was low (r = 0.327, p = 0.32), whereas the correlation with C₀ was high (r = 0.709, p < 0.05).

CONCLUSIONS

Intra-individual variability of CsA pharmacokinetics may be high in many LT recipients. In patients with high CV, the use of C₀ levels may be more appropriate for CsA monitoring than C₂ levels.

CYP3A5 polymorphism effect on cyclosporine pharmacokinetics in living donor renal transplant recipients: analysis by population pharmacokinetics

BACKGROUND

Cyclosporine is often used to prevent allograft rejection in renal transplant recipients. However, cyclosporine has a narrow therapeutic window and large variability in its pharmacokinetics. Individual characteristics and genetic polymorphisms can cause the variation. Hence, it is important to determine the cause(s) of the variation in cyclosporine pharmacokinetics. To our knowledge, this is the first reported population pharmacokinetic study of cyclosporine in living donor renal transplant recipients that considered the genetic polymorphism as a covariate.

OBJECTIVE

To build a population pharmacokinetic model of cyclosporine in living donor renal transplant recipients and identify covariates including CYP3A5*3, ABCB1 genetic polymorphisms that affect cyclosporine pharmacokinetic parameters.

METHODS

Clinical characteristics and cyclosporine concentration data for 69 patients who received cyclosporine-based immunosuppressive therapy after living donor renal transplantation were collected retrospectively for up to 400 postoperative days. CYP3A5*1/*3 and ABCB1C1236T, G2677T/A, C3435T geno-typing was performed. A population pharmacokinetic analysis was conducted using a NONMEM program. After building the final model, 1000 bootstrappings were performed to validate the final model.

RESULTS

In total, 2034 blood samples were collected. A 1-compartment open model with first-order absorption and elimination was chosen to describe the pharmacokinetics of cyclosporine. A population pharmacokinetic analysis showed that postoperative days, sex, and CYP3A5 genotype significantly affected the pharmacokinetics of cyclosporine. The final estimate of mean clearance was 56 L/h, and the mean volume of distribution was 4650 L. The interindividual variability for these parameters was 22.98% and 51.48%, respectively.

CONCLUSIONS

Using the present model to calculate the dose of cyclosporine with CYP3A5 genotyping can be possible for the patients whose cyclosporine concentration is not within the therapeutic range even with therapeutic drug monitoring.

The potential of steroids and xenobiotic receptor polymorphisms in forecasting cyclosporine pharmacokinetic variability in young kidney transplant recipients

The steroids and xenobiotics receptor (SXR) up-regulates the expression and the synthesis of key enzymes in CyA metabolism. In this study, we examined the possible interactions between CyA exposure and SXR polymorphisms during the first year after renal transplantation. The study involved 66 pediatric renal transplant recipients (25 women and 41 men, mean age 13.9 ± 7.4 yr). All patients were genotyped for two sequence variations in the NR1I2 gene: g.-205_-200delGAGAAG and 7635 A>G. CyA trough levels and CyA weight-adjusted daily dose were recorded at 30, 90, 180, and 360 days after transplantation and compared between the different genotypes. A third newly discovered SXR polymorphism was characterized and also included in the study. CyA trough levels and CyA weight-adjusted daily dose were comparable on four time points throughout the first year post-transplant in all three groups. GEE showed a significant reduction in weight-adjusted CyA daily dose in patients carrying the deletion of 6 bp in SXR with a significant group-by-time effect that persisted also when analysis was corrected for age, prednisone dose, and acute rejection episodes. In our group of patients, only the g.-205_-200delGAGAAG SXR polymorphism was able to influence the metabolism of CyA continuously, during the first year after transplantation.

The Emit® 2000 Cyclosporine Specific Assay, Extended Range: development of an application protocol for the V-Twin® analyzer

We evaluated a new protocol for measurement of cyclosporine A (CsA) 2 H after dose (C2) on the V-Twin® analyzer. Imprecision, recovery, and linearity were determined using CsA-spiked blood pools. Accuracy was evaluated using specimens from renal, cardiac, and liver transplant patients, and results were compared with those from liquid chromatography-tandem mass spectrometry (LC-MS/MS) and the Abbott TDx®/TDxFLx® assay. Cross-reactivity and interferences were assessed in the presence of 800 ng/mL CsA. Imprecision coefficients of variation were 3.3%-4.8% (within run) and 5.9%-8.7% (total). Recovery was within 10% of the expected values. Linearity was 350-2,000 ng/mL. Calibration was stable for ≥ 2 weeks. Method comparison showed regression statistics: V-Twin® = 1.01 × LC tandem MS + 36.1, r = 0.971; V-Twin® = 1.13 × Abbott - 92.4, r = 0.969. Metabolite cross-reactivity and interference (endogenous substances and drugs) were within ±10%. The C2 protocol on the V-Twin® analyzer provides acceptable assay performance and accurate determination of whole blood CsA drawn at 2 H after dose.

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.

Population pharmacokinetic study of cyclosporine in patients with nephrotic syndrome

Cyclosporine (CsA) is widely used in the treatment of nephrotic syndrome (NS). A population pharmacokinetic (PopPK) model was developed using trough blood CsA concentration data from 106 patients with NS. The pharmacokinetic analysis was performed using NONMEM with 1-compartment linear model and first-order elimination. Proportional and additive error models were used to describe the interindividual and intraindividual variabilities, respectively. Body weight (WT), serum albumin level (ALB), and combination therapy with rifampicin were found to be the most significant covariates explaining the variability of the apparent clearance (CL/F) of CsA among patients. The final model was as follows: TVCL/F=34.1x(WT/67.6)(1.08)x(1+RFAx0.67)x(1-ALBx0.0088); TVV/F=3.5xWT; Ka=1.28 fixed; where RFA=1 with concurrent rifampicin use and 0 otherwise. The interindividual variabilities of CL/F and V/F were 18% and 27%, respectively. The residual error was 0.064 mg/L. The mean+/-SD of CL/F and V/F of the 106 patients were 23.5+/-7.2 L/h and 232.3+/-71.5 L, respectively. The reliability and stability of the PopPK model were confirmed by nonparametric bootstrap procedure.

Haplotypic structure of ABCB1/MDR1 gene modifies the risk of the acute allograft rejection in renal transplant recipients

BACKGROUND

Bioavailability of tacrolimus (Tac) and cyclosporine is determined by cytochrome P450IIIA and by P-glycoprotein encoded by the CYP3A4/CYP3A5 and ABCB1 genes. Polymorphisms in these genes have been suggested to influence acute rejection and pharmacokinetics in renal transplantation. We aimed to validate these findings in a haplotype analysis.

METHODS

A total of 832 renal transplant recipients were genotyped for the CYP3A4 -288A>G, CYP3A5 +6986G>A, ABCB1 +1236C>T, +2677G>T>A, and +3435C>T polymorphisms. Their association with acute rejection and with pharmacokinetic parameters was analyzed in haplotype models.

RESULTS

Apart from human leukocyte antigen-DR mismatches, delayed graft function and age at renal transplantation, acute rejection was also predicted by the [ABCB1 +1236C; +2677G; +3435T] haplotype. Allograft survival was determined by donor age, age at renal transplantation, delayed graft function, cold ischemia, and history of more than two acute rejections. Homozygotes for the [CYP3A4 -288A; CYP3A5 +6986G] haplotype achieved earlier therapeutic concentrations of Tac and a higher concentration to dose ratio at week 1. ABCB1 haplotypes did not influence pharmacokinetic parameters.

CONCLUSIONS

ABCB1 haplotypes modify the risk of acute rejection, suggesting that ABCB1 allelic arrangement is a stronger regulator of P-glycoprotein activity than single polymorphisms. The risk of acute rejection determined by ABCB1 is independent of pharmacokinetic parameters. CYP3A haplotypes control the bioavailability of Tac, but do not modify the risk of acute rejection.

Effect of probucol on the oral bioavailability of cyclosporine A

We have previously reported the reduction in oral bioavailability of cyclosporine A (CsA) by probucol, a lipid-lowering drug. To evaluate the mechanism, we examined the effect of probucol on the transport of CsA across Caco-2 cell monolayers, on the influence of CsA pharmacokinetics in rats, and on the change of ultraviolet-absorption spectrum of the drug. Pretreatment with probucol (50 microM) inhibited (P < 0.001) both the apical-to-basal (-73.1%) and basal-to-apical (-77.8%) fluxes of [3H]-CsA. In rats, probucol orally given 6 h after, but not simultaneous with CsA did not decrease peak CsA concentration or area under the blood CsA concentration-time curve following a single oral dosing of CsA after the pretreatment with probucol for 7 days. These data indicate that P-glycoprotein-mediated active transport from intracellular to apical is not involved in the mechanism of probucol-CsA interaction, and absorption of CsA decreases in the presence of probucol in the gastrointestinal tract. In difference spectral analysis, probucol reduced the absorption peak of CsA in a concentration-dependent manner, indicating that probucol could form a complex with CsA. These results suggest that probucol interferes with CsA absorption probably by physicochemical mechanism such as complex formation, but not the enhancement of P-glycoprotein function.

Tuberculosis in renal transplant recipients: rifampicin sparing treatment protocol

The reactivation of mycobacterium infection in renal transplant recipients in developing countries is a common therapeutic dilemma, especially in those patients receiving cyclosporin immunosuppression. The inclusion of rifampicin in the antituberculosis protocol increases the risk of precipitating acute allograft rejection due to its interaction with cyclosporin and also increases the financial burden. We successfully treated 16 patients who developed mycobacterial infection post renal transplant with a rifampicin sparing antituberculosis drug regimen. Pyrexia of unknown origin was the most common manifestation observed and a therapeutic trial with antituberculosis drugs is justified. De novo diabetes mellitus appears to be an added risk factor and increases the susceptibility to mycobacterial infection.

Maintenance triple immunosuppression with cyclosporin A, mycophenolate sodium and steroids allows prolonged survival of primate recipients of hDAF porcine renal xenografts

To date, the best results in life-supporting pig-to-primate renal xenotransplantation have been obtained in recipients exposed to long-term immunosuppression with cyclophosphamide. As this agent is frequently associated with side-effects, we have explored the potential of a mycophenolate sodium-based maintenance immunosuppression in this model. Human decay-accelerating factor (hDAF) transgenic kidneys were transplanted into splenectomized and bilaterally nephrectomized cynomolgus monkeys immunosuppressed with mycophenolate sodium, cyclosporin A and steroids, and exposed to a brief induction course with cyclophosphamide (up to four doses). After transplantation, the primates were monitored daily for biochemical and haematological evaluations and for the measurements of haemolytic anti-pig antibodies (APA). A detailed histological analysis of each explanted graft was also performed. All the animals showed very poor initial graft function but survived for up to 51 days. In contrast to our previous studies in xenograft recipients on long-term immunosuppression with cyclophosphamide, minimal or no circulating xeno-directed antibodies, as measured by the evaluation of APA titres, were detected in this series although some degree of acute humoral rejection was observed in all the explanted grafts and was the primary cause of graft failure. Furthermore, in addition to areas of humorally mediated graft damage, we have observed for the first time areas with exclusive and prominent infiltration by CD2+ and CD8+ mononuclear cells presenting patterns compatible with tubulitis, glomerulitis and arteritis, which we have called acute cellular xenograft rejection (ACXR). In addition, CD68+ infiltrating macrophages and CD20+ B-cells were also present. This study demonstrates that a triple maintenance immunosuppression with mycophenolate sodium, cyclosporin A and steroids is a viable alternative to a cyclophosphamide-based immunosuppression to obtain prolonged survival of porcine organs transplanted into primates. However, a more stringent control of antibody forming cells remains essential to further extend the survival of xenografts in this model. In addition, the use of the immunosuppressive regimen reported here in the primate is associated with the occurrence of a new category of cell-mediated xenograft injury (ACXR) whose significance has yet to be clarified.

Pharmacokinetic considerations in the treatment of inflammatory bowel disease

This review describes the pharmacokinetics of the major drugs used for the treatment of inflammatory bowel disease. This information can be helpful for the selection of a particular agent and offers guidance for effective and well tolerated regimens. The corticosteroids have a short elimination half-life (t1/2beta) of 1.5 to 4 hours, but their biological half-lives are much longer (12 to 36 hours). Most are moderate or high clearance drugs that are hepatically eliminated, primarily by cytochrome P450 (CYP) 3A4-mediated metabolism. Prednisone and budesonide undergo presystemic elimination. Any disease state or comedication affecting CYP3A4 activity should be taken into account when prescribing corticosteroids. Depending on the preparation used, 10 to 50% of an oral or rectal dose of mesalazine is absorbed. Rapid acetylation in the intestinal wall and liver (t1/2beta 0.5 to 2 hours) and transport probably by P-glycoprotein affect mucosal concentrations of mesalazine, which apparently determine clinical response. Any clinical condition influencing the release and topical availability of mesalazine might modify its therapeutic potential. Metronidazole has high (approximately 90%) oral bioavailability, with hepatic elimination characterised by a t1/2beta of 6 to 10 hours and a total clearance of about 4 L/h/kg. Ciprofloxacin is largely excreted unchanged both renally (about 45% of dose) and extrarenally (25%), with a relatively short t1/2beta (3.5 to 7 hours). Thus, renal function affects the systemic availability of ciprofloxacin. Both mercaptopurine and its prodrug azathioprine are metabolised to active compounds (6-thioguanine nucleotides; 6-TGN) by hypoxanthine-guanine phosphoribosyltransferase and to inactive metabolites by the polymorphically expressed thiopurine S-methyltransferase (TPMT) and xanthine oxidase. Patients with low TPMT activity have a higher risk of developing haemopoietic toxicity. Both mercaptopurine and azathioprine have a short t1/2beta (1 to 2 hours), but the t1/2beta of 6-TGN ranges from 3 to 13 days. Therapeutic response seems to be related to 6-TGN concentration. Almost complete bioavailability has been observed after intramuscular and subcutaneous administration of methotrexate, which is predominantly (85%) excreted as unchanged drug with a t1/2beta of up to 50 hours. Thus, renal function is the major determinant for disposition of methotrexate. Cyclosporin is slowly and incompletely absorbed. It is extensively metabolised by CYP3A4/5 in the liver and intestine (median t1/2beta and clearance 7.9 hours and 0.46 L/h/kg, respectively), and inhibitors and inducers of CYP3A4 can modify response and toxicity. Infliximab is predominantly distributed to the vascular compartment and eliminated with a t1/2beta between 10 and 14 days. No accumulation was observed when it was administered at intervals of 4 or 8 weeks. Methotrexate may reduce the clearance of infliximab from serum.

Obesity in transplant patients: case report showing interference of orlistat with absorption of cyclosporine and review of literature

OBJECTIVE

To report a case of an obese patient who had undergone renal transplantation and who had subtherapeutic levels of serum cyclosporine after treatment with orlistat.

METHODS

The clinical and laboratory findings are presented, and the few cases reported in the literature are reviewed.

RESULTS

A 29-year-old woman had subtherapeutic plasma levels of cyclosporine after orlistat treatment (360 mg/day) was initiated. The subtherapeutic levels persisted even though orlistat was administered the recommended 2 hours before ingestion of cyclosporine and even though the dosage of orlistat was decreased to only 240 mg/day. Because an increase of body weight is common after organ transplantation, treatment with orlistat has been used. In such patients, however, six cases of reduced therapeutic plasma levels of cyclosporine have been reported. Although a drug-drug interaction has been suggested, this case suggests that the decreased plasma cyclosporine levels are due to reduced absorption of fats rather than a drug-drug interaction. Because this patient was unable to adhere to a low-fat diet, she experienced severe diarrhea, a factor that may have dramatically diminished the absorption of cyclosporine.

CONCLUSION

Adherence to a low-fat diet should be strongly recommended if orlistat is prescribed to patients taking cyclosporine. Moreover, strict surveillance of the plasma concentration of cyclosporine is important.

The effect of gut metabolism on tacrolimus bioavailability in renal transplant recipients

BACKGROUND

Tacrolimus, a substrate of CYP3A, has low and variable bioavailability similar to cyclosporine. Co-administration of ketoconazole, potent inhibitor of gut and hepatic CYP3A, has been shown to increase tacrolimus bioavailability in healthy volunteers. The purpose of this study is to assess the role of gut metabolism in the overall bioavailability of tacrolimus in a renal transplant population.

METHODS

We prospectively studied 19 adult renal transplant recipients who were receiving tacrolimus as part of a quadruple, sequential immunosuppression regimen. Each patient received tacrolimus (4-hr intravenous dose of 0.04 mg/kg between postoperative days 2 and 4). Whole blood samples were collected over 24 hr. After a 24-hr washout period, a single oral dose of ketoconazole (400 mg) was administered followed by the same intravenous dose of tacrolimus, and subsequent samples were obtained. Steady state oral pharmacokinetic profiles were obtained between 1 and 3 months after transplant while patients were receiving twice daily dosing of tacrolimus to maintain whole blood levels between 10 and 20 ng/ml. Two days later, 400 mg of ketoconazole was administered orally 2 hr before to the morning dose. Whole blood samples were collected over 12 hr.

RESULTS

In the absence of ketoconazole, 8.0% of the tacrolimus dose underwent first pass metabolism (E(H)), whereas in the presence of ketoconazole, first pass metabolism was 6.2% (P=0.01). Based on this difference in first pass metabolism, an increase of 2% in bioavailability is expected, but an increase of 47% is observed (P=0.001).

CONCLUSIONS

This indicates that the gut metabolism of tacrolimus is extensive and contributes significantly to its bioavailability.

Enhanced cerebral uptake of receptor ligands by modulation of P-glycoprotein function in the blood-brain barrier

Low cerebral uptake of some therapeutic drugs can be enhanced by modulation of P-glycoprotein (P-gp), an ATP-driven drug efflux pump at the blood-brain barrier (BBB). We investigated the possibility of increasing cerebral uptake of the beta-adrenergic ligands S-1'-[(18)F]-fluorocarazolol (FCAR) and [(11)C]-carazolol (CAR) in P-gp knockout mice (mdr1a (-/-)) and by modulation of P-gp with cyclosporin A (CsA) in rats. Specific and nonspecific binding of FCAR in the rat brain were doubled by CsA, while target/nontarget ratios and clearance from plasma (area under curve (AUC)) were not affected. Cerebral uptake of CAR in rats was much lower than FCAR and nonspecific. CsA increased this uptake 5-6-fold, not only due to P-gp modulation in the BBB but also to a 2-fold higher plasma AUC. In the CNS of mdr1a (-/-) mice, uptake of FCAR and CAR was, respectively, 2-fold and 3-fold higher than in mdr1a (+/+) mice. These results indicate that the cerebral uptake of beta-adrenoceptor ligands can be increased by administration of P-gp modulators such as CsA without affecting regional distribution in the brain. P-gp modulation could improve the count statistics in PET studies of the CNS.

Effect of assay methodology on pharmacokinetic differences between cyclosporine Neoral® and Sandimmune® formulations

The new oral formulation of cyclosporine (CsA), Neoral® (CsA-N), results in increased area under the curve (AUC) and decreased intra- and interindividual variation in blood concentrations and other pharmacokinetic (PK) parameters when compared with the current Sandimmune® (CsA-S) formulation. The present study examines the effect of assay methodology on variability in blood concentrations and PK parameters for renal transplant patients receiving CsA-N and CsA-S and whether this variation is reduced with CsA-N. The results show that interindividual variations in PK parameters for patients receiving CsA-N were less than those for patients receiving CsA-S. Both blood concentrations and dose of CsA better correlated with abbreviated (4-h) AUC after administration of CsA-N. For both CsA-S and CsA-N, blood concentrations at 4 h postdose exhibited the best correlation with AUC. All samples were analyzed by three common procedures: HPLC, RIA, and fluorescence polarization immunoassay (FPIA). There were no significant differences observed in blood concentrations or PK parameters obtained from FPIA and RIA. HPLC results, however, were lower because of specificity of this method for the parent drug. The assay methodology did not have an effect on interindividual variability, indicating that the cross-reactivity of metabolites in commonly used immunoassays for CsA does not contribute to the PK variability observed in renal transplant patients.

Clinical pharmacology in gastroenterology: development of new forms of treatment of inflammatory bowel disease

Kinetic-dynamic aspects of the development of slow-release mesalazine, Pentasa (now an established treatment of inflammatory bowel disease (IBD)), and cyclosporin, a T cell selective immunosuppressant (still in the investigative phase), are reviewed as examples of Danish contributions at an early stage to international, clinical drug research. Apart from increasing the therapeutic options for patients with IBD, current and future studies with these (and other) drugs may add important clues to a more precise understanding of the basic pathogenetic mechanisms (e.g. cytokines, adhesion molecules) involved in these diseases. The future development and clinical implementation of novel drug designs in IBD and other gastrointestinal diseases may be expected to benefit from a continued or even closer collaboration between clinical gastroenterologists and basic research institutions, including the pharmaceutical industry at an early stage.

Absence of the mdr1a P-Glycoprotein in mice affects tissue distribution and pharmacokinetics of dexamethasone, digoxin, and cyclosporin A

We have previously shown that absence of the mouse mdr1a (also called mdr3) P-glycoprotein in mdr1a (-/-) "knockout" mice has a profound effect on the tissue distribution and elimination of vinblastine and ivermectin, and hence on the toxicity of these compounds. We show here that the mouse mdr1a and the human MDR1 P-glycoprotein actively transport ivermectin, dexamethasone, digoxin, and cyclosporin A and, to a lesser extent, morphine across a polarized kidney epithelial cell layer in vitro. Injection of these radio-labeled drugs in mdr1a (-/-) and wild-type mice resulted in markedly (20- to 50-fold) higher levels of radioactivity in mdr1a (-/-) brain for digoxin and cyclosporin A, with more moderate effects for dexamethasone (2- to 3-fold) and morphine (1.7-fold). Digoxin and cyclosporin A were also more slowly eliminated from mdr1a (-/-) mice. Our findings show that P-glycoprotein can be a major determinant for the pharmacology of several medically important drugs other than anti-cancer agents, especially in the blood-brain barrier. These results may explain a range of pharmacological interactions observed between various drugs in patients.

The cyclosporins

This review presents the progress and some aspects achieved during recent years with cyclosporin sources, chemistry, biological activities, side effects, biosynthesis and metabolism. Although incomplete the results indicate future research trends and some white spots to be studied in the near future to afford unique insights into cell biology and to improve the search for similar and even more specific agents based on rational drug design.

A pharmacokinetic comparison of cyclosporin oral solution and cyclosporin capsules in heart and lung transplant recipients

Pharmacokinetic profiles were obtained for 16 heart or lung recipients following the administration of identical doses of cyclosporin as oral solution and capsules on consecutive days. A comparison of pharmacokinetic parameters (AUC, Cmax, Cmin and tmax) showed that there were no significant differences between the two formulations except for the tmax, which was significantly longer for the capsules. The mean variation in day-to-day trough levels produced by the two different forms was 25.6%. A retrospective study was carried out of consecutive cyclosporin levels in patients at steady state on oral solution. The mean variation in day-to-day trough levels was 32.3%. This was not significantly different from the variation in consecutive trough levels seen in the oral solution/capsule comparison. This study shows that cyclosporin capsules can be substituted for oral solution without causing acute changes in cyclosporin blood levels, and that the pharmacokinetics of the two formulations are similar.

Effect of etretinate on cyclosporin metabolism in vitro

Cyclosporin (CyA) is an effective treatment for psoriasis, including cases unresponsive to other therapies. The major side-effect of CyA treatment is dose-related nephrotoxicity. Combinations of CyA and etretinate (Et) have been tested with a view to reducing CyA dose requirements, and therefore minimizing adverse effects. We have studied the effect of Et on the cytochrome P-450-mediated metabolism of CyA. Microsomes prepared from histologically normal human (obtained from four cadaver kidney transplant donors; all male; age range 21-56) were incubated with CyA and various concentrations of Et. Metabolism was quantified by high-performance liquid chromatography with radiometric detection, and metabolites tentatively identified from the retention times of authentic standards. After 30 min incubation of CyA and microsomal protein at 37 degrees C, 10.1 +/- 3.0% (mean +/- SD) 3H-CyA was converted to the monohydroxylated metabolites M1 and M17, and 3.3 +/- 0.8% to the N-demethylated metabolite M21. At an Et concentration of 100 microM inhibition of CyA hydroxylase and N-demethylase was < 20%. This study indicates that there is no metabolic interaction between CyA and Et in vitro; it is likely that the two drugs are metabolized by different P-450 isoenzymes.

Cyclosporin pharmacokinetics after intravenous and oral administration in patients with Crohn's disease

Cyclosporin kinetics were estimated after single-dose intravenous and oral administration in 12 patients with Crohn's disease in accordance with a three-compartment model with zero-order inputs. Cyclosporin was measured in whole blood with a specific monoclonal radioimmunoassay. The median bioavailability (f) was 23.7% (range, 0-49.1%); the distribution volume at steady state, 2.3 l/kg (range, 1.0-3.5 l/kg); clearance (CL), 7.6 ml/min/kg (range, 4.8-10.8 ml/min/kg); and t1/2(z) 7.9 h (range, 3.2-13.9 h). Both the extent and rate of bioavailability were significantly lower in six of the patients, who had low or undetectable cyclosporin levels during a preceding therapeutic trial. After repeated oral administration significant correlations were found between the single-dose f/CL ratios and the steady-state blood concentrations, indicating that the kinetics did not change markedly with time. We conclude that the disposition kinetics of cyclosporin in patients with Crohn's disease are comparable to those of other groups, whereas the bioavailability may be decreased. It is suggested that cyclosporin levels should be monitored closely, and intravenous treatment should be considered in patients with a rapid gut transit time, because cyclosporin absorption seems to follow zero-order kinetics.

Cyclosporin metabolism by human gastrointestinal mucosal microsomes

The in vitro metabolism of the immunosuppressant cyclosporin (CsA) by human gastrointestinal mucosal microsomes has been studied. Macroscopically normal intestinal (n = 4) and liver (n = 2) tissue was obtained from kidney transplant donors, and microsomes prepared. Intestinal metabolism was most extensive with duodenal protein (15% conversion to metabolites M1/M17 after 2 h incubation at 37 degrees C; metabolite measurement by h.p.l.c). Western blotting confirmed the presence of P-4503A (enzyme subfamily responsible for CsA metabolism) in duodenum and ileum tissue, but not in colon tissue. The results of this study indicate that the gut wall may play a role in the first-pass metabolism of CsA, and could therefore be a contributory factor to the highly variable oral bioavailability of CsA.

Chronopharmacokinetics of Cyclosporine A in the Wistar rat following oral administration

The pharmacokinetics of Cyclosporine A (CsA) was studied in male Wistar rats weighting 300 +/- 50 g trained to a 12:12 light-dark cycle. Oral administration (40 mg/kg) was performed at 1 of 4 different temporal stages: 09.00 h, 15.00 h, 21.00 h or 03.00 h (local time) i.e. 0200, 0800, 1400 or 2000 HALO (hours after light on). Blood samples were collected over 72-96 h after dosing, plasma was separated by centrifugation at 37 degrees C and stored frozen until assay, using radioimmunoassay (RIA). Two experiments were performed: the first with 4 groups of 48 rats and a non-specific polyclonal antibody (P-RIA); and the second with only 2 groups of 48 rats and a more specific monoclonal antibody (M-RIA). Plasma concentration data were evaluated with model-based linear pharmacokinetic concepts, with apparent zero-order or first-order absorption and n-exponential disposition (n = 1, 2 or 3): models MN0 or MN1. A compartment-independent approach was also conducted and led to area under the plasma concentration-time curve (AUC) and mean residence time (MRT) determinations. A comparison of the pharmacokinetic profiles across time of administration indicates that absorption, first-pass metabolism and tissue distribution of CsA in the rat are circadian-dosing stage dependent.

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.

Cyclosporin metabolism by the gastrointestinal mucosa

The intestinal mucosal metabolism of the immunosuppressant cyclosporin (CsA) has been studied in vitro using the Ussing chamber technique. Histologically normal colon was obtained from six patients undergoing resections. The mucosal sheets were mounted between two perspex chambers. Three hours after addition of [3H]-CsA (0.2 microCi; 10 microM) to the mucosal chamber, more than 90% of the radioactivity was present in that chamber. Metabolite analysis, by high performance liquid chromatography, indicated that 77.6 +/- 9.2% (mean +/- s.d.) of the drug present was CsA, 9.9 +/- 4.4% and 8.7 +/- 4.7% were the oxidative metabolites M17 and M21 respectively (metabolites identified by co-chromatography with authentic standards). Total metabolite production in tissues from the six individuals was variable (10.1-30.6% at 3 h) and increased over the time period of the study. A different pattern of metabolism was obtained from a single sample of gastric mucosa. More than 20% of CsA was metabolised although neither M17 nor M21 were detected. The results of this study suggest that the gut wall is involved in the first pass metabolism of CsA in vivo and that this could be a contributory factor to the poor systemic availability of CsA seen in some patients.