Use of sirolimus in solid organ transplantation

Sirolimus is a mammalian target of rapamycin (mTOR) inhibitor that inhibits cell cycle progression and has proven to be a potent immunosuppressive agent for use in solid organ transplant recipients. The drug was initially studied as an adjunct to ciclosporin (cyclosporine) to prevent acute rejection in kidney transplant recipients. Subsequent studies have shown efficacy when combined with a variety of other immunosuppressive agents. The most common adverse effects of sirolimus are hyperlipidaemia and myelosuppression. The drug has unique antiatherogenic and antineoplastic properties, and may promote immunological tolerance and reduce the incidence of chronic allograft nephropathy. Although sirolimus is relatively non-nephrotoxic when administered as monotherapy, it pharmacodynamically enhances the toxicity of calcineurin inhibitors. Ironically, the drug has been used to facilitate calcineurin inhibitor-free protocols designed to preserve renal function after solid organ transplantation. Whether sirolimus can be used safely over the long term with low doses of calcineurin inhibitors requires further study. The use of sirolimus as a corticosteroid-sparing agent also remains to be proven in controlled trials. Postmarketing studies have revealed a number of unforeseen adverse effects including impaired wound healing and possibly proteinuria, oedema, pneumonitis and thrombotic microangiopathy. Overall, sirolimus is a powerful agent when used judiciously with other available immunosuppressants. As is true for all immunosuppressive drugs available for treatment of solid organ transplant recipients, the efficacy of the drug must be balanced against its considerable adverse effects.     

Benefit-risk assessment of sirolimus in renal transplantation.

Sirolimus (rapamycin) is a macrocyclic lactone isolated from a strain of Streptomyces hygroscopicus that inhibits the mammalian target of rapamycin (mTOR)-mediated signal-transduction pathways, resulting in the arrest of cell cycle of various cell types, including T- and B-lymphocytes. Sirolimus has been demonstrated to prolong graft survival in various animal models of transplantation, ranging from rodents to primates for both heterotopic, as well as orthotopic organ grafting, bone marrow transplantation and islet cell grafting. In human clinical renal transplantation, sirolimus in combination with ciclosporin (cyclosporine) efficiently reduces the incidence of acute allograft rejection. Because of the synergistic effect of sirolimus on ciclosporin-induced nephrotoxicity, a prolonged combination of the two drugs inevitably leads to progressive irreversible renal allograft damage. Early elimination of calcineurin inhibitor therapy or complete avoidance of the latter by using sirolimus therapy is the optimal strategy for this drug. Prospective randomised phase II and III clinical studies have confirmed this approach, at least for recipients with a low to moderate immunological risk. For patients with a high immunological risk or recipients exposed to delayed graft function, sirolimus might not constitute the best therapeutic choice--despite its ability to enable calcineurin inhibitor sparing in the latter situation--because of its anti-proliferative effects on recovering renal tubular cells. Whether lower doses of sirolimus or a combination with a reduced dose of tacrolimus would be advantageous in these high risk situations remains to be determined. Clinically relevant adverse effects of sirolimus that require a specific therapeutic response or can potentially influence short- and long-term patient morbidity and mortality as well as graft survival include hypercholesterolaemia, hypertriglyceridaemia, infectious and non-infectious pneumonia, anaemia, lymphocele formation and impaired wound healing. These drug-related adverse effects are important determinants in the choice of a tailor-made immunosuppressive drug regimen that complies with the individual patient risk profile. Equally important in the latter decision is the lack of severe intrinsic nephrotoxicity associated with sirolimus and its advantageous effects on arterial hypertension, post-transplantation diabetes mellitus and esthetic changes induced by calcineurin inhibitors. Mild and transient thrombocytopenia, leukopenia, gastrointestinal adverse effects and mucosal ulcerations are all minor complications of sirolimus therapy that have less impact on the decision for choosing this drug as the basis for tailor-made immunosuppressive therapy. It is clear that sirolimus has gained a proper place in the present-day immunosuppressive armament used in renal transplantation and will contribute to the development of a tailor-made immunosuppressive therapy aimed at fulfilling the requirements outlined by the individual patient profile.     

Everolimus: a review of its use in renal and cardiac transplantation

Everolimus (Certican) is an orally administered mammalian target of rapamycin inhibitor (proliferation signal inhibitor) derived from sirolimus (rapamycin), which is used as part of immunosuppressant therapy in kidney and heart transplantation. When evaluated as part of triple therapy with ciclosporin and corticosteroids, everolimus showed equivalent efficacy to mycophenolate mofetil after renal transplantation, and superiority to azathioprine in cardiac transplant recipients, in terms of reducing efficacy failure after transplantation. Everolimus potentiates ciclosporin-associated nephrotoxicity, and it is recommended that concentration-controlled everolimus is used with reduced-dosage ciclosporin in order to limit renal toxicity while retaining immunosuppressive efficacy. Ongoing trials with everolimus, such as the evaluation of ciclosporin-withdrawal strategies, should help clarify its optimal usage. The use of everolimus may be associated with reduced rates of cytomegalovirus (CMV) infection and of cardiac allograft vasculopathy. Available data suggest that everolimus may be cost-neutral for healthcare providers.     

Sirolimus: new preparation. No tangible advance in renal transplantation

(1) Sirolimus, an immunosuppressant, is chemically related to tacrolimus but has a different mechanism of action. (2) In a double-blind trial in patients also treated with ciclosporin and a steroid, sirolimus was more effective than azathioprine at preventing acute rejection during the first three months, but caused more adverse effects (especially renal). (3) An unblinded trial compared ciclosporin + steroid + sirolimus with steroid + sirolimus for maintenance treatment. Ciclosporin was withdrawn gradually from the steroid + sirolimus group. Side effects from ciclosporin were therefore reduced (mainly nephrotoxicity and arterial hypertension), but rates of acute rejection, hepatotoxicity, and thrombocytopenia went up. (4) Sirolimus has numerous adverse effects, including hyperlipidemia, thrombocytopenia, hepatic disorders and opportunistic infections. The adverse effects of long term treatment are unknown. Sirolimus is metabolised by the cytochrome P450 isoenzyme CYP3A4, so may induce drug interactions. (5) In practice, sirolimus offers no advantage over existing immunosuppressive treatments for people with renal transplants.     

Population pharmacokinetics of sirolimus in de novo Chinese adult renal transplant patients

AIMS

This study was aimed at determining the population pharmacokinetics of sirolimus and identifying factors that explain pharmacokinetic variability in de novo Chinese adult renal transplant patients.

METHODS

Data were retrospectively extracted from a formal multicentre clinical trial, which was originally designed to evaluate the safety and efficacy of ciclosporin dose reduction and ciclosporin elimination in patients receiving sirolimus. All patients received 12-month treatment, i.e. induction therapy with ciclosporin, sirolimus and corticosteroids during the first 3 months followed by either ciclosporin dose reduction or ciclosporin discontinuation thereafter. Eight-hundred and four sirolimus trough blood concentrations (C₀) from 112 patients were used to develop a population pharmacokinetic model using the nonmem program. A one-compartment model with first-order absorption and elimination was selected as the base model. The influence of demographic characteristics, biochemical and haematological indices, ciclosporin daily dose, ciclosporin C₀ as well as other commonly used co-medications were explored.

RESULTS

The typical values with interindividual variability for apparent clearance (CL/F) and apparent volume of distribution (V/F) were 10.1 l h⁻¹ (23.8%) and 3670 l (56.7%), respectively. The residual variability was 29.9%. CL/F decreased significantly with silymarin or glycyrrhizin co-therapy in hepatically impaired patients, and with increasing total cholesterol levels or ciclosporin C₀. Moreover, CL/F increased nonlinearly with increasing sirolimus daily dose. The median parameter estimates from a nonparametric bootstrap procedure were comparable and within 5% of the estimates from nonmem.

CONCLUSIONS

These results provide important information for clinicians to optimize sirolimus regimens in Chinese renal transplant patients.     

Gout in solid organ transplantation: a challenging clinical problem

Hyperuricaemia occurs in 5-84% and gout in 1.7-28% of recipients of solid organ transplants. Gout may be severe and crippling, and may hinder the improved quality of life gained through organ transplantation. Risk factors for gout in the general population include hyperuricaemia, obesity, weight gain, hypertension and diuretic use. In transplant recipients, therapy with ciclosporin (cyclosporin) is an additional risk factor.Hyperuricaemia is recognised as an independent risk factor for cardiovascular disease; however, whether anti-hyperuricaemic therapy reduces cardiovascular events remains to be determined.Dietary advice is important in the management of gout and patients should be educated to partake in a low-calorie diet with moderate carbohydrate restriction and increased proportional intake of protein and unsaturated fat. While gout is curable, its pharmacological management in transplant recipients is complicated by the risk of adverse effects and potentially severe interactions between immunosuppressive and hypouricaemic drugs. NSAIDs, colchicine and corticosteroids may be used to treat acute gouty attacks. NSAIDs have effects on renal haemodynamics, and must be used with caution and with close monitoring of renal function. Colchicine myotoxicty is of particular concern in transplant recipients with renal impairment or when used in combination with ciclosporin. Long-term urate-lowering therapy is required to promote dissolution of uric acid crystals, thereby preventing recurrent attacks of gout. Allopurinol should be used with caution because of its interaction with azathioprine, which results in bone marrow suppression. Substitution of mycophenylate mofetil for azathioprine avoids this interaction. Uricosuric agents, such as probenecid, are ineffective in patients with renal impairment. The exception is benzbromarone, which is effective in those with a creatinine clearance >25 mL/min. Benzbromarone is indicated in allopurinol-intolerant patients with renal failure, solid organ transplant or tophaceous/polyarticular gout. Monitoring for hepatotoxicty is essential for patients taking benzbromarone.Physicians should carefully consider therapeutic options for the management of hypertension and hyperlipidaemia, which are common in transplant recipients. While loop and thiazide diuretics increase serum urate, amlodipine and losartan have the same antihypertensive effect with the additional benefit of lowering serum urate. Atorvastatin, but not simvastatin, may lower uric acid, and while fenofibrate may reduce serum urate it has been associated with a decline in renal function.Gout in solid organ transplantation is an increasing and challenging clinical problem; it impacts adversely on patients' quality of life. Recognition and, if possible, alleviation of risk factors, prompt treatment of acute attacks and early introduction of hypouricaemic therapy with careful monitoring are the keys to successful management.     

Sirolimus: the evidence for clinical pharmacokinetic monitoring

This review seeks to apply a decision-making algorithm to establish whether clinical pharmacokinetic monitoring (CPM) of sirolimus (rapamycin) in solid organ transplantation is indicated in specific patient populations. The need for CPM of sirolimus, although a regulatory requirement in Europe, has not yet been firmly established in North America and other parts of the world.Sirolimus has demonstrated immunosuppressive efficacy in renal, pancreatic islet cell, liver and heart transplant recipients. The pharmacological response of immunosuppressive therapy with sirolimus cannot be readily evaluated; however, a relationship between trough blood sirolimus concentrations, area under the plasma concentration-time curve (AUC) and the incidence of rejection has been proposed. Furthermore, sirolimus can be measured in whole blood by several assays--high-performance liquid chromatography with detection by tandem mass spectrometry, or with ultraviolet detection, radioreceptor assay or microparticle enzyme immunoassay.Both experimental animal and clinical data suggest that adverse events and their associated severity are correlated with blood concentrations. To prevent rejection and minimise toxicity, a therapeutic range of 4-12 microg/L (measured via chromatographic assays) is recommended when sirolimus is used in conjunction with ciclosporin. If ciclosporin therapy is discontinued, a target trough range of 12-20 microg/L is recommended. Sirolimus pharmacokinetics display large inter- and intrapatient variability, which may change in specific patient populations due to disease states or concurrent immunosuppressants or other interacting drugs. Due to the long half-life of sirolimus, dosage adjustments would ideally be based on trough levels obtained more than 5-7 days after initiation of therapy or dosage change. Once the initial dose titration is complete, monitoring sirolimus trough concentrations weekly for the first month and every 2 weeks for the second month appears to be appropriate. After the first 2 months of dose titration, routine CPM of sirolimus is not necessary in all patients, but may be warranted to achieve target concentrations in certain populations of patients, but the frequency of further monitoring remains to be determined and should be individualised.     

Treating erectile dysfunction in renal transplant recipients

Erectile dysfunction is common in male kidney transplant recipients. Interference with the physiology of erections can be attributed to recipient co-morbidities, the renal transplant operation, medication adverse effects, relationship problems and changes in mental health. A treatment-oriented evaluation of erectile dysfunction allows the development of treatment plans that are patient-specific. Hypo-gonadal men whose hormone parameters do not improve after renal transplantation may respond to testosterone replacement therapy. Use of recommended doses of the phosphodiesterase-5 inhibitor sildenafil does not significantly modify trough concentrations of the calcineurin inhibitors ciclosporin and tacrolimus or result in impaired renal allograft function. Tacrolimus has been shown to increase the peak concentration and prolong the elimination half-life of sildenafil in kidney transplant recipients. Daily administration of sildenafil has resulted in decreased blood pressure in kidney transplant recipients with treated hypertension and tacrolimus immunosuppression. Intracavernosal injections of alprostadil, with or without papaverine and phentolamine, are effective treatments for erectile dysfunction after renal transplantation and have not resulted in alterations of ciclosporin concentrations or in deterioration of renal function. Penile prostheses can be successfully implanted after pelvic organ transplantation without significant risk of infection.     

Review: metabolism of immunosuppressant drugs

Pharmacokinetic concepts provide a basis for individualization of drug therapy to optimize outcomes of the critical-dose drugs cyclosporine (CsA), tacrolimus (TRL), sirolimus (SRL), and mycophenolate mofetil (MMF). The therapeutic range of a drug-defined as the concentrations at which the desired pharmacologic effect is produced without adverse effects in most patients-is difficult to achieve given the significant inter-and intrapatient variability of the effects of a given concentration of therapeutic agents. Because of the highly variable rates of absorption of immunosuppressive agents and clinical responses to given concentrations in transplant recipients, individualization of drug regimens by using therapeutic drug monitoring (TDM) is essential to optimize pharmacotherapy Assessing proclivity for acute rejection episodes in transplant recipients currently is attempted by estimating drug exposure using the area under the time-concentration curve (AUC) for MMF and the average concentration (Cav, the quotient of the AUC and the dosing interval) for CsA. These studies have revealed that low oral bioavailability was a more important predictor of rejection than was a rapid clearance rate. In addition, the degree of intra-individual variability of AUC values correlated with the development of chronic rejection in renal transplant recipients. Similarly, TDM of MMF requires AUC determinations. Low mycophenolic acid (MPA) exposure, as estimated by the AUC, demonstrates a significant association with an increased risk of an acute renal transplant rejection episode. The AUC0-2 estimate of MPA shows good agreement with the 12-hr AUC estimate from samples obtained during the entire dosing interval. In contrast, trough levels are utilized during treatment with TRL or SRL, potent new immunosuppressive agents that display a pleiotropic array of side effects. Standard body measures, including weight and body mass index, poorly predict the concentration of SRL in whole blood. Large inter- and intra-individual differences displayed in patients also could not be predicted by demographic features or by laboratory parameters. When SRL is given with other immunosuppressive agents such as CsA, which shares with SRL mutual microsomal metabolism by the cytochrome P450 3A system, pharmacokinetic interactions occur, especially when the agents are administered concomitantly. Because of the critical-dose nature of most of the recent generation of immunosuppressive agents, therapeutic drug monitoring is becoming increasingly important in the selection of doses and treatment regimens.     

Tacrolimus once-daily formulation: in the prophylaxis of transplant rejection in renal or liver allograft recipients

Tacrolimus once-daily (OD) is a new oral formulation of the well established immunosuppressant tacrolimus. Tacrolimus OD provided equivalent steady-state systemic tacrolimus exposure to that achieved with standard oral tacrolimus twice daily in stable renal and liver transplant recipients. The two formulations also provided broadly similar steady-state systemic exposure in de novo renal and liver transplant recipients. In a large, randomised, nonblind, multicentre, three-armed, noninferiority trial in de novo renal transplant recipients, the efficacy failure rates (primary endpoint) [any patient who died, experienced graft failure, had a biopsy-confirmed acute rejection or was lost to follow-up] of tacrolimus OD (14.0%) and standard tacrolimus (15.1%) were noninferior to that of ciclosporin (cyclosporine) microemulsion (17.0%) at 1 year, when each was given in conjunction with corticosteroids, mycophenolate mofetil and basiliximab induction. Data from a pharmacokinetic study suggests that tacrolimus OD has similar efficacy to standard tacrolimus in de novo liver transplant recipients over 6 weeks of treatment. In noncomparative 2-year trials, tacrolimus OD was effective in stable renal and liver transplant recipients converted to tacrolimus OD from standard tacrolimus. The overall tolerability profile of tacrolimus OD appears to be similar to that of standard tacrolimus in de novo and stable renal and liver transplant patients.     

肾移植受者环孢素血药浓度监测频度及其临床意义

目的:研究肾移植术后患者环抱素(CsA)血药浓度监测频度的临床意义。方法:对24例肾移植术后患者296次CsA血药浓度监测进行回顾性分析,分2组:规律组15例201次规律性监测;非规律组9例95次因各种原因不能定期监测。比较2组CsA血药浓度统计学变异系数(CV)的差异及排斥反应组与非排斥反应组CsA血药浓度CV的差异。结果:规律组CsA血药浓度CV小于非规律组(P<0.05);非排斥组CsA血药浓度CV小于排斥组(P<0.05)。结论:规律性CsA血药浓度比非规律性监测平稳;排斥反应的发生率与CsA血药浓度的CV呈正相关。     

Pharmacokinetic interaction between levofloxacin and ciclosporin or tacrolimus in kidney transplant recipients: ciclosporin, tacrolimus and levofloxacin in renal transplantation

BACKGROUND AND OBJECTIVE: Bacterial infections are common complications after organ transplantation. Fluoroquinolones are frequently used for treatment because of their broad spectrum of activity; but some of them, such as ciprofloxacin and norfloxacin, are reported to increase blood concentration of ciclosporin because they are metabolised by the liver through the same enzymatic pathway, the cytochrome P450 system. This study was performed to establish whether levofloxacin, a more recent fluoroquinolone that undergoes limited hepatic metabolism, interferes with metabolism and excretion of either ciclosporin microemulsion or tacrolimus. METHODS: Pharmacokinetic studies were carried out in two groups of renal transplant patients, on either ciclosporin or tacrolimus treatment, before and at the sixth day of treatment with levofloxacin. RESULTS: Levofloxacin significantly increased the mean area under the blood concentration-time curve (AUC) and the other pharmacokinetic parameters of ciclosporin and tacrolimus by about 25%. The interference of levofloxacin on the hepatic metabolism of these drugs was demonstrated by the concomitant decrease by 5% of polyclonal ciclosporin concentration, which is the expression of parent drug and its metabolites. Both before and during levofloxacin treatment we observed trough concentrations of monoclonal and polyclonal ciclosporin significantly lower in the evening (C(12)) than in the morning (C(0)); this observation suggests a circadian variation in the metabolism of this drug. However, no difference between C(0) and C(12) was observed with tacrolimus, confirming its more predictable bioavailability. CONCLUSION: Our data demonstrate that levofloxacin partially inhibits the metabolism of both ciclosporin microemulsion and tacrolimus, and therefore close therapeutic monitoring of these two drugs should be recommended during levofloxacin therapy.     

Calcineurin inhibitor-free immunosuppression in pediatric renal transplantation: a viable option?

The introduction, in the mid-1980s, of calcineurin inhibitors - namely ciclosporin (cyclosporine) and later tacrolimus - has significantly improved short-term renal graft survival by lowering acute rejection rates in both adult and pediatric kidney transplantation. Nonetheless, long-term transplant survival is still not satisfactory, with calcineurin inhibitor-induced chronic nephrotoxicity being one of the main causes of progressive nephron loss and declining renal transplant function. Hence, different immunosuppressant regimens have been proposed to avoid or ameliorate calcineurin inhibitor-induced nephrotoxicity. These comprise the use of non-depleting or depleting antibodies for calcineurin inhibitor minimization, calcineurin inhibitor avoidance, or calcineurin inhibitor withdrawal from mycophenolate mofetil-based immunosuppressant protocols. De novo use of a mammalian target of rapamycin (mTOR) inhibitor (sirolimus or everolimus) or conversion from a calcineurin inhibitor to an mTOR inhibitor may constitute another therapeutic option to avoid or reduce calcineurin inhibitor-induced nephrotoxicity. To date, complete calcineurin inhibitor avoidance seems to be inappropriate because other relatively potent immunosuppressant agents such as lymphocyte-depleting antibodies are needed for rejection prophylaxis, which are frequently accompanied by a higher incidence of infections and an unacceptably high acute rejection rate under calcineurin inhibitor avoidance. In some studies, calcineurin inhibitor withdrawal in adult and pediatric kidney allograft recipients with stable or declining transplant function has been associated with an amelioration of renal function; however, this is attained at the cost of a higher acute rejection rate in 10-20% of patients. It has been frequently stressed that conversion from a calcineurin inhibitor-based regimen to an mTOR inhibitor-based immunosuppressant regimen should be performed early (e.g. 3 or 6 months post-transplant) in patients with well-preserved renal transplant function without significant proteinuria in order to prevent, or at least limit, calcineurin inhibitor-induced tissue damage and provide long-term benefit. It should be borne in mind though that the use of an mTOR inhibitor carries the risk of potential adverse events such as aggravation of proteinuria, hyperlipidemia, myelosuppression, and hypergonadotropic hypogonadism. Even though everolimus may be better tolerated than sirolimus, studies on everolimus for calcineurin inhibitor-free immunosuppression in the pediatric kidney transplant patient population are lacking. At present, the safest therapeutic strategy for pediatric renal allograft recipients with chronic calcineurin inhibitor-induced nephrotoxicity appears to be a mycophenolate mofetil-based regimen with low-dose calcineurin inhibitor therapy and corticosteroids; available published data show that dual immunosuppression with mycophenolate mofetil and corticosteroids, as well as an mTOR inhibitor plus mycophenolate mofetil plus corticosteroid-based regimens, are associated with an increased risk of acute rejection episodes. In individual patients with evidenced chronic allograft dysfunction and over-immunosuppression leading to recurrent infections, dual maintenance immunosuppression with mycophenolate mofetil and corticosteroids may be appropriate. As stated in the annual report issued by the North American Pediatric Renal Trials and Collaborative Studies (NAPRTCS) Registry, currently the most popular immunosuppressant protocol consists of a calcineurin inhibitor combined with mycophenolate mofetil and corticosteroids: 59.1% and 53.2% of patients with a functioning graft receive a calcineurin inhibitor plus mycophenolate mofetil plus corticosteroid-based immunosuppression at 1 and 5 years post-transplant, respectively. 91.4% and 87.8% of patients are administered a calcineurin inhibitor-containing regimen 1 and/or 5 years after transplantation, respectively. Undoubtedly, the use of calcineurin inhibitor-free immunosuppressant regimens with or without antibody induction, plus an mTOR inhibitor and mycophenolate mofetil, requires more comprehensive long-term investigations to determine whether acceptable rejection rates and conservation of renal function can be achieved.     

肾移植受者应用西罗莫司治疗窗的临床研究

目的:探讨西罗莫司应用于国内肾移植受者的治疗窗范围。方法:采用多中心、开放性临床研究,来自国内4家移植中心的首次肾移植病人共100例。免疫抑制方案为西罗莫司联合环孢素和皮质激素的三联疗法。移植后48h内开始服用西罗莫司,首次负荷剂量为6mg·d-1,维持剂量为2mg·d-1,采用高效液相色谱法测定西罗莫司浓度。结果:100例病人西罗莫司总的全血谷浓度为(6.6±s2.8)μg·L-1,10及90百分位数浓度分别为3.2μg·L-1和10.26μg·L-1。肾移植后6mo内急性排斥发生率为10%(8/84),此8例病人急性排斥时的西罗莫司浓度明显低于非排斥时浓度(P<0.01)。主要不良反应为肝功能损害和高脂血症,三酰甘油浓度与西罗莫司浓度相关(r=0.276,P<0.01)。结论:西罗莫司浓度维持在4～8μg·L-1范围内较为合适,定期监测血药浓度,合理调整用量,可增加西罗莫司应用的有效性及安全性。     

盐酸小檗碱与环孢素合用的药物经济学研究

目的：了解盐酸小檗碱与环孢素合用能否降低环孢素的费用。方法：采用回顾性调查方法,进行盐酸小檗碱与环孢素合用的药物经济学评估。结果：盐酸小檗碱可显著增加环孢素的血药浓度。在满足正常疗效的同时,可降低环孢素的药物费用,每个每年可节约药费6000-8000元。结论：小檗碱与环孢素合用能降低费用,减轻病人和社会的经济负担。     

Review article: hepatitis C virus and calcineurin inhibition after renal transplantation

The impact of hepatitis C virus on patient and graft survival after renal transplantation remains controversial. However, recent studies have given emphasis on the detrimental role of hepatitis C on long-term patient and graft survival after renal transplantation. Various mechanisms can promote the lower survival in hepatitis C virus-positive recipients, i.e. post-transplant diabetes mellitus, liver disease and infections. Novel evidence has been accumulated showing the inhibitory activity of ciclosporin on the hepatitis C virus replication rate in human hepatocytes; ciclosporin has been shown in vitro to suppress hepatitis C virus replication as effectively as interferon alpha. This effect has not been seen with tacrolimus and is separate from its immunosuppressive activity. Data from patients with normal kidney function or after bone marrow transplantation show that ciclosporin inhibits hepatitis C virus replication. It appears that the progression of liver fibrosis is slower in hepatitis C virus-positive liver transplant recipients treated with ciclosporin than tacrolimus. In contrast, the clinical outcome of hepatitis C in hepatitis C virus-positive patients after liver transplantation treated with ciclosporin vs. tacrolimus has given mixed results. No information after renal transplantation is available. Various parameters can promote the worsening of hepatitis C after renal transplantation but choice of calcineurin inhibition is one of the few risk factors that can potentially be modified by the physician. Prospective, comparative trials of ciclosporin and tacrolimus with large size and adequate follow-up after renal transplantation are in progress.     

ABCB1 haplotype influences the sirolimus dose requirements in Chinese renal transplant recipients

Sirolimus, an immunosuppressive drug used to prevent organ rejection after renal transplantation, has a narrow therapeutic index and a large inter‐individual variability of pharmacokinetics. The aim of this study was to analyse the dose‐normalized trough blood concentrations (C₀/D ratio) of sirolimus in patients with different genotypes and attempt to investigate the possible associations between ABCB1/CYP3A5 genotypes and sirolimus dose requirements in Chinese renal transplant recipients. Blood samples were collected from 85 Chinese renal transplant recipients who were treated with sirolimus for at least 3 months and polymorphisms of the ABCB1 and CYP3A5 were determined by the SNaPShot multiplex assay. The blood concentrations of sirolimus were determined with HPLC. A significant allele‐dependent effect was observed between the CYP3A5*3 polymorphism and the C₀/D ratio of sirolimus. The patients bearing at least one CYP3A5*1 allele had a lower sirolimus C₀/D ratio compared with those with a homozygous CYP3A5*3 genotype (p < 0.05). No significant differences of sirolimus C₀/D ratios were observed among various ABCB1 1236C>T, 2677G>T/A and 3435C>T genotype groups. However, haplotype analysis including ABCB1 1236C>T, 2677G>T/A and 3435C>T SNPs showed that the mean sirolimus C₀/D of subjects carrying the CGC/CGC diplotype was about 30% lower compared with those carrying the CGC/TTT or TTT/TTT diplotype, whether or not they expressed the CYP3A5 (p < 0.05). These results demonstrated that the haplotype of ABCB1 might be a better index for the prediction of sirolimus blood concentration than single SNPs. Genotyping of ABCB1 and CYP3A5 might help to optimize individualized sirolimus treatments for Chinese renal transplant recipients. Copyright © 2013 John Wiley & Sons, Ltd.     

肾移植术后患者全血西罗莫司浓度监测结果分析

目的:探讨肾移植术后患者全血西罗莫司浓度的治疗窗以及西罗莫司对血常规、肝肾功能、血脂和尿蛋白的影响。方法:采用微粒子发光免疫分析技术（MEIA）测全血西罗莫司谷浓度。对3年来294例次肾移植术后患者全血西罗莫司浓度,以及西罗莫司对血常规、肝肾功能、血脂和尿蛋白的影响进行分析。结果:294例次全血西罗莫司浓度中有206例次（70%）在3～8ng·ml^-1范围内。肾移植6个月后,全血西罗莫司浓度测定值随移植时间延长而降低。服用西罗莫司后的尿蛋白数值升高,与服用之前相比差异有统计学意义（P<0.05或0.01）。结论:全血西罗莫司谷浓度治疗窗:术后1～3个月为4～6ng·ml^-1,第4～6个月为3～6ng·ml^-1,>6个月为3～5ng·ml^-1。     

A comparison of the effect of ciclosporin and sirolimus on the pharmokinetics of mycophenolate in renal transplant patients

AIM: To compare the pharmacokinetics of mycophenolic acid when given with either ciclosporin or sirolimus, and investigate in vitro the potential effect of ciclosporin, sirolimus, tacrolimus and everolimus on mycophenolic acid metabolism. METHODS: In renal transplant patients given mycophenolate mofetil in combination with ciclosporin (n = 19) or sirolimus (n = 12), concentration-time profiles of mycophenolic acid, mycophenolic-acid-phenyl-glucuronide, mycophenolic-acid-acyl-glucuronide and mycophenolic-acid-phenyl-glucoside were determined at one month post-transplant. The effect of immunosuppressive drugs on mycophenolic acid glucuronidation and glycosylation was investigated in vitro using human liver microsomes. RESULTS: The mean mycophenolic acid AUC(0-9 h) in the sirolimus group was 44.9 mg h(-1) L(-1) (95% CI: 34.7-55.1), vs. 30.5 mg h(-1) L(-1) (95% CI: 25.4-35.6) in the ciclosporin group, corresponding to 1.5-fold dose-normalized difference (95% CI: 1.1-1.9; P < 0.05). In addition, the metabolite/mycophenolic acid AUC(0-9 h) ratios were significantly higher in patients cotreated with ciclosporin than with sirolimus, giving values of 1.8-fold (95% CI: 1.3-2.3; P = 0.0009), 2.6-fold (95% CI: 2.0-3.3; P < 0.0001) and 4.3-fold (95% CI: 2.6-6.0; P = 0.0016) for mycophenolic-acid-phenyl-glucuronide, mycophenolic-acid-acyl-glucuronide and mycophenolic-acid-phenyl-glucoside, respectively. In vitro, none of the immunosuppressive drugs tested inhibited mycophenolic acid metabolism. CONCLUSION: Patients taking mycophenolate mofetil and sirolimus experience a higher exposure to mycophenolic acid and a lower exposure to mycophenolic acid metabolites than those being treated with mycophenolate mofetil and ciclosporin. This interaction is probably not caused by inhibition of mycophenolic acid glucuronidation or glycosylation, but is more likely to be due to the influence of ciclosporin on the excretion of mycophenolic acid metabolites into bile.